composite yacht meaning

A List of Composite Materials In Boats

Modern Composites Used In The Marine Industry

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Composite materials are broadly defined as those in which a binder is reinforced with a strengthening material. In modern terms, the binder is usually a resin, and the reinforcing material consists of glass strands (fiberglass) , carbon fibers or aramid fibers. However, there are other composites too, such as ferrocement and wood resins, which are still used in boatbuilding.

Composites offer the advantages of a higher strength-to-weight ratio than traditional wood or steel methods, and they require lower skill levels to produce an acceptable hull finish on a semi-industrial scale.

History of Composites in Boats

Ferrocement

Probably the earliest use of composites for boats was ferrocement. This material was extensively used in the first half of the twentieth century for building low-cost, low-tech barges.

Later in the century, it became popular not only for one-off home projects but also for production boatbuilders. A steel frame made of reinforcing rod (known as an armature) forms the hull shape and is covered with chicken wire. It is then plastered with cement and cured. Although a cheap and simple composite, armature corrosion is a common problem in the chemically aggressive marine environment. There are still many thousands of " ferro" boats in use today, however – the material has enabled many people to realize their dreams.

During the Second World War, just after polyester resins were developed, glass fibers became available following the accidental discovery of a production process using blown air on a stream of molten glass. Soon, glass-reinforced plastic became mainstream and GRP boats started to become available in the early 1950s.

Wood/Adhesive Composites

Wartime pressures also led to the development of cold-molded and hot-molded boatbuilding techniques. These approaches entailed laying thin veneers of wood over a frame and saturating each layer with a glue. High-performance urea-based adhesives developed for aircraft manufacturers were widely used for the new technique of molding boat hulls – typically for PT boats . Some adhesives required baking in an oven to cure and hot-molded hulls were developed, though there were size limitations governed by access to industrial ovens.

Modern Composites in Boats

Since the 1950s, polyester and vinylester resins have improved steadily and GRP has become the most prevalent composite used in boatbuilding. It is used in shipbuilding too, typically for minesweepers that need non-magnetic hulls. Osmotic problems from which early-generation boats suffered are now a thing of the past with modern epoxy compounds. In the 21 st century, volume GRP boat production follows a full industrial production process.

Wood/epoxy molding techniques are still in use today, typically for rowing skiffs. Other wood/adhesive composites have evolved since the introduction of high-performance epoxy resins. Strip planking  is one such popular technique for home boat construction: Strips of wood (typically cedar) are laid longitudinally over frames and coated with epoxy. This simple construction offers a cheap and strong build with a fair finish easily achievable by an amateur.

At the leading edge of boat building, aramid fiber reinforcing strengthens key areas of sailboats, such as the bows and keel sections. Aramid fiber also provides improved shock absorption. Carbon fiber masts are increasingly common, as they offer major performance and vessel-stability benefits.

Sailboats also use composites in their sail construction, with carbon-fiber or glass-fiber tape offering a flexible but dimensionally stable matrix to which synthetic sailcloth is laminated.

Carbon fiber has other marine uses too – for example for high-strength interior moldings and furniture on super-yachts.

The Future of Composites in Boatbuilding

The costs of carbon fiber fall as production volumes increase so the availability of sheet carbon fiber (and other profiles) is likely to become more prevalent in boat production.

Materials science and composite technology are advancing rapidly, and new composites include carbon nanotube and epoxy mixtures . Recently, a small naval vessel with a hull built using carbon nanotubes was delivered as a concept project.

Lightness, strength, durability, and ease of production mean that composites will play an increasing part in boat construction. Despite all the new composites, Fiber-reinforced polymer composites are here to stay for very many years, though it will surely be in partnership with other exotic composites.

• What is the Definition of a Composite Material?
• History of Composites
• Understanding CFRP Composites
• Composites in Aerospace
• What Is Epoxy Resin Used In?
• Thermoplastic vs. Thermoset Resins
• Uses of Fiberglass
• Properties of FRP Composites
• What Is Carbon Fiber?
• How Is Carbon Fiber Made?
• Aramid Fiber: The Versatile Polymer Reinforcing Fiber
• FRP Composites Around The House
• Defining Prepregs
• Recycling Composite Materials
• Boeing's 787 Dreamliner
• The Basics of Using Carbon Fiber Laminates

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Composite Construction: Decoding the Matrix

• By Tim Murphy
• Updated: October 18, 2013

Most of today’s hulls and decks are built from marine “composites”—a combination of materials in which each part keeps some of its original traits. Broadly speaking, composite construction dates back several millennia, to an era when grass was mixed with mud to build a hut. in this first of two articles, we’ll explore the two basic components that go into today’s composite boats: the reinforcing fiber and the polymer matrix. As we begin, remember that a whole composite structure has properties all its own, and is more than the sum of its parts. Also, all composite structures depend as much on technique—how the materials were put together—as they do on the materials themselves.

Fiber Reinforcement Modern composite boatbuilding needs fibers. Yes, composites start with polyester resin—the pour- able, sprayable thermoset- ting plastic that hardens after mixing with a chemical catalyst. if you tried to build a boat from polyester alone, you’d be able to create virtually any complex shape for virtually any hull form. in that regard, the material beats both wood and metal. in the 1940s, when engineers first started experimenting with boats made from thermosetting plastic, they loved the fact that they’d created entire hulls without any seams—no caulk, no welds. But with polyester alone you’d have an impossibly fragile boat.

In his excellent book Heart of Glass (International Marine, 2004), Dan Spurr tells how these materials were discovered and used. in the 1930s, researchers at Owens, Illinois Glass company tried to spin glass into fibers to replace mineral wool for insulation and filters. Almost accidentally, they revolutionized boatbuilding. Now, more than 90 percent of all boats are built from composites that started with their invention of fiberglass.

The glass fiber created in the 1930s is remarkably similar to today’s materials. the glass fiber exhibits astounding tensile strength and resists both stretching and contamination by chemicals. And, important for boatbuilders, the flexible fibers are relatively easy to work with.

| | Through the 1970s and 1980s, boatbuilders grew much savvier about creating composite structures with the best strength-to-weight ratios. Knitted fabrics, which allow designers to engineer strength into composite structures along the lines of filaments, are one of the keys. | |

| | Woven roving was one of the great FRP (for fiber-reinforced polymer) boons of the 1950s. Many thousands of boats were built with this fabric technology. It allowed laminators to build up bulk in a composite structure very quickly. The downside is that its loose weave invites a heavier, resin-rich layup. | |

| | Fiberglass mat, composed of either chopped, or short, strands (above, left), or continuous long strands (above, right), is ideal for small FRP parts or as one layer in larger FRP parts. But mat alone provides comparatively little strength in a laminate. | |

The silica-based fiberglass used in today’s boats comes in two varieties: E-glass and S-glass. E-glass is the workhorse of contemporary boatbuilding against which all others are measured. It delivers reasonable strength at relatively low cost. S-glass is stronger, lighter, and stretches less but costs three to four times more.

In the last 30 years or so, two new categories of fibers have changed the way high-performance boats are built: aramids and carbon fibers. Aramid stands for “aromatic polyamide.” Kevlar, the best-known aramid, is the trademarked name for a fiber that DuPont (the company that created polyester resin in the 1940s) originally developed for tires. Trade names for aramids from other companies include Technora, Twaron, and Heracron. Twice the tensile strength of E-glass; low weight; weavability; resistance to puncture, impact, and fatigue—these are the main virtues of aramid fibers. But they absorb water and don’t stand up to compression loads as well as glass fiber. For these reasons, they’re usually used in combination with other fibers.

For light weight and stiffness, the material to beat is carbon fiber. Its modulus of elasticity is roughly six times stiffer than E-glass. That stiffness, plus the fact that it doesn’t corrode like aluminum or stainless steel, makes carbon fiber ideal for such high-load components as masts and rudderstocks, and even for entire boats. But carbon-fiber parts need to be engineered carefully; carbon’s lack of stretchiness provides little warning before it fails, suddenly and catastrophically. It’s also by far the most expensive reinforcing fiber.

Think of reinforcing fibers in three dimensions: lines, planes, and cubes. Builders don’t use just fibers and filaments; they work with two-dimensional sheets of fabric called mat and woven roving and knits. The properties of a composite structure depend on both the fiber’s material and its orientation. Yacht designers can engineer each fabric layer, or ply, to provide optimal strength in a particular direction. Together, the three-dimensional layers in a composite structure are called the laminate.

In the first dimension, we need to know if the fibers are continuous or discontinuous; in other words, are they long or short? Chopped-strand mat is a sheet composed entirely of short fibers. Continuous-strand mat is composed of longer swirled fibers. Easy to shape and quick to saturate with resin, mat is used for building small composite parts for which weight and strength aren’t critical. In larger structures, mat is added among layers of continuous fiber for better wetting-out with resin. Mat offers an economical way to build thickness in a laminate. A chopper gun, which adds short strands of fiber to resin that’s sprayed into a mold, can also build thickness. But chopped or swirled fibers alone create a structure that’s more heavy than strong. Strength comes from fibers that run the length of a structure.

Two-dimensional sheets of reinforcing fiber may be woven or knitted. The first fiberglass boats in the 1950s were built mostly of fiberglass mat and cloth. Fiberglass cloth is a thin layer that’s composed of finely woven strands. Using cloth alone, it takes many plies to build up a structure that’s thick and strong enough for a hull. Cloth provides a smooth surface and is often used as the first ply in a hull that will be faired.

Woven roving, a loose weave of larger strands that results in a heavier cloth, came on the scene in the 1950s and was the workhorse of composite boatbuilding into the 1970s. With woven roving, thickness in the laminate can be built faster than with cloth, saving labor hours. However, the loose weave leaves lots of space to be filled by excess resin. A resin-rich laminate is heavier than it needs to be to achieve the necessary strength.

Until the mid-1970s, many composite builders equated the strength of the structure with the thickness of the laminate. Boats from that era tend to be heavier than newer boats. Over time, builders and designers became much better at fine-tuning the reinforcing fibers and optimizing strength-to-weight ratios. A light structure depends on minimum amounts of resin matched with the right fibers laid up in the right direction.

| | In the accompanying series of photos, a team of laminators demonstrate the boatbuilding process known as resin infusion. The first step is to build a plug, the male form from which the builders will take a female mold. | |

| | Next, they line the mold with sheets of dry fiber reinforcements, then seal it with a plastic bag. | |

| |_ Finally, they insert hoses into the bag and use vacuum pressure to draw resin through the laminate for an optimum fiber-to-resin ratio._| |

| | A laminator uses a chopper gun, a technique employed in the more traditional contact layup, that builds thickness quickly but at a cost of additional weight. |

In the past 30 years, technology advances have come not just in materials like aramids and carbon but also in how those fibers are arranged in a two-dimensional fabric. For example, knitted fabrics differ from woven roving, whose filaments of equal diameter cross at 90-dgree angles. In knits, the main or structural fibers are stitched together with fine nonstructural filaments, usually polyester. The structural fibers lie flat, not crimped, leaving less space for resin to fill. With knits, builders can get a lot more strength and stiffness per unit thickness.

This reflects a shift in perspective: Whereas earlier builders aimed for thickness (equating thickness with strength), the goal now is maximizing strength. In unidirectional knits, the structural fibers run in one direction that designers can specify for high-load areas, like rig attachment points. In biaxial knits, the structural fibers can be oriented at 45-degree or 90-degree angles for optimal strength in those directions. Further variations—triaxial, quadraxial—provide engineered strength where it’s most needed.

Knitted fabrics often incorporate a layer of mat. For example, 1808 is one popular reinforcing fabric that combines 18-ounce biaxial knit with 8-ounce mat in a single sheet. The mat wets out with resin thoroughly, and the knit provides the directional strength — a smarter way to incorporate engineered strength.

The Resin Matrix With epoxy and vinylester resins, it’s easy to forget what a revolutionary breakthrough good ol’ polyester was. Though we’ve come to know its shortcomings, polyester remains the keystone of the whole composites industry.

Polyester belongs to a class of chemical compounds called polymers, which can be either thermoplastic or thermosetting. Thermoplastics can be remolded and reshaped every time they’re heated up. PVC and polystyrene are two examples. Once thermosets are cured, the process is irreversible. If you heat a thermoset polymer after it’s been cured, it remains hard and retains its shape. Thermosets include polyester, vinylester, and epoxy. A cured polymer is one in which the molecules are cross-linked with each other. After curing, the product is solid, hard, and chemically resistant.

Polyester resin starts as a solution of carbon, oxygen, and hydrogen groups in a liquid, called a monomer, such as styrene. These chains of molecules link with each other on their own, which is important for builders because the containers of polyester they buy have a limited shelf life; over time, polyester turns from a liquid to a gel and eventually to a solid. Although “polymerization”—the cross-linking of the chemical chain that turns the liquid to a solid—happens naturally in polyester, it doesn’t happen quickly enough on its own to be useful.

When a part is being laid up, the boatbuilder adds a catalyst (often methyl ethyl keytone peroxide, or MEKP) to speed up polymerization to a workable scale of hours and minutes. Other chemicals, called accelerators and inhibitors, can be added to the uncured polyester before or during the process to either speed up or slow down the reaction time. The fact that polyester cures at room temperature is one of its greatest virtues; still, controlling humidity and temperature can help fine-tune the layup. Much of composite boatbuilding is about managing cure times.

In a composite structure, the polymer matrix fulfills three main jobs: It holds the reinforcing fibers in place, acts as a path for transferring loads between the reinforcing fibers, and protects the reinforcing fibers from a brutal environment. Those long reinforcing fibers resist stresses from many directions, but they can’t resist every load from every direction. The matrix must also support against these secondary tension, compression, and shear loads.

Between 1945 and about 1975, orthophthalic polyester was the one and only polymer used in virtually all composite boatbuilding. But several problems were eventually revealed. First, it’s permeable: It lets water in. Not much, but enough to cause problems in the laminate. The chemical mechanism that draws the water into the laminate is called osmosis. The symptom is blistering.

Blistering looks like bubbles in the gelcoat. And while blistering has occurred for as long as polyester has existed, it became a serious problem in the 1970s, as some builders began using resins with different formulas, and boats began breaking out with a pox that was horrendously expensive to fix. In response, builders in the last few decades also work with isophthalic polyester, vinylester, and epoxy resins. Choosing among resin materials is always about balancing properties with cost. As with fibers, savvy builders can mix and match materials to find the right overall blend.

| | A major theme in the 70-year story of composite boatbuilding is the quest for the ideal ratio of resin to fiber. The resin impregnator (above) hangs from a beam in the boat shop and uses a system of rollers to deliver optimally wetted-out sheets of fabric directly to a mold. |

Orthophthalic polyester, or ortho, is the most economical and popular resin used in boatbuilding today. Isophthalic polyester, or iso, has better thermal stability, chemical resistance, and workability. It also resists water permeation much better than ortho. But it’s about 25 percent more expensive. That’s why many cost-conscious builders use iso resin in the gelcoat (the first resin layer that meets seawater) and ortho through the rest of the laminate.

In the 1980s, some builders began experimenting with vinylester resin. Compared to polyester, it resists corrosion, fatigue, and impact much better, and it’s a far better barrier against water intrusion. But it costs about twice as much as ortho. Again, vinylester is sometimes used as an outer barrier coat.

Of all the boatbuilding resins, epoxy has the best properties overall. But it’s about four times as expensive as ortho resins, and it’s used mostly in high-end projects, especially one-off custom boats.

Click here for Part II of this series on boatbuilding. Editor at large Tim Murphy is the co-author of Fundamentals of Marine Service Technology (ABYC, 2012), from which this story is excerpted.

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Boat building: what will yachts be made from in the future?

• Sam Fortescue
• December 17, 2021

Sam Fortescue shines a light on boat building jargon and looks into a future devoid of fibreglass

Building with pre-preg materials is efficient, but the hull must be 'cooked' at a precise temperature to cure it. Credit: Eva-Stina Kjellman

The end of GRP? Sam Fortescue looks at past, present and future boat building materials

Glance at a brochure for a new boat or walk the pontoons at the Southampton show and you may have come across some terms that didn’t mean much to you.

The art of boat building is as recognisable as ever, but the science of it is constantly developing. New materials and new techniques can make it hard to compare like with like.

Take wood, for instance: the material of boatbuilding choice for millennia.

There are still plenty of wooden boat-builders out there, labouring away in dingy sheds and halls to craft pilot cutters, rowing skiffs and other emblematic vessels of yesteryear.

But perhaps the best known of the wooden boatbuilders is Spirit Yachts in Ipswich, building thoroughly modern boats – in composite wood.

The Spirit 44E is a ‘zero carbon’ cruising yacht. Credit: Richard Langdon

‘Certainly we use epoxy resin to bond the components together, but the amount of resin used is minute compared to GRP or carbon,’ says founder and head designer Sean McMillan.

‘Both carbon-fibre and GRP rely totally on being saturated with a high density of polyester or epoxy resins to impart structural integrity. Wood, whilst also a linear fibre material, is cross-linked with a cellular structure entirely created by nature and has full structural integrity in its own right.’

In fact, the 1.6-tonne Spirit 30 daysailer employs just 73kg of resin and 12.2kg of hardener in its entire construction.

‘In 20 years’ time, when GRP has become socially unacceptable – not to mention any future end-of-life legislation – who knows, we may look back and see the last 60 years of GRP boats as a historical niche,’ finishes McMillan defiantly.

Another example is racy French builder RM Yachts, whose boats are famously swift, with offshore hulls designed by Marc Lombard.

And yet they are built in plywood and epoxy.

Thought every Spirit yacht us built of wood, it is a composite of glue and epoxy sheathing.

It is flexible, robust and far more sustainable than standard glass-reinforced plastic.

Sheets of laser cut Okoumé plywood up to 22mm thick are bent around a mould and epoxied to plywood structural members.

The whole lot is also epoxy sheathed for longevity.

It’s a technique which means that the brand-new RM 1380 is 9.8 tonnes light – slightly less than the comparable X4-6 from X-Yachts.

‘Plywood is the soul of an RM. It a very useful material, allying a good stiffness with lightness – perfect for building the hull and the structure,’ says head of engineering Edouard Delamare.

‘But plywood is nothing without epoxy, because it ensures the waterproofing – vital in a marine environment.’

Boat building using glass-reinforced plastic

Many series production yards, from Beneteau to Bavaria , still use the most basic form of wet lay-up – splurging resin on to mats of glassfibre with a roller to get them well wetted out before laying down the next layer of glass.

It is very hard to control how much resin is applied and there are often air pockets between layers.

For this reason, hulls built this way tend to be overbuilt and heavier.

RM Yachts is unique in building its offshore yachts in plywood and epoxy

Polyester is the cheapest and most commonly used resin, but it can bond with water, creating the problem of osmosis.

That’s why isopthalic gelcoats are applied to the outside of the hull, to act as an effective barrier to moisture.

Vinylester creates many more bonds than polyester and is reckoned to be up to three times stronger, but it costs more too.

And epoxy is the best performing resin of all, used only in high-quality lay-ups. All are pretty toxic, and sport the ‘dead-fish’ icon on the side of the tin.

When vacuum infusion emerged as an industrial technique in 1990, it allowed boatbuilders to use less resin and spread it more evenly around the finished panel for greater strength.

But it generates a lot of waste, because each infused part has to be prepared with a host of plastic layers.

Besides the plastic of the vacuum bag itself, there’s a breather layer to distribute the resin and a peel ply to stop it sticking to the infused part; a thick bead of sealant tape; disposable feeder tubes are required every few inches, and many of the vacuum tubes must also be binned.

The technology has not stood still, though, and there are now reusable vacuum bags made from inert silicon, for instance.

Some bags have the mesh structure necessary to spread the resin built in, while the aerospace sector has pioneered the use of PTFE membrane that stops resin clogging up the vacuum pump side of the system.

Sweden’s Arcona builds its fast cruisers using vacuum infusion, and has for many years.

Hand lay-up is a process that has changed little over the years of boat building

But in order to add strength and stiffness, it laminates in a steel support frame amidships to transfer the loads from the rig into the keel.

Improvements in lamination techniques mean that the boats are lighter than ever.

Late Arcona designer Stefan Qviberg said the current Arcona 40 displaced a whole tonne less than its equivalent a decade earlier.

Other boat builders use other types of reinforcing for the high-load areas of the hull.

Aramids like Twaron and Kevlar often feature, as do selective areas of carbon-fibre on stringers and around keel bolts and chainplates.

High-end yacht builder Baltic uses carbon reinforcing, for instance, to add strength without extra weight.

Vacuum infusion uses less resin but creates a lot of plastic waste

Performance catamaran brand Catana likewise uses Twaron and carbon in its lay-up to save hundreds of kilos; some 700kg in the old Catana 47.

Some claim that aramid reinforcing makes a hull safer, for example in the event of collision with a container, but others refute this.

Naturally enough, carbon is still the ultimate performance material because of its blend of strength, stiffness and light weight.

It is also prohibitively expensive relative to other fibres and very resource-intensive to produce, as it requires temperatures up to 3,000º C and a plastic feedstock.

The bulk and waste of the infusion process has led to another step forward in the form of so-called pre-preg materials, where the sheets of fibre used to strengthen the hull come ready-coated with a pre-catalysed form of the resin that reacts very slowly at room temperature.

Instead of needing to mix epoxy with hardener and reduce its viscosity with toxic styrene to draw into the mould, a precisely-controlled curing process activates and sets the resin.

The result is a stronger, lighter laminate than can be produced through wet lay-up.

Gurit’s SPRINT system goes a step further by sandwiching a thin film of heat-activated resin between two layers of fibre.

Windelo uses basalt fibre to strengthen its hulls during the boat building process. It is said to be much less carbon intensive than using glass

The advantage of this is that the fibres remain dry until curing so air can be more easily removed under vacuum to produce a laminate with a void content of less than 0.5%.

Baltic Yachts uses this technique, building an oven around its hulls to cure them.

‘With one or two exceptions, we haven’t infused a boat for some time,’ says CEO Henry Hawkins.

‘Using Sprint and pre-preg materials saves weight compared to vacuum infusion. With hand lay-up, generally more resin is mixed than needed and a lot gets discarded. This is the same with infusion where resin is lost or wasted in the plastic hoses and pipes and breather film and within the distribution channels.’

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Even at this sharp end of the composite business, rapid advances are being made – driven by aerospace and Formula One.

‘We can now take away the expensive autoclaves and ovens – they can cure at ambient or 40-60ºC,’ says Ashley Parkinson, a research engineer with the UK National Composites Centre.

‘It’s a more expensive process to use, but in the high-performance market, it’s worth it.’

Greener composites

Now, there is nothing particularly sustainable about producing glassfibre – a technique that involves heating raw silica to 1,370º C, then pultruding the molten strands onto a bobbin.

You can use some recycled glass to lower your emissions, but it is an energy intensive process and it is very hard to extract the raw materials from end-of-life fibreglass.

Swiss supplier Bcomp tested alternative natural fibres 10 years ago, when it was a start-up in a garage.

‘Flax turned out to be the best in terms of mechanical properties, soil usage, water requirements and overall performance,’ explains marine and industry manager Paolo Dassi.

It actually locks up carbon rather than producing it – as much as 500g of CO2 per kilogram of flax.

Precise cutting is key to reducing fibre wastage in boat building

‘The plant acts as a CO2 sink during its growth. This completely offsets the CO2 emissions of the manufacturing stages.’

Bcomp’s extraordinary growth began when it managed to process the flax stems to be of uniform size and flatness, replicating the grades possible using glassfibre.

Its AmpliTex product is available as a unidirectional, stitched biaxial or woven twill, ranging from 200-500gsm.

In lamination it is 50% stiffer than glass and just a little weaker, making it an ideal substitute.

Couple this with an extra flax mesh called PowerRibs, and you end up with a composite that closely resembles carbon, but with just 25% of the emissions.

AmpliTex has already been used in niche boat building projects, including the glorious Flax 27 daysailer by Green Boats of Bremen, which sports cork decking.

Foam sandwich hull construction (green) or balsa core (wood) is much stronger, for little extra weight. Credit: Graham Snook/Yachting Monthly

It was a key part of the lay-up of the new Café Racer 68 from Baltic. Although her hull is in carbon, 50% of the structural members were in flax composite.

France’s Windelo has taken a different tack in its catamarans.

It uses basalt fibre – made from melted volcanic rock – which ‘is slightly stronger than E-glass and just one-10th as carbon intensive to produce and use’.

Its first 50-footer has a hull that also features a recycled PET foam core for strength and stiffness. But it is not just the fibre that is being decarbonised.

So-called ‘green epoxies’ have been developed, where a significant chunk of the synthetic oil-derived molecules of the resin are replaced by bio-sourced molecules.

Gurit’s Ampro for hand laminating is 40% bio derived, for instance.

Green Yachts focuses on environmentally-friendly boat building techniques. Its Flax 27 is built of sustainable flax fibre

And the ProSet range from West Systems includes epoxies containing up to 30% bio molecules.

They can essentially just be dropped into any process that would have been suitable for the equivalent synthetic resin.

‘Any customer that is familiar with epoxy processing, vacuum consolidation or post curing will be very familiar with the process,’ says David Johnson of Wessex Resins, European manufacturer for West.

‘Even wet lay-up with no vacuum bagging.’

There is a modest cost increase, but it amounts to less than 25% compared to a standard epoxy, and a drop in the ocean of the boat’s overall build.

‘Bio-based epoxies are more expensive because there’s more sophisticated chemistry involved,’ says Johnson.

Pre-preg flax fibres being laid up around a balsa core

‘Compared to building a boat in vinylester or polyester, you can use slightly less material because of the superior qualities of epoxy. The end cost differences are negligible and there are benefits in lighter weight: you become more efficient, and the loads are less.’

Suppliers like Gurit are also finding ways to substitute the synthetic foam core used in sandwich hull construction.

Standard foam is made of virgin PVC, with all the associated environmental pitfalls.

Gurit has developed more renewable alternatives using up to 100% recycled PVC and balsa wood.

Builders from Arcona and X-Yachts to Bali and Gunboat catamarans use foam cores in their lay-up to build boats that are stiffer and lighter than they would be otherwise.

Away from composites

Some innovative new boat builders are going in another direction altogether, eschewing the by-now traditional GRP for something that can be genuinely reused repeatedly.

Start-up Vaan is building its 42ft R4 catamaran out of a grade of aluminium alloy commonly used in window frames and road signs, so up to 60% of the hull is already recycled.

‘There’s no way to distinguish it from virgin material,’ says Vaan founder Igor Kluin.

Vaan uses a high proportion of recycled aluminium to build its hulls, which can then be easily recycled

It hasn’t been easy to secure supplies, however. That’s partly because window frames last for 50 years or more and also competition with other sectors.

‘In the short term the costs are higher because there are so many people jumping on the bandwagon, but it has only 5% of the energy use of virgin alloy, so in the end it should be cheaper.’

Vaan’s novel approach to sourcing more sustainable materials extends to the interior finish as well.

It uses a pineapple leaf fabric instead of leather, plentiful European poplar for cabinetry, cork instead of teak decking and recycled PET.

Greener boat building: A hull made from recycled aluminium

Parts of the boat are 3D printed – something that higher end brands are doing more and more of.

‘Recycled industrial PET is being 3D printed for the back of the Vaan spoiler because it produces a lower volume than moulding,’ says Kluin.

‘We want to see if it can become load bearing. We’re also 3D printing with aluminium, too. It’s useful for smaller structural elements that are hard to reach and would traditionally have been milled.’

Recyclability of boat building materials

Besides wood, all forms of composite suffer from the same problem; at end of life, it is very difficult to separate the component materials for re-use.

This is why using materials such as steel or aluminium can make sense, despite the higher environmental cost of the virgin metal. They can be reused repeatedly.

The composite recycling systems developed to date, which include pyrolysis, burning and shredding, are all unsatisfactory because of the energy intensity of the processes or the fact they yield a lower quality material that has to be downcycled.

In principle, it is possible to use resins that melt again at high temperatures and can be collected, refined and reused.

Elium resin from Arkema is capable of exactly that, and is already being used in recyclable wind turbine blades.

Laminate are expensive to separate for re-use. Credit: Rob Wilkinson/Alamy Stock Photo

They even built a 6.50m Mini Transat boat from it.

The process also yields reusable glass, but carbon and flax don’t support the heat: carbon loses as much as two-thirds of its strength and flax simply combusts.

However, an Australian study has shown how carbon-fibre composite can first be heated without oxygen in a pyrolysis chamber to burn off resin, then oxidised to yield carbon-fibre with most of the strength of virgin fibre but only 10% of the environmental impact.

Cured laminates can also be separated using a chemical process proven in the lab at the National Composites Centre, with a big vat of acetic acid.

Portsmouth University is researching enzymes to decompose plastic, starting with plastic bags.

The approach could eventually handle boats as well.

‘You have to find the right enzyme that works for snipping the molecules of a particular polymer. Practically, it’s a decade away,’ says Ashley Parkinson of the NCC.

• Construction
• Optimisations
• Performance
• Equipment care
• Provisioning
• Keeping afloat
• Precautions

Understanding composites for larger boat projects

What is the issue, why address this, how to address this.

• (i) The properties of the fibre
• (ii) The properties of the resin
• (iii) The ratio of fibre to resin in the composite (Fibre Volume Fraction)
• (iv) The geometry and orientation of the fibres in the composite

• 1. Good mechanical properties
• 2. Good adhesive properties
• 3. Good toughness properties
• 4. Good resistance to environmental degradation

• • Accelerator
• • Additives, e.g. Thixotropic, Pigment, Filler, Chemical/fire resistance

• • To reduce the cost of the moulding
• • To facilitate the moulding process
• • To impart specific properties to the moulding

• 1 Adhesive Properties
• 2 Mechanical Properties
• 3 Micro-Cracking resistance
• 4 Fatigue Resistance
• 5 Degradation from water ingress

• 1. The basic mechanical properties of the fibre itself.
• 2. The surface interaction of fibre and resin (the ‘interface’).
• 3. The amount of fibre in the composite (‘Fibre Volume Fraction’).
• 4. The orientation of the fibres in the composite.

• a. E-glass (electrical) - lower alkali content and stronger than A glass (alkali). Good tensile and compressive strength and stiffness, good electrical properties and relatively low cost, but impact resistance relatively poor. Depending on the type of E glass the price ranges from about £1-2/kg. E-glass is the most common form of reinforcing fibre used in polymer matrix composites.
• b. C-glass (chemical) - best resistance to chemical attack. Mainly used in the form of surface tissue in the outer layer of laminates used in chemical and water pipes and tanks.
• c. R, S or T-glass – manufacturers trade names for equivalent fibres having higher tensile strength and modulus than E glass, with better wet strength retention. Higher ILSS and wet out properties are achieved through smaller filament diameter. Sglass is produced in the USA by OCF, R-glass in Europe by Vetrotex and T-glass by Nittobo in Japan. Developed for aerospace and defence industries, and used in some hard ballistic armour applications. This factor, and low production volumes mean relatively high price. Depending on the type of R or S glass the price ranges from about £12-20/kg.

• a. strand - a compactly associated bundle of filaments. Strands are rarely seen commercially and are usually twisted together to give yarns.
• b. yarns - a closely associated bundle of twisted filaments or strands. Each filament diameter in a yarn is the same, and is usually between 4-13m. Yarns have varying weights described by their ‘tex’ (the weight in grammes of 1000 linear metres) or denier (the weight in lbs of 10,000 yards), with the typical tex range usually being between 5 and 400.
• c. rovings - a loosely associated bundle of untwisted filaments or strands. Each filament diameter in a roving is the same, and is usually between 13-24m. Rovings also have varying weights and the tex range is usually between 300 and 4800. Where filaments are gathered together directly after the melting process, the resultant fibre bundle is known as a direct roving. Several strands can also be brought together separately after manufacture of the glass, to give what is known as an assembled roving. Assembled rovings usually have smaller filament diameters than direct rovings, giving better wet-out and mechanical properties, but they can suffer from catenary problems (unequal strand tension), and are usually higher in cost because of the more involved manufacturing processes.

• 1. Parallel non-crimp fibres bear the strain immediately upon being loaded.
• 2. Stress points found at the intersection of warp and weft fibres in woven fabrics are eliminated.
• 3. A higher density of fibre can be packed into a laminate compared with a woven. In this respect the fabric behaves more like layers of unidirectional.
• 1. Heavy fabrics can be easily produced with more than 1kg/sqm of fibre.
• 2. Increase packing of the fibre can reduce the quantity of resin required.

• (i) Better mechanical properties, primarily from the fact that the fibres are always straight and non-crimped, and that more orientations of fibre are available from the increased number of layers of fabric.
• (ii) Improved component build speed based on the fact that fabrics can be made thicker and with multiple fibre orientations so that fewer layers need to be included in the laminate sequence.

• ABS - for rigidity, impact strength, toughness, surface hardness and dimensional stability
• Polycarbonate - for UV-stability, excellent light transmission, good heat resistance & self-extinguishing properties
• Polypropylene - for good chemical resistance
• Polyethylene - a general-purpose low-cost core material

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BoatNews.com

Composite construction, the material of modern production boats

Composite construction has been the most widespread method in shipbuilding since the 1970s. Easy to implement and inexpensive, it is used by many shipyards.

Composite construction consists of using a resin - often polyester - reinforced with fibreglass, kevlar or carbon fibre (more expensive, but lighter) applied in a mould to form the skin of your boat. The exterior is protected by gelcoat .

Two construction methods

There are two different methods for a polyester construction:

• Monolithic construction (resin and fiber reinforcement)
• Sandwich construction (a soul is caught between the two monolithic skins).

The sandwich allows to gain in weight/stiffness ratio if the right core is chosen. This can be made of foam (PVC, PET...) which is less water-resistant, balsa wood (light wood, but less water-resistant) or honeycomb for racing boats.

There are also two methods of applying the resins - contact (roller, brush) or infusion. The latter method allows you to gain in strength/weight, as the right amount of resin is used. It is also easier to use for larger boats.

Composite construction has many advantages, starting with the low cost of production, but above all with the possibility of reproducing a model at will thanks to this moulding technique. It is therefore useful for mass production sites.

On the other hand, monolithic boats are quite heavy, but don't cost too much to build. This is why it is the material used for large series.

Professional BoatBuilder Magazine

The quest for eco composites.

By Hans Buitelaar , Dec 2, 2020

Working with eco composites, the build crew at Innovation Yachts in Les Sables d’Olonne, France, applies Filava fiber to the balsa-cored hull of the Open 60 Ant Arctic Lab, a racing yacht intended to be fully recyclable.

Boat yards and design offices embrace new fibers and resins that promise to reduce pollution, consume less energy in production, and yield composite boats that can be recycled.

“It is going to be a big eight,” said skipper Norbert Sedlacek describing his planned solo nonstop sailing journey to prove the durability and go-anywhere quality of his new brand, Innovation Yachts. The Austrian sailor and filmmaker plans to sail from France through the Northwest Passage around Canada and Alaska, head south over the Pacific Ocean, go left around Cape Horn, circle Antarctica, come around Cape Horn again, and set course north to return to France over the Atlantic Ocean—a 34,000-nautical-mile world-record attempt.

His first attempts at this route around the Americas and Antarctica in 2018 and 2019 ended when equipment problems forced a return to France. His 2020 attempt was foiled by the COVID-19 lockdown when Canadian authorities denied permission to cross through the Northwest Passage, so Sedlacek again postponed. Fortunately, our primary interest is really in his boat, not the voyage.

Ant Arctic Lab under way. The boat has yet to make her ambitious long-distance voyage a reality.

Innovation Yachts’ First Builds with Volcanic Fibers

The boat he plans to sail on this challenging trip is the Open 60 (18.29m) Ant Arctic Lab , which he designed and built to be fully recyclable. It is Innovation Yachts ’ first build in cored-composite construction using balsa-wood panels for the core and volcanic-rock fiber—basalt and solidified lava—for the skin laminates. (The resin is a purpose-engineered epoxy.) The result is a yacht that required less energy to build and employs natural and renewable materials as much as possible. And at the conclusion of its useful sailing life, all the yacht’s composite materials can be separated and processed for reuse in another boat or some other composite construction. (See also Butterfly 46: A Yacht for 2050 )

Besides his own quest as an ocean racer, Sedlacek aims to illustrate that yacht building can be sustainable. “To start something new, you need to gain trust. I want to prove that building yachts from natural and recyclable materials results in better boats. If I can complete this immense trip, rounding the Americas and Antarctica, that will show the ruggedness of the boat,” he said.

Sedlacek and his partner, Marion Koch, founded Innovation Yachts in 2016, in the French harbor town and yachting hot spot Les Sables d’Olonne. While informed by some idealistic thinking, their plan to build ocean­going yachts from natural materials is also powered by a surfeit of practical building and sailing experience. Sedlacek’s first solo circumnavigation was in 1996 on the 26 ‘ (7.92m) composite boat Oase II he built himself. His next challenge was building an aluminum yacht to circumnavigate Antarctica through ice-fouled waters. He completed that in 2000 on Oase III . In 2009, he became the first Austrian to finish the Vendée Globe, the iconic French solo nonstop race around the world. Before he could compete in that race, he engineered modifications to the aluminum and composite construction of Austria One to bring her into compliance with International Monohull Open Class Association (IMOCA) 60 design rules.

Next, he created the concept and design and then served as project manager for the 91 ‘ (27.74m) aluminum luxury cruising yacht Bellkara , a sloop with a lifting keel built in 2016 at the Conrad Shipyard in Gdansk, Poland.

Ant Arctic Lab’s lightweight structural core of FSC-certified balsa wood from 3A Composites also provides a measure of sound and thermal insulation to the hull.

Innovation Yachts’ plan since 2016 has been to prove the concept of quality yacht building with a low carbon footprint and fully recyclable materials. Technical Director Marion Koch had written her master’s thesis on the hydromechanics and material properties of IMOCA 60 ocean-racing yachts. Together with Sedlacek and working with her company, Yacht Construction Consulting in Altlengbach, Austria, they introduced volcanic fiber into boatbuilding. The first marine application of the laminate was in the 4.9m Open 16 sloop Fipofix . Sailing this small boat in 2013–14, Harald Sedlacek, Norbert’s son, claimed three world records crossing the Atlantic from Europe to North America and back. (Fipofix, or Fiber Positioning Fixation, is a patented method of processing volcanic fibers into unidirectional fabric, explained below.)

Eco Composite Products and Processes

While modern, the design of Ant Arctic Lab is not dramatically different from other ocean-racing yachts. Recyclability comes largely from its materials. The hand-laid hull is a conventional balsa-cored composite structure. Balsa is super-lightweight, with good strength, stiffness, sound-dampening, and thermal-insulation properties. Innovation Yachts’ balsa supplier, 3A Composites , harvests from Forest Stewardship Council–certified plantations in Ecuador. Because balsa trees grow to 98.43 ‘ (30m) high and 3.28 ‘ (1m) in diameter in just five years, the planting-to-harvest cycle is so short it causes no measurable deforestation, making it a sustainable and quickly renewable resource. As it is absorbent, it also provides an excellent bond with the fiber and resin layer.

The innovation comes from the fiber, a laminate textile called Filava, made of volcanic rock and produced by the Belgian company Isomatex . Volcanic rock is melted at high heat and drawn into fibers, resulting in a strong, water-repellent, lightweight material that resists high temperatures and chemicals. Filava is available as unidirectional fiber tows and as woven fabric. Although the largest European production facility in the town of Gembloux, southeast of Brussels, opened in 2008, volcanic rock fiber has previously been used in composite windmill blades, airplane and car parts, and sports gear.

Cutting the woven Filava fiber from Belgian composite supplier Isomatex. To produce the fiber from basalt and lava rock, the raw materials are melted at high temperature and drawn into fibers that are then processed as unidirectional fibers or woven roving

Volcanic fiber has a melting point of 2,516ºF (1,380ºC), meaning that walls and doors made of Filava can be applied as fire-protection barriers. The fiber also absorbs vibrations and is highly shock resistant. Innovation Yachts considers laminates from volcanic fiber comparable in strength to carbon fiber but at a lower cost, which would make it a desirable boatbuilding material.

Made from basalt rock and other natural components, Filava’s fibers compare favorably to other more common fibers in composite construction: high impact resistance like aramid or Kevlar, better elasticity than fiberglass and carbon, resistance to acid and alkaline environments, and no galvanic corrosion where it’s in contact with metals.

In Isomatex’s proprietary process, raw materials are carefully mixed in a computer-assisted blender and transported by a pneumatic conveyor to the electric induction furnace to melt and refine the lava. The complex process requires high temperatures. The electric furnaces operate two to three times more efficiently than oxy-fuel or gas-fired alternatives. While Filava consumes less energy to produce than do most carbon fibers, it requires more than flax or glass fiber does.

Recognizing that the main dis­advan­tage of raw volcanic fiber is its fragility, Koch’s Yacht Construction Consulting and Norbert Sedlacek, in collaboration with the Austrian telecommunications and logistics company Kapsch, developed a patented process called Fiber Positioning Fixation, or Fipofix. The technique processes the brittle, touchy volcanic fibers into rugged unidirectional fabric purpose-built for marine applications. Other conventional assembly methods (weaving, stapling, and sewing) damaged as much as 40% of the roving filaments, decreasing the product’s performance under compressive and tensile loads. Fipofix bonds the positioned fibers to the respective matrix in the mold for final processing without using foreign materials such as yarns, clamps, or other adhesives that additionally weaken the part. The Fipofix proof of concept was Harald Sedlacek’s record-breaking Atlantic crossing in the Open 16 of the same name.

Custom Epoxies

The composite’s third and final component is the resin. Innovation Yachts chose the resin supplier bto-epoxy (Build to Order, in Amstetten, Austria), an innovative company producing custom epoxies since 2012. The resin shows no shrinkage, contains no harmful solvents, and is intended to remain with the fiber and balsa beyond the end of a yacht’s life, allowing all three materials to be reused. Koch: “We will not heat the epoxy, as it will take a lot of energy to heat all of the materials to the melting point. A lot of the material will then be burnt, so will not be available for recycling anymore. Yet the remaining fibers will be shredded and only need a bit of epoxy to be applied again.” Innovation Yachts has tested the reusability of shredded fibers recovered from composite test panels for the Ant Arctic Lab by incorporating them into non-load-bearing components for new boats, including the dashboard of a yacht tender.

As bto-epoxy is processed from fossil oil, Sedlacek explains this somewhat counterintuitive choice for a yacht largely built with renewable components and materials: “We do not want to use any material that is not developed for yacht building. Yes, there are ‘green’ epoxies available, but they do not have the same properties yet as the resins made out of fossil oil. We do not want to use any construction materials in the hull that are not specially produced for maritime use, or that don’t outperform the ones commonly used in maritime applications.” In some parts of the interior, Innovation Yachts uses epoxy made of vegetable oil, but Sedlacek says it lacks the material properties to have the endurance, water resistance, and impact absorption that the bto-epoxy offers. “As soon as an epoxy resin is developed out of renewable resources that does have the right properties, we will use it,” he said.

Sedlacek is confident of his vision and the leading role his company intends to play: “When an Innovation Yachts hull comes back to the yard after its 30-year lifetime, or even longer, the owner should be getting money for the materials that can be derived from the boat. They have value because of the reusability.”

Sedlacek says he’s looking for long-term investors, because it “takes time to develop something new.” He is convinced that Innovation Yachts is on the right track ushering in an era of more sustainable materials in boatbuilding. “Our new technology is better and cheaper, and recyclable. Massproduction yards will follow. I am convinced they will need to.”

Scaled Up at Amer

Amer Yachts , builder of motor­yachts from 20m to 30m (65.6 ‘ to 98.4 ‘ ) in San Remo, Italy, chose Filava for their composite hulls. As the super­yacht industry requires class society certification, the yard has started a cooperation with the Italian composites company GS4C to test and further develop composites from the recyclable fiber. Class societies ENEA (the Italian National Agency for New Technologies, Energy and Sustainable Economic Development) and RINA (Registro Italiano Navale, the Italian class society for ship safety certification) are studying Filava’s properties to assess durability. As this certification takes time, the Amer yard will introduce the new fiber in small steps. First, it will be used in nonstructural components. Following successful application, more parts may be constructed from the volcanic fiber.

A rendering of the proposed sailing beach cat for La Bella Verde charter company. The final boat is intended to be sailed by a professional captain and as many as 11 guests. Auxiliary propulsion and onboard power are provided by electricity from solar panels.

An Eco Composite Beach Cat

To provide the most sustainable boats possible, the founders of the yacht charter company La Bella Verde tapped Innovation Yachts to design, engineer, and build their new 10.6m (35 ‘ ) sailing beach catamaran. The boat accommodates 11 guests and a professional captain, with ample space to relax on the trampoline. There is a head in one of the hulls, a fridge, and a sound system—requisite items for beach-hopping in the Bal­earic Islands, where these new catamarans will be chartered at waterside locations on Ibiza and Formentera.

La Bella Verde set out to prove that ecologically benign boating can be a modern, fun luxury experience. Maarten Bernhart, one of the three founders, explains how the company started in 2014: “We bought one open catamaran and converted it to electric propulsion for getting out and into harbors. We continued to convert more open catamarans to green electric-propelled boats [and] sold about seven refitted beach cats.” In search of a suitable day charter catamaran, Bernhart said he found a Rush 10 (32.8 ‘ ) owned by a former builder, and the company bought the molds to build and sell these cats.

Looking for a boat with an even smaller environmental footprint, La Belle Verde teamed up with Innovation Yachts’ Sedlacek and Koch. With a new design ready, the first boats started being built at the Innovation Yachts yard in 2020. They are a sandwich composite of FSC-certified balsa core—made with Filava and bto-epoxy skin laminates. “We offer the La Bella Verde cat to small charter companies that want to stand out with a nonpolluting boat,” Bernhart said. “And we will expand our own fleet with those catamarans.”

A deck detail of the port quarter of the Judel/Vrolijk-designed Flax 27 illustrates the superb aesthetic qualities of the sustainable building materials— clear-finished flax-fiber composite and cork decking—that Green- Boats (Bremen, Germany) selected for the performance daysailer.

Flax Fiber and Linseed-Oil Epoxy

Friedrich Deimann, founder of Green­Boats , a start-up boatbuilding company in Bremen, Germany, calculates that it takes five times as much energy to produce glass fiber rovings, and 20 times as much to make carbon fiber, compared to growing and making fibers from flax. “It is really not nice to work on the construction of composite yachts built in the conventional way,” he said. “The glass fiber or carbon fiber is invasive to the body. The resins and solvents are toxic. Still, after having built a lot of handcrafted wooden sailboats, I was attracted to the possibility of building strong and lightweight in composite. So, when I found flax as a possible fiber, I was eager to use it.”

The high resin absorption rate of the flax fiber makes hand lamination challenging. Resin infusion at GreenBoats allows for better control of the ultimate resin/ fiber ratio.

Next, researching a sustainable core material for sandwich composites eventually led him to cork. It is lightweight, does not absorb water, and has good impact resistance. The hardest ingredient to find was a nonpetrochemical resin. Linseed-oil-based epoxies are available, but most of them do not generally yield the watertightness, durability, stiffness, and shock absorption required in yacht construction. But after extensive testing, Deimann found the right linseed-oil-based epoxy to bind a unique composite of flax fibers and cork core together. In that quest, he said he has tried numerous epoxy resins. The tested epoxies range between 20% and 80% bio-content and are produced by multiple resin manufacturers. Some are better optimized for hand layup, while others are best for infusing, he says. In short, the best resin depends on the material qualities of the fiber and the structure it is being applied to.

The most recent tangible manifestation of Deimann’s research, the Judel/Vrolijk-designed Flax 27 daysailer, is also the boatbuilder’s most complete natural-fiber composite project to date. Finding just the right combinations of flax cloth and linseed-oil epoxy provided the solution for that build. Because flax fully absorbs the resin but is lighter than glass, the resulting laminate can be quite dense. Together with a good core material, the flax/epoxy laminate yields a composite Deimann says is good for building boats. He warns that the high resin absorption rate makes hand lamination of flax material a challenge. He prefers to use resin infusion which better controls the resin/fiber ratio. But he depends on using tightly twisted flax fibers in a dense weave that has high surface density and leaves little space for extra resin to pool between the yarns.

Because the fiber naturally absorbs wet resin, a dense textile weave of tightly twisted flax strands is best for most composite uses.

When they started building the first flax composite boat by hand in a shed with a group of friends and no budget, Deimann and his co-workers had to prove that natural materials could result in an even better composite boat than those made out of petrochemical sources. They’ve come a long way with the 2019 introduction of the much-praised daysailer Flax 27 (8.2m) weighing just 2,645.55 lbs (1,200 kg). GreenBoats offers a choice of core material: cork, or foam from recycled PET soda bottles.

While boatbuilding and sailing remain its focus, the company’s production use of natural-resource composites reaches many other industries, including power generation, automotive, architecture, and outdoor sports. “We do a lot of prototyping to introduce other companies to the use of natural-fiber-reinforced composites,” Deimann said. “The materials selected and the manufacturing process depend on the requirements for the product: life expectancy, quantities, mechanical requirements, etc. This is where the journey with our customers begins, and together we work out various options and compare them in costs, performance, and sustainability.”

GreenBoats has conducted extensive testing to determine the structural properties and the best combinations of sustainable fiber, resin, and core material, such as this flax/cork sandwich composite.

Big Companies Invest in Eco Composites

While the first yards to explore the practicality of building boats from recyclable or sustainable composite materials had to search for the right resins, the large resin manufacturers—often petrochemical companies—are now developing and introducing recyclable and bio-based resins. While I was writing this article, the French chemical company Arkema gave me a questionnaire about the need for eco-resins and the demands boatbuilders would have for such a bio-epoxy. Within weeks, the outcome of the poll and the company’s answers were shared. Arkema has been working to improve its Elium thermoplastic resins to make them recyclable. The resin, though still fossil-oil based, can be separated from the fiber and core material at the end of a boat’s service life.

In practice, composites recycling can be done in two ways: mechanical and chemical. Mechanical is grinding the composite into small pieces and reusing them as a filler material that can be bonded by adding new resin. The chemical approach is to heat the composite so the Elium resin will melt out of the fibers. The resulting crude recycled monomer can be distilled into pure recycled monomer, which can be used as a resin to build new composites.

The Flax 27 daysailer is an effective proof of the materials and build process for the flax/epoxy boats. It’s also an attractive hull and rig design that performs well, which is vital for a model intended as a production-built consumer product.

Global composites supplier Gurit has been working with Swiss high-tech start-up Bcomp, which produces flax fiber. Products now sold through Gurit’s broad distribution networks are Bcomp’s ampliTex and powerRibs. The latter is a structure of flax fibers inspired by the veins of tree leaves to create extra stiff structures at minimal weight. Gurit also sells foam-core material from recycled PET soda bottles; and in its Ampro epoxy resin line, the company offers Ampro Bio, a plant-oil-based epoxy containing roughly 40% plant oil and 60% fossil oil. While none of these fibers, core material, and epoxies are designed for recycling, after being shredded at the end a boat’s service life, the composites may have a second application as material for nonstructural parts—much like the reuse of Filava composites described by Koch.

About the Author: Freelance journalist Hans Buietlaar, who lives in The Nether­lands, specializes in yachting and the maritime industry, focusing on technology and sustainable innovations.

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Composite Yacht Construction

A better way to build boats, the preferred yacht & boat construction method among the most knowledgeable designers, builders and owners..

New Boat Construction Advantages.

Westport composite yacht construction maximizes the life of the yacht, reduces maintenance costs & maintenance time, & maximizes resale value & enjoyment.

Every Westport yacht features proven technology in composite construction. Westport exclusively builds all hulls and major deck parts in one-piece, precision-engineered molds. Fewer parts mean greater structural integrity and resistance to stress.

For the Westport yacht owner, that translates to year after year of enjoyable, trouble-free cruising.

All Composite Boat Building – Superior Results and Value

As a yacht builder of long standing, Westport also takes a long-term view of the future, and has invested heavily in facilities, processes, and proven technologies to secure our position at the forefront of the industry.

We were among the first to recognize the attributes of all-composite construction, and have worked closely with the composites industry, even pioneering new techniques and materials that currently are used industry-wide.

Thanks to their lighter weight, composite yachts are faster and more efficient than their comparably powered steel or aluminum counterparts.

Space-age materials give composites superior strength and impact resistance for unexcelled structural integrity.  Composites can have a very high strength-to-weight ratio.

A composite structure effectively isolates and absorbs sound, reducing hull and mechanical noise levels for quiet operation. You benefit from a more enjoyable operation both while cruising and while stationary at dock or anchorage. The spread of noise and and vibrations associated with noise are reduced.

A composite yacht offers superior thermal insulation properties, making it easier to air condition for greater comfort in warm-water cruising, or to heat in cold climate cruising. Generators operate more efficiently because of reduced air conditioning loads.

Less Maintenance

Composite materials are not susceptible to rust or galvanic corrosion, and so require less maintenance than metal. You spend more time on the water while reducing the cost of upkeep.

A composite yacht offers exceptional structural integrity to ensure long life and maximum return at resale time. Advanced coring materials and resins give composites exceptional impact resistance for long, trouble-free life.

Advanced Design and Engineering

Westport Yachts is unsurpassed in the application of computer-aided design and manufacturing methods within the mega-yacht, boat building industry.

We are unmatched in the precision of tooling, patterns and finished parts, fundamental to a first-class build.

Westport Yachts – Exceptional Yacht Building & Superyacht Craftsmanship

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• Hull Materials, Which Is Best?

As Phyllis and I think about what our next boat might look like, one of the primary decisions is hull material.

We have several chapters in this Online Book about the characteristics of the four general available options, steel, aluminum, wood and fibreglass (see Further Reading below), but that still leaves the question: Which is best, not just for Phyllis and me, but for you, too?

As usual, the answer is the oh so annoying: it depends on what we plan to do with the boat.

But what I can say, is that there are two materials that are pretty easy for Phyllis and me to drop from the hull materials prospect list. So let’s start with that, and then move on to the two left standing to pick a winner.

Hull Material We Won’t Consider

We will not even be looking at boats made of steel or wood—not quite true, we might consider a good wood epoxy saturation build—and that’s also our advice to most of you.

Why neither of those two materials? Both are intrinsically unstable. Or, to put it another way, no matter how well the boat is built, if left to their own devices, wood will rot and steel will turn into a pile of iron oxide.

OK, before you take me to the woodshed in the comments, let me make clear that I understand that good boats can be built of both wood and steel.

One of my good friends has a wooden boat that has given great service (including a bunch of ocean crossings) for decades, and will continue to do so for many more. But he built her himself, has cared for her meticulously, and has incredible skills. But I’m not Wilson (that’s his name) and, in all likelihood, neither are you.

The same applies to steel. If you built the boat yourself, or supervised every step of the build, and then cared for her yourself, it can work. Just look at the amazing voyages made by AAC contributor Trevor Robertson in Iron Bark .

But we are talking about second-hand boats for most of us, so steel and wood are out because it’s difficult to be reasonably sure in a pre-purchase survey on either material that something horrible is not going on deep within the structure. Something that, when discovered, can turn our new-to-us boat into a worthless pile of junk—we are talking the risk of serious wealth destruction here.

Still not convinced? Let’s dig deeper.

There’s another big problem with wood. If we find say a rotten stern post, or any other structural member after purchase, the skills and time to replace it are prodigious. Heck, just replacing a single plank in a way that will actually be watertight takes great skill and perseverance. Way beyond practical DIY for most of us. And I have seen professional replacement of just a few rotten members in a wooden boat cost over US$100,000.

What about steel? Well, on the positive side, repairs require less skill than wood. But the problem is it is very difficult to build a boat of steel under about 45 to 50 feet that will sail or motor well. The reason is that steel plating must be of a certain minimum thickness to be workable and not deform, regardless of boat size, so small steel boats are pretty much always too heavy, at least for the performance that Phyllis and I want.

And, finally, the maintenance of a steel boat is simply no fun—unless you have some perverted love of chipping rust and working with toxic chemicals—and to make that worse, any breach of the coating must be dealt with promptly and properly.

The bottom line is that I know a lot of people who own a steel boat, or have done so in the past, but I have never met anyone who has owned a second steel boat.

All that said, I guess purchasing a steel or wood boat with a history like those I mention above, from someone you really trust, would be OK—particularly if you make clear that if they have lied to you, you will hunt them down and… And the advantage of this course is that you can often get a lot of boat for very little money.

Hull Materials We Will Consider

Where does that leave Phyllis and me, and probably you, too? Yup, with fibreglass and aluminum. Both are intrinsically stable—assuming we don’t do something stupid, and, when built right, a hull of either does not deteriorate just because of the passage of time.

And both can be surveyed prior to purchase to make fairly sure (there is no certainty) that there is not something horrible lurking. Yes, I know there are many horror stories (I have one of my own) about fibreglass boats with hidden faults, but that’s a survey failure, not a material one. (More on how to avoid survey failures coming soon.)

So which is best, aluminum or fibreglass? Brace yourself. I’m going to do it to you again. It depends on what you want to do. Let’s look at each.

As a 30 year aluminum boat owner, I love the material. And if Phyllis and I were planning to go to seriously hazardous places (as we have in the past), aluminum would be our only choice.

But on the other hand, aluminum is a bitch to keep paint on, an expensive bitch. And, by the way, don’t think for a moment that leaving the hull bare solves that. Prepping and painting the deck and cabin of an aluminum boat to the yacht standard that many owners want and want to maintain, will, if done right by professionals, cost as much or more than painting an entire fibreglass boat.

The point being that if you are considering aluminum, you need to do as I do: take your glasses off when you see the paint bubbling. Or, better yet, seriously embrace the industrial look and have no paint on deck or hull, other than non-skid.

Also, although there is no question that most of the horror stories you hear about aluminum are just that—stories—the material does require caring for, including closely supervising anyone who works on the boat. Most boatyard professionals are dangerously ignorant about aluminum and many will make that worse by not appreciating their own ignorance.

So that leaves fibreglass. And for Phyllis and me, who now want a boat that we can safely leave unattended far from home—we are now part-time cruisers—that’s the way to go.

Also, as we age further, we will be paying boatyards to do more and more for us, another plus for fibreglass, since it’s more resistant to unsupervised ignorance—boats with core in the hull, particularly balsa, not so much—than aluminum.

Bottom line, if you are not willing to learn the basics of aluminum boat care and won’t be constantly present to rigorously enforce that knowledge on others, choose fibreglass. On the other hand, the good news is that said aluminum boat care is not hard, and not magic. See Further Reading for our complete guide.

I’m guessing that many of you steel boat owners are now seething and reaching for your keyboards to tear me a new one. Feel free to disagree and tell me why steel is great, but be realistic.

And please keep in mind that we have a lot of readers who do not have a lot of boat ownership experience. So if you blow sunshine about the issues with steel boats, particularly old steel boats, you may make yourself feel better, but you may also tip someone into a life altering decision with substantial negative consequences. Not something any of us need on our conscience.

Further Reading

• How to care for an aluminum boat in 27 easy steps.
• Much more on buying a boat .
• How to care for a cruising boat, once you have bought her.
• The engineering characteristics of hull materials.
• Impact resistance and why it matters .
• More on boats from Boreal .
• More on Ovnis .

Please Share a Link:

More Articles From Online Book: How To Buy a Cruising Boat:

• The Right Way to Buy a Boat…And The Wrong Way
• Is It a Need or a Want?
• Buying a Boat—A Different Way To Think About Price
• Buying a Cruising Boat—Five Tips for The Half-Assed Option
• Are Refits Worth It?
• Buying a Boat—Never Say Never
• Selecting The Right Hull Form
• Five Ways That Bad Boats Happen
• How Weight Affects Boat Performance and Motion Comfort
• Easily Driven Boats Are Better
• 12 Tips To Avoid Ruining Our Easily Driven Sailboat
• Learn From The Designers
• You May Need a Bigger Boat Than You Think
• Sail Area: Overlap, Multihulls, And Racing Rules
• 8 Tips For a Great Cruising Boat Interior Arrangement
• Of Cockpits, Wheelhouses And Engine Rooms
• Offshore Sailboat Keel Types
• Cockpits—Part 1, Safe and Seamanlike
• Cockpits—Part 2, Visibility and Ergonomics
• Offshore Sailboat Winches, Selection and Positioning
• Choosing a Cruising Boat—Shelter
• Choosing A Cruising Boat—Shade and Ventilation
• Pitfalls to Avoid When Buying a New Voyaging Boat
• Cyclical Loading: Why Offshore Sailing Is So Hard On A Boat
• Cycle Loading—8 Tips for Boat and Gear Purchases
• Characteristics of Boat Building Materials
• Impact Resistance—How Hull Materials Respond to Impacts
• Impact Resistance—Two Collision Scenarios
• The Five Things We Need to Check When Buying a Boat
• Six Warnings About Buying Fibreglass Boats
• Buying a Fibreglass Boat—Hiring a Surveyor and Managing the Survey
• What We Need to Know About Moisture Meters and Wet Fibreglass Laminate
• US$30,000 Starter Cruiser—Part 2, The Boat We Bought
• Q&A, What’s the Maximum Sailboat Size For a Couple?
• At What Age should You Stop Sailing And Buy a Motorboat?
• A Motorsailer For Offshore Voyaging?
• The Two Biggest Lies Yacht Brokers Tell

What are the hull and deck panel thicknesses on MC?

As I remember, hull 1/4 to 3/8 in the keel. deck 3/16″. That said just looking at plate thickness does not tell you a lot. For example MC is built with very closely spaced frames and stringers which add a lot of strength but less weight than heavier plate and fewer frames and stringers.

John, I hear your warnings about steel, and I know this might be a complicated route to go. My main reservations about fiberglass boats is that the majority of them come with external keels which is fine for me for a one or two weeks charter but something I absolutely do not want for my own future boat. Encapsulated keel structure (or welded on as with steel hulls), a deep V forefoot, and a rugged skegged rudder, are characteristics that can more often be found with steel hulls as with “plastics”. When going for my survey I plan to come with a fiber optic to inspect all those remote places, and would certainly rule out a boat where I would not have access to most if not all hull places. That said, if I were to buy now, my current favourite on the market is a fiberglass ketch 😉

I would not recommend discarding all external keel boats from your list. Yes, the modern trend to bolting through light skins and then using a glued in web to stiffen things up is intrinsically dangerous, but there are plenty of external ballast boats that are built properly.

And internal ballast is not without problems. Like with most things it all depends on the execution.

And there are good hull forms in GRP too. In fact, in my experience, a lot of steel boats are designed very poorly.

Anyway, I would not take on the risk and maintenance burden of a second hand steel boat for those reasons.

Agree with everything you say about steel boats. When I got back from Vietnam in 1969, I took all of my savings and bought a steel 45 steel schooner and lived on her. I went to work at the Naval base in Pensacola, FL and left my wife to chip, sand and paint the rust spots that seemingly appeared almost every day inside and outside ( no wonder she divorced me! ) I finally sold the boat to a “know it all” and bought a Hinckley 50 fiberglass yawl — problem solved!

Hi Patrick,

Thanks for the report. Another person who has owned one steel boat!

I totally agree with your conclusions on this. No material is perfect but fiberglass has a lot to be said for it overall and aluminum is great when a bit extra is required. Aluminum is actually the only material you have listed that I really don’t have much experience with beyond little skiffs so it is the one I can’t properly comment on but I like the concept.

I have had a lot of interactions with wooden boats including having a good sized one in the family and working aboard several. While I love these boats and think they look great, our boat is fiberglass and that is intentional. For that matter, our boat doesn’t have any wood on deck at all. With wooden boats, like most things, it really comes down to who the owner is. An owner who gets it and stays ahead of maintenance puts in surprisingly little time (still a whole lot) dealing with rot and paint that won’t stick. An owner who is a little less vigilant and deals with a deck leak by hanging a diaper under it rather than getting out their irons to fix it will find the boat falls apart on them incredibly quickly. In my experience which is all salt water based, deck leaks are the biggest killer of these boats by far and they are actually comparably one of the easiest to track down and fix. Even for an owner who farms out the wood work, I would say that if you can’t fix a deck leak and don’t have oodles of money, then it is a disaster waiting to happen.

With steel boats, all I have to say is that I hate the sound of a needle scaler. If you have a ton of money, there are great examples like the Columbia replica but that is not attainable for most of us.

I realize that there are a lot of people who get very nervous with keel bolts (and bolts in general in anchors and other things) and while it is something to watch, I think that it is a good trade-off given the other options. I think that a lot of the issue is that the average person does not know how to evaluate whether a bolted connection is a good connection and there have been an awful lot of poor connections built over the years. An example of a good connection is most connecting rod bolts which have enormous numbers of cycles, vibration and other factors to contend with but yet basically never fail unless there is another underlying issue such as the caps being mixed up. By getting the bolt stretch length long enough, using appropriate materials, having appropriate mating threads and using enough torque/tension, you end up with bolts that don’t back out and do not fatigue. Keels are a bit tricky as very few materials won’t suffer from some sort of corrosion if there is any water and fiberglass creeps so it is difficult to maintain constant tension but I think that you would find an extremely low failure rate on well designed connections and that most of the failures were on connections where an analysis would have shown that the margins were low and best design practices were not followed.

On wooden boats, although I have little first hand experience, as you say, and I see demonstrated by Wilson, a skilled and diligent wooden boat owner can make the maintenance look easy, but let a wooden boat get away from you and there will be tears.

On keel bolts, a question for you? If contemplating buying an old boat with external ballast, would it make sense to insist that before purchase the keel bolts (assuming accessibility) were torqued to the proper value for their material and size?

My thinking is that, assuming the construction and bolts were right when built, the biggest risk, particularly with SS bolts, is that they have wasted at the keel to deck joint due to water ingress, so if they withstand the appropriate torque without breaking we can be pretty sure that that they are not appreciably weakened. Does that make sense?

I would make no such assumption about the keel bolts. They may be seized, in which case you’ll see the correct reading on the torque wrench but the pre-load tension in the bolt will be wrong. They may also be partially corroded, in which case they may withstand the torque but still be capable of failing in tension if the boat were to, for example, ground on a reef.

If it’s possible to get at them to check their torque, it shouldn’t take much longer to completely remove the nuts, one at a time, to check the studs or the cavities for signs of corrosion before re-torquing them to the proper specs. If it’s not possible to do this, then it’ll be difficult for *any* non-destructive examination to reveal what you want to see.

Thanks for coming up on that. How about just loosening a half turn and then torquing to spec? What I’m trying to come up with here is a way to at least check for a really bad keel boat situation in a way that will be acceptable before purchase, and I fear that if we try and actually remove the nuts and backer plates the seller will reject the idea—just torquing the bolts is going to be a hard enough sell.

So, I get that the bolts may still be a long way from original after this test, but at least it will catch the ones that have corroded really badly. Also, I’m not sure that removing the nuts would tell us much since the bad bolts I have seen were corroded where the keel meets the hull, but would have looked fine from above, even with the nuts off.

Bottom line, I get that this is not a great solution, but my thinking is that it’s practical and a lot better than nothing. Would you agree?

Pull a few and inspect is probably the only real way to to be sure. At least this is done on a woodenboat.

Ignoring whether a seller will or should allow retorquing keel bolts, the theory is good but the practice is somewhat more problematic. Proof testing is a well established industry practice that has proven to be pretty effective. Periodic hydrotesting of pressure vessels such as boilers, tanks, etc is just one example of something that has been successful at eliminating a lot of dangerous failures.

The first practical issue is what torque do you apply. I design capital equipment not sailboats so don’t know exactly what is done as there are multiple schools of thought but if I were designing one of these joints, I would figure out my worst case loads, choose a preload of ~2X and then upsize the bolts from there a bunch to give a corrosion allowance but not increase the preload any more. The question is, what was done on the boat you are looking at. The average person does not have the knowledge to calculate what the maximum per bolt load is and then we don’t know the factors from there. I suspect that there are some boats out there where the torque value from the factory is 75% of yield just like most bolts are but I also suspect there are a lot of boats out there where the preload will be more on the order of 30% (I have it written down at home but I believe this is approximately what I calculated for ours with the assumptions I made). In the case where the designer did not leave a corrosion allowance, then a torque to 75% of yield is entirely appropriate but on other boats, you could break a bolt which while corroded was actually still well within allowable parameters or you could crush the laminate if there is insufficient load distribution for the higher tension. All of this can be calculated with fairly simple calculations but having anybody without training apply it is problematic and even then, you are really doing a proof test not just a retorque as you likely won’t know the original torque. If anyone knows of a standard that all designers hold to so a way to avoid the guessing game of the factory torque, I would love to know it.

The other practical issue that comes to mind is the imperfect relationship between torque and tension. Engineers refer to this relationship as K factor which is basically friction between the threads and the faces. When tension is really critical, the standard thing to do is to actually use oil or grease which are more repeatable and represent a lower K factor. If there has been any galling at all which is a real problem with stainless, all bets are off and you could even break the bolts before bottoming out if it is really bad. This is really the long way of saying that it is really inexact if you do it dry, you would really want to clean everything well and then oil the threads. Of course, if you are NASA, then you can actually measure tension on the bolts but everyone else is left using torque as a proxy.

Given all of this, I am not sure that most sellers could be made to agree to a specific torque number unless original build documentation can be found with a number which I don’t think that I have ever seen (unfortunate and kind of scary). Retorquing is definitely not a bad idea and I have done it on our boat, I just don’t know how to implement it simply and quickly unless someone knows that all keel bolts were originally torqued to some % of yield or something equivalent.

Hi Eric (and Matt),

Thanks for going to all the trouble to explain that. As so often happens, I’m a lot wiser after reading your and Matts thoughts. And clearly my idea is not a good one.

The sad part about that is that I think those of us considering an older boat may have a real problem that’s not generally recognized: Having wandered around boat yards a lot lately, I’m seeing a lot of otherwise good looking boats with stains indicating that water has penetrated between the keel and hull. I’m also guessing that a lot of boats for sale have had those stains covered up with paint.

Add in that many of those boats will have stainless steel keel bolts and I’m starting to think that the only good answer with a boat like that is going to be to drop the keel to check the bolts before heading offshore.

Of course we will not be allowed to do that before purchase, so that leaves walking away from a lot of good boats, or assume the risk. And the risk is not trivial. If the bolts are bad, replacement can be a serious matter. One experienced person at a quality builder said that the best and least expensive solution is to recast the keel with new bolts! The point being that most keels have J bolts cast in, and he said that hacking them out is a disaster—he has seen it tried.

So the more I think about this, the more I think that a lot of people who think they have refitted their boat for sea may in fact be sitting on a pretty nasty problem that would be hugely expensive to fix. And that as the years go by, this is only going to get worse. (A lot like the problems with SS in old rudders.)

I would really appreciate any other ideas of how to deal with this, or alternatively reassurance that I’m overthinking this. Also, do you think bronze keel bolts relieve at least some of this worry? With SS all I can think about is those bolts sitting in a wet oxygen deprived environment for 30-40 years! How about industrial x-ray? Expensive, I imagine, but probably a hell of a lot less than a keel bolt replacement.

John, you just elaborated very wisely the reasons why I will certainly not be looking for a boat with an external keel. You just can’t look inside (and I doubt even industrial xray could reliably see cast-in bolts). It is just like playing lottery, and what I learnt is at least that I will never win 😉 You’re right that encapsulated ballasts have their own issues, but at least they cannot fall off during a passage.

Your call, but what I’m finding is that there are so few really good boats out there for sale that even come close to my critical needs that to settle on a single keel construction type would limit my choices. This is particularly true since I want a boat with good performance, which is harder to do with an encapsulated keel, particularly in GRP.

Also, a boat with a bad encapsulated keel can be really bad. Think steel punchings in concrete. If that lot gets cooking and splits the outer sheath (I have seen 3 of these in the last month while wandering around boat yards) the repair would be way harder than new keel bolts. Just think about jack hammering out all that stuff!

Point being there are good boats built both ways, ditto bad boats.

Just to clarify, I was not asking about X-raying the bolts inside the lead. The problems I have seen are wasting in the hull to keel joint and a bit above. Seems like X-rays would pass through the GRP and show the bolt, but then again I have no clue, which is why I asked the engineers. As I remember Matt has worked on medical imaging equipment, so we may easily get a good answer.

Hi John, Your question highlights for me that another valid comparison (apart from hull material) might be long run production boats vs short run / custom boats. Long run production yachts of course favour fibreglass of course and tend to have more than a few things worked out over time – one of which is to make them as “charter friendly” (aka idiot proof), as possible. But am I right in my supposition that for this reason, most long run production boats will have steel keels, secured with stainless bolts tapped down into the metal keel? And short run designs (not generally being for charter markets) take advantage of the performance gain with lead keels, but have studs penetrating up through the hull, with securing nuts? Reading between the lines of Matt and Erics’ responses, it seems you must remove the keel to really check the studs on a lead keel and even then there could be something lurking deeper inside. Conversely, to check the keel bolts in a steel keel yacht, you could simply specify removing say 25% of the bolts at pre-purchase survey time. For total peace-of-mind, replacing all the keel bolts on our Beneteau 473 with original OEM bolts costs about $200 US, available ex-stock from the Beneteau Spares web-site (as are most other parts by the way, even now 15 years since launch). Now I get there are pro’s and cons of lead vs steel keels. But the simplicity and integrity of a steel keel is really hard to beat. I know of a Beneteau 473 that hit a rock doing 8-9 knots under motor, coming to a crash stop. The only damage the surveyor could find on the Monday (up on the hard) was a fleck of anti-foul chipped off. No gap in the hull joint, no weeping at the keel / hull join, no cracking in the anti-foul. Internally, no damage to the lay up or the supporting girders either. No harm, no foul as they say in America. So how about a long run production boat, John? br. Rob ps – no, it wasn’t our B473!

That’s a good point although I do wonder about the actual practicality of unscrewing a keel bolt that’s been imbedded in steel for years without it shearing off. I guess it would depend on how well the original builder had treated the bolt threads with an anti-seize of some type. As usual, we are at the mercy of the builder’s QC since one small mistake in construction can lead to a world of hurt 20 years later.

And good to hear that a Beneteau withstood a grounding so well. However, I would not want the impression left that this is always the case with boats from Beneteau since at least some of their later boats are built with a keel construction technique that is fundamentally dangerous, particularly after a grounding: https://www.morganscloud.com/2014/06/05/cheeki-rafiki-tragedy-time-for-changes/

I also need to point out that if the boat in question was built using the same methods as “Cheeki Rafike” there is no practical way to know for sure that she was not damaged.

(Both are conclusions from the report on “Cheeki Rafike” and engineering done my the Wolfson Unit at Southampton University. https://www.morganscloud.com/2015/06/25/cheeki-rafiki-report-misses-an-opportunity-to-make-boats-safer/

All that said, I have no problem with the idea of a production boat and have thought about several. In fact, as you say, there are a lot of advantages to one, particularly later in the series when the bugs have been worked out.

I think you could get pretty good contrast and detail of a set of keel bolts in cross-section via X-ray, given sufficiently high quality X-ray equipment. And if the X-ray crew has access to a megavoltage source like Co-60, you’ll be able to see the bolts cast into the lead quite clearly.

This is not going to be cheap, however. And whether it tells you anything useful will really depend on the exact design of that particular boat.

You could try ultrasound, but that’s highly dependent on the technician’s skill and on the access situation for that hull.

If stainless steel, or galvanized mild steel, bolts are cast into the keel (forming studs that protrude into the boat), and there’s evidence of water intrusion, then I think dropping the keel a few inches is the only reliable way to tell the extent of damage.

With lead keels, bronze bolts are definitely the correct choice; the bronze/lead combination is basically indestructible for more than the life of the hull.

Galvanized mild steel bolts with a cast iron keel also seem to be OK as long as the bolts are accessible for periodic replacement, and I’d definitely undo one or two to check during pre-purchase survey. Stainless makes me nervous. Bronze bolts with a cast-iron keel make me nervous.

Don Casey has a good article on assessing keel joint issues here: https://www.sailmagazine.com/diy/how-secure-is-your-keel

Thanks for that great information. Sounds like there’s nothing for it but to plan to drop the keel unless it’s bronze bolts into lead. Good to know what the reality is.

Thanks for linking to that article. I’m way better informed after reading it. Casey is the real deal.

Thanks for posting link to Don Casey’s article.

I was worried what you would ask what to do about it. Unfortunately, I don’t have great ideas beyond actually taking a look. I work on the design side of things and so don’t know a lot about non-destructive testing other than where I need to make allowances for it to be done (this is something that is definitely not done in the design of these joints). My experience with X-ray is limited to inspection of welds and castings and I am not sure how it would work on keel bolts so I can’t really add anything beyond what Matt said. I believe that there are also design solutions to make this a much smaller concern that could involve changing materials, designing to be inspectable, designing to be repairable (iron keels that are tapped and bolted from the top being an example), etc but that doesn’t deal with the already built boats.

In my case, there are a few things that made me feel comfortable with our boat. Looking at the ISAF statistics compiled in 2013, of 72 recorded keel failures, only 3 could be attributed to the bolts (important to note that 40 were undefined so the actual number could well be higher). Weld failures, and internal structure failures both had a more than double incidence ratio. I actually find this failure rate pretty low given the number of poorly designed (or designed with low margin for racing), poorly maintained and poorly repaired joints out there. Our boat has a pretty conservative keel attachment, the lever arm is small and the attachment is wide in both directions and the bolts are large. Given that, I calculated the required bolt strength and then looked at the bolt size on our boat and concluded that the designer had been appropriately conservative in upsizing to allow for corrosion. Next, our boat did not show any of the problem signs such as large rust streaks, signs of grounding damage, etc. Finally, I did exactly the test that you were hoping to do which is a torque test on all of these bolts (note, this and all the calculations were done post purchase) to values I calculated and felt comfortable with. Obviously this is not perfect but has mitigated the risk to a level where I feel there are other more important places to put my efforts.

Actually pulling the keel in a properly equipped yard is not that big of a deal, often on the order of what people spend on electronics for the boat. What becomes really problematic is if the bolts are found to be compromised to the point where they must be replaced. Given our location, I would contact Mars Metals if I ever got to this point. For people who do not live near a facility like this, it gets more tricky. I have limited experience installing bolts from the bottom of a keel and I could see it working in some instances but not all.

Thanks very much for expanding on that. Obviously it’s disappointing not to have a generally applicable risk reduction strategy. But then again, when did that every happen around boats!

The good thing is that I now understand the issues and how to reduce the risk to acceptable levels. One thing I would say is that I would need to think long and hard before buying a boat that say had tankage or mast step structure over the keel bolts since that can make the job of dropping the keel from, as you say, comparatively simple, to a much bigger job.

Hi John, thought I should address the keel questions for anyone considering a Beneteau cruiser and reading this. Cheeki Rafiki, was a Beneteau First designed primarily as a racer / cruiser. They have light hulls and rely on a structural liner for much of their hull rigidity, with bulkheads and “furniture” glued in. In the main, the boats are fit for purpose and they don’t have a history of losing their keels, even though there seems to be a serious question over the keel to hull design. I personally wouldn’t sail one offshore but would have no hesitation in owning one around the NZ coast, if I raced more.

The Beneteau Oceanis 473 was designed by Beneteau as their offshore model and as I have heard it told, the model was built to help alter their “bendy Beneteau” reputation. The Clipper Oceanis range (of which the 473 is one), are the last of the all hand laid fibreglass models before European regs changed to enforce epoxy, vacuum bagging and sandwich construction. The hulls were built super-thick of solid glass fibre and more so around the keels and other high stress areas. 473s then have massive supporting girders glassed into the bottom of the hull. The bulkheads are also glassed in not glued. The flanges of these girders are wide to improve the hull bonding and spread the keel load. Around the front and back of the keel area, the girders are only about 250 mm apart. The keel bolts go through both the girder flanges and the hull. Unlike the First, the 473 in particular has a much wider keel base and a double row of bolts (single row on the First). Comparing the two boats for offshore use, is like comparing a Toyota MR2 with a Toyota Land Cruiser – built for two very different things. My experience with owning a Beneteau is the QA processes were (are?) excellent, but I must add inspecting one or two bolts a year to my maintenance list. I haven’t so far because we run a dry bilge and the bolts are like new. And John, therein lies an opportunity for an astute buyer – there are gems in most production yacht manufacturer’s ranges, just as there are bad’uns. It is finding those good’uns that can pay off – the 473 is an absolute diamond. best regards Rob

Good to hear that the 473 has the bolts through the flanges and the grid glassed in. The key to the Cheeki Rafiki disaster is that she and her sisters had neither. Also, the report stated that other boats of her class had keel problems.

I wonder what Beneteau is doing these days with their newer boats.

Also it’s important to realize that Beneteau sold the class that Cheeki Rafiki was a member of as ocean capable. They make the same assertion for most of their current offerings.

Summary: any buyer needs to check to make sure the keel support structures are glassed in (not just glued) and that the bolts pass though the flanges, not just the hull skin. If they find this is not the case, run a mile.

And anyone considering buying any modern boat with a fin keel should read the Cheeki Rafiki report so at to know what to look for.

One more thought. Sorry to be such a pain in the ass on this. But one thing I have learned over the years running this site is that people skim (particularly the comments) not read carefully. They also tend the hear what they want to hear.

The point being that while I fully understand that you are not saying all Beneteaus have safe keels, just yours, I still need to jump in with the realities from the report.

Hi John, Why do sailboat keels smile? Because they are thinking about how much fun it would be to swim freely in the ocean like the dolphins, free of the heavy burden on their backs!

Of course we all know that GRP is forever. Even after you scrap the damn thing it’ll still be recognizable land fill or artificial reef for the next thousand years. Still there is one other material that deserve a passing derisive remark: Concrete. It’s a material used exclusively by amateur builders that never seems to survive the first owner.

Insurance company do not underwrite concrete boats in Canada. Not sure of USA. Since they need civil responsibility, place are limited for an owner. Altough it was a most decent material, well insulated, cheap, partially insulated.

Yes, we have friends with a concrete boat that has served them well. That said, I decided to leave the material out since good concrete boats are pretty rare.

For what it’s worth Joe Adams (the designer of our boat) had his first big success with the original Helsal that was a ferrocement boat. It smashed up records for the Sydney Hobart classic and was forever known as the ‘Flying Footpath’.

http://rolexsydneyhobart.com/news/2012/pre-race/helsal-tribute-to-joe-adams-in-rolex-sydney-hobart/

What a great name!

Ask any physicist about the stability of Aluminum alloy and they will say ; the aluminum stability derive from its oxyde layer which is the strongest material on earth after diamond. Thus any object built of aluminum alloy should make sure that oxyde layer is preserved. A simple piece of wood on an aluminum plate staying outside in the rain will get holed in a few months and will prove you that it can be attacked easily once the Al2O3 layer is depleted in oxygen poor environment. And aluminum is born of electricity and can be destroyed by electricity.

The ebook should have started with the french joke: Circumnavigators knows that 50 % of the boat going around the world have a metal hull, the remaining are US boats.

Each aluminum boat is a unique closed loop battery and had to be kept under cathodic state under all conditions. Some boat well builts have it naturally, some others don’t and with maintenance mistakes, this is were horror stories come from.

I am not found of polyester boats because the environnmental cost of getting rid of those tons of plastic polluants at the end of life have never been taken into consideration is the first price. Polyesther fiberglass is not recyclable. We are just pushing the problem forward to the next generations. One day not to far someone will wake up and put environnemental cost on the new GRP production boat and people will realise its not cheap.

Wood as said before, is only up to the maintenance made. My marina neighbor has a magnificient wood boat that he built himself, on the plan of Joshua. He told me last weekend, 6000 to built and 6000 hours to maintain since 30 years. A tribute to those brave men.

Steel… if only the genius of the french architects who recommended to build hulls in steel and the deck and infrastructure in stainless would have been more commonly communicated, we would have less steel boats relics today. 95 % of the paint maintenance of a steel boat is on the deck. A steel hull/stainless deck has about 1 hour of touch up maintenance every year (for all those logs and obstacles hit on the water)

Thus for metallic boats ultimately the material is not the problem, its the way it has been put together and maintained. A production aluminum sailboat could be the perfect boat for circumnavigators. For some specific usage, only steel can survive. This special boat is quite an achievement, almost 20 years in the polar sea: https://vagabond.fr/en/vagabond/

(Of course i am biased i have a year of mechanical engineering classes in material resistance and my full welding certification for both Aluminum alloys, Steel and 304 and 316 stainless on conventional SMAW and also on GMAW and GTAW.)

My experience over nearly 30 years is that the aluminium alloys used in boat building are a lot more durable than you indicate. For example my boat had teak decks and toe rails for the first 12 years of her life. And, despite the fact that water had got under the teak in many places and been there for years, we found only a little surface corrosion of no consequence when we removed the wood.

Yes, as I said in the article, it’s important to follow the rules with aluminium, but that’s far from rocket science and occasional mistakes do not result in a wrecked boat in a few weeks, as many will tell you.

Also the horror stories of wrecked aluminium boats are in my experience pretty much all of the “my cousin has a friend who knew someone who…” variety rather than reality. In fact I have yet to see an aluminium boat trashed by corrosion of any type and I have seen a bunch that have been horribly neglected.

I think the key point in all of this is that marine grade aluminium is far more durable that the grades most people have experience with in other uses.

And it’s also worth keeping in mind that aluminium has a higher strength to weight ratio than steel, so in fact a stronger boat can be built in aluminium on a practical bases. That said, aluminium is not as abrasion resistant as steel.

As to the environmental issues with GRP, I hear you but I don’t think it’s that simple. For example steel boats use a lot of really nasty coatings and insulation. Also those coatings must be renewed at a regular basis. And the making of both steel and aluminium plate have a pretty big environmental impact. Point being, it would take an in-depth study taking all these factors into account to determine which, over the life of the boat, inflicted the most environmental harm.

Hi John at the marina were my boat is (Québec city) we had to get rid of an old 30 feet fiberglass sailboat unused and leftover. The city environmental personnel came in and said we could not use the city garbage service and it had to be destroyed on site and buried in a special area (city owned) for about 100$ per ton. It ended up costing us 2000$ to get rid of this boat. If it would have been alu or steel people would have paid to pick it up.

If course Quebec is very serious with garbage and landfill management and not all jurisdictions are equal. But the trend has started here…

As for alu alloy indeed 5083 is a magic material if properly maintain. I did own a 34 feet powerboat for 6 years in my auxiliary coast guard previous life and there was a corrosion meter on the dash of it (silver anode isolated under water connected to the hull) and the owner book went to great lengths explaining the potential issue. At sea no problems because electrolytic voltage are low. But I had a AC current leak from the battery charger once and I noticed a month later(boat in water) tiny droplets of water appearing at the inside of the hull in the engine room just over the propeller. I wiped it everyday and when I hauled the boat out it could be seen from outside that the aluminum was severely pitted at 3 places… almost 1/8 depth. I had to replace and reweld the plate… it was full of tiny holes. I had magnesium anodes on the boat ant they were untouched. So it was galvanic corrosion at its worst. One season…

I agree it’s a worst case scenario but I was a first line witness of it. In this case the corrosion meter didn’t showed any problem although a problem was occurring.

Do you have a corrosion meter on MC?

This being said I would not be nervous of having another aluminum boat built of marine grade alloy by professionals- it’s is certainly the best boat material if properly built and maintained.

The meter you you had would not have warned you about that particular problem. Also, my guess is that the boat was not fitted with an isolation transformer, which is absolutely required for any aluminium boat plugged into shore power.

For a complete guide to aluminium boat ownership, including a gauge that would have warned you immediately about the current leak, see the links under further reading.

Having a strong electronic/electrical background like John, I’d like to reinforce his point on isolation transformers. It’s my view they should be mandatory on all metal boats, and considered highly desirable on all others. They serve at least three safety critical purposes:

1. The obvious one is that they isolate the ground loop to the shore power ground. Essential to prevent electrolysis and ensuring swimmer safety.

2. They provide inherent shore power reverse polarity protection. This is often an overlooked and not very well understood benefit.

3. The secondary of the transformer effectively becomes a ‘local power source’ and the neutral bonded to the boat hull ground. This provides a rock solid ground path for the boat that is independent of the shore power ground. This is essential to ensure any Earth Leakage/Residual Current Balance protection devices will work reliably. Depending on a shore ground loop that may have multiple cables and connectors, all subject to corrosion and miswiring, is a hidden and underestimated danger.

While the first attribute is highly relevant to metal boats, the second and third are common to all. Probably most boats don’t have an isolation transformer, and if they all were beautifully wired to a high standard it’s a compromise I’d be more sanguine about. But isolation transformers aren’t expensive in the wider scheme of things, and from an electrical perspective I regard them as the single most valuable investment you can make.

I agree. I would never own a metal boat without an isolation transformer, and would even seriously consider one for a GRP boat.

Hi John indeed it didn’t had an insulation transformer, and i took care of installing a Victron one on my steel sailboat. The anodes barely work on my boat i have the same since 2011 🙂

Andre, GRP is recycled in Europe and on an industrial scale. Additionally GRP boats are deposited in land fill, cut up, as it is considered inert. In the UK land fill sites are now sealed for future reclamation as well as the avoidance of leaching. Regarding recycling, it is not commercial for smaller batches but tends to be the waste streams from large GRP users. Alastair

Thanks Alastair for the information, Europe is in advance on us ! Indeed fiberglass is most inert … but 10 000 years later we don’t know… probably it would still be there !

You have [predictably] left out Ferro Cement – order should be (I owned a Ferro Cement yacht for many years so speak from experience)

Fibreglass Ferro Cement Aluminium

Although I have friends with a very good ferro cement boat I did not put it in because there are so few good FC boats available. Also, to say FC is “better” than aluminium is to ignore each materials characteristics. For example aluminium has a much higher strength to weight ratio and is far more ductile.

As my wife reminds me every time I look at a “beautiful” steel boat: “Rust never sleeps”

Donald that is also true for everything apart gold, platinum,titanium and a few other incorruptible elements.

We human live in the bottom of an air ocean and the O2 is a powerful oxydant. By chance is it diluted in nitrogen because otherwise we would have all burned including everything around.

Oh and that brings a point. A steel and férocement boat would survive a fire but others not. GRP is like a gallon of gasoline waiting for its match…

One of the secrets to a good life: marry a wise spouse.

I’ve had three steel cruising boats, two of which I’ve cruised extensively with. Each were bought used, 20 or more years after they were built. If I was in the market for another boat, I’d definitely consider a steel one.

Everything depends on how the boat was built and maintained.

My current steel boat was built very well, with no longitudinals to trap water, and–more importantly–flame-sprayed with zinc inside and out (properly-prepped & applied epoxy coatings can be almost as good as this). Rust is not a problem with this boat.

Yes, there are poorly built and/or maintained steel boats that will require a lot of work to go sailing (and may not be worth restoring). I think that holds true for any hull material–a couple of years ago I was offered a once-beautiful boat, professionally-built of fibreglass, effectively for free. I turned the offer down. The boat had been neglected, and while the solid fibreglass hull was undamaged, the plywood bulkheads and most of the interior had rotted due to water sitting inside the boat (it was left unattended in a boatyard for a few years).

A steel boat with: * properly-applied coatings, * easy access to most areas (to all areas would be best, but realistically, you’re unlikely to remove tanks to inspect the plating under them unless you suspect a problem), * few or no areas where water can sit, shouldn’t be a maintenance problem.

Everyone I’ve met with a stainless steel deck, as Andre mentioned above, has had good things to say about them (none of my boats had stainless steel decks, so I don’t speak from personal experience, here).

It is true (and important) that damaging the coating on a steel boat requires fixing it promptly (how promptly depends on temperature–corrosion happens very slowly below freezing). Zinc coatings on the steel have some advantage here (if underwater), as the zinc migrates to the bared area electrolyticly, but this is only for small scratches. POR-15 (buy some small cans before leaving North America, as it isn’t all that widely available), a coating developed for the antique car restoration market (which deals with thinner steel plate), makes maintenance painting of damaged areas much easier, since it doesn’t require sandblasting before applying.

>This is the reason that by far the majority of experienced high latitude sailors have aluminum boats. Are you sure of that? When I went thru the NW Passage, there were more steel boats than aluminum boats. In Antarctica, I don’t recall aluminum boats outnumbering steel boats. In Patagonia, I saw more fibreglass boats, and roughly equal numbers of steel and aluminum ones.

Steel probably isn’t suitable for you, because you are looking at buying a considerably smaller boat than the one you have. But for someone looking to cruise long distances, high latitudes and remote places, a used steel boat could be a good choice. It all depends on the construction and maintenance that has been done, and that’s something that mostly can be determined before buying.

Best regards, Richard

Hi Richard,

Thanks for a great report from someone who clearly knows. Clearly you are the exception to the second steel boat crack I made!

As to my assertion about high latitude sailors. No, I don’t know for sure, although it has been my experience, but of course that’s not definitive. One thing I have noticed is that several high latitude sailors with substantial steel experience ended up with aluminium. Skip Novak and Hamish Laird are two that come to mind.

One thing I would say is that I would have no worries about you buying another steel boat, but I don’t think that alters my concern about buyers without your experience taking one on.

Yes, two professional, high-latitude sailors, Skip Novak & Hamish Laird have moved to aluminum charter boats after extensive experience with steel ones. I think most people who own steel boats would consider or have considered aluminum boats.

I don’t think there is any definitive list of boat types that are out doing high-latitude cruising. Records are kept of vessels that go through the NW Passage. I did a quick search of the sailboats that went through the NW Passage in 2017. I counted 4 of aluminum, 4 of steel, 3 of fibreglass, 2 of wood, and 8 that I was unable to determine the construction of. Of the two sailboats that went thru in 2018, one was ferrocement, and I don’t know about the other one. The NW Passage is very much a high-latitude trip, and anyone who has gone through it has at least that much high-latitude experience (and, I would greatly hope, a lot more experience than that before they attempt it!). Those NW Passage numbers are pretty recent, and are in accordance with what I have observed while cruising. So I respectfully disagree with the statement, which the article puts in bold print, ‘by far the majority of experienced high latitude sailors have aluminum boats’.

Some people considering a metal boat will find themselves in the situation of feeling they can afford to buy a steel one, but can’t afford to buy an aluminum one, and see their choice being to own a steel boat or not own a boat. I would encourage people considering a steel boat to read books about them (‘Steel Away’ and Tom Colvin’s ‘Steel Boatbuilding’ were both of much use to me when I was a beginner), talk to people who’ve owned steel boats, and talk to boatbuilders, yards and surveyors that work with them. I don’t know of any particular site on the internet to recommend for information on steel boats.

I agree that steel boats are not for everyone, but disagree that they are only suitable for those who have owned them before–steel boats can be learned about.

I agree, a hard to define stat. I should have written something like “most of the high latitude boats I have encountered are aluminium” or some such.

That said, I still think that steel is a tough material to own, particularly for those new to boat ownership.

I changed the line in the post. Thanks.

Thanks, now we’re in agreement.

Jut some musings.

There is an aluminium boat from 1936 still floating around and the oldest aluminium boat builder started building aluminium hulls in 1898, Savage Aluminium Boats. I think there are GRP hulls from the early ’50s still pottering about today.

I read that a typical, modern 40’ish GRP yacht has around £5000 worth of materials to make it. Today we see new and old GRP yachts sailing around the globe frequently, managing the stresses and strains of the Souther Ocean and plenty of arctic and antarctic voyages. A colleague ran his Contessa 34 onto a boulder lee shore, F5, big damage, the boat dragged off and significant repairs; owner of a Sigma 41 ran into a rock and snapped the steel toe of the hull flange from the keel all theta through, as well as significant hull damage, I too rammed a ledge at spring tides at speed and busted GRP stringers etc, none of these yachts sank. One thing that GRP has going for it, is that it flexes considerably on impact before it yields, although the area will have been significantly stressed and weakened. The same for aluminium, recently at Ardfern Marina, a modern aluminium yacht was on the hard, after the owner ran her over rocks and bashed the hull significantly at the turn of the bilge, I guess the aluminium though would have maintained a lot of it’s strength. The skills were not available to fix and she was being prepared for road transport back to the builders yard in France when I saw the boat; GRP on the other hand can be fixed easier, I suggest. The point I wish to make, is that GRP is a strong material, it has resilience and a history of surviving neglect and abuse. This is what makes it a superior material in my opinion. Sailing is a minority pastime, the vast majority of participants will have reasonable funding and GRP has proved to be very cost effective and allowed some fantastic low cost, extreme voyages to be made by amateurs. I don’t particularly value steel or aluminium for their strength in hull choice as avoiding the sort of impacts that damage hulls should be the name of the game for any serious voyager. If one is in a situation that impact damage is happening, then it is luck that is stopping the hull from foundering. I think hull design with collision bulkheads and water tight compartments is more relevant for security against foundering than GRP v aluminium v steel. It is this sort of design feature that buys time and allows options to be worked. There are always exceptions of course.

John, I think your reasons for going GRP are very valid. I am a lazy hull cleaner, preferring to let the waves do the washing. But about every 3 years I polish and wax the hull and it comes up beautifully.

Hi Alastair,

Lot’s of interesting points. One thing I differ a bit on is GRP repair. Yes, you can repair a GRP boat easily, but, and it’s a big but, it’s very difficult to be sure that said repair is properly bonded, at least without using epoxy, which has its own difficulties. Secondary bonding is a far bigger problem is generally recognized. More in a future post.

Also, metal boats have another advantage, other than just strength, and that is it’s much easier to make them stiff, and that in turn makes it much easier to make them watertight for the long haul.

And finally, strength is very important in the high latitudes where, no matter how careful, sooner or later we will hit something, either ice or an uncharted rock.

In summary, having owned both for long periods, I don’t think that GRP is “better” than aluminium, just better for my needs going forward.

We chose steel because we saw the boat we purchased had been prepared properly and we were aware of the need for prompt maintenance. Everything in “adventure cruising” being a compromise, the key to happiness is, we feel, this awareness. We are a few weeks from leaving on what we hope will be a five-year circ with an emphasis on independence from the shore and the ability to do our own repairs save for major refitting. Few people get to do this, irrespective of hull material. The wisdom of our choice will soon reveal itself, one way or another. Now, if you’ll excuse me, I have to wire up a fridge compressor…

Hi John, A few vignettes;

Steel: Bernard Moitesser’s Joshua; Washed ashore in a hurricane in Cabo San Lucas– filled with sand. Given away to two guys walking on the beach. Pumped out and motorsailed all the way up to the Pacific Northwest where she became a dock mate to my Cape George 36. Every fiberglass boat that washed ashore on the same beach was cut up and hauled away.

Brewer Atlantic 45: Built by a well know Canadian yard. Sailed around the world and arrived in Trinidad with several overlaid hull patches. Spent a year being “completely” re-plated and re-decked while sitting outside as is the practice there. (and rusting all over again) Repainted and looked “smooth as glass.” Sold to a naive young couple who panicked the first time they hoisted sail. I was offered it for $15,000 and turned it down.

Classic 110 ft. Feadship In our yard for a complete restoration. Hull built with overlapping strakes — every overlap rusted out. Re-plated the majority of the hull, re-powered and restored interior to new. Fixable, but at tremendous cost.

John Guzzwell was one of the earliest pioneers of cold molded wood boat construction. I met him when he hauled his Laurent Giles ketch out in our interior storage area. It was built in the days before epoxy— he used resorcinal glue just like the Spruce Goose. Planking was mahogany rather than the more rot resistant Alaskan cedar. And the hull sheathing was Dynel in polyester resin. John spent the winter removing the old sheathing and replacing it with glass cloth and epoxy out of concern over moisture penetration from the resin. I made it a point to chat frequently to pick John’s brain and learn everything possible about cold molding. When he finished bringing “Treasure” back to bare wood there was only a small area of discolored wood— the planking was as sound as new and she was ready to receive her new modern sheathing.

I built my Cape George 36 deck without fasteners, epoxy bonded over an epoxy/glass base over Port Orford Cedar. Lived for 36 years outside with no covering and little care by multiple owners, but was still watertight and serviceable.

So yes, properly built wood boats can be durable.

At the same era the PT Shipwrights Co-op worked on a caravel planked boat that was built in 1898. She required a new stem timber and about 40% of the bow planking replaced. The repairs probably cost little more than all the Beneteaus that were being peeled and glassed under warranty at the same time.

So yes,traditional wood boats that have been properly built can be repaired over and over again so they last forever.

Fiberglass:

A J130 that has a perfect black paint job, new carbon sails, the latest electronics, and a custom $30,000 factory upgrade interior just sold for $15,000! Underwater delamination and extensive wet core. My proposal was to completely re manufacturer the hull bottom with epoxy resin infusion and close spaced foam/carbon ribs and stringers and no core. The end result would be the best J 130 in the world.. Some extensive rebuilds actually make sense!

And not all fiberglass boats last forever! Especially if they have a balsa core underwater.

All good examples that can teach us a lot. As you say, many of these problems can be solved. But, at least to me, the key take away from all those stories is that the fixes take huge expertise and if done wrong the result can be huge wealth destruction. Bottom line, I would have no worries about you taking on any of the above situations, but for the average person my advice would be “not a good idea”.

Hi John My little stories weren’t chosen as examples of good projects for do-it-yourself dreamers! What I was trying to illustrate is that good (and bad) boats can be built of all materials. I could have included an aluminum Italian motor yacht with black AC current “peppercorns” in the hull that you could push a screwdriver through, or a 90′ fiberglass motor yacht where the underwater exhaust outlets had burned all the resin completely away from the adjoining area and was a single wave away from sinking.

The skill level required to undertake repairs runs the entire range:

John Guzzwell’s 24 year preventive maintenance project required a strong back and weeks of work with a heat gun and scraper, but technically anybody could learn how to do it with a couple of weeks of practice. The guys who nursed the battered Joshua up the Pacific coast were adventurers, not shipwrights. Hundreds of graduates of wooden boat schools know how to re-plank a traditional wood boat– that skill has not entirely disappeared. A teak deck originally built like my Cape George only takes a day with a grinder to be ready to be glassed over, unlike the can of worms in a screw fastened fiberglass, aluminum, or (heaven forbid) steel boat teak deck.

On the other hand, the hull rebuild I suggested for the J 130 is probably more technical than building an entirely new boat and requires engineering and solutions not found in the typical professional boat yard.

All in all, i am not sure the hull material is a strong discriminating factor in a purchase. If i my boat would be lost and have to shop for another one, the first criteria for me would be a metallic hull. Because it is a metallic hull it can have also a safe swing keel and a flat bottom to go on the beach or where there is tides. Shopping for a boat is a matter of luck for the availability of what we want. And age is important also. i have 58 and plan to use my boat for another 20 years if God helps. But suppose my boat would be lost and i would be 70 – knowing that in 6 to 8 years the boat will have to be sold back would mean a very important criterion would be to be able to sell the boat rapidly and profitably. For this reason i would opt for a good aluminium sailboat or if a catamaran then GRP. Not because technically they are better (in my humble opinion) but rather because its easy to sell. I thinks its also the thinking of many prospective buyers….

I submit that it is possible to find a world cruising sailboat for under $100K that is not a project boat: http://www.cruisersforum.com/forums/f152/aluminum-30-ted-brewer-cutter-for-sale-202692.html This is also a not too subtle plug for checking out Cruisers Forum when researching said topics. Full disclosure, this has been my beloved boat for nine years, and AAC is the first site I recommend to not only aluminum hull boaters, but every boater. Thanks John, Phyllis and crew

She certainly looks to fit the specification and supports the my thinking that when constrained by that budget the best alternative is to go a bit smaller than the 40′ that seems to be the new “standard”. Better a smaller good boat than a bigger crap boat.

And thanks very much for the kind words.

Also, if you feel like sharing, it would be interesting to know what comes next for you after she sells?

Hello John, I guess I’d like to also throw in my little “grain of salt”. I am one of those “idiots” who is on to his second steel boat…The first one, a 1975 van de Stadt ketch, I spent 10 years rebuilding, while living on board and working full time, in the heat and humidity of the Florida Gulf coast. I never finished! However, my second boat, a one-off Treworgy 38 built in 1995, is of a combination you haven’t mentioned, but which is used in a large proportion of the luxury mega-yachts, as well as military and work ships: Steel hull and aluminium deck and superstructure. They are built using a flatbar, called a Datacouple, that has one side of steel imploded onto the other side of aluminium. This is welded to the steel hull and the aluminium deck, and the junction being a very fine micro-line, presents absolutely no electrolytic corrosion problem whatsoever, is 100% watertight, maintenance free, and very strong. It allows the eternal problem of maintaining steel horizontal surfaces to disappear, and lowers the weight topsides. Isolation transformers: Obviously a must, although most GRP boats can get away with a galvanic isolator. One thing to be careful of: The Marinco deck receptacles for the AC connection, as they come out of the box, have a small chromed metallic jumper that connects the ground terminal with the casing. Pleas make sure this is removed! Last but not least, no one has mentioned lightning! With 20 years working professionally on boats in the Tampa Bay area, which is also know as the lightning capital of the US, I can assure you that when you are living aboard full time, and have these daily and very scary lightning storms pass right over you, such that you know is a lottery and at any moment one of those blasts will be right on top of you, having a metal boat is a big reassurance. It won’t keep equipment from being damaged, but it will certainly keep you from being damaged if inside the boat. Very cozy! Best regards and thanks for the great website. Jonathan

Hi Jonathan,

Yes, I have a friend with a boat with a steel hull and aluminium deck, who is, or was (we have lost touch) happy with the boat. That said, I personally would prefer to go all aluminium if considering another metal boat. And yes, I agree that metal is really nice when the flashing and banging starts.

I agree, a really good paints system goes a long way on steel. (On aluminium its just cosmetic.) That said, getting to that point on steel is seriously hard: https://www.morganscloud.com/2012/02/16/why-not-steel-part1/

And, judging from what I see out there on the water, a paint system that good is not that common.

Dear John your comment is not scientific… the sample of steel boats you might have seen doesn’t necessarily represent the reality. We should not compare amateur built steel boat versus commercial built aluminum boats.

When I built my boat I visited a professional alu boatbuilder who had learned in French yards his skills. Although I had welding skills I find out that I was not capable of building correctly without experience a first aluminum boat. I turned to steel with the compromise of a stainless steel deck and superstructure and using commercial Amercoat primers and finishing paints + a certified paint inspector. The sandblast + paint costed me 18000$ CAD in 2008 which account to approximately 3 % of the total cost of the boat.

And frankly unless the builder as in your example as strictly adhered to products and applications guides an as proof or it we should not even consider it in a fair comparison.

This being said, almost all semi professional and professional yards have turned to aluminum in the last 20 years.

In the commercial world, steel boats, freighters, petrol carriers, liners etc.. all got a paint system valid for their 50 years of life. We don’t have the number but I guess that if we count all the ships in the world the number of square feet built of aluminum would be less than 0.01% (probably even less) of the worldwide commercial fleet.

Demonstrated valid protection system exist for steel immersed in sea water with 50+years of useful life.

Conclusions: 1-We should compare apples to apples in our discussion otherwise we get lost in armchair stories.

2-Shopping for an amateur built steelboat should involve much more scrutiny than a professional made steel or aluminum boat.

I never claimed it was scientific, that why I said “judging from what I see”.

Yup, Colin did a great job on that piece. As you say, they did a great job on the boat. That said,I would not class it as “over and above” but rather the minimum required to be a happy steel boat owner, and that in turn is why I don’t recommend second had steel boats. Just easier for most of us to own GRP or aluminium.

Hi John Judging from what I’ve seen, a really good paint job on an aluminum boat is not that common either! The difference with steel construction is that the most important area for protection is on the inside where perfection is the hardest to achieve and recoating is difficult or impossible. Thats’ why steel boats rust out from the inside. And why there are so many home built rust buckets.

re aluminum boat structures: As you mentioned in an earlier comment, an aluminum design with multiple frames and stringers covered by relatively thin plate like MC and aluminum race boats is stiffer per pound than one with thick plate. However I’ve never seen that method of construction result in a surface with so little distortion that it doesn’t require fairing and paint to look decent. Isn’t that the reason you’ve never stripped MC back to bare aluminum?

I’ve worked on two heavily framed aluminum boats— a 12 meter designed to Lloyds scantlings and a 300,000# motor sailor where the owner insisted that the longitudinals be continuously welded on both sides “to make it stronger.” The 12 meter had 3/8″ of mud in some places, and the megayacht had so much accumulated welding stress that it crushed the decks and engine room overheads.

At the other extreme of aluminum construction, my friends Garcia Passoa was built with 12mm plate up to the waterline because they wanted to be able to set it down on rocky bottoms in Patagonia without damage. Back in those days Sr. Garcia used a massive roller to shape 50′ long curved aluminum panels that were so fair you could paint directly onto them and it would look like molded fiberglass. Or you could leave them bare and marvel at his craftsmanship. As I recall the ribs were over a meter apart, and served more to attach bulkheads to than to add stiffness. Different boats for different folks– and purposes.

Thanks, John, for featuring a lovely photo of us and our boat at the beginning of this post. However, and with great respect for all the contributors, I think that the discussion of the “best” hull material misses a couple of essential points.

Most of us build, own and sail boats simply for the pleasure they give. For me at least, a large source of pleasure lies in the boat’s look and feel. Does the boat look good from afar and up-close? Is it pleasing to your eye and comfortable under your bum as you sit in the cockpit with drink in hand? Is the cabin warm, dry, and cozy? Do passers-by offer compliments? Does it perform well under way and at rest?

Hull material strongly influences the look and feel of the boat. Metal boats tend to the industrial strength go-anywhere-any-time look that can be very impressive and pleasing if well executed. Wooden boats tend to fall into the fussy, look-but-don’t-touch category or, at the other extreme, the hairy old, gaff and baggy-wrinkled character boat group, irresistible to some, anathema to others. Fibreglass is the most adaptable of materials but seems to be dominated by a white desert of angular shapes and shiny metallic trim.

My suggestion is to consider “best” material in the context of the ways in which you expect to gain pleasure from your boat. Don’t buy/build something that is built of a material that can survive pounding on lee shore rocks or banging into ice floes unless the resulting look and feel and knowledge of its strength will please you every time you climb aboard.

Our boat is made of wood because that’s what I know and like. I have confidence in its strength and durability for the type of sailing we have done and dream of doing. Countless times we have had folks say to us something along the lines of “what a beautiful boat, but it must be a lot of work”. Well, it is a lot of work, but keep two things in mind. First, I enjoy the work and annual rhythm of varnishing and painting (at least most of the time). If I didn’t like that work, I would have a different boat. Second, structure and finishes that attract onlookers’ initial response are relatively small parts of the whole boat in terms of initial cost and ongoing effort. Our wooden boat has the same needs as any other boat in terms of underwater paint, rig, sails, electrical and mechanical systems, ground tackle, safety, and other gear.

So, my advice is to get a boat that will give you pleasure in the overall scheme of things and consider hull material within that context, not as a starting point.

Hi Wilson, Nicely put and a wise way to look at things. My best, Dick Stevenson, s/v Alchemy

As Dick said, well put. However, I still think that you are discounting the importance and the level of your own skills and how that affects your enjoyment of owning a wooden boat. Or to put it another way, I stick by my assertion that wooden boats can be heart breakers for those with less skill and dedication.

All I was doing in my comment was explaining that one can’t view plate thickness in isolation. I was not saying that the light plate many frame construction technique was a better idea, just different. As to paint on aluminium, I agree, in fact I made that point in the article above.

But the key point in all of this is that a good paint job on aluminium is cosmetic, on a steel it’s a matter of boat preservation.

No disagreement from me. I was just trying to point out that there are always connections: in this case the relationship between how an aluminum boat is engineered and whether it is a good candidate for bare aluminum finish.

You make a very good point. I have never enjoyed the boat part of cruising so much as when sailing on an extended family member’s beautiful wood S&S. As someone who has worked on several nice wooden boats, I always felt a bit awkward when I would answer the inevitable question of which yard takes care of the boat and I would explain that it was not yard kept and also that no, I couldn’t claim credit for most of it either, I was just lucky enough to get to enjoy it.

When getting our current boat, we really thought hard about whether we should take over stewardship of that boat. In the end, we went to the opposite end of the spectrum and decided to get as low a maintenance fiberglass boat as possible. We certainly have given up something that is hard to describe but the design is much more suited to the actual sailing we do and we can keep up with doing all the maintenance ourselves. I am someone who enjoys metalwork but does not enjoy the more artistic elements of woodwork which means that while I can spile a plank just fine, I have trouble motivating making elements that require an “eye” and as a result they don’t come out very well. Every time I see a picture of that boat, I wonder whether we made the right call as the feeling of being aboard was just so wonderful despite it lacking the creature comforts of newer boats.

Great way of describing the Real Purpose of owning a boat! If she doesn’t warm your heart every time you row out to her at anchor, perhaps it would be best to invest in a motor home with the obligatory wavy graphics on the side!

While talking to Larry Pardey years ago on the dock a passerby commented: “what a beautiful boat, but it must be a lot of work” LOL Larry didn’t say anything for a minute, having heard the same comment a thousand times in a hundred harbors. “Well, we don’t have anything else to do” he said. (having just crossed the North Pacific from Japan in a self-built wooden boat with a 24′ waterline)

Nobody has raised the difficulty of getting a good antifouling for an aluminum hull, when i was building i remember the ban on TBT taking place in Europe. Is there good protection available today ? (this article is old) for current owner of alu boats what is the current state of the art antifouling ?

https://www.practical-sailor.com/issues/37_17/features/10783-1.html

Steel hull is very easy to protect with a simple copper oxide suspension.

We have a good solution that we have been using since the end of tin: https://www.morganscloud.com/2009/06/18/zinc-based-antifouling/

E Paint also does consistently well on tests at Practical Sailor and has the other advantage that it’s less environmentally damaging that copper based paints.

Colin is also having very good results from a new copper free paint from Petit.

Hi Rob, I find your report of a Beneteau 473 hitting a rock at 8-9 kn and then a surveyor finding no damage extraordinary. I know you were discussing lead vs steel keels, but, less others think that sailboats can get away with that, I will share a couple of observations. For years I lived near a boatyard in a town with a very seductive rock a few miles away. Most every year, boats would limp in having hit that rock. Every one (or almost every one, I can’t remember) that hit that rock at hull speed with an external keel was considered a total write off by surveyors and the insurance companies. Usually the killer was structural damage of the fiberglass just aft of the keel, sometimes forward, as the keel tries to lever its way off the hull. Beyond that there always was near to the keel bulkheads pulling their tabbing from the hull and furniture etc. being dis-lodged. That was usually enough for the complete insurance write-off. Now, a steel keel would, I would think, transmit the forces more abruptly/directly into the hull as lead has a bit more “give” to it. I suspect the difference altogether may not be all that great. It is my understand that the average boat will not survive a keel to rock grounding at hull speed. I have been told, by those who know about these things, that it would be very hard (read expensive) to have a boat that could withstand an external keel to rock grounding at hull speed (I suspect full keels and some shoal draft could come closest). My best, Dick Stevenson, s/v Alchemy

We saw a Beneteau 50 (2004 ish) hit a rock at speed last year and damage the hull with water ingress. Damage was as described, fore and aft of keel, stringer damage. I think after removing the interior, reglassing and putting everything back, it was around 50-70k ish which the insurance company paid.

Hi William, Absolutely horrible thing to witness as a sailor I’m sure. I think I am right in saying the Beneteau 50 you refer to above is a completely design to the B473 I referenced above. I have never sailed one, but from the pieces I have read, it seems to share the hull liner design of the lighter First models, like Cheeki Rafiki. I am sure the hull would be thinner, too. That doesn’t in anyway detract from your corroboration of Dick’s point about many boats being massively damaged or written off by such impacts. It just doesn’t mean that well designed production boats and in particular the Beneteau 473s and their smaller sister-ships 423 and 393 have the same issue with their external steel keels. br. Rob

Would it really be that hard to engineer a keel joint to survive routine impacts at hull speed?

Today in 3 Minutes of Rough Physics Approximations:

Say it’s an 8 knot boat…. round that to 4 m/s. Displacement 10,000 kg. Draught 2.5 m (of which 0.5 m is hull and 2 m is keel). The keel tip hits a rock, the boat pitches forward, she comes to a dead stop in half a metre (measured at the waterline), average acceleration 16 m/s2. About 80 kJ of kinetic energy needs to be dissipated. Impact forces are on the order of 160 kN at the keel tip, for a pitching moment of 320 kN.m. Couple that through a keel root joint with a 2 m chord length that’s already supporting maybe 5 tonnes of keel, and simplify to pseudo-point loads at leading and trailing edges, assuming the middle part does nothing. That looks like about 190 kN of tension shared among the leading keel bolts and 140 kN of compression on the trailing edge of the keel root joint.

So the question “is it possible to make a 10,000 kg fin-keel boat with a 2m keel survive an 8-knot hard grounding on solid rock” is reduced to “is it possible to share 19 tonnes of tension among the first few keel bolts, and carry 14 tonnes of compression from the trailing edge of the keel joint into the hull, plus appropriate safety factors”. 19 tonnes is below the proof load of four M16x2.00 – Class 5.8 bolts, which seem considerably undersized for a boat of this class. 14 tonnes from a point load can easily be spread through a tapered U-shaped rib/frame about 20-30 cm in moulded depth, or a partial bulkhead, spanning most of the beam of the boat.

I think it’s not a matter of “that’s hard” or “that’s expensive”, but rather a matter of “we build to the scantlings in the class rules and they don’t consider this load case to be routine”. But it seems to me like, at build time while the hull is still in the mould, you’re talking maybe a three-digit dollar figure for this kind of reinforcement.

Hi Matt, how right you are! The boat in question (Beneteau 473) has internal “U” shaped tapered beams almost exactly as you describe, but with thick, wide flanges. The beams are probably slightly over 30cm at their deepest, in the centre, near the bilge and the keel bolts, tapering to not very much at the turn of the bilge (fairly flat bottom especially around the back of the keel). The beams are very close together at the front and back of the keel and about 20 cm wide. These beams are so tough that during our pre-purchase inspection, the surveyor’s hammer bounced off them like they were steel. He called me over to remark on their size and thickness and how many there were around the keel area. Being an ex-yacht designer, offshore sailor and boat builder he didn’t seem the sort to be easily impressed. We both thought they might have a steel core, but I later discovered they are 100% moulded fibreglass. Matt, I think these beams may have cost a little more than a three digit number more, but as you say – not a lot. But I have heard that due to EU heath regulations, such hand lay-up techniques can’t be used anymore, and that most large items like beams would be epoxy injected and vacuum bagged, then cured and simply glued in. I wonder if this is not as inherently impact resistant. Do you have a view on this? br. Rob

The Cheeki Rafiki report makes clear that a glued in grid is intrinsically dangerous and, if memory serves Matt has already agreed with that in our original discussion about said report.

Bottom line, your boat may be a battleship, and that’s great. But I need to make sure others understand that extrapolating that construction to any other Beneteaus, without carefully checking, might be a very big mistake, particularly in light of what you heard about EU regs.

This is my biggest problem with modern fiberglass boats. Boatbuilders that still exist are exceedingly good at value engineering. The ones who weren’t went bankrupt decades ago.

Value engineering requires warranty claims for its feedback mechanism: make something weaker, and if there aren’t any claims then it’s still too strong.

But most pleasure craft spend nearly all their time floating next to a dock, plus an occasional few hours underway in Force <5 conditions.

So value engineering is walking boats down to the point where they're good at floating next to a dock and occasionally sailing in benign conditions—plus Class.

But Class is controlled by manufacturers, and they'll continuously make the case that real world experience shows that Class is too conservative. So Class is value engineering with a delay, and that's how we end up with (for instance) brass thru-hulls and glued matrix liners.

Yes, sadly, I think you are right in every detail on that one. Definitely narrows things down. I’m starting to think the sweet spot is around the 90s when better techniques became available but value engineering had not kicked in quite as much as it has today. Also I totally agree that class is inadequate and in fact has just become a fig leaf to cover up poor boat building:

https://www.morganscloud.com/2015/06/25/cheeki-rafiki-report-misses-an-opportunity-to-make-boats-safer/

Dick, If you go to YouTube and search for “Crash Test – Dehler 31 yacht” you can see Dehler ramming their yacht against all sorts of objects at hull speed. It’s a GRP hull with a standard fin bolted to the hull, not a bonded in grid or encapsulated. The video is worth watching all the way for all the ramming scenarios this boat is going through, including a keel strike against a breakwater base. I am not doubting your observations. My position is that GRP hulls can be designed strong enough for extreme loads at sea, and that inherently makes them strong enough for many types of impact. As design changes over time we now see hull designs with very efficient keels that meet a performance criteria with some sacrifice in strength and are less resilient. I do agree that steel can be stronger but I think GRP can be relied on as safe and secure material, where the design demonstrates that. I won’t post the link here as I am not sure if that is allowed. Regards, Alastair

Hi Alistair, I fully agree that fg hulls can be built to withstand almost anything the sea may challenge it with. I also agree that fg hulls can be built strong enough so that the keel to hull joint is not compromised by anything the sea has to offer. In fact, it is my take that most are. It is a non-sea event that I was referring to: hitting a rock at speed low down on a conventional keel. It is a predictable event for a certain (hopefully small, like lightening) percentage of those who put significant miles on their boats. It is my take and observation that the average sailboat can’t tolerate hitting a rock down low on a keel (possibly excepting shoal draft and full keel where the lever arm is mitigated to a large extent) without substantial damage and often leading to total loss. As to the video, you cited: hitting floating wood objects and log booms should leave only a dent and did leave gauges as shown in the video. But that should be all the damage. I believe the video shows the boat hitting the rock wall with the underbody leading up to the keel high up on the keel, not low where the lever arm is most powerful. This is augmented by the video of a keel placed well aft and the boat rising at first and then largely stopping dead with very little tipping forward. A boat hitting the bottom of their keel at hull speed looks like it will pitchpole. It is incredibly dynamic and looks to eject the people in the cockpit into orbit. This hitting the breakwater was gentle by comparison and says they were sliding up the hull, absorbing the loads till they got to the keel. Very little was shown of keel dents or evidence on the forward underbody where I suspect there was contact. Also, the keel to hull footprint is one of the tiniest I have ever seen on a fin keel boat: harder still to believe it could survive unblemished a bottom of the keel rock grounding at hull speed. Your Dehler video was not, to my observation telling or compelling: it was an advertising stunt. (Reminded me of the old Hunter destruction tests done back in the day: I am not a fan of manufacturer testing.) Now, I am largely unfamiliar with Dehler boats and they may make great boats, but I am not impressed by the video as evidence that a conventional fin keel boat can survive a bottom of the keel rock grounding at hull speed. My best, Dick Stevenson, s/v Alchemy

Hi Dick, that was my understanding entirely, so I fully understand your note of surprise. This was also the owner’s expectation at the time – the boat was rushed back to the nearest haul out facility, with crew in life jackets, coastguard on standby and bilge pumps primed. Most people are reticent about admitting things like going aground, never mind crashing into a rock at full tilt. So I have no reason to doubt a first hand account of the incident, from the owner to me, on board their boat some months later. At the time of the impact the owner was down below, having handed over the helm to a friend to check something. The rock concerned is well marked by a beacon and for some inexplicable reason, the EXPERIENCED sailor and friend took the beacon on the wrong side – hey stuff happens. The crew were lucky to avoid injury. Please see my answer to John above, on the way Beneteau Oceanis 473s are built for the reason why I think they could withstand such force, without any visible damage. Not that I am looking to test it mind. Inside the hull the keel bolts, girders and hull are all completely visible by simply removing a few floor boards. All easily checked by an experienced surveyor. I have to say if it was me, I would have insisted the insurer pay for the keel to be removed, keel bolts changed and the whole thing re-seated at a minimum, and this may well have been done – I don’t have the detail of that. By the way, I do wonder that marine insurers don’t sponsor more marine buoyage. We have a notorious rock near us, that collects about four launches a season. br. Rob

Just to clarify, the Cheeki Rafiki report makes clear that after a grounding it is extremely difficult, perhaps impossible, to determine if dangerous damage has been done to this kind of construction.

So to say “Inside the hull the keel bolts, girders and hull are all completely visible by simply removing a few floor boards. All easily checked by an experienced surveyor.” is simply not correct.

The report also goes on to show that with this type of boat repair is not cost effective and so to be safe the boat will probably be written off.

I think it would be a really good idea if you would read said report, and the associated Wolfson unit report.

Sorry to be so harsh, but this is important stuff and further me constantly arguing with you and quoting the report is only going to get us crosswise, which would be sad.

Hi Rob, It sounds like you have a very solid boat and you must be re-assured to have it validated especially if you were not the one doing the testing. My interest in responding to your initial letter was primarily to point out that, in my experience and in talking with others, most of the regular sailboats out there could not survive unblemished what you described. And I concur with your thought of further examination of the keel. Internal furniture etc. are one thing, but I would also be concerned about the shock load’s effects on the rig, chainplates etc. My best, Dick Stevenson, s/v Alchemy

Hi John, I am not convinced that the average offshore boat buyer need be so pessimistic and precautionary about keel to joint integrity. For those boats being considered for offshore use (for ex., Malo, Hylas, Rival, Valiant, J Boats etc.), I would think that a good survey, boat history (no evidence of groundings), general consideration of the quality of boat construction (including details on the keel to hull joint, caulking, bedding etc.) and the history of sister ships would reveal a lot and make it likely that the keel would stay attached during her sailing life. I think for most boats nowadays (including those mentioned above), all bets are off for untoward events like groundings. That said, I think there is a good long way to go ensuring that new builds are better done in this area and in inspecting those that have been around awhile. My best, Dick Stevenson, s/v Alchemy

Hi Dick, I agree with your conclusions. However I have some interesting information, several fg yachts with fin keel in Scandinavia are built so strong that they can tolerate to hit a stone with the keel in good speed. The ones I have sailed are X Yachts of Denmark, Arcona Yachts of Sweden and Baltic Yachts of Finland. The keel construction of this three are all different, but looks very strong and stiff. You can find the drawings on the net. They all sail well. I like to sail in uncharted waters and then you must be prepared to meet this problem every year. Then it is not so difficult, but most fin keeled fg boats are not built to handle this difficulty.

Hi Svein, Thanks for the info. When sailing your part of the world, I saw those boats pretty regularly and thought they looked fast and well built, like J boats from the US, but had no other contact with them. I was unaware they were robust enough to tolerate hitting a rock at cruising speed unscathed. My best, Dick

I have just bought my *third* steel boat – so there you go, you do know of at least one person who has bought more than one!

One of these is coming up to 100 years old and has not had a spot of rust on the undersides in the last 15 years – though to be fair, she sits in freshwater.

The game changer for steel is proper grit blasting and professionally applied two part epoxy paints. Done properly, it lasts for decades.

Steel is a nightmare if not maintained and if poor quality preparations / coatings are used. A pure DIY life of grinding and painting rust is indeed a mugs game. With proper blasting and painting however, you have an extremely strong, durable and low maintenance system.

My latest steel boat is 30 years old and the paint failed about five years ago so there is some remedial work. With that done and a visit to a Dutch yard for an SAE3 blast and glass flake epoxy paint job (when I can afford it!) – I expect it to go another thirty years. How many fiberglass boats can confidently expect to last 60 years?

Hi Richard well said. Here in USA/Canada people are afraid of steel boat..European are not and they have made plenty still traveling the globe. We should not forget “attainable” in the adventure cruising. I’m talking of used boats of course as I made it clear that all professional yards have turned to aluminum and I’m fine with this.

People look after non metallic boat as a magic bullet for secure world traveling but there are all sort of dangers awaiting: rocks, corals, UFOs, containers, fire, and the most dreadful and invisible… the 1 million cycle of flexing in the ocean after a few years. Attainable cars still have their coil-springs and chassis made of steel. Every polyester boat owner have experienced the need tighten up the rig after a rough passage…

I would have no problem of buying another steelboat if mine one day would be lost. You are right that with proper preparation steel in marine conditions can go many decades – just look at the oil rigs they are built for 40 years up.

Thanks for the informated post!

Just to be pedantic, what I wrote was:

I know a lot of people who own a steel boat, or have done so in the past, but I have never met anyone who has owned a second steel boat.

As I suspected would happen, we have had a bunch of comments from steel boat owners defending the material and extolling steel’s virtues. These comments make many good points. The most important being that steel when properly coated can have a long and useful life.

That said, I do need to make clear that none of this alters the basic fact that steel is a fundamentally unstable materiel, or as one commentator said “rust never sleeps”.

As I said in the article steel can work for those with the knowledge, time and dedication to care for it properly.

“If you built the boat yourself, or supervised every step of the build, and then cared for her yourself, it can work. Just look at the amazing voyages made by AAC contributor Trevor Robertson in Iron Bark.”

And there is no question that a buyer can often get a lot of boat for a good price in steel. But for most of us steel boats, and particularly old steel boats, are not the best option. Nothing I have heard changes that.

As a steel boat owner I understand why people have their reservations. The way in which an old steel boat can crumble before your eyes is disheartening and if that kills your confidence in it then that is that. And as another person mentioned, the fear of old steel boats does seem more prevalent in North America than elsewhere; there may be good reasons for this.

Personally I’d love a good aluminium hull, but all the ones I could access in Australia were well out of my budget. And many of the fibreglass ones came with other problems, osmosis, cracks, delamination, water logged cores and so on. Or they were really heavy old designs that sailed like slugs.

Plus I really wanted rigidity, as an engineer this attribute seemed fundamental to me, so in the end I went with steel despite knowing full well that rust never sleeps. And truly modern coating systems really are remarkable and quite surface tolerant. They’re designed for aggressive industrial applications where ideal surface preparation isn’t possible or economic.

If I could build new it would be a steel hull with no horizontal stringers, stainless deck, integral tanks, total bilge access and a full noise Jotun or International paint system. Thirty year life easy.

Still I don’t feel any pressing need to defend steel; it’s not as good as aluminium and it will never be as popular as fibreglass. Besides there aren’t that many really good steel hulls out there and those of us who like them wouldn’t want to see them become too much in demand 🙂

A good analysis, thank you. I agree particularly about the stiffness advantage of steel.

And, even though I’m an aluminium fan, I would not say it’s simply better than steel, just better for most usage profiles. That said, steel is easier to weld and more abrasion resistant than aluminium.

Hi I would love to meet and talk hulls, but that would ruin your “I never met” a second steel boat owner. I am on my second steel boat. I have owned steel, fiberglass and wood boats in my sailing life. My first steel boat was an Ebbtide 36, built like a brick shithouse as they say, in the UK. As a newbie to cruising, I read Jimmy Cornell’s “Ocean Cruising Survey” where most long term cruising boat owners preferred metal. I sailed it hard across the Atlantic and Pacific and points in between (over 35k passage miles in 5 years). I even had the opportunity of living through an experience of driving it ashore in a strong wind. My (now ex) wife fell asleep on her watch and let us drive it directly into a rocky shore of an island in the Caribbean at about 7 knots. The boat was eventually hauled off and the dents in the hull needed to be repainted. No leaks, no lost keel, and after, no rust. My current steel boat is a Folkes 42. I had the electrical system completely rebuilt after my purchase. On a trip from WA state mainland to the San Juan islands, we had a voltage regulator (brand new, just installed Balmar regulator) fail, start on fire and allow two batteries to explode before the fire suppression system blew the fire out. We had to abandon ship into our dinghy. The boat did not sink, but was totaled per our insurance company. After many months negotiating with Balmar they finally admitted fault and paid for a complete rebuild of our boat. As we gutted the interior to bare steel we got a chance to check for interior rust and found none. Now (three years later) we are back on the water sailing again. With modern coatings and a minimum of maintenance chasing after any scratches a properly built steel boat offers an inexpensive (relative to the other metal choice-aluminum) safe and strong boat. I think the boat has to be properly built originally (professionally) and then properly coated inside and out. One other advantage of steel is that it can be repaired anywhere in the world. Charley s/v Hongvi

As I am still considering buying some (used) steel boat in a couple of years time this tells me one important lesson – access to the inside of the hull must be able _everywhere_, at least good enough for proper inspection using some fiberoptic or the like. Even (and especially) below tanks, or similar built-in structures. It is quite easily possible to blast and recoat the outside, and doubtful areas on the outside can be easily spotted. But it must absolutely be possible to routinely inspect the complete hull area from the inside as well, without too much ado. If (heaven forbid) there would be some blasting and recoating necessary it is still a chore removing parts of the internal structures, but you need to be able to detect it first.

And the story about your exploding batteries makes me shiver. What had you done if your boat was from plastics?

There would be a different ending to the story.

Yes, I think that’s the key: inspect every square inch of the inside of the boat. The trouble is I’m pretty sure that’s a lot harder than many people will have you believe. But it must be done since I understand from people that know that steel boats die from the inside out, so re-coating outside does not solve much.

Very good advice John, all boat need total inspection capability. Unprotected steel can rust, aluminum should be kept free of any standing water (wood is terrible in contact with bare alu) that can attack the oxyde and start up a crevice corrosion.

On any metal boat the bilges should be dry all the time.

Aluminum corrosion protection is not a simple science…if only aluminum could be alone but the problem start when attached to another metal or with itself sometime.

On the periodic table of element Aluminum is a much more active element (less stable) than iron. But neither are used on a boat, it is rather in alloy: Alu 5083 is an alloy, Steel is an alloy and the same for 304 and 316 stainless. All have their corrosion issues and can be attacked with the proper conditions/oxidant.

I have read on Collin post that his Alubat seacocks are in plastic…what are yours John on MC ? Mine are stainless steel and for the plastic speed and depth transducer i have built a safety chamber over it. I would NEVER leave a plastic seacock alone (without side impact protection or safety chamber) on a metal hull.

I think we are starting to go in circles here since I have coved all of this on aluminium and sea cocks in other articles and comments.

As I have written before, I have never had problems with aluminium from standing water or contact with wood, and I have owned an aluminium boat for nearly 30 years.

As to dry bilges, simply not practical once the water temp gets below about 8C, due to condensation. The result is that our boat’s bilges have been wet for most of her sailing life and still we have no significant corrosion problems.

As for plastic seacocks, the good ones are very good, and I would choose them over any other material if building a boat from scratch. Nor would I worry about a safety chamber, as long as they were properly installed. And, as a general rule I don’t like stainless steel below the waterline.

Hi Charles,

Wow, if I had been through the same two experiences I would be living on a farm…in Saskatchewan!

One thing I do need to clarify. Generally a Steel boat is only less expensive that aluminium is both boats are painted. Leave the aluminium boat bare, except for the underwater surfaces, and I’m pretty sure the equation reverses.

Hi John, I also have had 2 steel yachts. The first had no corrosion issues as it had only paint on a rather bare internal fitout. Surprisingly, in Sydney Australia it had almost no condensation due to adequate ventilation. It was 6 t, and 20 years old. The second yacht had a full internal fitout but the hull was done in corten steel which only ever showed minor surface rust. However the mild steel frames in the anchor locker were rusted out to half their original size. It was 20 t , and 28 years old. It should be noted that Lloyds would not let me build in Corten due to its brittleness in subzero temperatures. If I were looking to buy another yacht I would look for another steel one with these provisos. 1/ a good design. Backyard builders don`t pay for a high quality design 2/ The price has to allow for a total strip out, sandblast and paint ,and refit, rewire etc. 3 If the insulation is sprayed on foam then walk away. According to the US Navy their paint systems are good for 25 years. My third yacht was an alloy 55 ft 1969 racer. At 14 t it always felt fragile and it`s motion too lively. In asking what alloy they used I could not say, but probably not the modern 5083 and not the old duralium.

Hi William,

That’s interesting about corten, thank you. Just spent an interesting 10 minutes reading about corten. I had heard of it, but really did not know much about it. Always more to learn.

And a good point about design. I never understand why anyone would cut corners on that vital step.

Lloyds is out to lunch. Old Corten A was brittle (which is why USS sold Corten B) but modern A588/A606 has excellent cold notch toughness for an HSLA and is significantly better than A36.

A588 is sold primarily for bridgemaking and is an excellent structural material in most conditions.

To be fair to your mild steel frames: they almost certainly sacrificed themselves to the corten, which is more noble than mild steel.

Hi, what about plywood builds? Would you consider them an option? What would your conditions be, what would you survey? My first reaction when I read your specifications for your next boat was “that’s a RM1200!”. I’m not stating that they are perfect: they definetly have some drawbacks, and I wouldn’t be able to assess if one is a safe buy. But their twin keels are well-designed (just as the twin rudders of the Boréals, maybe!), and make for boats that are quite good upwind, despite being roomy, light, and of moderate draft.

Depends what you mean by “plywood”. If we are talking about cold molded with epoxy, then yes, certainly an option. And yes, I agree RM1200 is a really interesting boat. Thank for pointing her out.

Just to clarify, the Boréals have single rudders, and two dagger boards aft.

Ouch, plywood without epoxy? I don’t even want to know about this!

Sorry for the mistake regarding Boreal: I meant “aft daggerboards” and not “rudders”, of course. The point being that, as far as I know, the RM were the first twinkeel boats on which the keels are properly angled, so as to reduce leeway when sailing upwind.

I was pretty sure you knew that, but just had to clarify.

Fun facts, back in the day some quite good boats were made with “tortured plywood” in much the same way as metal boats with chines are made. I think this was one: https://www.sail-world.com/Australia/Ragtime-Revisited/-28564?source=google

Also, I have a very faint memory that there were some early IOR race boats with toed in boards to help with pointing. We also experimented with auto jibing centreboards in the 505 class, with the same idea. As I remember, it was a trade off because drag goes up as we angle the board—you point higher but go slower.

Thanks for the information! I didn’t know about tortured plywood.

I see on the internet that the best trade-off for an auto-jibing 505 centerboard is around 2.5-2.8°. And something I didn’t suspect: if the daggerboard is well-made, slightly lifting it brings it back to the centreline! Which would be ideal downwind. The keel angle on RMs and similar designs is less than that (around 2.0°?), but keels have to be kept in place when not sailing upwind! In my experience, the advantage of this is not that you could point higher, but that, for the same angle between the wind and your route, the hull can point a little further from the wind, yielding 1) a better hull shape through the sea (there is another saying about sharp edges: when the sharp edge opens the way, it works better!) and 2) a little more distance between the two sails, which seems to help, too. I know it may sound like I’m overmaking this, and 2 degrees may not seem that important, but the difference is quite visible, especially with 15kts of wind and a flat sea (it becomes all the more visible if you heel too much, but that’s not advisable anyway).

Yup, the 505 boards in my time were made so they only jibed when all the way down.

As to the exact mechanism of how jibing boards works, way beyond my pay grade, but if the 505 fleet are still using them clearly they do work since the boat has always attracted some of the best minds in sailing.

Tortured Plywood? A Kamanu catamaran built with the Hughes Cylinder Mold process has been in daily commercial service in the rough Hawaiian waters for THIRTY YEARS. That is perhaps equivalent to 100 years use for the average full time cruising yacht.

Fairly recently an entire half hull of a 70′ CM catamaran was built in the Philippines in a single day using the process. It is a full curvature hull shape, not a chine boat like Rags.

A few years ago I met the skipper of a 55′ CM cat built 20 years ago for Lake Tahoe. It sits outside in the snow every winter and carries passengers every summer. The best story over beers was about the time a jet ski hit it at full throttle and ended up inside of the hull. Sailed it to the dock, pulled the jet ski out, scarfed in a new hull section, and went back to work carrying tourists.

Tortured plywood, a phrase you won’t hear anywhere but AAC!

Thought all you metal heads would like to know that a new process for refining wood has been developed in the lab. All the lignin is chemically removed, and then the remaining fiber massively compressed. The resulting material is stronger than steel on a weight basis. May never be a boat building material, but who knows!

Hi John, As a metal head, my perfect hull material is SAF 2205 ( DUPLEX ) stainless steel. It has a yield strength 3 times that of mild steel and excellent corrosion resistance, as well as great fatigue resistance. See sv tanielle Thanks Jordan Bettis for the update on Corten

Composite materials in the superyacht industry

Most of the hulls built in the marine industry today are created, in some part or form, with the use of marine ‘composites’; a combination of materials in which each part keeps some of its original traits.

Glass fibre

Glass fibre in its early form was originally discovered as a composite in the 1930s when researchers at Owens, Illinois Glass tried to spin glass into fibres to replace mineral wool for insulation and filters. Almost accidentally, they revolutionised boat building, and now, more than 90% of all boats are built from composites that started with their invention of fibreglass.

This glass fibre is remarkably similar to today’s silica-based fibreglass, which is strong and resistant to scratching and contamination by chemicals. These flexible fibres are remarkably easy to work with.

E-glass or S-Glass

Silica-based fibreglass comes in two forms; E-glass or S-glass.

E-glass is the workhorse of the contemporary boat building against which all others are measured. It delivers reasonable strength at a relatively low cost. S-glass is however, stronger, lighter and scratches less, but costs three to four times more than E-glass.

Arriving on the boat building scene in the last 30 years, aramid (along with carbon fibre) has changed the way in which boats and luxury superyachts are built. Aramid stands for ‘aromatic polyamide’.

Kevlar, Technora, Twaron, Heracon

Kevlar is the best-known aramid material. It is the trademarked fibre that DuPont (the company that created polyester resin in the 1940s) originally developed for tyres. Technora, Twaron and Heracon are other branded aramids.

Aramids offer twice the tensile strength of E-glass. It is lightweight, weave-able, resistant to puncture, impact and fatigue. However, they do absorb water and don’t withstand compression as well as glass fibres. This is why they are commonly used with other fibres.

Carbon fibre

As the most expensive of reinforcing fibres, carbon fibre is lightweight and stiff – roughly six times stiffer than E-glass. It therefore doesn’t corrode like aluminium or stainless steel, making it perfect for mast or rudderstock components, or entire boats.

Carbon fibre is however tricky to work with. It needs to be engineered carefully to account for its lack of stretch, providing little warning before it fails suddenly and catastrophically.

Why use carbon fibre?

According to Luke Hendy from Branagh Marine Composites , superyacht owners and project managers are increasingly requesting carbon fibre as the material of choice for a range of cosmetic and structural yacht equipment.

The unique qualities of carbon fibre include:

• Thermal stability
• Improved moisture stability
• Low weight and low mass

Carbonfibre is 70% lighter than steel, 40% lighter than aluminium and 35% lighter than magnesium alloy. It has excellent strength-to-weight ratio and optimal energy absorption properties for safety solutions and design flexibility.

In addition, carbonfibre yacht equipment has a unique aesthetic quality, which showcases the ultimate in high-end technology.

Core foam ‘sandwiching’

As a way to reduce cost and added weight in boat building, composite designers determined early on that ‘sandwiching’ a low-density, lightweight core material, such as foam, honeycomb or balsa wood, between thin face sheets of composite can dramatically increase a laminate’s thickness and stiffness, while requiring a lesser supporting structure.

This core composite service is a great way to distribute loads and stresses on the structure of a superyacht or vessel, preventing wrinkling and buckling during impact or stresses.

Open-moulding versus closed moulding composite technique

Luke Hendy from Branagh Marine Composites explained some of the jargon around composite services, and commented on the different types of core moulding techniques used in the industry.

He said, “There is a slow transition from open moulding techniques, such as hand lay-up and spray-up, which utilise more manual labour and consume more time, to a slew of closed moulding techniques such as resin transfer moulding (RTM), vacuum assisted RTM (VARTM), RTM Light, vacuum resin infusion moulding (VRIM), vacuum infusion processing (VIP), closed cavity bag moulding (CCBM) and the Seeman composites resin infusion moulding process (SCRIMP).

“These closed moulding processes offer more flexibility in terms of part size, complexity and faster production rates, (due to automation and less manual labour) resulting in a higher quality part and minimal void content.”

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With in-house design capabilities, we have the ability to create new models based on client needs and aesthetic liking. Our team will work with you to bring your dream yacht from concept to reality.  Vessels can be designed to meet Coast Guard Inspection requirements.

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