Sam Fortescue clarified shipbuilding terminology and looked forward to a future without fiberglass
It is effective to build with prepreg materials, but the hull must be "cooked" at a precise temperature before it can be cured. Image credit: Eva-Stina Kjellman
The end of GRP? Sam Fortescue looks at the past, present and future of shipbuilding materials
Take a look at the new boat brochure or stroll the pontoon at the Southampton show, and you may come across some terms that don't make much sense to you.
The art of shipbuilding is as widely known as ever, but its science is constantly evolving. New materials and new technologies can make it difficult to compare similar products.
Take wood as an example: the material of choice for shipbuilding for thousands of years.
There are still many wooden boat builders working in dirty shacks and halls to make pilots, rowing boats and other iconic ships of the past.
But perhaps the most famous wood manufacturer is Spirit Yachts of Ipswich, who uses composite wood to build completely modern ships.
Spirit 44E is a "zero carbon" cruising yacht. Credit: Richard Landon
"Of course, we use epoxy to bond the components together, but compared to GRP or carbon, the amount of resin used is very small," said founder and chief designer Sean McMillan.
'Both carbon fiber and GRP rely entirely on saturation with high-density polyester or epoxy resin to impart structural integrity. Wood, which is also a linear fiber material, is cross-linked with a honeycomb structure created entirely by nature and has complete structural integrity.
In fact, the 1.6-ton Spirit 30 dayailer used only 73 kg of resin and 12.2 kg of curing agent in the entire structure.
"In 20 years, when GRP becomes unacceptable to society-let alone any future scrap legislation-who knows, we may look back at the past 60 years of GRP ships as a historical niche," McMillan finished provocatively.
Another example is the lively French manufacturer RM Yachts, whose ships are known for their swiftness and whose marine hulls are designed by Marc Lombard.
However, they are made of plywood and epoxy.
Think that each of our Spirit yachts is made of wood, which is a composite material of glue and epoxy resin sheath.
It is more flexible, robust and more sustainable than standard FRP plastic.
Laser-cut Okoumé plywood up to 22 mm thick is bent around the mold and epoxy-bonded to the plywood structural member.
The entire batch is also epoxy sheathed to extend the service life.
This technology means that the new RM 1380 weighs 9.8 tons-slightly lower than X-Yachts' similar X4-6.
'Plywood is the soul of RM. It is a very useful material with good stiffness and lightness-very suitable for building hulls and structures," said engineering supervisor Edouard Delamare.
"But plywood is inseparable from epoxy resin because it ensures waterproofness-which is essential in the marine environment."
From Beneteau to Bavaria, many series of production sites still use the most basic form of wet laying-using rollers to spray resin on the glass fiber mats so that they are fully wetted before laying the next layer of glass.
It is difficult to control how much resin is used, and there are usually air pockets between layers.
For this reason, hulls built in this way tend to be overbuilt and heavier.
RM Yachts is unique in building offshore yachts with plywood and epoxy
Polyester is the cheapest and most commonly used resin, but it can combine with water and cause penetration problems.
This is why the iso-gloss gel coat is applied to the outside of the hull as an effective moisture barrier.
Vinyl ester produces more adhesion than polyester. It is estimated that its strength is as high as three times, but the cost is also higher.
Epoxy resin is the resin with the best performance among all resins and is only used for high-quality laminates. All of these are very poisonous and have a "dead fish" icon on the side of the jar.
When vacuum infusion emerged as an industrial technology in 1990, it allowed shipbuilders to use less resin and distribute it more evenly around the finished panel to increase strength.
But it will produce a lot of waste, because each infusion part must be prepared with a large number of plastic layers.
In addition to the plastic of the vacuum bag itself, there is a breathable layer to disperse the resin, and a peeling layer to prevent it from sticking to the infusion part; a thick sealing tape; a disposable feeding tube is needed every few inches, Many vacuum tubes must also be boxed.
However, this technology has not stagnated, for example, there are now reusable vacuum bags made of inert silicon.
Some bags have the mesh structure required to diffuse the resin inside, and the aerospace department is the first to use PTFE membrane to prevent the resin from clogging the vacuum pump side of the system.
Arcona of Sweden used vacuum infusion to build its fast cruiser, and it has been in use for many years.
Manual laying is a process that has hardly changed in many years of shipbuilding
But in order to increase strength and rigidity, it is laminated in the steel support frame in the midship to transfer the load from the rig to the keel.
Improvements in lamination technology mean that the boat is lighter than ever.
The late Arcona designer Stefan Qviberg said that the current Arcona 40 displacement is a full ton less than ten years ago.
Other shipbuilders use other types of reinforcement for high-load areas of the hull.
Aramids like Twaron and Kevlar are often present, as are the carbon fiber selective areas on the stringers and around the keel bolts and chain plates.
For example, the high-end yacht manufacturer Baltic Sea uses carbon fiber reinforced materials to increase strength without adding weight.
Vacuum infusion uses less resin, but generates a lot of plastic waste
The high-performance catamaran brand Catana also uses Twaron and carbon fiber in its laminates to save hundreds of kilograms; the old Catana 47 weighs about 700 kilograms.
Some people claim that the aramid reinforcement makes the hull safer, for example in the case of a collision with a container, but others refute this.
Naturally, carbon is still the ultimate performance material because it combines strength, rigidity and lightweight characteristics.
Compared with other fibers, its price is also very expensive, and it is very resource-intensive to produce, because it requires a temperature of up to 3,000º C and plastic raw materials.
The volume and waste of the infusion process has led to a step forward in the form of so-called prepregs, in which the fiberboard used to strengthen the hull is pre-coated with a pre-catalyzed resin that reacts very slowly at room temperature.
There is no need to mix epoxy resin with curing agent and reduce its viscosity with toxic styrene to be sucked into the mold. The precisely controlled curing process activates and cures the resin.
The result is stronger and lighter than laminates produced by wet lamination.
Gurit’s SPRINT system goes one step further, sandwiching a heat-activated resin film between two layers of fibers.
Windelo uses basalt fibers to strengthen the hull during shipbuilding. It is said that its carbon strength is much lower than using glass
The advantage of this is that the fibers remain dry before curing, so the air can be removed more easily under vacuum, resulting in a laminate with a porosity of less than 0.5%.
Baltic Yachts uses this technique to build an oven around its hull to heal them.
"With one or two exceptions, we haven't filled the boat with water for a while," said CEO Henry Hawkins.
'Compared with vacuum infusion, the use of Sprint and prepreg materials can reduce weight. For hand lay-up, usually more resin is mixed than needed, and a lot of it will be discarded. Resin is lost or wasted in plastic hoses and pipes, breathable membranes, and distribution channels in the same way as infusion.
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Even at this cutting edge of the composites business, aerospace and Formula One are making rapid development.
"We can now get rid of expensive autoclaves and ovens-they can be cured at room temperature or 40-60ºC," said Ashley Parkinson, a research engineer at the National Composites Centre in the United Kingdom.
"This is a more expensive process, but in the high-performance market, it's worth it."
Now, there is nothing particularly sustainable in the production of glass fibers-this technique involves heating the virgin silica to 1,370º C and then pultruding the molten wire onto the spool.
You can use some recycled glass to reduce emissions, but it is an energy-intensive process and it is difficult to extract raw materials from scrap glass fibers.
The Swiss supplier Bcomp tested alternative natural fibers 10 years ago when it was founded in a garage.
“Facts have proved that flax is the best in terms of mechanical properties, soil usage, water requirements and overall performance,” explained Paolo Dassi, Marine and Industry Manager.
It actually locks in carbon instead of producing carbon—up to 500 grams of carbon dioxide can be produced per kilogram of flax.
Precise cutting is the key to reducing fiber waste in the shipbuilding process
'Plants act as carbon dioxide sinks during their growth. This completely offsets the carbon dioxide emissions during the manufacturing stage.
The extraordinary growth of Bcomp began when it managed to process flax stems to uniform size and flatness, and to replicate possible grades using glass fibers.
Its AmpliTex products are available as unidirectional, stitched biaxial or woven twill fabrics in the range of 200-500gsm.
When laminated, it is 50% harder than glass, but its strength is slightly weaker, making it an ideal substitute.
Combine this with additional flax netting called PowerRibs, and you will end up with a composite material that is very similar to carbon, but with only 25% emissions.
AmpliTex has been used in niche shipbuilding projects, including the glorious Flax 27 daysailer from Bremen Green Boats, which is decorated with cork.
The foam sandwich hull structure (green) or balsa core (wood) is much stronger, with almost no additional weight. Photo Credit: Graham Snook/Yacht Monthly
This is a key part of the shelving of the new Café Racer 68 from the Baltic Sea. Although her hull is carbon fiber, 50% of the structural members are flax composites.
The French Windelo has adopted a different strategy for its catamarans.
It uses basalt fiber-made from molten volcanic rock-"slightly stronger than alkali-free glass, and the carbon intensity produced and used is only one-tenth of that."
Its first 50-foot hull also has a recyclable PET foam core to increase strength and rigidity. But it's not just the fibers being decarbonized.
So-called "green epoxy resins" have been developed, in which most of the synthetic oil-derived resin molecules are replaced by bio-sourced molecules.
For example, Gurit's Ampro for manual laminating is 40% bio-derived.
Green Yachts focuses on environmentally friendly shipbuilding technology. Its flax 27 is made from sustainable flax fibers
West Systems' ProSet series includes epoxy resins containing up to 30% biomolecules.
They can basically be directly added to any process suitable for equivalent synthetic resins.
“Any customer familiar with epoxy processing, vacuum curing, or post-curing will be very familiar with this process,” said David Johnson of West's European manufacturer Wessex Resins.
"Even wet stacks without vacuum bags."
The cost increased slightly, but compared with the standard epoxy resin, the cost increased by less than 25%, and it is a drop in the overall structure of the ship.
"Bio-based epoxy resin is more expensive because it involves more complex chemical processes," Johnson said.
Pre-impregnated flax fibers are laid around a balsa core
'Compared to building a boat with vinyl ester or polyester, you can use fewer materials due to the superior quality of epoxy resin. The final cost difference is negligible, and the benefits of lighter weight are: higher efficiency and less load.
Suppliers like Gurit are also looking for alternatives to the synthetic foam cores used in sandwich hull structures.
The standard foam is made of virgin PVC and has all the relevant environmental deficiencies.
Gurit has developed more renewable alternatives using up to 100% recycled PVC and balsa wood.
Manufacturers from Arcona and X-Yachts to Bali and Gunboat catamarans use foam cores in their laminates to build ships that are stronger and lighter than other methods.
Some innovative new shipbuilders are moving in another direction, avoiding the current traditional GRP, and instead using things that can be truly reused.
The start-up company Vaan is building its 42-foot R4 catamaran from an aluminum alloy commonly used for window frames and road signs, so up to 60% of the hull has been recycled.
"There is no way to distinguish it from the original material," said Vaan founder Igor Kluin.
Vaan uses a high percentage of recycled aluminum to build the hull, which can then be recycled easily
However, ensuring supply is not easy. Part of the reason is that window frames can be used for 50 years or more, and they also compete with other industries.
"In the short term, the cost will be higher because so many people follow suit, but its energy consumption is only 5% of the original alloy, so it should be cheaper in the end."
Vaan's novel approach to sourcing more sustainable materials also extends to interior decoration.
It uses pineapple leaf fabric instead of leather, a large amount of European poplar is used for cabinets, cork instead of teak flooring and recycled PET.
A more environmentally friendly shipyard: a hull made from recycled aluminum
Part of the boat is 3D printed-high-end brands are doing more and more things.
"Recycled industrial PET is being 3D printed for the back of the Vaan spoiler because it produces a smaller volume than molded ones," Kluin said.
'We want to see if it can bear weight. We are also using aluminum for 3D printing. It is useful for smaller structural elements that are difficult to reach and have traditionally been milled.
Except for wood, all forms of composite materials face the same problems. At the end of the service life, it is difficult to separate the component materials for reuse.
This is why it makes sense to use materials such as steel or aluminum, despite the higher environmental costs of virgin metals. They can be reused.
The composite recovery systems developed so far, including pyrolysis, combustion and crushing, are not satisfactory because of the high energy intensity of these processes or the low quality of the materials they produce and must be degraded for recycling.
In principle, it is possible to use resins that are remelted at high temperatures and can be collected, refined, and reused.
Arkema's Elium resin can do just that, and it has been used in recyclable wind turbine blades.
The cost of separating laminates for reuse is high. Photo Credit: Rob Wilkinson/Alamy Stock Photo
They even used it to build a 6.50m Mini Transat boat.
The process also produces reusable glass, but carbon and flax do not support heat: carbon loses as much as two-thirds of its strength, and flax only burns.
However, a study in Australia showed how carbon fiber composite materials are first heated in a pyrolysis chamber without oxygen to burn off the resin, and then oxidized to produce carbon fibers, which have most of the strength of the original fibers, but are not environmentally friendly. The impact is only 10%.
The cured laminate can also be separated using a vat of acetic acid using a proven chemical process in the National Composite Materials Center laboratory.
The University of Portsmouth is studying enzymes that break down plastic, starting with plastic bags.
This method can eventually also deal with ships.
'You have to find the right enzyme to cut the molecule of a particular polymer. NCC's Ashley Parkinson said that, in fact, it will take another ten years.
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