Types of material
There are many methods and different materials for building a cruising yacht these days. The four main materials most used for yacht construction are Wood, Steel, Aluminium and Fibre Reinforced Plastic (FRP). Glass Reinforced Plastic (GRP) is the well-known name for fibreglass boats. However, it is only one type of Fibre Reinforced Plastic (FRP) that is used these days. A lot of people have differing opinions of which is the best materials for yacht construction, and which is their favourite. There is no such thing as the perfect material, they all have good and bad points. With the rapid advance in technology, new materials and techniques are helping to alleviate some of the problems experienced in their use. I have written here, some of the good, bad, and ugly points of each material with an unbiased opinion. With the ever-growing concern and need to protect our environment, thought must be given to the recycling of the materials used. See more on Steel or Alloy yachts on my blog Steel and Alloy.
The beauty, warmth, and pure romance of wood as a boat building material is a virtue, compared with plastic or metal. Wood has good thermal and acoustic properties which other materials cannot match. With boats being mass-produced these days, a wooden boat is as unique as its owner. Wooden boats are the best-known traditional way of building yachts. There are wooden yachts still afloat today which were built over one hundred years ago. Most wooden boats built today are cold moulded using strips of wood and resin. Coating the wood in the epoxy resin can reduce maintenance but will not eliminate all problems. Unfortunately, yachts were mostly made of wood, now they are mostly made of fibreglass. This has led to a shortage of skilled wooden boat builders. Ideally, wooden boats need to be built from hardwoods like teak or mahogany which is expensive. With forests shrinking, wood should be from a responsible source. Never from places where they destroy the forests. Responsible sources replant trees to make the supply of wood sustainable. Maintenance is a big thing with wood. All that lovely shining paint and varnish needs looking after to stay nice and shiny. Even if the yacht’s hull is not made of wood. Wood will be used in the interior for the furniture, doors, and hatches. Although adding some weight the beauty of a teak laid deck, will add a touch of class.
Deciding which timber, you are going to use for building your boat will depend on several factors. Not all woods are suitable for boatbuilding like softwoods such as pine. I have owned a 22-meter Greek built wooden motor sailor, with a Caique type hull for over 20 years. These vessels were build using locally sourced wood which is usually pitch pine. This wood is not the best timber for building wooden boats and I am forever cutting out rot. In the past, the timber and labour were cheap, so repairs each time the boat was hauled out were accepted and tolerated. Nowadays wood is not cheap, and labour prices have gone through the roof. I used to keep the boat on the island of Corfu, and I would haul the boat out at the boatyard pictured below, on the left. They started to use Oak to replace any rotten frames and Cedar which was still green for the underwater planking. I now have the boat on the island of Lefkada and the best wood available is Iroko. Iroko is a hardwood that is hard on the tools but has good rot resistance. Every piece of wood which I now replace myself, gets a liberal coating of Epoxy Resin to protect it, should any rain leak into the boat.
Fibre reinforced Plastic (FRP)
Fibre Reinforced Plastic (FRP). Glass Reinforced Plastic (GRP). Most people mistakenly call all fibreglass yachts GRP. However, some composite yachts are now built with other fibres like Carbon Fibre and aramid fibres such as Kevlar® and Nomex®. Composite construction is a binder (usual resin) reinforced with a fibre material (like glass strands, carbon fibres, aramid fibres). The three types of resin used is polyester, vinylester and epoxy. Orthophthalic polyester is a cheap general-purpose resin. In the earlier days, there were only Orthophthalic resins and they are still the cheapest. Isophthalic polyesters are more expensive but more water-resistant. GRP boats moulded since about 1995 are now being moulded with the more moisture resistant Isophthalic resin. They are used for the gel coat and the outer layers of the hull, as water absorption into the hull, is the main cause of blistering. E-glass is the cheapest fibreglass cloth commonly used. S-glass is the strongest cloth and has the best mechanical performance of the two. It has come from the aircraft industry and is expensive. There are various types of fibreglass mats and cloths used for boat construction. An ordinary mat (Chopped strand) is made up of random fibres held in place by a resin soluble binder. Woven Rovings is a bulky loose fabric and is used to build up bulk quickly and cheaply. Its interlaminar bond is weak so a good practice is to be inter-layered with a chopped strand mat. Woven rovings are measured in grams per square metre and the heaviest made weight is 100g. Uni-directional fibre is a mat made up of the fibres running in one direction only. These are held in place with single fibres glued across or sewn in place. Having very high directional strength it is used in areas with higher loads. Then there are others with fibres crossing in different ways, with different thicknesses and weights. Glass mat is measured in grams per square metre usually 300, 450 or 600.
Fibreglass yacht hulls can be built with layers of fibreglass only. However, to achieve the strength and stiffness required, they must be made thick and then end up heavy.
To keep the weight of a yacht hull down and achieve enough strength and stiffness. A lot of fibreglass yacht hulls are built with a material core. This can be end-grain balsa, foam or a honeycomb material. One method of infusing the fibre mat is hand lay-up. This is done by wetting the fibres by hand with a brush or roller. However, along with the advances in materials for composite construction, is the advances in build methods.
Vacuum bagging is a technique where a bag is put over the wet laminate. This squeezes out the excess resin which only adds weight to the laminate. It is the fibreglass that gives the laminate strength. With resin being oil-based, it has risen with the price of oil making fibreglass boats more expensive. So, using less resin also helps to bring the cost down. The vacuum infusion method also uses a plastic film and vacuum to give a good resin-to-glass ratio. The vacuum draws the resin from feed tubes in the plastic film through the cloth. This gives a more precise measurement of materials and an even pressure over a large area.
Of all the materials Fibre Reinforced Plastic (FRP) has the worst green credentials. There are millions of boats coming to the end of their lives. What can be done with them all? No one seems to know. The only thing that can be done now is to bury them in landfill sites. The cost of cutting it up and transporting it to a landfill site is going to cost money. This is not ideal as an old abandoned hull is worth nothing.