Technical yacht design: the bignami of shipbuilding materials


[vc_row][vc_column][vc_column_text]All’inizio fu il legno. Per decine di migliaia di anni questo è stato l’unico materiale con cui si sono costruite le barche. I tronchi scavati all’interno tipici delle piroghe polinesiane, le travi inchiodate sovrapposte dei drakkar vichinghi, il compensato marino dei primi yacht da diporto del 1800. Materia prima abbondante in ogni luogo del pianeta. Possibility of setting up a building site even on a beach. It only takes a few months for a sailboat of about ten metres equipped with the bare essentials. Practically with the right technical knowledge and manual skills, and a minimum of expenditure on tools, anyone could build a sailboat and sail around the world. As indeed he did Joshua Slocum and also Bernard Moitessierafter an unfortunate shipwreck against a rocky shoal on the Chagos Islands.

Wood, however, had two major problems: maintenance and caulking. For maintenance we mean the constant periodic re-painting of all immersed and non-immersed parts to prevent rot and the invasion of teredines, a species of woodworm that feeds on wood fibres, weakening them to the point of crumbling. It was not uncommon to have to dry-dock a boat to replace a course of planking or two that was on the verge of splitting. Caulking on the other hand, it is the technique used to make watertight a wooden hull, which, being composed of planks placed side by side longitudinally, has cracks between one planking and the next. Cracks that must be plugged with a semi-solid paste composed of straw (or thin strips of fabric) and tar. Work that is obviously done with the boat drybut then once in the water it has to be refinished and checked, because in the meantime the wood has become moistened, then swollen, and things have changed a bit. A big bitch in short. Solved in part with the so-called West Systemor the technique of using marine plywood panels, suitably bent with steam, and painted on the outside with epoxy resin.

The ultimate solution to the problems of wood, however, came from a new material that has enabled boating to become mass-produced (or almost mass-produced): GRP. In English it is called GPR, (glass reinforced plastic) and was the first composite material, i.e. made of two distinct substances: a glass fibre fabric of varying size and consistency; and a hardening resin produced by methods similar to those used to make plastic. The manufacturing process, known as rollingis carried out by arranging the various pieces of fibreglass cloth on a mould and then passing the resin over them with a brush. In this way the first layer is made, which is left to dry. Then another is made on top, and so on, until it is thick enough to withstand the mechanical stresses which the naval architect (yacht designer's old name) will have considered.

At the beginning, in the 1970s, fibreglass thicknesses were considerable (even 15 cm) then it became apparent that the mechanical skills were more than sufficient and started to reduce the thickness in order to have lighter and faster boats. Today we have reached the absurdity of having racing boats that have 2 cm thicknesses in the hull, from which keels that can weigh up to 4 tonnes hang. Boats with which it is good not to stray too far from the shore. The only defect of fibreglass is osmosisbut for the last ten years or so, the artisanal production method described above has been replaced by the semi-industrial infusion method, which allows standardisation of quality, some economies of scale and above all osmosis-free hulls when epoxy resin is used.

A mixed wood-glass construction technique is known as 'sandwich construction'. which basically consists of creating two thin fibreglass skins with balsa-type light wood bricks in between. The main advantages are: greater lightness, better insulation, equal mechanical properties. A technique used, for climatic reasons, mainly by Scandinavian shipyards, which has only one disadvantage: in the event of a collision with a dock or another boat, if the outer fibreglass skin cracks, moisture penetrates inside the hull, making it unusable in a short time.

In parallel with the spread of GRP, in a niche of the nautical market aimed at large ocean-going sailors, another shipbuilding material has also become established: aluminium. Heavier than GRP, but resistant to oxidation and above all to impacts with the seabed and cetaceans (orcas have often been seen to attack GRP boats, as happened to Surprise, the boat of Ambrogio Fogar and Mauro Mancini) aluminium ensures that in any weather and sea conditions the sailor and his family will be safe inside the hull. Specialists in nautical construction with this metal, which requires special welding, are French and Dutch shipyards. The weak point of aluminium, apart from its higher specific weight compared to GRP, is galvanic corrosion, which forces one to use a large number of sacrificial zinc anodes and to be careful where one moors (there must be no large metal masses around). Of course, as a metal material there is also steelbut is practically only used for large vessels (over 50 metres), both motorised and sailing, because the high specific weight penalises performance too much. Moreover, corrosion by oxidation is an ever-present risk that requires constant care, especially of the inner surfaces of the hull.

Early 2000s technological progress has made available to yacht designers a new composite material with amazing physical characteristics: carbon fibre. Extreme lightness, superior hardness to steel, absence of galvanic corrosion, excellent insulation, these are the qualities of carbon fibre, which is made like fibreglass, with hardened fabric panels glued together using epoxy resin. Only at the end of the rolling process, the hull needs to be baked at a temperature of between 80 and 120 degreesTherefore, large industrial furnaces are needed. For this reason, combined with the cost of the raw material, making a carbon fibre hull is still quite expensive (about twice as much) compared to a fibreglass hull of the same length. With the spread of the material, however, costs are slowly coming down. Today, carbon fibre production is reserved for the racing sailboats and a few high-performance motor yachts.

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