Sailcloth … Art and Science

The use of sails is as old as history itself. Maybe the modern era was born with the yacht America in 1851. She sailed to Cowes and unlike her fellow competitors had not only chosen cotton for her sails but had developed a weave that gave greater stability. America was by no means the first boat to use cotton but in 1850 Cult and Lawrence of Pennsylvania designed and tested a special, tightly woven cotton. They realised that this would enable flatter cut sails and predicted a gain of one knot to windward. The results matched their predictions and the boat pointed much higher, in part due to the sails. A year before Singer patented the sewing machine, they developed a stitch that would not tear the cotton and enable smooth seams. America entered the Royal Yacht Squadron (RYS) One Hundred Pound Cup and, as they say, the rest is history.

Developments in the sailing world are somewhat slow and conservative. Seventy years after the impressive display at the RYS the British view had not really shifted, if Thomas W. Ratsey’s paper of 1924 is anything to go by. He argued the case for Flax. It is true that this material gave proven strength in classic sails and the source of the fibre was local, but looking back there was apparently a stubborn resistance. Sail makers like Matthew Orr tried new cuts, especially in the unsupported head sails. Old techniques were refined, the selection of bolt ropes, their diameter and the amount of pre-twist you gave them before sewing them to the sail. Leech stretch was controlled this way. These documented skills became the basis of the art of sailmaking.

Lead-150318_TODD_1010The cotton flax debate was never really concluded until the new synthetic fibers appeared in the forties and fifties. Early Nylons and Polyesters enabled new engineering possibilities. In 1950 the Delaware property of Dupont manufactured ‘Dacron’. Mylar polyester film was introduced in 1952.

In the sailing world an early exponent of this new material was Ted Hood. He developed, and to great effect, a Dacron that basically used traditional weaving techniques. The cloth was not stable enough to be large and his adage ‘a sail is never good until re-cut,’ probably derives from the fact that though truly strong the cloth was still relatively elastic. This approach was artistic in many ways but shaped by trial and experience.

With cloth and early sail design, Lowell North, a Cal Tech graduate, and his team tried to engineer the process further. They systemized fibre choice and weaving speeds. Finishing processes were elaborated and the use of shrinkage to tighten the weave, through heating, was exploited. With Newtonian like analysis, a quality larger width Dacron was developed. Special attention was paid to the straightness and weave stability of the load-bearing fibres.

In the seventies Mylar was considered for sailcloth, twenty years after electronics had adopted this material. Straight load carrying fibres were laminated to one or more films. This freed sailcloth from the necessity of the loom and it opened the door to new sailcloth suppliers and new sail makers. Diverse fibres were introduced and sail design evolved. The sailing community were having a field day developing thoughts and exploring ideas. This reached its logical conclusion in the 3DL process of continual fibres molded upon a three dimension adjustable form. A host of lookalike copies exist but none have achieved the same level of control and logic.

Sailcloth Art ScienceRather than an evolution a real revolution is the 3Di process. This layers ultra-thin spread filament tapes that are consolidated by a two-part resin system. The dynamic molds determine finished shape as with 3DL. The design process simultaneously accounts for the sails dynamic world and incorporates appendices and functional structures. This represents a true leap in our thought process. Though America may have introduced the idea of ‘race sails’, with 3Di you can cruise with the same sail in comfort and safety while, if you wish, being fast on the race course. These sails are minimalists in their appearance, unique in their stability and infinite in their structural design.

The new science of simulating loads and engineering for the dynamic world of a yacht sailing through water and air is very present. New materials have changed much of the sailmakers universe, but the century old art of finishing a sail to give easy, pleasurable sailing over a long period is not at all lost.

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