Sails and High Technology
Sails … A history
If the wind provides the energy necessary to propel sailboats forward, then the sails are the boat's engine power. The materials used, how they are set, the size and their shape determine the boat's power.
Computer software has replaced the drawing table for sail designers and offer the best compromise between the objectives to be attained and the restrictions which are imposed. Thus, depending on the type of boat to be equipped (cruiser-racer, ocean racing trimaran or round-the-world monohull) and, in accordance with the conditions which the boat is expected to encounter, the master sailmakers, with their computers will gradually design the boat's wardrobe in the same way as a great couturier preparing his spring-summer or fall-winter collection.
The distribution of the cloth panels of the sails is fundamental in order to give the sails their desired shape so that they can best exploit the masses of air which are transformed into a driving force. Certain points of the sail can be put under enormous strain and so panel layout and stitching have to be sufficiently resistant, which usually means placing both in the same direction as the strongest effort.
Traditional cloths have disappeared from the landscape of modern sailing. Synthetic Fibers have now replaced cotton, linen or Jute in the threads of the sailcloth. Dacron or Tergal, polyester fibers, nylon, polyamide fiber are the most commonly used. Resistant, easy to handle, and capable of great results whatever the conditions, they comprise the large majority of sail wardrobes currently on the water and are available for a reasonable price.
Kevlar, aramid fiber, Spectra, polyethelene fiber, Vectran, carbon fiber are just some of the new materials. Increasingly light, varying in degrees of elasticity and resistance to ultraviolet, these materials equip top competition boats.
Whatever the material, the threads have to be woven first. Traditional weaving involves crossing the threads at right angles.The fill or weft is formed by running threads across the cloth, the warp being formed by running threads across it lengthwise. Cloth stretches mainly across the bias rather than along the yarn direction of the warps or the filling. Weave density is of the utmost importance. In order to improve its resistance still further, the cloth is treated, coated with a resin polymer which tempers the yarn, locking the weave.
We must not overlook the famous sandwiches which combine materials to obtain the advantages of both.
The Kevlar laminate fixes Kevlar threads between a polyester film and another film whose fill is made of polyester and whose warps are made of Kevlar. Likewise, films of Mylar, a very fine polyester, fix Kevlar threads whose density and angle of weave are able to withstand enormous loads.
The main thing is to give a nice round shape to the curve of the canvas and to give the right shape to the depth or camber which will be filled by the wind. Part of the boat's performance will depend on it.
But before the sail can grace the boat with its presence, it has to pass through skilled hands of "couturiers" who must bring the panels together, punch the cringles into place in the three corners and reinforce parts which will be subjected to relentless impacts against the pars or the guardrails.
So, on all three of the edges, the luff, leech and foot, extra layers of cloth are added to protect the sail. Wavy straps called "bolt ropes" are also sewn along the foot and the luff (of mainsails) which they strengthen to enable the slides and other cables to fasten the sail onto the rig.
Next to follow are the batten pockets for sails which need them, reef points, pennants and eventually the ultraviolet tape of the roller / furler genoa.
Depending on their size, tonnage and sailing classification, sailboats require lightweight or heavyweight sails, some of which is just advisable, some compulsory.
It is not apparent from the mainsail's same but it is not the largest sail on board a sailboat. It is a triangular sail, hoisted along the mast and generally held horizontally by the boom. Surface area can be reduced if necessary. That's where the clew outhaul, the cringle and the reef pendants come in useful. Battens are slipped into their pockets and serve to stiffen the sail providing better shape holding in the wind.
A second mainsail is to be found on boats which have a second mast, for example, ketches whose mizzen mast is set aft.
Genoas are the big foresails, banked onto the forestay (or jib-stay) and are set fore and aft overlapping the mainsail mast. Most of the genoas on pleasure cruisers are now set on roller-furlers and can be unfurled and furled again as needed. This avoids the delicate sail-changing manoeuver in heavy weather.
jibs are the triangular sails which are hanked on to the forestay and which almost all dinghies, cruisers and pleasure sailboats have. An intermediate-sized sail, the staysail, can be set onto the inner forestay. The smallest jibs of all are the storm jibs.
Spinnakers are the air-filled sails which look as if they are well ahead of the boat from which they are flown.
Source by Johnny Routledge