Sail Design

Over the years a succession of ‘generic’ sail design software packages have been developed. These are used by many sailmakers, producing considerable uniformity in the design process. Individual sail lofts have gone beyond this framework to develop customized packages. The larger sailmaking enterprises have invested considerable capital into the kind of sophisticated load mapping and design packages that are necessary to build sails that are competitive in grand prix racing. This technology is then made available to local lofts, either on a wholly owned basis (e.g. most North lofts) or as a franchise (e.g. Doyle, which has five world-class designers on staff at the head office).

There was a time when this proprietary software went well beyond what was commercially available, putting smaller lofts at a significant disadvantage. However, commercially available software now incorporates many of these advances. Performance-focused lofts can additionally sub-contract with independent designers who are on the cutting edge of aero-dynamic and finite element analysis. These specialists can do everything from training staff in the use of the latest software, to checking designs produced by the staff, to doing a complete design. Carol Hasse has just such a relationship with Sandy Goodall, a world-class independent designer. It enables her to claim: “I am confident our sail design is on the cutting edge.”

The more performance oriented a sailor, the more critical the sail design process: adjustments of a few tenths of an inch in seam widths can make the difference between an OK sail and a winning sail. It is important to use a sailmaker with a proven track record with the kind of boat in question. Where performance starts to give way to durability, ease of handling, longevity, and similar issues of concern to many cruising sailors, it is just as important to use a sailmaker with a proven track record with this kind of sail.

‘Pin Stripe’ Cloth

When a cloth is woven, the threads across a loom (the ‘fill’ threads) have to be maintained at some tension, and as a result those running the length of the cloth (the ‘warp’ yarns) tend to bend (crimp) around them. Under load, crimped threads straighten, and the cloth stretches in this direction. For this reason, it is easier to minimize stretch across the cloth than along its length. This is generally the exact opposite of what is desirable for minimizing the number of seams in a sail!

The ideal cloth would have heavy, low-stretch warp yarns run without crimps with just enough lightweight fill threads to hold it together. Laminates achieve this effect by placing the warp yarns between two sheets of plastic without any fill threads (other than those specifically required to balance the loads on the cloth) and then gluing the sheets together to hold the warp yarns in place.

The Challenge ‘Pin Stripe’ cloth seeks a similar result in a woven cloth by laying a heavy high-tech warp yarn with minimal crimping into a lightweight woven (Dacron) substrate. There is no lamination. Because all Dacron-based cloths need to be heat treated after weaving to shrink the fibers in the cloth into a dense mat, only high-tech fibers that are heat tolerant can be included in the matrix. Unfortunately, none of the heat tolerant fibers are optimized for cruising (they are not UV resistant, or will not tolerate bending, flexing and flogging, etc.). The best fiber from this perspective is Spectra, but it is not heat tolerant.

Recently, Challenge has found a way to overcome the heat issue and integrate Spectra into a woven matrix. It looks like it may be the best available fabric for performance cruising apart from its price!

‘Free Luff’ Sails

The single-handed racing community has popularized free luff sails. The sail is given a Kevlar or similar luff rope, with a furling drum at its foot and a swivel at the head. The drum is tacked down to a deck fitting or to the end of a sprit, and the swivel hauled aloft by a halyard. There is no stay (the luff rope acts as the stay). By turning the drum, the sail can be furled around its own luff rope. Note that it cannot be used in a partially furled state – it is either fully open or rolled up – and cannot be rolled up under load (the luff rope would twist). This is a roller furling, not a reefing, mechanism.

Because the sail is not held in a rigid foil, after being rolled up it can still twist from the foot to the head in a strong wind, partially unrolling the head of the sail and allowing it to flog itself to pieces. Despite the fact that some cruising sailors leave these sails permanently rigged, they should be taken down and stowed when not in use, although this is not as easy as with other sails because the rolled up sausage of sail cannot be stuffed into available spaces in quite the same way as other sails (especially if the sail is built from laminated sailcloth). Another reason for taking the sails down is the fact that most are made from nylon, which does not stand up well to extended exposure to sunlight.

Free luff sails cannot be used hard on the wind (without a stay to support the sail, there is too much sag) but can be used from close reaching to broad reaching. They come in a wide variety of shapes, sizes, cloth weights and cloth types. The hardware – the drum and swivel – can be made detachable from the sail and used on other free luff sails. This versatility is making them increasingly popular for filling ‘gaps’ in the sail inventory on performance-oriented boats.

However, the hardware is surprisingly expensive, and there are the stowage issues. On a cutter-rigged boat, it should be possible to achieve a balanced sail inventory without free luff sails at a lower cost and with no more work to set and stow sails. As a result, they are the last sails on my list.