Sail Shapes

by Lin Robson

When you are lined up against other FD's, it is easy to see what your performance is in relation to the other boats, but how can you tell how much the sail shape is contributing?
On shore before we go out sailing, we can take a look first at genoas, which particularly because of their overlap have a major effect on performance. Because in our class we are restricted to using woven dacron for the working sails, and because of efforts to keep production costs down, we find that some parts of the genoa wear out long before others. The first indicator of fatigue on a FD genoa is when the head of the sail becomes "tubular" instead of that nice airfoil shape. This effect has a detrimental effect on the rest of the sail, causing drag, necessitating a looser leech tension and in some cases requiring an adjustment in luff tension beyond the normal design shape.

We could delay a lot of the above problem by more elaborate corner patches and putting different weights of dacron in differently loaded parts of the sail, but that drives up the production costs of our sails. Having gone down different paths such as Pentex and lighter square weave dacrons, at least at this point I am convinced that the best cloth options open to us are either the Dimension 200 F, or the Contender 4.52 High - Aspect weaves. Both of those cloths have proven over time to be the longest lived and reliable in terms of shape retention.

Of course there have been many ideas on what constitutes a fast shape in genoas. The design that you choose has a lot to do with you sailing style, and the conditions you think will exist on a regatta day. Picking the closet thing to an all purpose genoa is a good start, since you don't have to wrestle with making sails other than those in the middle work right in conditions outside their intended range.

We tried an Ullman Brazil headsail copy that was very full and powerful, but very finicky on how it was trimmed, etc. It did not work for us on that basis.

With mains, The North-Diamond DMU-9 has been a staple for many years, with good reason. Older mains may have to have their luff rope loosened on the cloth over time, due to luff rope shrinkage, but unless abused, mains can last a long time. Again with used mains, look for cloth weakness at the inboard end of the batten pockets and the luff rope shrinkage.

With spinnakers, typically too flat is better than too full. In used sails, look for fatigue at the retrieval patch, as well as any tears or repairs.

With care and attention, sails can last a long time if problems are addressed early.