David Flynn

Carbon is legal under Beneteau 36.7 class rules. That said, the choice of carbon versus aramid fibers for your Beneteau 36.7 is probably not as critical as it seems; both are excellent options. Quantum’s class sails for the 36.7 are a blend of carbon and aramid fibers. Fiber modulus (ability to resist stretch) is the key factor in a racing sail's performance and is similar in carbon and some aramids. While some carbon fibers can have a considerably higher modulus, they also tend to be more brittle and less resistant to flex fatigue, so the modulus of carbon used in sailmaking today is very close to that of the best aramid fibers. The only real potential advantage for carbon is durability; it does not degrade in sunlight. A carbon sail will be slightly more expensive, but the increased durability may be worth it. 

The most important issues for the durability and performance of membrane sails are not so much the type of fiber, but the amount. The more fiber the better. Balanced strength, with plenty of fiber in all directions, not just the direction of the primary load path, is the key. It is also important that the fiber bundles are as small and flat as possible. Large fibers have much more initial movement under load. 

Sail choice for cruising is another issue. Pure racing sails are typically "film to film" construction. This means there is no woven component. The working fibers are sandwiched between two layers of polyester (Mylar^®) film. Most cruising applications demand exterior layers of woven polyester (taffeta) to protect the guts of the material. The penalty for this protection is weight. It will literally be twice as heavy. If you can live with that, you can have a dual-purpose sail that delivers great performance for both racing and cruising.