"Sails made from (Kevlar) are very light but far from durable in a cruising context.
Cruising and Kevlar shouldn't even be in the same sentence. That's like taking the Maserati to the corner store to get a gallon of milk. In a "cruising context" Kevlar is a complete waste of money.
Kevlar is brittle and does not stand up well to flogging and flexing"
Yup. When you compare it to polyester, it sucks. Carbon is worse.
Further in the text he states "It's not unusual for a woven sail to last 10 years or more, while the lifespan of a laminate sail is closer to five years," but he's talking Mylar here as opposed to Kelvar.
Couple things here.
1. Woven sails will retain a triangle shape longer than string sails. However, their aerodynamic shape is long gone before the triangle explodes. This was discussed in the other thread. For racing, I want a sail that's going to hold it's shape in a wider wind range for a full 5 years of hard service. Lightweight is a nice plus. Dacron will stretch a lot over a 155% between 6-8 kts and 15 kts true. This is not good on the course. Not only that, but it will gradually stretch out over the next 5 years losing performance every year. Until at the end of 5 years, the laminate is pulling and pointing much better than the dacron. This is huge on the racecourse. Not so much for the cruiser who just wants to close reach around the harbor.
2. Mylar is a scrim that is applied to each side of the sail. The aramid strings/threads are sandwiched between these two layers. Mylar can't carry the load of any decent size sail. Small boats and wind surfers have plain mylar sails w/ no strings, their loads are much much lower.
Racing Laminates - Sailcloth Technology by DIMENSION-POLYANT - Sailcloth and laminates for high performance sailing and polyestersailcloth for surf
Scroll down to Flex line and hover over the cross hairs. A graphic pops up that shows the film (mylar) on either side with the string fibers inside the sandwich. Glue, heat, and preassure keep it all together.