I have yet to hear anyone report breaking their mast using a Whirlwind sail.
I never said the boat would break. I said the boat wasn't designed
for a square-headed main.
A big part of getting a square headed sail to work properly is being able to put enough leech tension on it with the mainsheet, with resistance provided by the mast. A 17s Comptip isn't going to provide that resistance. (This experience comes from 4 years of racing Tigers with an STX main - and an 9:1 mainsheet.)
Whirlwind sells a square headed main for the 17. Doesn't mean it works the way it's supposed to, or it provides significantly better performance. It's kind of like the big-ass wings that tuners put on the back of their rice rockets. It looks cool, but it really doesn't do
I will say that the Pentex material is far superior to the stock 17 sail, which is stuck using an outdated Mylar taffeta that should have gone away years ago.
I've raced 17s for 20 years. I've won the H17 North Americans twice. You're asking the wrong guy. I'm never going to get anything but a class legal sail for my boat.
BTW, the 17 is a much more fragile boat than a 14 or 16. A lot more durable than say, an A Class Cat, but it's a lot easier to punch a hole in the hull from using rollers on the trailer or letting water freeze in the wing tubes.