I re-read Bethwaites "High performance Sailing" for the umptent time last week, and he said that mast breakages was common if the mast was 15xdiameter out of column. I am sure there are more to it, e.g. compression and dynamic loads, but he has a point.

As for twist and sheeting loads. On sloop rigs we want twist in the top of the main to offset the jibs effect on the wind. Also, at certain windspeeds, we need to trim the top of the main to the different angles of wind at the surface and the mast-top. If owerpowered, we let the top of the main fall off to depower. As long as you are trimming to your telltales, you should be in the ballpark.


I find it hard to determine what twist I sail with unless I go to lie down aft and under the boom to sight up along the leech. I really prefer to follow after the boat or have pictures taken to determine mainsail twist.
What I am wondering about, is what Wouter think is twisted vs. what Gary think is straight?
Do you guys have any numbers for what kind of twist you think is too much or too straight? It depends on conditions of course, so some pictures taken from aft of your boat would be preferable.

Take a look at this picture of Bundy and Forbes for reference: http://tornado.aussailing.com.au/beat.jpg


Gary: Sounds to me like the luff curve of your mainsail doesn't quite fit the mast? No wonder, if Ashby cut it for the A-class mast you have, and you beefed it up to handle the spi (just guessing here really). Next iteration probably will be better, if you have Ashby use what you have learnt