Here are the settings that we are using on a couple of Alter Cup Blades with the Glaser sails.
Ed's Mast
Prebend - 1 & 1/8"
John's Mast
Prebend - 1.5"
We just started racing so we'll see how it goes. Ed
An extra almost 1/2" is a lot given the shape of this mast. Watch the luff track as you get a lot of prebend as it will get very wavy.
Also you need to match the sail to the prebend. Too much or to little and you get a discontinuity in the shape around the top of the diamonds. Also look at the sail before messing around too much. If you can apply down haul and sheet pressure and get a flat sail, any additional pre-bend is doing nothing for you except either messing up your shape or just lessening the range of conditions it works well in. It is not possible to get flatter than flat.
