[allene]

My Lapworth-36 was dismasted on May 28 and I just had the new mast delivered. The mast is 45 feet long and P is 35 feet. There is an adjustment plate at the mast end with a range of 1.1 inches. The builder suggested putting the plate so that with it all the way back, the heel of the mast would be directly under where it goes through the cabin top, up 69 inches.

The question is what should I set the rake and prebend to be. One possibility would be to center the adjustment plate and put rake and prebend in the center of what is possible with the heel in that position so I would be able to tune either equal amounts. The mainsail will be made to the new mast. The mast is 7 inches cross section front to back.

If I understand the physics of the mast-prebend-heel position correctly, that might be a spot like 1.5 degrees of rake and 2 inches of prebend.

I read somewhere that prebend should be between 25% and 50% of the mast section. I read somewhere else that it should be 100% of the mast section, which would be 7 inches. On post 1174 Brion said and inch or two on a Catalina with a 42' mast, which is similar to mine.

There are two questions here. One is where I should drill the holes for the adjustment plate. Second is what should we shoot for on the rake and prebend.