pre bend

[Capt Ken]

I have a 1990 Catalina sailboat. one piece keel stepped aluminum mast. Not sure who manufactured the mast. At a mast tuning seminar I was told all masts should have some aft pre bend in them. The speaker was a rep from Selden very familiar with the masts they supply, but didn't seem quite as knowledgeable about boats with my mast. Winds where I sail are usually light, 5-10, with an occasional day in the upper teens. If I should have some pre bend, how much? The mast extends about 42' above the partners.

[Brion Toss]

Hello,
The range of mast bend varies depending on end fixity (deck stepped vs keel stepped), number of spreaders, masthead vs fractional rig, intended use, cut of mainsail, and for all I know barometric pressure.Ah, variables. Prebend is a simpler matter. Basically, you want to prejudice the middle of the mast forward, so that the aft pull of the mains'l won't "invert" it. A little bend also makes the mast more stable, so it won't wobble fore-and-aft as you hit chop or gusts. On your boat, an inch or two of prebend will be enough to accomplish this. If you have an adjustable backstay -- and you really should -- you can increase this bend to flatten the main as the wind builds, simultaneously tightening the jibstay. But that is a matter for a larger tuning discussion.
Fair leads,
Brion Toss