Excessively Full Main with Mainsheet Two-Blocked at the Set Rake

written by Stuart Walker  on  September 22  of  2005 and read by 1634

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Problem - I realized after the first race of the North Americans that my new Halsey main was fuller than my previous ones - and that using it in the usual manner and with the usual rig trim, I was slow (5-9-8-10 in the first four races).
I recognized that this main (at the usual mast bend) was fuller than my previous mains with its draft farther forward and found that I went better with more backstay/mast bend than usual. But I also found that (1) in a breeze (at my usual rake and mast base angle), I couldn't get the leech tight enough and (2) with the increased mast bend the mainsail needed, that I couldn't sag the jibstay sufficiently in light air.
Solution:
1. Lengthen the jibstay wire (with an extender at the connector above deck) and shorten (pull in) the underdeck jibstay control lines - to prevent the underdeck jibstay from two-blocking against the bulkhead and thus permit more jibstay sag.
2. Reduce the rake by shortening the underdeck jibstay control lines (as above)
3. Increase the backstay tension so as to produce a minimum mast bend of 2 1/2 inches- the amount of mast bend this sail requires at all times.
4. Reduce the mast base angle by taping a 1/16 inches thick bent SS washer beneath the back edge of the mast base - so that with the reduced rake and increased mast bend the mast would still lie flat on the deck plate. (Ultimately I will recut mast base - or alter the base plate angle - to match the rake angle.)
5. Use much more mainsheet tension to keep the leech tight and the upper telltales stalled (50% of the time).
Principles
1. Rake is less important than jibstay sag and mainsail shape and should be sacrificed in order to correct the latter.
2. Rake/mast base angle should always be at maximum possible consistent with jibstay sag and mainsail shaping.
3. When changing rake, the mast base must be recut to the new rake angle.

Too much rake for cut:
Cannot tension leech with mainsheet (as back of mast base provides no resistance)
Too little rake for cut:
Cannot sag jibstay sufficiently with tensioned backstay/ mainsheet
Result
1. We were fast to windward in the final races (a 2nd and a 3rd)
2. A. In moderate air we were able to stall the upper mainsail leech (upper batten telltale stalled 50% of the time) with a bent mast and a flat main
B. In light air we were able to sag the jibstay at a tension of -10 (Loos guage)


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