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post #15 of Old 09-26-2011
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Originally Posted by MarkSF View Post
I have heard contradictory things : that use of boomvang on a beam reach flattens the sail, reducing drag and weather helm, and the opposite - let the boom rise to spill out some air.
Everything you describe makes me agree with svHyLyte. I describe it as, your main is creating "lift" from the wind being directed around it by the Genoa.

Originally Posted by svHyLyte
directs the air-flow on the weather side of the sail back and into the leeward side of the main, i.e. "back winding" the main. Depending upon the wind speed and apparent wind, as little as 25% of the aft end of the main may be generating power
The "lift" is created by the main toward the aft end of the main. The leading edge of the wing (luff) is producing little force.

Originally Posted by svHyLyte
which is far aft of the center of lateral resistance, hence weather helm. Either figure out how to rig a twig for you headsail sheet from the end of the main boom or simply roll in some of your head sail and move you lee fairlead forward to the widest portion of the yacht
The easiest way to reduce the main force is (as stated by svHyLyte), move the genoa car much more forward to reduce the genoa effect on the main. This has another more direct effect. That is, it reduces the twist in the genoa creating more gen power which counteracts the weather helm.

You should also tighten the vang to flatten the main. This flattening of the main does two things. First, it reduces the curvature of the main so that "lift" effects caused by the genoa air flow are dramatically reduced. Secondly, it moves the windward side main forces more forward toward the luff changing the point of force on the main. This flattening gives you back the power you lose when the genoa "lift" forces are taken off the main.

Thank you svHyLyte for the idea to use a whisker pole to move the genoa out to further reduce these "lift" effects. I now have another reason to get a whisker pole.

I was quite certain what was happening when I first read your post Mark. Today, I had the oppotunity to verify everything I have posted. I carefully adjusted the main and Genoa to first create huge weather helm by moving the genoa car back to enhance the "lift" effect.

Loosening the main sheet had little affect because it caused the "lift" effect on the main to increase even while the windward main forces reduced.

Moving the car forward reduced the weather helm immensely at the expense of speed. I was able to get that speed back by tightening the vang and adjusting the traveller (in my case) to get optimum speed with only a bit of weather helm.

Hopefully this helps

Last edited by BryceGTX; 09-26-2011 at 12:42 AM.
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