I’ve asked this before and got no answer. Maybe now there is some newer members someone will know. When you are making sails how do you cut more (or less) twist into them?
Don
Don Case
Vancouver IslandDon -
I don’t think twist is “cut” into sails. It seems (to me) it is a combined factor of boom position, leech tension (using mainsheet and vang) downhaul and amount of camber. Just my view - will be interested to see other responses.
On my big boat - if I travelled out my traveller and added mainsheet tension, I had very little twist and stiff leech (trailing edge). If I brought traveller to center, but eased mainsheet I had a lot of twist in the upper portion of the main. My boom was deck mounted so I didn’t use a vang. Just my experiences.
Dick,
You are basically right. But you can change the twist distribution by changing the curvature of the luff.
Assuming a perfectly straight mast:
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If you add more luff curve near the head of your sail then this will tighten the upper leach and reduce the twist in the upper part of the sail.
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Conversely, if you add negative luff curvature near the top of the sail, you will increase the twist in the upper leach.
Many of the better sail makers are working very carefully to control the twist distribution of the sails (guys like Carr and Sterne). The overall twist is still controlled by the vang, but the distibution of twist is controlled by the cut.
- Will
Will Gorgen
Forgot to add that part about that the “location” of the twist can be controlled by luff cut location.
Also forgot to add that the softness of mast also has an effect - in that “if” the top of the mast can fall away (no top diamonds, jenny struts, jumpers or shrouds)this allows main to fall to leeward which in turn loosens up the leech letting it fall of to leeward too. As leech moves to leeward with less tension, then twist can take place as well.
After posting this I will probably remember another thought or comment too! [:-ashamed] [:-dunce][8][:-paperbag]
Rod Carr has quite a write up on his “High Twist” main sails, I think it is still available on his site… if not he will mail it out.