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post #1 of 3 Old 03-27-2006 Thread Starter
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Sail shape, discussion in detail

I have a 42ft, 8500kg IOR Racer with a masthead rig.
My biased perception of the sail wardrobe for a yachts like this is:

Genoa1 Light: 1-5m/s, 150%
Genoa1 Heavy: 4-8m/s, 140%
Genoa2: 8-12m/s, 125%
Genoa3: 12- m/s 110%

G1-G2 should go up the top of the forestay for best aspect ratio. G3 should be somewhat reduced

I think conventional wisdom says that G1L should be very flat. G1H should have more depth, G2 same depth, and G3 flater again. The idea is that very light wind need a flat sail (G1L) to be able to follow the sail around. A bit more wind makes it possible to get more force/speed with a deeper sail (G1H). Even more wind just reduces the sail area (G2) and finally with even harder wind it is time to reduce both the area and the heel by making the sail flater.

My question is. How much.

Should:
-the G1L be 10% or 12% deep at the top or something else?
-The G1H be 14% or what?
-The G2 be 14%?
-The G3 be 12%?

What should the relation be between the depth at the bottom and top of the sail and the position of the maximum depth of the sails. Should the position of maximum depth vary on the different head sails? I think it should be around 35-45% for a head sail but were should it be?
How much twist should there be in the different head sails.

The figures above are guesses? I would find it very interesting to have a discusion about this. Also suggestions for good books or websites on this topic is welcomed.
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post #2 of 3 Old 03-27-2006
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The theory around here is that in lighter wind you want deeper, baggier sails. This is so that the little wind there is doesn't get deflected off and create turbulence instead of drive. In lighter air you need drive to keep you moving through the chop/waves. Heavier air, you move to flatter sails. My interpretation of this is that in heavy air, you could put up sheets of plywood and still be able to move the boat with them. In light air, the plywood would simply create turbulence, not drive. In light air "Baggy" sails with greater chord depth don't make the little wind there is bend too much at once; they sweep it in a big gentle curve and keep you moving. Talk to your sailmaker.
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post #3 of 3 Old 03-28-2006 Thread Starter
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sail trim in light wind

I (humbly) disagree with this.

I do agree that the most basic rule is "more wind - flater sail" but not for very light wind.

Racers usually have special sails for very light winds and they are flat. ( In my case the G1L. A big sail in very light material that would be ruined in winds above 4m/s.)

The idea is that in very light wind the air can't create enough low pressure on the leeward side to fill the sail, I have heard sailmakers sometimes refer to this as "the wind doesn't have enough energy to follow the sail around".

Anyway - what I am after is really independent figures-numbers on the depth (or camber) and position of maximum depth (camber) as a function of the height of the sail and twist for the different sails in a sail wardrobe.
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