All this discussion has made me anxious to try something. Since I am in the process of trying to figure out how to get a rig on my plywood proa, I thought that I might combine the efforts. I have a couple questions (of course) on how to calculate the shapes involved. Here is a description:
I would like to try a soft wing sail with a short gaff rig and both top and bottom plates. I would like to try a version of this on my plywood proa, but I don't have all the measuremts fro that, so let me use ToyyoT as an example.
Luff: 32 ft
Foot: 8 ft
Head: 6 ft
sail area: 224 sq ft
aspect ratio: 4.5
I would like to use Tom Speers paper for the foil, with a 30% ellipse as the wing part. That would make the wing section 2.4 ft long. I would make this dimension constant all the way up, so that the trailing flat bit varies from 5.5' at the foot to 3.5' at the head. Both the head and foot endplates will be cut to extend 6" beyond the sail.
So, given that this sail will rotate, the idea is to trim it so that it is always at the correct angle of attack. From http://www.kastenmarine.com/gaff_rig.htm, I would estimate that the rig will have a L/D of about 7.5 at an angle of attack of 10 degrees. So, how do I find the wing shape, as specified by Speer for a 30% elliptical wing?
- Gardner
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