I'm trying to compare total mainsail areas between different mainsail designs - some with the point of maximum roach positioned higher on the leech than others. Does anyone know how to measure the area in just the roach part of a mainsail (I think it's called the arc segment)? Can I get to this measurement from the leech cord length and the distance from a right angle at this cord to the point of maximum roach (convexity) on the leech? Thanks, Neil
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Here's one way
It's difficult to use area formulas because the arc segment you're talking about is the arc segment of an ellipse, and you don't have any way to know what the major/minor axes lengths are. If you know the total area claimed for the sail, you can find the roach area by calculating the area of the "triangular" part of the sail, then substract that from the total area given for the sail. Roach Area = Sail Area - ((Luff * Foot) / 2)
It's difficult to use area formulas because the arc segment you're talking about is the arc segment of an ellipse, and you don't have any way to know what the major/minor axes lengths are. If you know the total area claimed for the sail, you can find the roach area by calculating the area of the "triangular" part of the sail, then substract that from the total area given for the sail. Roach Area = Sail Area - ((Luff * Foot) / 2)
Ask the sailmaker
The sailmaker will know exactly how big the roach is from his design program. And I'm sure any good sailmaker would be glad to share the information with you - especially if you are considering the purchase of a new main. David Lady Lillie
The sailmaker will know exactly how big the roach is from his design program. And I'm sure any good sailmaker would be glad to share the information with you - especially if you are considering the purchase of a new main. David Lady Lillie
Try This
My main is fully battened and I noticed that the leech is very nearly straight between batten pockets. So I just measured the length of each batten pocket and the distance between them. Then a little geometry gave the total area as the sum of the rectangles plus the small triangles between each batten. Now subtract the basic triangle to get the roach area. For my H376 it amounts to 27% of the basic no roach triangle.
My main is fully battened and I noticed that the leech is very nearly straight between batten pockets. So I just measured the length of each batten pocket and the distance between them. Then a little geometry gave the total area as the sum of the rectangles plus the small triangles between each batten. Now subtract the basic triangle to get the roach area. For my H376 it amounts to 27% of the basic no roach triangle.
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