In case any of you want to build an asymspin, I can provide instructions that are pretty easy to follow.
For example, I will provide instructions for how to build this Getaway asymspin.
You will need 15 yards of 60" nylon fabric. eBay sells it for about $7 a yard. You can get it even cheaper, though, if you by in 5 yard increments. You will also need about 2 yards of 60" dacron fabric for the corner reinforcements. You will need a sewing machine. Zig Zag is faster.
Distance from Halyard to front crossbeam 18'5" or 560 cm
Distance from Halyard to sheet point is also 18.5 interestingly enough
Distance from front crossbeam to sheet pt that is 13'10" or 422 cm
This ratio of 420/560 is the ratio we use to determine actual leach length after we decide on foot (I've decided on 12 ft or 360 cm which makes the leech come in at 475 (I use cm since math is easier in cm).
Gore Length is determined by cloth. We have 15 ft (460 cm) available in a single length. Cloth Width is 150. SO gore can be as long as 460 or as short as 550-150 or 400.
420 Sounds good (closer to midgirth is best) so let's use that for our gore length. It will leave us with 130 to fill up the luff and 55 at the leach at the bottom with a horizontal panel
To get 360 for a foot, we need about 330 to be used by gores. We can make each gore 90 but that'd use up all our 360. 330/4 is 82.5
84 rounded this is our gore base dimension
Gore shapes are a widened triangle with an 84 base. At the 3/4 point we want 90% of 84 or 76 (rounded)
At the half way point we want 65% of 84 or 56 (rounded)
At the 1/4 point we want 34% of 84 or 30 (rounded).
The 90, 65 and 34 make a very full asymspin which is what I want for my local conditions and the way I sail. If you like to reach more make the percents smaller.
Make 4 gores and sew them together. AFter you are done, cut off the bottom (it will look like a part of a circle) for a straight line. Choose one side and cut off that edge to a straight line (that will be your leach).
Lay out the finished dimensions with string. Cover the bottom with a horizontal panel. Sew the bottom panel to the top gores. Don't finish the luff end from the first gore in.
This is the only critical step in making the spin work. You must make the luff (leading edge) be as short or shorter than the actual distance between the head and the tack. Basically you have to create a pocket.
finish the corners and the edges and add straps or grommets, you are done. Takes me a weekend or about 12 hours total to make one.
Formerly raced F24 Mk II