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PostPosted: Sat Mar 25, 2017 3:20 pm 
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Joined: Sat Oct 04, 2014 1:30 pm
Posts: 591
Location: Benicia, CA
I'm going to make another sail for my Hobie, but noted something interesting when I was taking measurements, both for this sail and for the windseeker I just finished.

With the mast raked "correctly" for me which is when the mainsheet is nearly twoblocked with the mainsail tight for upwind work--the boat tracks perfectly with only a tiny bit of weather helm (8 mississippis before I have to correct steering).

The distance from the mast head to the front bar is identical to the distance from the mast head to the rear bar (26'). The distance from the hound to the front bar is identical to the distance from the hound to the rear bar (18'5").

I just thought that was kinda cool.

In case you wonder, I'm making an asymspin to be tacked to the front bar with the head just above the jib hound (where I mount my symspin). It'll be sheeted at the rear bar. Should be about 120 sq ft. and I hope the two 55mm ratchet blocks will give me enough friction to hold the sheet. I am going to make the asymspin to be a deep running sail which should reduce the pull as well as help keep the boat on its feet. Obviously, with the sail so close to the jib, I'm going to have to gybe outside...which is how I prefer anyway. I went rad with the colors...purple center with gray on the edges.

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R/Thom
Triak
Getaway
BMW C600
Formerly raced F24 Mk II


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PostPosted: Tue Mar 28, 2017 3:57 pm 
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Joined: Sat Oct 04, 2014 1:30 pm
Posts: 591
Location: Benicia, CA
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.

_________________
R/Thom
Triak
Getaway
BMW C600
Formerly raced F24 Mk II


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