fusioneng wrote:
Tpdavis473:
Yes a radial cut design would have been much better but nobody usually shares any design specifics. Hey if you PM me some of the design specifics I can design and build one, in return I'll send you the design specs on the parafoil leading edge wing mod. The leading edge wing mod just goes along for the ride and does nothing at all when running down wind. It only engages and puffs up into a wing foil when trying to use the spinnaker on a reach (most people take their g2 spins down at that point and put up code zeros or big genoa's at that point. I was simply trying to get a little better side wind performance without increasing the heeling moment too much (wings have less heeling moment). I think I had the right idea but wrong basic spin design to start with. Unfortunately code zeros or big genoas don't work well with the TI (way too much heeling moment and weather helm due to the itty bitty rudder on the TI and the very flexible mast) so I was trying to cheat the design limitation just a little. The other dilemma I have is with my wing jib and main in low winds (under 10 mph) and my hybrid setup I already run downwind at 2x plus wind speed so if I unfurl the spinnaker it acts like a break (that's why I don't use it much anymore). My TI is specifically rigged for the typical low winds we have typically, works great upwind, and downwind but really sucks on a reach. I suspect I've reached the limitations of the basic boat design. I suspect you will have way better luck with your getaway (way better mast/sail setup and cat hulls)
Hey it's fun for me just playing around with the stuff. I have no goals or expectations, just havin fun.
Bob
Be happy to share the design. Do you sheet/tack to the akas or the bow with your spinnaker? The process is slightly different for an asymmetric. If you sheet and tack off the akas, do you use two lines at the clews (one for the guy when you are on that gybe, the other for the sheet when you aren't).
Basically, though, the design process starts with deciding overall luff length and foot length and midgirth. Those dimensions are determined by how high the mast (or halyard exit is) and how long/wide the boat is and how full you want the spinnaker to be (A full spin works best running, a less full spin reaches better-one that does both well will have a midgirth about 80-85% of the foot). Then you decide how long to make the gores (the misshapen triangles that form the radial head). Typically, it is half the desired luff length. Next step is to determine how many gores you need. With 5 ft (153 cm) fabric, the maximum width of the gore can be 90 cm because you will cut two of them from each length of fabric by turning one upside down. SO, if you chose the midgirth length of the gore, divide the desired midgirth length by 90 and round to the next even whole number (sailmakers typically use metric measurements because they are much easier to use). Once you have that even whole number, divide that into the actual measurement you want the midgirth to be and that number will be the "base width" of each gore. The smaller the number, the more waste cloth.
Gore design is now possible, On the floor place two parallel strings. Each string will be located half the "base width" from each edge of the cloth that you will be laying on the floor. On the string mark the 1/4, 1/2 and 3/4 places. OK, here's the real design stuff for the gores. The width of the triangles must be expanded at the 1/4 spots to 34% of the base width. The 1/2 spot is to be 65% of the base width. The 3/4 spot is to be 87% of the base width. Connect the spots you just marked with string on the floor so you can see the two misshapen triangles. Lay the fabric over the string and cut along the strings. Once cut out, sew all the gores together (leave a seam width at the top). Note that this radial head shape will be a smooth curve...it would be better to flatten it at the leach if it is to be an asymmetric or to flatten it in the middle if it is to be a symmetric because that overall shape will fly better with less turbulence. You can achieve that by making one gore with straight sides for the assymetric and by making the middle two gores for the symmetric similarly with straight sides.
Anyway, this isn't clear, I know. But you can see the process here (but it was a mainsail I was making)
https://www.youtube.com/watch?v=gQwhRKERclU
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