tpdavis473 wrote:
HI Robin,
IN a normal crosscut sail, you are stitching full panels and you broadseam each panel as it approaches the luff.
In the video, since there are no panels, you have to create a spot to broadseam. The seams should look like inverted golf tees where it gets wider as it approaches the luff.
For these sails, you should do a broadseam measuring up from the tack about every 30"...Mark the spot and measure the distance from that spot to the leach (measuring parallel to the foot)--just for an example let's say it is 72". Take how many inches that distance is and divide by 3 (72 divided by 3 is 24)...that distance is where you cut from the luff spot toward the leach (ie, cut from the luff toward the leach 24" (make the cut parallel to the foot)). That will be the position of maximum camber. Now you are going to sew the slit back together. How much overlap will you want? That depends on how firm the fabric is. Stretchy fabric needs less broadseaming. Let's use 12:1 for mylar (no stretch), could go up to 30:1 for tarp. so we want 2" at the end to be sewn together at the luff end of our slit. Since we want it to look like a golf T, we'll save half (1") for the last quarter distance (6"). So, start from the end of the slit and move the fabric together 1/4" for the first 6". Move the fabric together total of 1/2" at the 12" spot. At the 18" spot you will have the fabric together by 1". The last six inches will move it together the remaining 1".
(when you get toward the top of the sail, the seams are really short, so don't bother).
Clear as mud, right? I learned some of the art of sailmaking from Sailrite -- they used to have a series of books. I don't bother with software because then someone else is making decisions about where to put the camber and how much. I would be willing to walk you through it once you get the material you need. We could skype while you are in the throes.
I apologize, I re-looked up the broadseaming guides from the book (Jibsails, design and construction by James Lowell Grant), Mylar is 1/2 inch for 14 inches (or 1 to 28) not the 12:1 I said above). Since I don't make crosscut sails often anymore (I like radial head designs), I've forgotten most of what I need to know about broadseaming. You can still get the books I bought way back when but they are pricey and outdated given today's materials, but it does provide a good grounding in sailmaking techniques
https://www.amazon.com/gp/offer-listing/B003OXVQLC
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