I think I’ve convinced myself that this strategy for a shelf-foot sail could work. Although, there were some hiccups in the test model.
I used the fabric from one of Leeway’s old sails for the tests. Because it is 1/3 scale model, all the stitching is a single row where the real sail will have double rows of stitching.
Many of the panels in the sails are the same, so I’m making templates for all of them out of 3mm plywood door skin. It’s inexpensive, rigid and doesn’t steal much heat from the hot-knife, so cutting is reasonably quick. I’m using my cheap old soldering-gun style hot knife, I tweaked it by filing the cutting edge a bit so it gets hotter, but otherwise I think it is up to the job. I find the hot knife works better on a hard surface, in the past I’ve used tempered glass, but the melamine panel provides a larger surface and seems to hold up to the hot knife just fine.
Sewing the sailmaker’s style batten pockets to the shelf-foot lens is easy and quick with nice small bits of fabric to work with.
Sewing the doubled-over tabling to the luff/leach of the hourglass-panels worked very well, I used rectangles of cloth a little over-length and just cut off the excess after sewing with the hotknife (using the same template as to cut the panel).
The oval patches that span the leach panel joints were easy to do, just lay the cloths flat and sew.
The patches that span the tabling over the shelf-foot lenses at the luff were a bit more tricky. I liked the paper models I started with because they’re good at showing you if your trying to force a panel into a shape it doesn’t want to go in. Since the patches seemed easy in the paper model I had high hopes for the cloth scale model working easily. This was not the case. I first tried sewing the patch to the leading edge, and then working the rest of it to the shape of the sail before sewing. Done this way there was no way to get the patch fabric to lay nicely with the rest of the sail.
I also tried a “taco holder” form to see if having the sail close to its set shape would make the patch seat nicely.
This variation involved 3M Super 77 adhesive and basting tape, the fit was much better, but painful to do and still not quite right. I did notice in this version that the leading edge of the patch only met the sail at the ends of the patch.
Finally, the light dawned for me (probably much slower than it would for many others), I splayed the sail flat at the leading edge, centred on the batten pocket. This leaves the leading edge of the sail in a very shallow V-shape. With the sail splayed flat like this, the patch matches the leading edge only at its periphery and spans the hollow of the “V” for the rest (this is what I had missed seeing in the paper models).
With the luff splayed flat it is easy to tape and sew the patch in place, and when you fold the sail back into its set shape everything lays nicely. It does result in a slight bulge in the leading edge of the patch and you have to run the first row of stitching a bit back from the edge of the patch to make sure you catch the panel fabric below. Overall, I think this is a compromise I can live with.
