Don't know how ancient in techniques you want to go, dmk
sails, but I have "candled" seams. Take the stub or the tip of a candle and plop it on a saucer. Light the candle. Drip some wax onto the saucer and stick the bottom of it in the wax, to hold it still. Run the seam slowly past the candle just till it starts to melt. Keep the
fabric moving slowly and steadily, and of course, keep it just the fuzzy part of the seam going by. It works fine, and you'll get better at it quicky.
It is also tedious, and I prefer a hot knife, too. The one we had that I liked best was a butane powered Waller that also had soldering tips.
Ann