Sail tape, wonderful though it is for an emergency, is a poor substitute for stitching. Duct tape is even less desirable. While it is true that you can make a strong repair with contact cement, it stains the sail and its grab-'n-grip nature risks potentially disastrous alignment problems. For permanently joining two pieces of woven fabric, nothing beats thread.
Having a good sewing machine takes most of the work out of sail repairs. Consider having one of these on board at all times.Seams Restitching is by far the most common sail repair. Because the stitching stands proud on the hard sailcloth, the thread is subject to chafe. Exposure also takes its toll. Eventually the stitching becomes too weak to do the job and a little extra stress on the seam pulls it apart.
Restitching a seam is not particularly difficult, and as long as you maintain the original alignment of the two panels, your repair will have no effect on sail shape. The existing needle holes simplify alignment, but because sailcloth is as slippery as cold butter, the trick is maintaining alignment while you sew. Sailmakers use basting tape, a Mylar film with adhesive on both sides. A roll of Seamstik would be a good addition to your ditty bag but an office-supply glue stick also works quite well to glue seams together for sewing. Never, ever try to restitch a seam without gluing the two halves together first.
For permanent sail repairs you need polyester fiber thread-the same kind your sailmaker uses-in either V-69 or V-92 thread weight. If sooner rather than later you are going to have the sail restitched-a very good idea-then almost any heavy duty polyester thread will serve for a season. Never use cotton, nylon or monofilament.
Use the largest ball-point needle your machine will handle, probably a No.16 or a No.18. Set the stitch length on your machine to its longest setting. If you have a zigzag machine, adjust the seam width to get a square pattern, or each stitch at 90 degrees to the previous one. A zigzag stitch is not essential. If foot pressure is adjustable, set it to its maximum. Sew a few practice stitches on two thicknesses of sailcloth (or through the leech tape if you don't have scrap sailcloth) and adjust the top-thread tension until the threads form a tight knot on the underside of the seam. Sailcloth is too hard for the interlock to bury inside the fabric.
Feeding will be your biggest problem; feed dogs tend to slide on the slick Dacron, so you have to help them by pulling the cloth through the machine. Experiment with how much pressure you need to apply to get regular stitches. Rubber fingertips-like bank tellers use-on the fingers of your left hand can give you better stitch control by allowing you to push the fabric through the machine. Enlist a helper to handle the rolls as they come out the back.
Reverse the sail end for end and again place the edge of the zigzag at the edge of the top panel, or straight stitches a stitch-length from the edge. Finish the repair with a third row of zigzag stitches or two more rows of straight stitches between the first two.
Next time, we'll cover how to repair tears and batten pockets, so don't fall apart at the seams just because your sails are in need of some attention. Just get out the sewing kit and get to it.
Sail Repair Materials