Stretching canvas on a frame in preparation to sewing up the seams.
(I've never seen this trick in the voluminous literature on kayak building. It's probably been describedsomewhere!)
I suspect that there are a lot of craftspeople out there who, like me, have no trouble cutting and bending and lashing wood but have little experience with cloth and have found their canvas skins weren't as tight as the rest of their construction
The easiest, best known and traditional way to get a canvas skin tight while sewing up the seams is to pre-tension it by zig-zagging a length of line between loops of string sewn temporarily into opposite sides of the canvas skin just above the gunwales.
The traditional method of tensioning the skin for sewing entails the use of pebbles tied into the skin: a lot of museum kayaks still show the little puckers from these pebbles.
Instead of just sewing loops into the skin, if the loops in the skin are threaded through little plates (sort of like buttons) you can really pull the skin tight without serious puckering of the cloth. The little plates spread the tension over a bigger area than the loops of string without plates.
I used some poleythelene about 1/16 inch thick left from an industrial job but anything more rigid than cardboard, even aluminum sheet or big buttons, would work. I make the plates about 1 by 1/2 inch with two 1/8" holes punched near each end. The plates are sewn to the top (outside) of the skin with 2” loops of nylon line. Sew them near the gunwales. It’s the inside of the loops that the zig zag tension lines go through
To start the skin should be stretched lengthwise, with the frame settled into it. I use porch posts and vise grips and Spanish windlass things tight.
Nylon cord works well for this tensioning for the same reason that it doesn't hold knots well - a low coefficient of friction - the long zig-zag tightener slides through the loops quite easily. I tie (bowline!) each tightening cord onto the stem- and stern-most loops thread it alternately through opposing loops and work back to the cockpit. I don't pull on the line to tighten, but rather I grab the two edges of the skin above the center deck beam and squeeze and twist a bit with one hand while taking up a little tension on the long running tightening string. Do this in several passes and you’ll find that the cloth will get quite tight. Tie the loose end of the tightening cord to a wooden member in the frame when the skin is tight enough and start sewing the center seam.
This sketch doesn't show the canvas skin. The five rectangles are the plastic plates or buttons and they are on the outside surface of the canvas. The loops of string go through them, and through the canvas.
I sew the seams from the cockpit to the ends, figuring that the ends can absorb any longitudinal slack that may be developed in the skin, whereas sewing from ends to cockpit I've had to put in a gusset occasionally.
After the top seam is all sewn up, snip each loop, pull them out and pull the long tensioning string out.
LOL
BV
|
