FWIW,

In Greenland, where canvas is the most widely used kayak cover, water is not used to tighten the cover. The traditional method of tightening the fabric is with a lacing cord. There was a thread recently on the Greenland forum about canvas, see http://www.qajaqusa.org/cgi-bin/GreenlandTechniqueForum_config.pl/read/6726.

BTW, marine enamel is commonly used in Greenland, on canvas. Generally eight very thin coats are used (straight out of the can), with light sanding between the later coats. This produces a surface as smooth as a glass kayak (generally fewer coats are used on the deck to save weight). I have repeatedly folded small discarded sections of kayak skins treated this way and they were more flexible than common-sense would assume.

Greg Stamer