I think a lot of the lifespan depends on the actual coating used and how you store the kayak.

Some coatings get brittle over time, leading to cracks and eventually leakage. I would think that cheaper single-component polyurethanes would not last as long as better single- and two-part polys, but that may not be true across the board. As far as other coatings go, I've personally experienced Rustoleum becoming very brittle after just one year out in the sun (while another kayak coated with Zar had no noticeable change).

Storing your boat outside in the sun will also shorten a skin coatings life due to the UV damage, even "outdoor" or "marine" coatings do not last forever under heavy UV exposure. Just keeping your boats out of direct sun exposure will no doubt extend the skin life noticeably.

Recoating gets tricky - some coatings (like most (poly)urethanes) once fully cured, will not allow additional coats to bond. One can sand the coating to help adhesion, but many report that trying to refresh coatings after many years does not work. Spiritline's "goop" is one notable example of a coating that refuses to let any additional coats to stick to it once cured. Enamels and other paints that are not solvent resistant may well be easier to refresh with additional coats of the same product.

: Saw a discussion on Qajaq and thought I would ask here. What sort of life do
: you expect from your nylon skin on a boat? Assuming no accidents, no cuts
: or damage to the skin.

: Some of these guys are saying as short as 3 years. I would think that as long
: as you don't damage the skin, you could just recoat and keep going? Am I
: wrong? Is the life span that short? Unless you damaged the skin itself I
: find that hard to believe.