I used Schooner (high gloss) on my kayaks and stopped at the first good looking coat after 4.  I will note that I think they look better after I paddle them a couple of years then do a couple of maintenance coats than they did new.

If you have not started yet and don't want a high gloss finish, you may want to save some work by going with Epifanes Rapid Clear or Rapid Coat.  It is a new varnish that is very easy to apply, does not have to be sanded between coats and can be recoated in 5 hours.  I used Rapid Clear Semi on the interior of my Goat Island Skiff and am very happy with it.