You choose by coverage. The number of coats it takes to give the desired coverage is what you go by. You want the whole boat sealed against water intrusion and the outside with some extra abrasion protection. The actual numbers given in the manual are a serving suggestion based on some kind of observed average of builders throughout the decade.

Hope this helps,

Laszlo

   I suppose it is possible to put on too much paint, but 3 coats certainly is below the "too much paint" limit, in my opinion. (And maybe 5 on varnish.) More paint/varnish will add just a little bit of cost, and a little bit of weight. But when all factors are taken into consideration - consider this: it is likely the extra coat now (costing you maybe $20 in material and an extra day's work) will gain you at least one or two YEARS before needing to be redone (for total re-paint, not talking about touching up damage).  And adding paint is never easier than during initial construction.  Recoating/refinishing an in-use boat is a very big deal and much effort (setting up the shop and tools, finding the color match, removing fittings, cleaning, sanding, etc.), so getting an extra year or more before needing to do so is a big benefit. With varnish and paint I always try to convince myself to bite the bullet and do that "one extra coat" during initial construction.

   Somehow I lost my first paragraph to the post above.  In that I said basically the same thing about an extra coat of epoxy and that I tend to use more coats than less (I don't worry too much about weight), but that really, as long as the epoxy had everything well sealed and protected it was, in my opinion, the less-necessary extra coat as compared to the extra coats of paint or varnish.

My thanks to Laszlo and Bubblehead. I appreciate the advice. Getting close, but not really in season yet, so I have no pressure to try hurrying (and hurrying doesn't usually work well for me). Particularly since I am new to this, it seems to make a lot of sense to go for the insurance of a third interior coat.

Mike