I read somewhere -- I don't remember where -- a suggestion to drill a larger hole through the bulkhead (maybe 1/4"), then stick one of those tiny plastic tubes like you get with WD-40 through the hole, fill the gap with caulking (maybe seal first with epoxy, if bulkhead is wood), then trim the tube flush with bulkhead. That couldn't let very much water through, but air would vent nicely. I think the suggestion related more to thick foam bulkheads than thin wood bulkheads.

A question - is a vent recommended even with hatches? I assume the hatches would let excess pressure vent out, unless held down extremely well. But in the case of a vacuum, the seal on the hatch may become even tighter than usual.

: The subject of venting sealed compartments has been discussed on this forum
: before, but, with hot weather here in in earnest for a lot of us, it bears
: repeating.

: A hot, black hull soaks up a lot of heat on the beach at the put-in, and
: especially for boats without hatches, the strain on the hull when the
: kayak is put into significantly cooler water can be impressive --- and
: serious --- if the decrease in pressure as that hot, expanded air in your
: forward and aft compartments cools and contracts. (This is most
: significant for boats without hatches but with inspection ports in the
: bulkheads.) A compartment, if not allowed to vent to atmospheric pressure,
: can literally implode, opening up a small, fractured surface in the deck
: or hull --- nature finds the weakest section after a while. It's bad if
: it's the deck --- a lot worse if it's the bottom and you're a half mile
: offshore when the atmosphere abhors the vacuum enough to equalize it for
: you.

: To keep this from happening, drill a small hole in the bulkhead, fill it with
: epoxy, let it cure, and then drill out a very small hole --- it doesn't
: take a lot to vent a compartment, and a 1/64" inch bit isn't too
: small --- as close to the center of the bulkhead's surface area as you can
: find. (Technicially, it's the metacenter, but that doesn't mattter much.)

: I've only experienced a hull failure once, but it reminded me what
: atmospheric pressure can do to a boat when a compartment is very well
: sealed.

: Jack Martin