If you are going to have truly water tight hatches, they are going to be air tight as well. If you ever close the hatches when the boat is warm and try to open them when it is cooler, you will be fighting a vacuum. Unless you have a hole some place.

It doen't need to be big. I put a 1/16" hole through the middle of my bulkhead. This is enough to balance the air presure but not so big that it will let much, if any, water in even if it is submerged. For water to come in, air must come out, if there is only one small hole it will be take a long time for a significant amount of water to get in.

You can't have perfectly airtight without problems with vacuum. You may be able to put some kind of handle on your hatch so you can lift it better, but a 1/2 PSI difference in air pressure on a 12" x 12" hatch will create 72 lbs of force holding the hatch closed.

: Finally getting to spend some time in my boat and realizing I have airtight
: hatches. I built the Vaclav style hatches with the Leidy bungies and am
: afraid its so air tight that with temp changes my boat is going to
: implode. I am not excited after succeeding in getting my hatches to be
: water tight to drill into my bulk heads. Any recommendations on the best
: way to do this? Can I fill the hole with something that is water tight but
: not air tight? Cork or valve? Any info much appreciated. For what its
: worth the boat is a CLC west river 180 with a strip built deck and okeme
: hull and bulk heads glassed in and out. Thanks, Todd