I had a SuperCat 17 that had a weird pressure problem. It had no inspection ports but it did have drain plugs. After sailing and having the boat in the sun for the time it took to de-rig for trailering, I'd open the drains to drain out any water. I'd get a huge hiss of outgoing air followed by a pint or so of water. I finally decided that some small leak would let water IN during sailing but sealed itself, not letting air OUT later. It was some kind of one way leak, a diode of sorts. I never did anything about it but it did make me wonder about pressure buildup. It's always something! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />