oldsparkey said:
I still do not like the idea of holes in flotation chambers unless they are called Hatches.
I think Chuck makes sense on this - if there is going to be an opening at all, make it big enough to let in fresh air and dry out the space when not in use. And if you are doing that, you need a secure hatch so that the space won't flood in an accident.
(My boat doesn't have any enclosed space at all, which means I have no flotation. I need to do something about that)
As to pressure differential, I imagine you'd be dealing more with temperature change than with altitude. A big temperature change can cause quite a bit of pressure (positive or negative, according to the circumstances)
In manufacturing insulated glass panels for windows and doors, we didn't worry about altitude until it got up around 8000 feet. Shipping out of Atlanta (call it 1000 feet) Denver was not considered a problem. Eight, ten, twelve thousand feet, we started using various kinds of breather tubes to relieve the pressure.
George
ps I was thinking about what I was just posting, and I did a bit of research. Cardinal Glass says the threshold of concern for insulated glass is 2000 feet of altitude difference. I know at the window company I worked for we shipped to Denver all the time (about a 4000 foot difference) and got away with it. Insulated glass is probably a lot more sensitive than a wooden boat would be - the glass bowing out becomes a cosmetic problem - It isn't like it blows up or anything, just looks funny.