I talked with our boat designer
which was very useful. He mentioned that basically with our boat having around 100 cu ft of air space forward in a water tight foreward locker (8 ft long, 6 ft high) for around 6300 lbs of lift and probably around 10 cu ft for 630 lbs of lift in the aft transom in another water tight compartment. Should we get a breach amidship, our boat would float with the bows above the water and the transom awash IF we actually make the forward compartment completely water tight by replacing the access door with a water tight door to prevent it flooding. So obviously thats what I'm going to do!
If we kept the forward compartment with a non water tight access hatch
or had just a big opening up to the bow with a birth in it, then any breach would have no interior
bulkheads to stop the entire hull from flooding and sinking. One thing he mentioned as well, which we never thought of and are very guilty of, is not being diligent about making sure the forward escape hatches
are dogged and locked before we go out. If we were to flip with those hatches open, then the otherwise trapped air flows out the escape hatch
and the boat sinks pretty far down to the level of the opening of the hatch.
Basically the boat needs trapped air to float and the mast
, the galley
stove the engines, heavy provisions all weigh the boat down. A criticism that boat designers have with boat builders is that often the boat builder
will compromise all of the water tight compartments that they designed to try to make the floor plan in the hulls open and maximize the useable space in the bows with things like forward births that can't be sealed off.
Of course the heavier the boat, the more trapped air one would need in water tight compartments to remain floating.