Hi David - The pressure thing is certainly a potential issue, but the plug is mainly to ensure there are no un-ventilated spaces in your boat. Even a small amount of moisture trapped in a space for long enough can cause nasty damage.

A drain plug is easier to totally seal than a day hatch, but the bulkheads do make useful dry space for bits and pieces, and a day hatch allows you to get in there if any maintainence is needed.  You only need one or the other, but if you use day hatches only, remember to check in the lowest corner of each bulkhead when you get home. There could be few ounces of water, which could still sit in there for a long while if not mopped out.

I went with day hatches, no drain plug. Works fine.

David 

David

Thanks for the response.

That makes sense to me, I am thinking hatches, but if not, now I know why I need the plugs.

Thanks 

I have to add my two cents.  I built several lap stich boats and found that the bow and strern compartments  tend to leak.  I may not have been careful enough filling the joints. The drain plugs are useless where they are specified in the plans.  I ended up drilling a 1/4 inch hole in the deck and drain the compartments with the boat stored upside down.  I would install inspection ports instead of the drain plugs so the compartment can be sponged out.