I've wondered from time to time about pressurizing the fore and aft sections as a way to increase overall strength of the boat. Cola and beer cans, as well as jet airliners, are much stronger when pressurized than when not.(Crush a full unopened can; crush it after consuming the contents. In aircraft, as I understand it, loss of cabin pressure is dangerous more because of the loss of this strength, not just the loss of breathing air). Even 5 to 10 psi might be enough. One could more or less reverse the normal hatch flange so that pressure from inside would press the hatch out, and into, the seal gasket. Pipeline access manways are made that way, in an oblong shape so that it can be removed by lowering then rotating.

Then, as if to compensate, the central section of the boat could be reinforced with more glass to prevent the cockpit section from folding in extreme conditions.

Something of a pipe dream, I know, and it would take an engineer or two to figure out what could be expected. I know pressure vessels generally do not have acute interior angles such as you'd find at the bow keel. I don't see any weight savings; in fact, reinforcing needs may require extra epoxy & glas in places it wouldn't otherwise. So, for the same weight, or more, maybe a stronger boat is possible.

I'm just not sure 'WHY?' do it, except as research.

Back to the original question:

My Pygmy Coho instructions said to do the bulkheads and hatches AFTER the boat was built, so I did. And the whole time I wished I'd done it all at the step just before final attaching of the deck to the hull. As it was all pretty well shaped and fairly stiff at this point, I don't think any distortion would occur providing you were carefull.

Clamping a scrap accross the sheer would hold the hull while the bulkheads were fitted and epoxied in place. Leave, say, a 1/8" gap on the top to keep it from pushing the deck up. This would leave just that one edge to fillet and glas from inside the boat afterwards.

Likewise, the hatch flange installation would have been easier, as well as a little neater.

On the other hand, I haven't heard of others complaining about doing it the way Pygmy's instructions said to. I just had trouble, particularly in the front, getting an arm, my head, and a lamp in there and still have room to move. Maybe all three are just a little too big, eh?