I think there was simply no economically feasible alternative to the composite hull, so Lochridge was fired. I also suspect that if you go with a metal hull, y

I think there was simply no economically feasible alternative to the composite hull, so Lochridge was fired. I also suspect that if you go with a metal hull, you don't have positive buoancy anymore - you need syntactic foam. You need larger thrusters, those are heavier too, so more foam etc. The engineering becomes harder and also costlier, in addition to the material and equipment costs. What you gain is the ability to evaluate your pressure vessel for growing defects - which you didn't do in the first place (and can't do) with your composite hull.