You should, if haven't already, study the development of submarines in WWI and WWII. Shortly after WWII, I think, the US Navy abandoned direct drive setups in favor of diesel electric. I think the latter are much less complicated, and more flexible in installation, etc.
Plus, one should look for all off-the-shelf components for this, if possible.
Plus, one should look for all off-the-shelf components for this, if possible.