I dunno about specific components, but keep in mind that water is really hard to push thru, and takes more power than pushing thru air.
If you want it to be fast it'll take a lot more power than to go slow; much more than for the same thing to go fast in the air.
BTW, you might want to ask a mod to move this over here
where the other watercraft stuff is.
I don't know that any of the stuff there applies, but htere's a couple of "diver" and "rov" threads that might have some useful info. (I havent' read them, just glanced thru titles).