Yep, it´s called "propellers".
Don´t know if a standard fan can be modded. Sounds like shortcircuits to me.
http://www.mercurymarine.com/mercury_2.5_classic
Might be some noise and foul smell, but definetely a propeller.
OK, sorry, that one was a bit rude.
Haven´t heard about underwater propellers. Can´t a standard submersed pump do the trick? Don´t connect the hoses, and it will create a waterflow.
regards
Mikael S.