You could also buy a cheap used bike for 50 bucks and take apart the bottom bracket to see how it all works.

Here's some How To:

http://www.parktool.com/repair/readhowto.asp?id=94


Are you going to submerge a bicycle chain, too? Bike parts won't last very long if you submerge them. I don't even want to think about if you're talking salt water, here. Maybe consider a shaft-drive or belt-drive?

Please keep us updated on this project!