In either case of the previous suggestions, I have reservations that they will be powerful enough as the main source of propulsion for a boat or submarine.
While the Graupner bow thruster is a bit overpowered as a thruster. I don't believe the propellers were designed for high powered thrust.

Actual jet pumps may be adaptable to your application by extending the shaft connection into a WTC. Since the submarine is below the water surface, jet pumps should not have any trouble with water intake.

Graupner Jet drives from Hobby Lobby
http://www.hobby-lobby.com/jetdrives.htm

KMB jet drives
http://www.jet-drive.de/

MHZ >product>drives>jet (probably a bit high powered)
http://www.mhz-engines.com/

Swashdrives, (also high power)
http://www.swashdrive.com.au/
http://www.swashdrive.com.au/phpBB2/index.php