How To Make An Inexpensive Watertight ROV Thruster
Here is a great inexpensive "thruster" $15.99 if you want the housing $12.99 if you want just the cartridge. The run on 12 volts and draw about 3 amps.
http://www.overtons.com/modperl/overtons/detail/pdetail2.cgi?r=detail_view&item_num=20107&fcat=
http://www.overtons.com/modperl/overtons/detail/pdetail2.cgi?r=detail_view&item_num=20112&fcat=
You can take the impeller off and replace it with an electric model plane propeller adaptor and use airplane propellers. The shaft on the Mayfair bilge pumps are 1/8" approx. 3mm diameter. They cost $4.49 each. Airplane props are about $3.00. If you could find three bladed propellers that would be best.
http://www2.towerhobbies.com/cgi-bin/wti0093p?&C=GHJ