How am i going to make a submarine project-a mini submarine that is?

i have this project for physics...a submarine that uses an electromagnetic motor..my problem is that..how am i going to make that motor?? and what are things I need to consider so that it would submerge 2 meters (approx) below that water surface? what could be the most ideal material that can be used for the body? one that is not that expensive...another problem is, the motor might get wet...how about the propeller?? which is better..two-props or single prop-submarine...we are to make sure that it'll travel along a straight path...by the way, this is also for a race...please do help me...thanks!!!!