The first problem was that we had to use paddles, not propellors. A quick conversation with the teacher solved that problem. It went a little bit like this:
"So we can use paddles, right?" (yes) "and paddlewheels?" (yes) "Are we allowed to tilt the paddles on the paddlewheel so that they are slanted?" (yes) "And we can move the paddlewheel from the side of the boat to the front?" (yes) "So we can use a propellor?" (and of course, the answer was yes)
That taken care of, construction began.
We had to build the boat from scratch, which we did, except for the propellor. We basically built a plywood box, sealed it with "The Great Stuff", then got working on the propulsion system. We built the crankshaft from pvc, and after deciding upon a belt system, built pulley's from layers of plywood, with a bike inner tube belt. The gear ratio was about 11:1, so with every rotation of the crankshaft, the propellor spun 11 times. The propellor had to be mounted slightly underneath the boat using a sort of box made out of 2x4s with a 3/8 inch threaded rod coming out of it. We slapped on a Walmart 2-bladed trolling propellor, and set sail to test it.
It ended moving painfully slow. like a mile per hour. So we took it out of the water, and put on a three-bladed propellor with a higher pitch that we got from a scrapyard. It ended making little difference. Prepared for impending failure, we painted the boat and brought it to the regatta.
It really sucked and was slow, but was one of the best boats there, and many people really found it interesting, especially the Army Corp of Engineers. I even added a little mouth-powered foghorn on the boat to increase its public appeal. We ended up winning "Best Design and Construction", one of seven or so awards given to seven lucky teams out of the 40 teams that showed up.
After witnessing this failure of a propulsion design, I turned to the submarine that had inspired me. Turns out, everyone on the H.L. Hunley died. No wonder our boat was such a failure.
Its a cute idea, but if you really want a boat with a propellor, just get an 80 dollar weedwacker, slap on a trolling propellor, and be on your way.