Human Powered Amphibious Vehicle
(Original Challenge spec.)

The idea is a classic junkyard wars amphibious vehicle build with the twist that the vehicles must be human powered.
In this tradition I will proposed two different vehicles and the race rules.

Rules - to build a human powered vehicle to traverse a course across both land and water. This transition between land and water, water and land will consist of boat ramps. Number of team member powering vehicle is not restricted (it will be 1 for us most likely because we don't have a big junkyard). Vehicles may be pushed and carried when needed by the humans powering the vehicle (boat ramps are steep and these vehicles may not have the gearing necessary to climb up them). Race will consist of 3 laps starting on land driving into water, across water, onto land and the racing back to start line). Teams may perform / transform their vehicle at the entrance and exit of water all team member may help in this effort.

Notes: My target course is MiraMar lake is San Diego (a small lake with nice bike / pedestrian paths and a 15 mph speed limit) with boat launches at each side of the lake. I think it would be about 2 miles on road and .5 miles on water per lap.

Two different vehicles notes.

1. Pontoon bike. Pontoon would have roller or wheels and a trailer mount to attach it to the bike seat post. It would be dragged behind, set down, bike put on top and prop lowered at water entry point. The pontoon would have a front wheel lock post of some kind and a cord attaching the bike to it (we don't want the bike to end at the bottom of the lake as this about recycling not dumping ).

2. Canoe bike. First off if it is possible I'd love to build it out of a kayak so that we had a really good, aerodynamic, low drag bike / boat with an easy to paddle profile. Reason for suggesting canoe; it is easy to mount anything you want to a canoe, a kayak you would have to cut open for the peddles, and they tend to be plastic or fiberglass. The sketch I drew tries to show everything mount on the outside and running on the outside of the canoe (no holes to seal mean no new leaks). The rear axle would be fixed so that when one wheel goes they both go or we would just power one wheel and as long a we aren't breaking with the other we shouldn't notice any steering compensation or we have 2 chains connected one to each rear wheel. These suggestions are because bicycle wheels are not designed to be linked on axles. Next water power, just using a paddle is a very good alternative. A neater alternative is to link the rear wheels in a paddle wheel arrangement. This would give great speed in the water if done right, and the front wheel could have the aerodynamic inserts that would make it work as a rudder. Disadvantage of paddle wheels is at around 10-15 mph the turbulence from the wheel is going to slow down the bike on land (may not ever come into play).
This is the one I'm think of making first, especially if I can find the right kayak (I think it would make a great, silly recumbent bike to ride to work).