http://www.vintageprojects.com/boats/bicycle-boat.html Plans here
thank you so much every body for your comment :)but I have a problem with a float, and its type buoy ?how to calculate the power of a float if the load is more than 500 kg ?
Mythbusters did a segment on riding a bike underwater. It didn't work. You can't get enough traction to push the bike through the water.
You do something like this.http://inhabitat.com/transportation-tuesday-the-diy-floating-water-bike/