How do I make a boat out of recycled materials?

Use a fat person.

I think an aluminum soda can split in half lengthwise would fill the requirements! Use the half that does not have the tab opening. Split using a hacksaw.

google for origami boats. Are made from papper.

Recycle an old boat.

we used to make boats out of the squarish milk containers you cut the opened half off and the other half had a leak proof wax surface that made a great boat and would surely hold 100 grams these are the two litre milk containers.. in the store .... if you are in a non metric area it would be probably 2 quart milk containers.. baring that you need something with a solid sealed bottom if you want it to look like a boat it must be semi rectangular but doesnt have to be perfectly rectancular any shape would float in water its the surface area that is important for a rectangular shape the surface area is 0.15*0.15 = 0.0225 get any shape that is about the size you want a shoe box or a ceraal box something whatever you need for the shape that is 15 cm for the outersurface you will want to use metal or wax material to be waterproof so you could use the inner bags from cereal box's glued like plaper mache to the outside of a paper box make many layers of this you could also use tinfoil or plastic wrap peices from food stored in the fridge ... these should be glued overlaplping each other on the bottom of the boat till you are confident it is water proof ... for a home made glue try this http://sustainableecho.com/homemade-natural-glue/ http://thegreenbacksgal.com/how-to-make-glue-for-making-homemade-holiday-gifts/ this allows you to make the glue from materials at home too thats what i would do to make the boat I think it would make the strongest boat if you use light materials like tinfoil or wax paper ... you could even try using melted wax from discarded candles for the water prooof coating once it hardens should be good as long as the water is not too hot... those are my first guess's at how to make the boat hope it helps you could use the plastic bags used for milk containers to waterproof a paper box that would be glued on and that would definitely be considered recyclible.. to make it non tippy i would put a small weight in the middle of the boat ....i think this would be able to be made thin and very able to hold full weight .. with sides of 15 cm should be very able to hold many kg or pounds I would make the dimensions less than the maximum so if it stretches you dont loose from disqualification i would make it maximum 14.5 cm by 14.5 by 14.5 good luck ..