HELP! How to make a sailboat that can float and move with wind blowing on it?

I'm building a boat. The mast, boom, and sail can be made out of anything but the remainder of the boat has to be made of paper(in my case cardboard). there has to be a keel and the sail has to be adjustable. The sailboat has to be able to carry 500 grams of cargo and it cant be more then 30 cm in length. And the keel cannot exceed 10 cm vertical length from bottom of boat to keel.