b.) Rectangle - begin with a rectangular sheet like A4 or Letter-size paper. If you used a small paper plate to make your boat, you may need to cut the paper in half for a smaller sail.
Fold one top corner of the paper down to meet the opposite edge, forming a triangle. Cut and discard the excess paper below the triangle.
Instead of a paper sail, create one from fabric. Choose a plain piece of fabric or a colorful patterned one. Cut it into a triangle and glue it onto a craft stick or wooden dowel.
Check out these crafts for ideas on for fabric decorating ideas: