A keelboat is a 50- to 75-foot-long ship that is 15 to 20 feet wide and has a few oars to supplement its single mast with a square sail. It has a crew of 8 to 15 and can carry forty to fifty tons of cargo or 100 soldiers. It can make sea voyages as well as sail down rivers. (It has a flat bottom.) It moves about 1 mile per hour.