cog

A replica of the Bremen cog

A cog is a type of ship that was used during the Middle Ages, mostly for trade and transport but also in war. It first appeared in the 10th century, and was widely used from around the 12th century onward. Cogs had clinker-built sides but a flush-planked bottom which was built shell-first. The timber used was, generally, oak. Cogs were fitted with a single mast and a single square sail. They were used primarily for trade in north-west medieval Europe, especially by the Hanseatic League. Typical seagoing cogs were from 15 to 25 meters (49 to 82 ft) long, 5 to 8 meters (16 to 26 ft) wide, and were of 30–200 tons burthen. Cogs were rarely as large as 300 tons, with a few considerably larger at over 1,000 tons.