Now I don’t know much about naval history, but from what I have found in my research the Cog Boat was an early version of a Kneelboat used between the 10th and 12th century. Found typically in the Baltic sea, they were primarily used for trade due to being able to carry around 200 tons of goods. But some were converted into warships, resulting in some interesting varieties of this ship. Many believe it was first constructed somewhere around Limfjord and was known to be able to navigate bad geographical conditions and currents.