Kogge

A cog (or cog-built vessels) is a type of ship that first appeared in the 10th century, and was widely used from around the 12th century on. Cogs were generally built of oak, which was an abundant timber in the Baltic region of Prussia. This vessel was fitted with a single mast and a square-rigged single sail. These vessels were mostly associated with seagoing trade in medieval Europe, especially the Hanseatic League, particularly in the Baltic Sea region. They ranged from about 15 meters to 25 meters in length (49 ft to 82 ft) with a beam of 5 to 8 meters (16 ft to 26 ft), and the largest cog ships could carry up to about 200 tons.

Cogs were a type of round ship, characterized by a flush-laid flat bottom at midships but gradually shifted to overlapped strakes near the posts. They had full lapstrake planking covering the sides, generally starting from the bilge strakes, and double-clenched iron nails for plank fastenings. The keel, or keelplank, was only slightly thicker than the adjacent garboards and had no rabbet. Both stem and stern posts were straight and rather long, and connected to the keelplank through intermediate pieces called hooks. The lower plank hoods terminated in rabbets in the hooks and posts, but upper hoods were nailed to the exterior faces of the posts. Caulking was generally tarred moss that was inserted into curved grooves, covered with wooden laths, and secured by metal staples called sintels. Finally, the cog-built structure could not be completed without a stern-mounted hanging central rudder, which was a unique northern development. Cogs used to have open hulls and could be rowed short distances. In the 13th century they received decks.

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