The hulk was a north-European sailing vessel, that developed from early medieval types (as early as 800) to become the Baltic and North Sea version of the Mediterranean nao or carrack as a cargo ship.
During the High Middle Ages it was similar to the contemporary cog, but by the 15th century it had overtaken its competitor in both capacity and importance. It finally developed into a carvel built, sometimes keel-less, three masted, full-beamed (usually a length to width ratio of 3:1) ship of up to about 400 tons, suitable for the relatively shallow waters of its region.
Hulk can also refer to a disused or decommissioned ship used as either a floating storage facility in a port, or as a work station for replacing masts without having to careen the ship. In the late 18th, early 19th centuries hulks were used as prisons, notable as holding facilities for those awaiting transportation to the New World and, later, New South Wales.
Reference: "The Oxford Companion to Ships and the Sea." 1979 p. 406