Most Viking ships are based on literary references, mainly from sagas. The Viking ship design had many different forms and sizes to meet local circumstances and particular requirements. The Vikings understood the warship as a specialized type, the langskip or herskip, distinguished from others by its size and long, narrow hull form, which was known as snekkja or "snake". Ships of all sorts in the Viking tradition of double-ended, clinker-built vessels were measured by "rooms" or thwarts. The "room" is a section of the hull defined by two adjacent sets of frames and beams. In undecked ships the rowers sat on thwarts spanning the frames, and the number of rooms was the same as the number of pairs of oars. Throughout the Viking age, twenty rooms were common on long ships. Smaller ships were used often by Norwegian fleets when it was necessary to portage ships over land (Rodger, 392-403).
Imported wines offer some valuable clues to the nature of the mercantile shipping. Wine prisage might have had something to do with the growth size of the hulc and ceol. Early mercantile regulations went through three successive stages. The first stage is their apparent recognition of their coeval roles in trade. The second stage is their apparent difference in the size of the two types of ships, the ceol being able to carry more than the hulc. The third stage had to do with the ship's capacity in tons of wine. A tax was based and altered from the type of ship to the capacity. The .
ceol and the hulc seemed to have changed in size due to the change in the prisage laws (McCusker Jr., 279-285). .
The hulc originated as a small sailing vessel used in local river and coastal trade. The ceol was different in its made of propulsion because it could both use an oar and sail. The past twelfth century saw a remarkable change in the mercantile shipping of northern Europe with the development of large sailing vessels.