What is the X in X-mas?
method of shipbuilding characteristic in north European waters during ancient and medieval times, in which the planks were overlapped and, in earlier times, usually joined by sewing. The earliest-known specimen, found in Als, Denmark, dates from about AD 300. The Viking ships that raided Europe and discovered America were clinker built, as were the ships with which William the Conqueror invaded Britain in the 11th century. Clinker construction provided less efficient streamlining than edge-to-edge (carvel) construction but gave the extra strength needed for safety in stormy waters