The cog was the general trading vessel of the Middle Ages in north-west Europe. The first mention of a cog (kogge) occurs in a Dutch inventory in 948. Until overtaken in popularity in the 15th century by the hulk most of the deep-water carriage of freight off the Atlantic and Baltic coasts from Scandinavia to Spain and across to the British Isles was done in cogs.
They developed out of an amalgam of celtic boat-building practices and the flat-bottomed river-boats and barges of the Roman era and became increasingly common in their larger forms in subsequent centuries. They had clinker-built sides, butt-jointed carvel bottoms, were single-masted, single-sailed, square-rigged, wide-beamed vessels that were generous in their carrying capacity, had excellent stability, shallow draft, but were not exactly speedy. Keels appeared before the thirteenth century, increasing their draft and increasing the requirement for docks when loading/unloading, but reducing leeway. A sternpost rudder appeared during the thirteenth century.
Whilst known as a trading vessel they were occasionally active in war – the Battle of Sluys during the Hundred Years War was fought on cogs – although that was more of a case of a land battle fought on ships than the normally perceived naval engagement.
William the Conqueror's invasion force force crossed to England in 1066 on a Norman variety of the cog, and this type influenced the development of the French nef (see Nao.) Three centuries on, Edward III’s official royal ship was the Cog Thomas.
They were the vessel of choice of the Hanseatic League traders until, gradually, during the fourteenth and into the fifteenth century they were replaced by the hulk. Much of what we know of the vessel’s construction comes from one of these vessels - the “Bremen Cog”, parts of which were recovered from the sludge of the Weser River at Bemen, Germany, during the 1960s.
- The Oxford Encyclopedia of Maritime History 2007
- The Medieval Sea Susan Rose 2007
- Dictionary of Ship Types 1986