= The Holk (German: Holk) =
In the 15. century the reliable Cog became increasingly replaced by the Holk. The naming as well as the form can be traced back into the pre-hanseatic Flanders as with the Cog. By then, the Holk sailed predominantly between the western european continent and England. It was a single masted clinker built ship. Through many English and Dutch seals, the development from the simple bananaform like clinker ship to a ship with keel and stem can be traced. Based on the change of the length width ratio from 3:1 for the Cog to 4:1 on a massive keel with stem, the dimensions increased. As this also impacted the castle, the Holk became a strong and spacious transport ship. Until the mid-15th century the Holk could carry between 100 and 150 bales. 
[c]The Holk in its late form[c]
Due to the upgrade to 120 bales capacity and the transition to a carvel-built hull, the rigging became more and more difficult. The necessarily oversized sail proved to be difficult to control even in good weather conditions. Through the use of three masts the surface of the single sail could be reduced. The carvel-built Holk was probably the first one to carry three masts. After this structural form had been established, the castles were reinforced to carry additional weapons and fighters. The crow's nest was replaced by a top on the main mast. Later, the other masts were also equipped with these bigger top castles, which could carry several marksmen. Long lasting battles and the resulting need for convoys required these changes. The shipwrights fulfilled this requirement by the construction of these fortified ships, which antedated the development of warships. More artillery could then be loaded onto the ship.
Source: Günter Krause, Handelsschifffahrt der Hanse, 2010,  S. 135 ff.