Thanks, Herzog, for the articles.
From them I get the same conclusion that I translate into Coca and Cog.
The feudal petty kings had no money for their warships, and for their wars they forced the merchants to give them their boats, to which they superimposed the castles of bow and stern as separate structures of the ship, with what depending on the carpenter there was a huge variety of designs of those structures. (Cog)
Finally, some king decided to have a war fleet of his own, independent of his merchants and the structures were incorporated into the design of the ship from the beginning. (Coca)
What defines both is the design of the ship's hull, with high boards and the rear rudder (until then they had a large oar on the side as a rudder).
The main deference between Coca and Cog is the prow of the ship, designed one in the Atlantic Ocean and the other in the Mediterranean Sea.
I hope you understand what I say, because I do not know how to translate from Spanish to English Google. Translation in the reverse direction is sometimes incomprehensible
@Mahazona;
I think that the designs of the Viking ships were all very similar, differentiated by the length and the sleeve of the hull, according to what I read. However, how to make four Viking warships, a merchant ship, another transport vessel, a fishing boat, all of them different, besides the longship?
[This message has been edited by CaveCanem (edited 06-30-2018 @ 12:39 PM).]