Fourteenth century

The image decorating the keystone of one of the vaults in the cathedral at Bayonne is one of the first depictions of a ship with a stern (or sternpost) rudder. This central position allowed for much swifter steerage than the soon obsolete side-rudder, shown on the seal of San Sebastian. This improved manoeuvrability made it possible to increase the tonnage or cargo capacity and add a second deck. The new rudder required a straight sternpost which meant lengthening the keel. This increased the speed and helped create a vertical surface which, combined with the effect of the rudder, reduced drifting or sideways movement of the boat. According to the Tuscan chronicler Giovanni Villani, the Basques introduced this type of ship “which they called the coca (cog)”, into the Mediterranean in 1304.

The ship on the keystone of the vault in Bayonne cathedral. The foreshortened shape is due to the fact that the master masons who carved it needed to adapt it to specific dimensions of the keystones or lintels, within the general aesthetics of each building. © José Lopez

Although some authors have suggested that it was the Basques who invented the stern rudder, other seafaring cultures also used it, as we can see in this Arabian illustration, known as the ship of al- Harïrï, dating from 1237. At the same time, Chinese navigators, who were in close contact with the Arabs, already knew of a similar axial steering system as early as the second century. © José Lopez

This magnificent relief comes from the tympanum of the fourteenth century portico of the cathedral of Santa María in Vitoria- Gasteiz; it shows a cog of a different kind to that seen in Bayonne cathedral. The straight stem and the large freeboard of the ship is reminiscent of the wrecked cog found in Bremen, dating from 1380. Given the similarity, this relief may depict a ship of Hanseatic origin. The men who worked the stone in the cathedrals were travelling artists and often came from distant lands, bringing with them their own patterns and designs. © José Lopez

Coin depicting Edward III of England, from 1344. It shows the Bayonne design of ship. This is evident in the curved bow of the cog, which is different to the cogs of the Hanseatic League. -–Curved bow. © José Lopez

Model based on a colour picture in Bayonne cathedral. It has the same general characteristics as the one shown on the keystone; however the proportions have been stylised in line with studies of vessels from the period. The model makers have taken account the artists' need to compress the motifs they sculpted to fit the limited space available. –Aftercastle (or sterncastle). –Stern rudder. –Forecastle. © José Lopez

Here we can compare the Bayonne cog, with its curved bow, with the straight-bowed one from Bremen. © José Lopez

Bremen cog. Further evidence that the ship shown in the cathedral at Gasteiz might not be local came with the archaeological/ sailing experiment made with three replicas of the Bremen cog. This showed that the ship design was best suited to summer voyages on the relatively sheltered seas of the Baltic; it is therefore unlikely that such vessels were common along Basque coasts, given the harsh conditions of the Bay of Biscay. © José Lopez

Together with the straight sternpost and the stern rudder, the poop deck became larger, and was built closer to the mast. The bow has a discreet forecastle. The ship is considerably larger in size. © José Lopez