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
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