I love sailing modern small boats, and coupled with my re-enactment interests, I've spent some time looking into the development & evolution of ship technology throughout the Middle Ages.
While returning from Flanders in the late Spring of 1997, I visited the Antwerp Maritime museum (well worth it, for a bijou version of Greenwich) and spotted this excellent model on display in their Medieval section.
It's what we English would call a nef, and it dates from (handily enough) the middle of the 13th Century. It is typical of the sorts of sea-going ship that would have carried goods and people across the channel and around the coasts of Britain and western Europe in the 1260's. Wine from Gascony to the tables of well-off English lords, and wool to Flanders to pay for these costly imports would all have travelled on vessels like this.
Even to the untutored eye, it clearly resembles Viking period ships of over three hundred years before, and it is a continuation of northern European ship building techniques developed over the preceding thousand years. The extreme slowness of this evolutionary process is as a direct result of the attitude of both the makers and users of ships.