Can't build ships

Ok, this is a stupid question, but the problem is this:

I'm Casse, having invaded the isles and going to expand to the mainland, but I cannot build any ships, in any of my towns. I cannot build any naval ports either in anywhere, do you need to make any other buildings first? If you have to, what?

I have played EB from 2007 and having problems with stuff like this :wall:

Military harbours can only be built in a few provinces. On the British isles, you can only build ships in Ictis and Ivernis. You can find a map with the naval provinces in this thread.