The good thing is, with the geography of the S2 campaign map, you had the choice to never bother with any ships unless you wanted to go to Chosokabe land. In FotS, they even got rid of that, though in FotS, it was easier to build 'Iwineverything' navies, which in S2 was kind of hard, unless you went Christian and started building the trade galeon things.

During a FotS co-op campaign, my friend and I essentially split the entire map in half with a curtain of ships and armies reaching from the northern edge all the way to the southern edge to keep the AI from sending naval invasions to the other end of the map. It was fairly hilarious and a little ridiculous.