I know there are some maps including ship-like-territories to symbolise seas and oceans, but I thought of another kind of map. I'll explain in an example: Let's say it's a map of the UK, and around the archipelago are territories for, for example, the Irish Sea, and one can only reach it from the, for example, Lancashire through the harbour or port of Lancaster.

Or one could create a map for "naval warfare", for example the Adriatic Sea. The only territories would be harbours and parts of the depicted sea, for example the Strait of Otranto, and the only bonuses would be the harbours, such as, for WWI, the Austro-Hungarian and the Italian ones (e.g. Trieste, Fiume/Rijeka, Zadar, Split, Dubrovnik, Cattaro/Kotor for Austro-Hungary, Bari, Venice, Ancona, Rimini, Pescara and Pesaro for Italy). So, what do you think?

So there would be little to no fighting from one bonus into another ?

Sounds interesting, i would pick a sea surrounded by land to make it though.

I think the Black Sea would work, as the Mediterranean has been done too often already. Finding subdivisions for the sea will likely be a problem, unless you want to name them all the same.

A nice RP game would be to make the players keep attacking with an x (say 100) stack each time, to represent a ship. These ships can obviously be damaged (you can't deploy to them - neutrals are worth 0) by being attacked and will lose health by moving around a lot. It would be a fun game :)

You could do the Carabian, black sea, baltic sea, english channel, Caspian sea, Indonesia and around there, pacific.