I'm not sure what period your campaign takes place or what nations will be represented in your campaign. The map would have to have Gibraltar and Spain with the entrance to the Mediterranean. Gibraltar was a key port for the British and was a stop for American ships before the War of 1812. I would prefer to use a map with larger sea zones for a type of strategic movement instead of hexes. Ships would change sea zones or go to port for repair, supply, or to escape enemy ships during strategic moves. Enemy ships within the same sea zone either would become involved or have the possibly of becoming involved in combat. Ships in a port or blockading a port would not become involved in combat in a sea zone unless they were being specifically attacked. Otherwise ships could pass through the zone freely unless there were other ships patrolling at sea. Ships in port would have to fight their way out or run the blockade. There are many maps of the Mediterranean on the net you could print out or if you prefer get a wall size map. You could then create your own sea zones. Just some thoughts.