I really like this so far.
I have a suggestion regarding capture zones and raids. The new forts seem massive from the wip screens we have seen, so I think it is very difficult to destroy them or maybe even impossible. I suggest, that forts, which are close to the water and reachable, are an own capture zone and can be captured by ships with marines. In this case marines have another use instead of just being crucial for boarding combat. I believe you once said, that players can upgrade the defense structures of ports (in this case maybe bigger guns, more (better) marines, barricades etc.). Obviously it will be difficult for the big SOLs to get very close to the shore and get their marines to the fort, so we have another use of small ships in port battles (no animated small boats, who ferry the marines to the fort, we have to imagines that for now)
Finally capturing a fort should not be needed to capture the port in the end, but it will make it a lot easier (fort guns can be used against the defenders now) and give better rewards. Marines could also be used in raids in a similar way.