About realistic sailing towards port before battle...what a mess could be this when rest nations pvp players will camp port and sunk/grief and frustrate future participants of port battle? Well if i have to sail few hours toward port and get ganked nearby what fun will be that?
Invitations - on early game stages system from ranks could work well. Priority for high ranked Admirals and Commodores but later when more poeple level up? Not sure here - fully random invites would be not fair. So far im up for few encounters and summary results form them gave final score who win port battle. That allow most players who interested in RvR participate. Lets say huge ships battles will give more points at the summary - economically correct - lost/sank more expensive ships = more influence for score. That could lure more players to RvR instead few same "core" pvp/rvr faces like was in PotBS. I like idea how shallow waters ports battles will bring ship size cap - more fun and variety fighting in small ships plus all those "realism" lovers love it:) As well in future - Not sure but if guild can control port, members of that guild should get priority when invites out.
Forts etc - not sure how will be determine how strong forts could be and what damage they can deal to attackers. Again maybe should be connected to goveror feature or economy (more taxes = more money in port to upgrade)
Port Vulnerability - not get how this could work. You saying : "The time slot is determined by the defending nation" - so in theory US players will set up time frame for them convenient making impossible for EU players...
Grinding - i like idea no NPC fleeting/grinding near port - so boring at the end...
Questions: how exactly we can make port battle will take place? By pvp? ...any ideas? How long port battles will last - 2 hrs? Map will be reset after certain time/nation win?