I think that in an hour the ring should start to shrink every 3-5 mins to prevent long battles.
Obviously a ship could just anker and board the enemy's ship and sail it out of the ring before the person/people respawn if the ring gets too small but that's skill tbh.
Also personally i think that outposts should not be allowed to be inside the circle as that can lead to people restocking or selling mid battle which can be an unfair advantage.