PotBS - Port Battles @ Official Site
A new dev log at the official Pirates of the Burning Sea site takes a closer look at the development of port battles.
There are two ways for an attacker to capture a port. First, they can defeat all the defending ships. When there are no defenders left, the port is lost. Second, they can assault the port itself, landing and attacking in hand-to-hand combat.
On the maps that follow, the port is a green dot labeled ‘P’. Near every port is a gun emplacement that will fire on any attackers that come near. If the emplacement is active, the port is locked to both attackers and defenders. As soon as the emplacement is destroyed, a timer begins; 30 minutes after its destruction, both sides can enter the port and fight for control of it.
Source: Flying Lab Software