PotBS - Dev Log @ Official Site
The latest dev log at the official Pirates of the Burning Sea site takes in open sea spawns.
The open sea spawn manager is responsible for spawning and routing most of the ships in the open sea. The content department can still define custom spawns and patrol routes, but most of the original custom spawns will be removed. The spawn manager's job is to constantly try to make sure every port in the game has a set number of ships heading to it at any given time. Once a ship reaches its destination port it will sit outside the port for a set interval and then de-spawn. On a regular pulse, the spawn manager will find any ports that are below their desired spawn count and spawn another ship to head to the under-visited port. So for example, the spawn manager sees that Port Royal only has 3 ships heading toward it when it wants 5, so it spawns another ship at Jenny Bay and sends it on its way to Port Royal. Players destroying spawned ships bound for a destination port will also cause the spawn manager to create a new ship next update interval.
Source: Flying Lab Software