Underwater currents wind through the Churning Archipelago, giving the region its name. These currents are the reason long-range shipping is difficult or even impossible between the mainland and the islands, as the flows create bizarre and violent weather patterns to the east and west of the continent, effectively blocking off easy travel.
Navigating the Churn to go between regions requires an Int/Sail or Wis/Sail check at difficulty 12. Failure by 4 or more will eject the ship at a random point along the Churn, and potentially damage or sink the ship attempting the journey.