What is the function of breast lines on a vessel?

Breast lines are essential mooring lines that serve the primary purpose of preventing the lateral movement of a vessel while it is docked. When a ship is secured to a pier or slip, breast lines are typically run from the ship to the dock, oriented in a direction that helps keep the bow and stern of the vessel restrained against the dock. By providing this lateral restraint, breast lines help maintain the vessel's position relative to the shore, thereby minimizing the risk of the hull coming into contact with the pier or other vessels, especially in varying weather conditions or water movements. This stabilization is crucial to ensure safety during loading and unloading operations as well.

While other lines and anchoring methods may also contribute to a vessel's stability, breast lines specifically address the issue of lateral movement, making them vital for safe docking practices.