What are the lines called that are erected around the edges of the main and weatherdecks for safety?

Lifelines are the safety lines that are installed around the edges of the main and weather decks on a naval vessel. Their primary purpose is to provide a barrier that prevents personnel from falling overboard, enhancing safety during operations or while the ship is in motion. Lifelines are typically made of strong, durable materials and are designed to withstand harsh marine conditions, ensuring they remain effective at all times. They are an essential safety feature, particularly on vessels where crew might be working near the railings or during rough weather.

The other terms listed do not describe safety lines. The rudder is a crucial component for steering the ship, the stem post refers to the forward vertical component of a vessel's hull structure that provides stability, and the main deck is the primary horizontal surface of a ship where operations take place, but it does not serve the function of preventing falls.