What is the primary purpose of monkey lines in maritime operations?

The primary purpose of monkey lines in maritime operations is to hold the boat crew during a hoisting operation. Monkey lines are specific types of safety lines that are rigged to provide secure handholds for personnel working on the deck, especially when they are involved in hoisting activities or when conditions are potentially hazardous. These lines serve to enhance safety by preventing crew members from falling overboard or losing balance while performing tasks that require them to be near the edge of the vessel.

The other functions mentioned, such as assisting in navigation, securing cargo, and raising or lowering sails, do not align with the specific safety purpose that monkey lines serve. Navigation is typically supported by other tools and devices like compasses and GPS systems, while cargo is secured using specific lashings and equipment designed for that function. Similarly, sails are managed through rigging systems distinct from monkey lines, which are not designed for handling sail operations.