What is a rat guard used for on a ship?

A rat guard is specifically designed to prevent rats and other pests from boarding a ship. It is typically a circular or funnel-shaped device placed on mooring lines that go from the ship to the dock. The guard acts as a barrier that makes it difficult for rats to climb up the mooring lines, thereby helping to maintain the ship’s hygiene and protect its stores from rodent infestations. This is especially important in maritime environments where rats can pose significant health risks and damage to food supplies and equipment.

The other options do not align with the primary function of a rat guard. Enhancing the ship's aesthetic appearance is not a practical or relevant use of the device. Providing a barrier against flooding relates more to watertight integrity features of the ship's hull or compartments. Protecting crew members from injuries could involve safety equipment or practices but is not a role played by a rat guard.