Lifeboats, which are used for evacuation during an emergency on board a ship, are designed to be unsinkable and have buoyancy that cannot be damaged. They are usually manufactured using reflective or fluorescent material that is strikingly visible. A necessity on board ships, ship-launched lifeboats have covers that functions as a protection from weather elements, and are usually stocked with signaling equipment, basic first-aid supplies, rations worth several days, and oars.