Ships frequently encounter difficult conditions, whether by storm or combat, and the crew frequently called upon to cope with accidents, ranging from the parting of a single line to the whole destruction of the rigging, and from running aground to fire. On a ship, cargo must be stowed evenly so that the ship sits upright. All ships are vulnerable to cargo shifting, causing the ship to develop a list to one side. However sailing ships are particularly vulnerable because the ship naturally heels over in reaction to the force of the wind on the sails. If the cargo is not adequately secured the cargo may fall to the leeward side of the ship. Loose cargos flow downhill like water if not adequately secured (e.g. by shifting boards) and are particularly prone to shifting. If a large quantity of cargo shifts the ship may develop such a heavy list that she capsizes. A catastrophic cargo shift caused the loss of the tall ship Pamir in 1957.