A voluntary departure from the usual course of the voyage, without any necessary or justifiable cause: a step which discharges the insurers from further responsibility. Liberty to touch, stay, or trade in any particular place not in the usual course of the voyage must be expressly specified in the contract, and even this is subordinate to the voyage. The cases of necessity which justify deviation are 1, stress of weather; 2, urgent want of repairs; 3, to join convoy; 4, succouring ships in distress; 5, avoiding capture or detention; 6, sickness; 7, mutiny of the crew. It differs from a change of voyage, which must have been resolved upon before the sailing of the ship. (See change.)