(in marine insurance) The departure of a ship from an agreed course. A ship must follow the course specified in a voyage or mixed insurance policy (see time policy); if no course is specified, the ship must follow the usual course for the voyage. Deviation discharges the underwriters from all liability for subsequent loss (even though it may not increase the risk) unless it is caused by circumstances beyond control or is justified on certain very limited grounds (e.g. to ensure the safety of the ship or to save human life, but not merely to save property). Unreasonable delay may also amount to deviation. Insurance cover does not revive when the ship rejoins the original course. Between the parties to a voyage charter, the possibility of deviation is normally the subject of an express deviation clause in the charterparty. For goods carried under a bill of lading, permitted deviation is dealt with by the Hague Rules.