Deviation

Deviation is an unjustified departure from the contractual or usual geographic route. At common law it was treated as a fundamental breach that displaced the contract and stripped the carrier of its exceptions and limitation. Under Article IV Rule 4 of the Hague-Visby Rules a deviation to save life or property at sea, or any reasonable deviation, is not a breach; an unreasonable one still exposes the carrier. The doctrine bears on cargo insurance, because an unjustified deviation can discharge the underwriter.