Deviation may include any unjustified delay such as remaining at authorised ports longer than necessary, or acting beyond the agreed scope of the voyage.
For example, if a ship makes an authorized call at a port, but stays on to trade or break bulk, this action may amount to a deviation.
[12] In Glynn v Margetson (1893), a vessel was to carry a perishable consignment of Seville marmalade oranges from Malaga to Liverpool.
The contract included a "liberty clause" which allowed the vessel "liberty to proceed and stay at any ports in any rotation in the Mediterranean, Levant, Black sea or Adriatic, or on the coasts of Africa, Spain, Portugal or France.." On leaving Malaga, the vessel did not head straight for Liverpool, but made her way to Burriana, 350 miles up the coast.
They gave the clause a limited construction, namely that the vessel could have liberty to proceed and stay only at ports reasonably close to the agreed route from Malaga to Liverpool, such as Cadiz or Lisbon.
Just as in Glynn v Margetson, the Court of Appeal held that the deviation was unjustifiable and was not permitted by the liberty clause, so the carrier was liable for the lost cargo.
Using the criteria of differential bargaining strength of the parties, whereby the carrier is usually deemed to have greater bargaining power than the shipper, note that the parol evidence rule may be relaxed if a shipper seeks to rely on any verbal promises of the carrier (rather than vice versa, as in Leduc v Ward) .
An unjustified deviation is by nature a serious breach of the contract of carriage, and the carrier will be prevented from relying upon any exclusion clause which limits his liability.
[15] Here, a comprehensive and well-drafted exemption clause could not protect a car dealer who had supplied a used Buick with its cylinder head adrift.
First, prudent cargo-owners (shippers or consignees) will insure their cargo, and, secondly, carriers (shipowners) will have cover for third-party liability from their P&I Club.