Shipowner, whether operating a liner service or under charterparty, impliedly undertakes that his vessel, while performing its obligations under the contract of carriage, will not deviate from the contract voyage. Deviation has been defined as ‘an intentional and unreasonable change in the geographic route of the voyage as contracted’. In order to determine whether such a deviation has occurred it is first necessary to ascertain the precise route envisaged by the contract of affreightment. A few standard charter forms make express provision for the route to be followed but, in the absence of such provision, the presumption is that the proper route is the direct geographical route between the ports of loading and discharge. This presumption can, however, be rebutted by the shipowner adducing evidence as to the customary route in the trade, or even as to the route previously followed by the particular shipping line involved. So in Reardon Smith Line v Black Sea and Baltic General Insurance a vessel chartered to proceed from a Black Sea port ‘to Sparrow Point’ in the United States, departed from the direct geographical route to bunker in Constanza, where cheap supplies
of oil fuel were available. On proof that vessels engaged in that trade invariably put into Constanza and that 25 per cent of ocean-going oil-burning vessels passing through the Bosphorus followed a similar practice, the House of Lords held that there had been no deviation from the normal route. The relevant law was neatly summarised by Lord Porter: ‘It is the duty of a ship, at any rate when sailing upon an ocean voyage from one port to another, to take the usual route between those two ports. If no evidence be given, that route is presumed to be the direct geographical route but it may be modified in many cases, for navigational or other reasons, and evidence may always be given to show what the usual route is, unless a specific route be prescribed by the charterparty or bill of lading.’ To constitute an unjustifiable deviation the departure from the contractual voyage must be the result of a deliberate act on the part of the owner or the ship’s officers. Consequently, there will be no breach of this implied undertaking if the vessel is blown off course during a storm, or is set on a wrong course as the result of the illness of its navigation officer or reliance on a defective compass.