An article related to the Hague Visby Rules and goods on deck.
Article 1 of Hague-Visby Rules determines that â€œcargo which by the contract of carriage is stated as being carried on deck and is so carried is excluded from the application of the Rules. This means that cargo on deck which complies with these two requirements is subject to freedom of contracting. Parties have the liberty to negotiate their own terms and liabilities. Deck Cargo means cargo which by the contract of carriage is stated as being carried on deck and is so carried, Carriage of Goods by Sea Act 1971. But, if these requirements are not met the carrier may be considered to be in breach of his contractual duty.
According to judgment by the House of Lords in Royal Exchange Shipping Co Ltd vs Dixon  LR 12 App Cas 11 there is an implied term in a contract of carriage of goods by sea that the goods are to be stowed under deck. In the absence of legal requirement, express agreement or custom/usage/practice, the only approved or recognized location of stowage is below deck. This leads to the carrier to be in breach of his contractual duties.
Lord Pilcher J. in Svenska Traktor v Maritime Agencies (Southampton) Ltd  2 QB 295 considered that the statement indicating that the cargo is carried on deck serves as a notification and a warning to consignees and endorsees of the bill of lading to whom the property in the goods passed.
Mr. Justice Langley in the Kapitan Petko Voivoda  EWHC 1306 (Comm) : An owner who contracts to carry goods under deck but in fact wrongfully carries them on deck cannot, I think, rely on the exemptions of “perils at sea” to exclude liability if the cause of damage to the cargo is the deck carriage and it would not have occurred if the cargo had been carried under deck… A peril of the sea sufficient only to cause loss to cargo so carried is the risk undertaken and accepted by cargo owners. This judgment was confirmed by the Court of Appeals (Neutral Citation Number:  EWCA Civ 451, Case No: 2002 1554 A3)
If cargo is carried on deck, and if it is not stated in the bill of lading and a loss occurs, Hague-Visby Rules may apply if the Bill of Lading is issued in a Contracting State, or if the bill of lading included the Hague Visby Rules to govern the carriage contract. The owner is benefited with the limitation of liability stated in the HVR, due that the doctrine of fundamental breach is unlikely to be applied with respect to cargo carried on deck. (The Doctrine of Fundamental Breach prevented the carrier to take advantage of any of the contractual limitation and exclusions of liability. Paul Rodgers. Postgraduate Diploma in Maritime Law 2010/2012 , Module 3 Bill of Lading Contracts, section 3-181)
Under US law unauthorized deck cargo may be considered as an illegal deviation: St. Johns N. F. Shipping Corp. v. Companhia Geral, 263 U.S. 119 (1923)
By stowing the goods on deck, the vessel broke her contract, exposed them to greater risk than had been agreed, and thereby directly caused the loss. She accordingly became liable as for a deviation, cannot escape by reason of the relieving clauses inserted in the bill of lading for her benefit.