Dunnage is timber used to prevent metal to metal contact between cargo and the ship’s hold or between steel plates and to stop loose items from moving around in the hold during the voyage. Dunnage is a bit of wood, sacking, inflatable rubber bags, in fact, anything which is used to prevent damage to the cargo.
Stowage is an integral part of the loading and is therefore the shipowner’s responsibility unless there is a term in the charter-party transferring it to the charterer. Stowage includes arranging and securing the cargo in such a way as to prevent damage or deterioration to any of the cargo loaded. In addition, materials such as dunnage (wooden planks and timber used to keep bagged cargoes or cases away from the steel hull or to act as a separation between different cargoes), lashing wires, and ropes must be provided to achieve the safety of the cargo and ship. Where loading or discharging is to be carried out at more than one port, the ship must be seaworthy and have a proper trim (draught of the ship forward and aft to allow efficient use of the propeller and rudder) whilst steaming between the interim ports. Some current seaworthy trim clauses render the charterers liable for the costs of ensuring seaworthy trim.
In a tween-decker ships’ cargo compartments other obstructions possible are columns or pillars supporting overhead decks. It is essential to check on the location of such obstructions if intending to use a ship for large, bulky cargo. Some tween-deck ships are fitted with cargo-battens (strips of timber fixed at intervals usually horizontally but very occasionally vertically) along the sides of holds and tween-deck spaces and designed to keep bagged and baled commodities from being damaged by touching the sides of a ship which are invariably wet through condensation and/or slight seepage through microscopic faults in the plating. Cargo-battens also increase ventilation and reduce damage from moisture or sweating. However, they are frequently damaged and have to be removed entirely and stored elsewhere when handling a bulk commodity. Since cargo-battens are expensive to maintain in good condition and it is labor-intensive to keep repairing and removing cargo-battens, it is nowadays unusual to find tramp general-cargo ships fully equipped with this facility. Instead, cargo-nets might be used, but more commonly cargo is protected when necessary by a combination of kraft-paper and other dunnage material fitted sometimes by the crew but more commonly by shore stevedores as loading progresses.
Dunnage can be of various material but is usually loose wood of various kinds and sizes laid at the bottom of a cargo hold to keep lower-stowed goods clear of bilge water and from obstructing drainage, and also wedged between parts of the cargo to keep the stow secure and safe (e.g. for the carriage of drums). Certain trades traditionally use other, local materials for similar purposes, ‘cargo-mats’ and bamboo, for example, being utilized as dunnage material for the export of bagged rice from South-East Asia.