Dunnage

Dunnage is the general term for the loose material used in a ship's holds to protect and secure cargo during carriage. It has been part of the art of stowage for as long as goods have been carried by sea, and it does several jobs at once. It keeps cargo up off the steel tank top and away from the ship's sides, where condensation, known as ship's sweat, and any water in the bilges could damage it, so moisture-sensitive goods are stowed on a floor of dunnage. It separates different parcels of cargo, or cargo from the structure, to prevent chafe, crushing and contamination. It fills the gaps and voids between packages and around the stow so that the cargo is packed tightly and cannot shift when the ship rolls and pitches in a seaway. And it helps spread heavy loads and allows air to circulate for the ventilation that some cargoes need.

Traditional dunnage is timber (planks, boards and battens) but many materials are used, including plywood, plastic sheeting, matting, inflatable air bags to fill spaces, and fibre or foam. The right choice and arrangement of dunnage depend on the cargo and its needs, and laying good dunnage is a skilled part of stowage, because cargo that is poorly dunnaged can shift, break loose, be crushed or arrive damaged by moisture.

Dunnage works alongside the lashings, chocks and other cargo-securing arrangements that hold cargo in place, and together with them it is covered by the ship's approach to safe stowage. It matters commercially as well as for safety, because cargo damage leads to claims, and it matters for stability, since a shifting cargo can endanger the ship. Even in the container age, dunnage remains important for break-bulk, project and general cargo, and knowing how to use it well is a mark of good seamanship in the carriage of goods.