Dunnage is the name for the materials used in holds and containers to protect goods and their packaging from moisture, contamination and mechanical damage.
Dunnage may include plastic films, jute coverings, tarpaulins, wood (wooden dunnage), rice matting, nonwovens, liner bags or also inlets etc. Depending on the use to which it is put, dunnage may be divided into floor, lateral, interlayer and top dunnage.
On general cargo ships, the most important of these is floor dunnage. It protects moisture-sensitive cargoes, such as bagged cargo (e.g. coffee, cocoa) or bales (e.g. tobacco, tea) from sweat, which forms on a ship’s sides and runs off over the decks. The floor dunnage “lifts” the cargo off the deck, so that water is able to flow off without coming into contact with the cargo.
In the case of very sensitive cargoes, the space between cargo and deck has to be enlarged or at least great care must be taken to ensure that the cargo does not under any circumstances come into contact with the deck over which sweat may flow.
Where spar ceilings are present in a general cargo ship, the purpose of side dunnage is to protect the cargo from contamination. Top dunnage generally fulfills a two-fold function:
- protection against moisture (sweat dripping from the deck, in particular the weather deck)
- protection from contamination (dust, cargo residues, hydraulic oil etc.).
Dunnage is used to:
- Prevent cargo from shifting and chafing.
- Chock off and secure containers.
- Block off broken stowage and fill void space that cannot be filled with cargo.
- Protect cargo from contact with water or other liquids that may get into the holds.
- Provide air passages for effective ventilation.
- Provide spaces for air circulation in refrigerated holds.
- Distribute weight.
- Separate cargo.
Dunnage material can be :
- Rough lumber of the same thickness but of different widths and lengths is the most common type of dunnage. Rough lumber may consist of pieces of pine, hemlock, spruce, or similar woods.
- Paper is often used to protect cargo from dirt, dust, and moisture and to separate shipments.
- Burlap is often made up in rolls or squares and used in the same way as paper.
- Plywood is extremely functional for container partitions, dividers, and auxiliary decking.
- Inflatable air bags are available in paper or rubber and may be reusable or disposable. Inflatable are used for light and medium duty bracing. Inflatable are not used to prevent cargo from moving when subjected to impacts such as those resulting from rail car coupling
How dunnage is removed ?
- Cargo handlers normally remove dunnage from the ship during discharge. While the cargo is being worked, dunnage is made up in drafts as it becomes available. When a draft is complete, cargo handlers should remove it. This procedure will ensure that dunnage is handled a minimum number of times aboard the ship.
- Cargo handlers remove the drafts of cargo or dunnage from ships in cribs constructed and used in the holds or in slings. A crib is 4 feet wide, 10 feet long, and 5 feet high. The dunnage crib holds 80 to 100 board feet of dunnage. When responsible personnel discharge a crib or sling load of dunnage to the pier, the crib and/or dunnage are then removed by truck or forklift to the port dunnage yard. Lastly, personnel return the crib (if any) to the ship for further use after the ship is unloaded.
- Once received at the port dunnage yard, cargo handlers immediately sort and bundle dunnage according to size. The nails are taken out and the dunnage is sorted and accounted for at this time.
- Wooden dunnage must be dry (water content 12 – 15%, air-dried).
- Wooden dunnage which is too fresh or has been stored in the open air and thus exposed to precipitation must not be used as dunnage. Moisture may lead to considerable damage