|Infobox on Dunnage|
|Example of Dunnage|
|Stowage factor (in m3/t)||-|
|Humidity / moisture||See text|
|Risk factors||See text|
Description / Application / Risk factors
Dunnage has far too many uses for this article to cover in detail but it is felt that some general advice on the use of dunnage will assist masters and shipowners.
Dunnage is defined as a material used between, beneath, at the sides of or on top of cargo stowed either in a ship’s hold, or on deck or in a container with the aim of protecting the cargo from damage by chafing or wetness or to help stabilize a stow. If a shipowner does not use dunnage in the correct manner than he may be held liable for any resulting damage.
Dunnage material comes in many forms, the most common being timber, plywood fibre board, hardboard, kraftpaper, plastic sheeting and bamboo. Timber dunnage can be of either hardwood or softwood and of differing thicknesses and widths. It is often unseasoned and roughly cut from logs unsuitable for other uses, still with the bark on and although cut to the same thickness, of uneven width and varying length. Ship’s masters should be extremely vigilant when dunnage of any form is supplied to their ship. They should check that the amount of material ordered is correct in number and size. This may mean measuring packages of timber, as it is usually ordered in cubic meters or counting sheets in packages of plywood. The most important check, however, is to make sure that the material supplied is dry, if it is to be used underdeck or inside containers. There is usually no problem with board materials such as plywood. However, timber dunnage can be unseasoned and is often stored outside without protection. The outside of a package of timber may appear to be dry but the inside wet; therefore, a superficial examination of the outside of a package is not sufficient. Timber dunnage should not be used with moisture sensitive cargoes if the moisture content of the timber is above 15%. Unfortunately, timber may appear dry, even with a moisture content of 25%, and the only sure way of testing the timber is with a timber moisture reading instrument. Most ships do not have this instrument on board, although one may be available for hire locally, or a local surveyor could be employed to verify the moisture content of the timber. Any suspect timber dunnage should be rejected or the supplier asked to prove the moisture content. The presence of bark on the timber does not necessarily mean that the timber is unseasoned. However, the bark may retain moisture or insects and such timber should be treated with caution, especially if the cargo to be loaded is foodstuff. Timber dunnage is sometimes so rough that it will damage and tear bagged cargo. Consideration should be given to durability of any bagged cargo, if rough timber dunnage has been supplied. If there is a likelihood of damage to the bags then rough timber dunnage should be rejected.
Timber dunnage is frequently used in the shipment of hygroscopic cargoes (sugar, tobacco, rice and coffee etc.) from warm climates tom cold climates. This dunnage is used on the tank top and the sides of the holds, or on the floor and sides of a container to prevent the cargo from coming into direct contact with the steel structure of the hold or container, thus preventing wetting of the cargo by condensation, if any. Timber dunnage is also used to support air or ventilator channels in this type of cargo. Great care should be taken to make sure that only dry seasoned timber dunnage is used for this purpose, as wet timber dunnage may cause local damage due to moisture migration.
Hardwood timber dunnage is frequently used to assist in the stowage of steel cargoes. Again, this dunnage should be dry, as wet dunnage may cause rusting of the steel. Timber dunnage and even plywood and board dunnage are often stowed on deck after use, and exposed to the elements. Problems can arise if this dunnage is re-used with moisture sensitive cargoes and a prudent master should be aware that dunnage should be properly stowed for use.
Various types of dunnage are used in the stowage of chemicals (plywood sheets are frequently used in drum stows). Dunnage that has been used in the stowage of chemicals should never be used afterwards in a stowage of food cargoes or any other sensitive cargo. It is often best to dispose of this dunnage, especially if it has obviously been contaminated by any spillage of chemicals.
Care should be taken when ripping out dunnage (especially timber dunnage that has been secured by nails) during discharge of ship’s holds or unstuffing of containers, as this can cause damage to the cargo that the dunnage was originally intended to protect.
Kraft paper and plastic sheeting are now frequently used on the tank top instead of the usual timber dunnage. Great care should be taken during loading to ensure that the kraft paper or plastic sheeting remains in position and is not torn. It should also be noted that kraft paper is not waterproof, and, if the tank top is, or becomes wet, the kraft paper may not prevent moisture from eventually damaging the cargo.
Sometimes it may be necessary to saw timber dunnage in the ship’s hold. It is important that the sawdust is cleared up as cargo interests may allege that a sensitive cargo is contaminated by the sawdust. There has also been at least one occasion when the sawdust reacted with a chemical cargo causing a fire. It is important, when ordering dunnage for the shipowner and master, to determine the type of dunnage available for the cargo in question. Usually, if a cargo is commonly loaded in a port, then that port will have available suitable dunnage material for that type of cargo.