Dunnage handling technics - general cargo ship procedure

Dunnage handling technics - general cargo ship procedure

Dunnage requirement

The traditional reasons for the use of dunnage have been largely superseded with the introduction of containers and general cargo ships with shallower decks and holds. Additionally, the many refrigerated cargo ships now in service (forming the bulk of "traditional" ships afloat) invariably are fitted with some form of permanent dunnage, usually gratings. However, it is worth considering the traditional reasons for placing dunnage as they can still be valid and important, even with new technology and methods of stowage.

Depending on the nature of a particular cargo, dunnage can serve any or all of the following purposes:

Protect cargo from contact with water, be it from bilges, other cargo or leakage from the ship's side or tanks.
Protect cargo from moisture or sweat condensed on the ship's side, frames, bulkheads, etc. which naturally collects on the tank top and eventually runs into the bilge.
Protect cargo from condensed moisture or sweat which collects and lays on side stringers, bulkhead brackets, etc.
Facilitate the passage of air when cargo is being ventilated.
Prevent chaff and damage to cargo by chocking off and securing areas of broken stowage, i.e. areas that cannot be filled with cargo.
Spread the load of deep cargoes or heavy stowages.
Provide working levels and protection for the cargo on which stevedores can work.
Serve as a form of separation.
Provide access for cooled air around and through temperature controlled cargo .

Recommendations are given regarding the use of dunnage, matting, etc., to protect cargo from contact with metal decks, bulkheads, beams, etc. However, faster ships with consequent reduced passage times, fewer stanchions and other metal obstructions in `tween decks and holds, together with high labour and materials costs, have combined to make the matter of using or not using dunnage a matter for serious consideration. Whilst a lack of dunnage may generally result in a satisfactory out-turn of cargo, a less than satisfactory out-turn might well result in a claim that all reasonable precautions for the safe carriage of the cargo were not taken.

Permanent Dunnage

Traditionally, double bottoms were often completely sheathed with heavy planking laid on battens thus providing an air space so that any leakage from tanks below or from cargo above and condensed moisture coursing down the bulkheads was drained into the bilges. Similarly, ship's sides were fitted with dunnage boards or spar ceilings spaced close enough to prevent packages from protruding into the frame spaces and thus interfering with ventilation or coming into contact with condensed moisture on frames or shell. Such sheathing is now very uncommon and will generally be found only in older ships.

However, if loading a cargo in a ship so fitted, the permanent ceiling or dunnage is usually sufficient, provided it is dry, clean, free from oil stains and otherwise in a condition unlikely to cause damage to a cargo such as bagged or baled goods.

Care should be taken that the spar ceiling brackets are flush and not liable to damage the cargo otherwise dunnage and matting will be necessary. It should also be remembered that a cargo such as bagged grain coming into close contact with the ceiling, the surface of which may appear to be dry, may draw moisture from the timber by capillary action and thus sustain damage.

Increasing costs of dunnage material and labour have led to the development of several types of permanent dunnage over the years, particularly for use in insulated compartments.

i. Permanent Collapsible Dunnage (P.C.D.). Usually 50mm×50mm or 75mm×50mm varnished or painted timber, the lengths of which are hinged and easily collapsed together. The fitting is secured to the bottom of the inboard or outboard bulkhead with a swivel fitting, so that the dunnage when not used can be housed vertically against the bulkhead. More suitable for lockers rather than open `tween decks.
ii. Aluminium Strip Dunnage. Closely corrugated aluminium made in portable sections 3m×500mm. Sufficiently strong for fork lift operation, this dunnage can normally be left under general cargo and is easily cleaned. With this method, squares of `tween deck hatches have to be battened in the conventional manner.
iii. Steel Grating Dunnage. Similar in principle to (ii) but more permanent and particularly suitable for tank tops. Sufficiently strong for fork lift work.
iv. Permanent Gratings. The most common type now in use in refrigerated cargo ships, generally of strong plywood but bamboo is also in use and recent experiments have been carried out with plastic units. Pieces are grooved and perforated to facilitate ventilation as well as being treated to be resistant to fungus and micro-organisms.
v. ISO Containers. Insulated and refrigerated Containers usually have extruded aluminium "T" section floors built in.

All types of permanent dunnage must be closely inspected, damage made good and thoroughly cleaned prior to loading.

Dunnage Materials

Many varieties of timber and other materials are used as and make good dunnage, but it is always necessary to ensure that it is dry, clean and free from oil or grease, and matter likely to develop maggots, etc. Many authorities prohibit the landing of bark covered dunnage (e.g. Australasia) and there have been numerous cases of vessels being delayed during discharge when fumigation has been required and/or incineration ashore after the detection of insect infested dunnage.

Oily or greasy dunnage should never be used with dry goods while wet dunnage must not be used with any commodity. It should be noted that International Standards for Phytosanitary Measures (ISPM 15 of 2009) apply to all timber packaging including dunnage and each piece of timber used should be marked to show compliance with ISPM 15.

Battens

Of 50mm×50mm (2×2) or 76mm×76mm (3×3) used largely with refrigerated cargo.

Boards

Generally of rough timber 150mm×25mm (6×1) or 100mm×50mm (4×2) and largely used for `tween deck dunnage, laying over stowed cargo as a platform for further cargo or for laying on bulkheads, spar ceilings, etc.

Inflatable Dunnage Bags

The use of inflatable dunnage bags is now very common and they are particularly useful with, for example, palletised cargoes. Compared with timber fencing they are inexpensive and easy to put in place and remove. There are many manufacturers in the market with various sizes, strengths and materials available in both re-usable and disposable bags. Both types are inflated with compressed air and by choosing the most appropriate size and material, almost any cargo can be restrained.

Re-usable units incorporate a valve to allow the quick release of air at the port of discharge, where the bags should be collected and stowed away for future use. Although disposable bags also incorporate a valve they are usually deflated by puncturing. The inclination to keep and re-use apparently undamaged disposable bags should be avoided as being designed for only one use they are likely to fail if used again. The technique for securing cargo for both types is to work the cargo from a bulkhead or other secure position from two sides, e.g. in an empty `tween deck, from both ships' sides towards the centre line. The gap remaining in the middle of the cargo stow is then filled with dunnage bags which exert pressure on both sides, restraining the cargo and providing a wide area of pressure.

Plywood

Usually in sheets 2,440mm×1,220mm (8´×4´) or 1,830mm×915mm (6´×3´). Used to protect bagged and baled cargo, etc., from contact with ships' metalwork, other cargo and for separation. Often used as a slide between pallets to facilitate, firstly, a tight stow and, secondly, the damage-free removal of a key pallet.

Laths

Usually wood or polystyrene 9mm (³/8) thick and 25mm to 50mm (lto 2) in width. Used between tiers and/or cartons of refrigerated cargo so as to assist the circulation of air.

Paper

Kraft or similar paper is frequently used to good effect in protecting cargo from contact with bare metal, and in separating one cargo from another. Care must be taken in ensuring that the paper does not shift out of position after being laid, particularly when the practice of "dumping" bagged cargo into an open hold is carried out.

Sawdust

Traditionally used to absorb the drainage from certain cargoes such as gambier, hides, etc. However, when impregnated with oil, sawdust is very liable to spontaneous combustion. Consequently, it should only be used to absorb oils as a spillage control agent, i.e. when it will be removed and disposed of immediately.

Weight of Dunnage

Full cargoes of some commodities require a considerable amount of dunnage and it should be borne in mind that, when a vessel is chartered on a deadweight basis, the "weight of dunnage used and necessary for stowing cargo is to be counted part of the deadweight called for by the charter".

Some goods (e.g. rattans and bamboo) may be shipped at a low rate of freight on the understanding that they can be used as dunnage and/or for filling broken stowage, but with the proviso that their use as such must be confined to clean cargoes. In such cases the bill of lading should contain a clause authorising their use for such a purpose with the mate's receipt similarly endorsed.

Dunnage with Refrigerated Cargo

Dunnage used with refrigerated cargo serves the twofold purpose of providing channels for thorough circulation of cooled air and, as with other cargoes, even distribution of weight. To ensure the former, dunnage is to be in line with the air flow; the amount used being dependent on the installed refrigeration system .

ISO containers usually require no dunnage for refrigerated cargo as the floors, walls and ceilings have their own built in battening .

Dunnage over Refrigerated Cargo Spaces

When general or chilled cargo is loaded in a deck over a hard frozen refrigerated space adequate dunnage must be laid to ensure that the cold does not penetrate through to the cargo stowed in the compartment above and that any condensation formed does not come into contact with that cargo. On unsheathed decks it is advisable to have at least 127mm (5) of dunnage, i.e. 50mm×50mm (2×2), crossed and overlaid with 150mm×25mm (6×1) boards, and as additional insulation a sprinkling of approximately 50mm (2) of odourless sawdust between the 2×2 bearers. On sheathed decks, approximately 76mm (3) of dunnage is sufficient. Hatch coamings, steel ladders, etc., should be well covered.

Summarized below some more details on general cargo ship cargo handling procedure and operational info:

Cargo handling procedure for general cargo ship

Dunnage handling technics - general cargo ship procedure

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