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Bulk carrier types: Ore carriers, OBO ships, Self unloader, Forest product carriers & more
Bulk carriers are single-deck vessels, designed with top-side tanks and hopper side tanks in cargo spaces and are intended primarily to carry single-commodity solid bulk cargo. Many bulk carrier types are available namely the Ore carriers, OBO ships, Self unloaders, Forest product carriers & more.
Some modern bulk carrier types are explained below:
Ore carriers are specially designed and may only be employed for a specific trade, eg carriage of iron ore in bulk from major Australian or Brazilian ports to specific ports in China or Japan.
Ore carrier sea passage
Ships that are designated as ore carriers have to be strengthened by class standards. In a seaway these ships tend to be stiffer due to the high density of ore cargoes.
Typical dimensions of a large ore carrier are:
- LOA 340 m
- Breadth 60 m
- Draught 21 m
- Deadweight tonnage 323,000 metric tonnes.
Oil/Bulk/Ore OBO Ships
These ships were designed to alternate between dry bulk and oil cargoes, avoiding a non-earning ballast passage by carrying both cargoes in the same cargo spaces at different times.
They were designed with large hatches to facilitate loading and discharging. However, the hatch covers were designed to be `oiltight' so the same ship could be loaded with oil cargoes with strengthened holds for ore cargoes. For this dual purpose operation, OBOs were fitted with pipelines, pumps and other oil tanker equipment. Major problems on these ships included gas freeing to load dry cargo after an oil cargo and the high maintenance costs caused by heavy wear and tear. Owing to the number of losses, notably the Berg Istra (1976), Berg Vanga (1979) and the Derbyshire (1980), combined with the high maintenance costs, there has been a reduction in the number of these ships, with few new OBOs built. Most remaining OBOs are limited to one cargo type.
OBO construction is similar to that of a bulk carrier except that they have larger wing tanks and their DB tanks are deeper to improve stability when carrying ore cargoes. Many OBOs have void spaces formed by fitting transverse bulkheads between two cargo holds. Other features of OBOs are:
- Oiltight hatch covers to allow the carriage of liquid cargoes
- dedicated slop tanks
- pumproom for load/discharge of liquid cargoes
- inert gas system
- tank/hold cleaning system similar to the crude oil washing system on oil tankers · ullaging equipment
- pipeline system (ballast, bilge and cargo) fitted through the duct keel
- bilge lines (for use with dry cargoes).
Self-Unloader Bulk Carriers
Similar in hull structure to other bulk carriers, these vessels are fitted with one of two systems for discharging cargo:
i) A gravity fed self-unloader: the cargo is dropped onto a conveyor belt running in a duct keel under the cargo holds that carries the cargo towards the bow or stern of the vessel where another conveyor lifts it for discharge ashore. The discharging arm is connected to a boom that can be slewed into position for discharge
Fig: Self unloader components in operation
ii) a hybrid self-unloader: commonly used, this method does not require any special structural design of the vessel. The cargo is discharged by grabs into hoppers where it feeds onto a conveyor belt. The hoppers can be permanently fitted on the ship or may be placed on the deck of the vessel when discharging.
These ships can discharge cargo in ports without any unloading facilities. The discharging rates achieved can be the same or higher than those of similar shore based facilities. An added advantage is that a totally enclosed conveyor system can discharge cargoes such as cement, coal, grain, ores and fertilisers without causing problems such as dust, cargo wastage, or damage to the ship's structure by grabs or weather effects.
While the initial cost may be high and the ship's carrying capacity is reduced by fitting an unloader, this is offset by the quick turn around and reduced port stay.
Read more on self-unloaders various components and handling guide....
Open hatch bulk carrier : Courtesy OSHIMA eco-ship
Open Hatch Bulk Carriers (OHBCs)
These vessels do not have upper and lower wing tanks . Instead, they have straight sides to carry square shaped bundles of forestry products such as unitised wood pulp, rolled paper or packaged timber cargoes. They can even carry twenty foot containers. They may have fixed or travelling gantry cranes for loading/unloading. Due to the nature of their cargoes, these vessels may be fitted with:
i) Dehumidification systems
ii) vacuum equipment for loading/discharging cargoes such as steel slabs/pipes, rolled paper, unitised wood pulp, newsprint, kraft liner board, kraft paper etc.
Forest Product Carriers
Open Hatch Bulk Carriers (OHBCs) can also be regarded as a forest product carrier. These carriers are required to transport and handle a variety of cargoes, including packaged sawn timber, logs (bundled or loose), and refined products such as pulp, paper and boards. The cranes must therefore be suitable for working with special attachments like clamps, multi-lifts and frames.
Open Hatch Bulk Carriers (OHBCs) collective term generally refers to the following ship types:
- Woodchip Carriers
These vessels are designed to carry woodchips (shredded wood) in bulk. Woodchip is described as a `neobulk' cargo that requires methods and precautions similar to those for bulk cargoes. They are usually constructed with 6 watertight (in contrast to weathertight) cargo holds to prevent water ingress. This is particularly important as contact with water causes woodchips to expand and could cause severe damage to the structure of the ship. Additional security measures to prevent water penetration through air pipes and ventilation ducts to cargo compartments are also incorporated to protect the cargo.
Carriage capacities are usually expressed in cubic feet (or metres), eg for a Panamax size woodchip carrier of length 205 m, breadth 37 m and draught of 10.5 m, the capacity is 3.6 million cubic feet (CFT).
As the cargo holds fill, bulldozers are used to press the cargo. Some ships are fitted with cargo loading/ unloading equipment including cranes, grab buckets and wings with conveyor belts on deck (to pour the chips into cargo holds).
When discharging, the ship's cranes are used together with a grab bucket system running at the bottom of the cargo compartments. The cargo is carried to the forecastle by conveyor, where it is discharged ashore through a single discharging point. However, many ships use conventional grabs to discharge the cargo.
- Timber Carriers
These vessels are used for carrying timber or logs in the holds and on deck. The machinery space and accommodation are located aft to provide clear deck space for the cargo. Generally, they are fitted with cranes that can handle logs that weight up to 25 tonnes. This means that the decks, tanktops, hatch covers and other structures are additionally strengthened to withstand these loads.
These ships usually have fixed or portable uprights to support logs/ timbers lashed on deck. It must be ensured that there is clear access to the mast houses, sounding pipes, etc, during loaded voyages.
These vessels carry lashings that include turnbuckles, wire ropes, chain, etc, fitted with a quick release mechanism such as a senhouse slip to release the deck cargo in case of emergency. On some ships, air powered `speedlashings' automate the lashing and tightening procedure.
The ship's lashing plan should be adhered to as prescribed in the approved cargo loading manual.The Code of Safe Practice for Ships Carrying Timber Deck Cargoes should be complied with for the carriage of timber on these ships.
- Wood Pulp Carriers
Wood pulp from soft trees such as pine, larch, hemlock, fir and spruce is the most common material used to make paper. The major hazard of wood pulp cargo is that it swells if it comes into contact with water, exerting enormous pressure on the structure of the cargo hold and possibly causing a structural failure. Additionally, this cargo depletes oxygen from the environment and generates carbon dioxide, making the atmosphere in the hold unsuitable for entry.
Considerable attention is required to avoid contamination of the cargo by dirt or by residues of the previous cargo. Wood pulp is typically carried in bales that have a protective covering to avoid any contamination to the cargo. To assist in the protection of a wood pulp cargo, holds are frequently repainted. Air bags are used to prevent the movement of bales in the hold.
- Hybrid Configuration (HyCon) Bulk Carriers
A recent advancement in bulk carrier design is the `hybrid configuration' or `HyCon'. In this design, the most forward and most aft holds have a double skin but the other parts of the ship still have a single skin . In this way, the areas that require additional protection are strengthened without greatly increasing the lightship weight.
A double skin enhances safety, security, dependability, reliability, and reduces the possibility of damage from accidental flooding. In addition, structures such as frames and brackets located inside the double skin structure provides a smooth surface for the cargo, reducing problems with inspection or maintenance. The potential for damage caused by cargo gear like grabs or bulldozers is reduced, increasing the speed of cargo discharging in port. The double hull makes inspection much easier through the use of passageways, ladders and manholes in the double skin. Ballast capacity is also increased, which is an added advantage in ballast voyages.
Bulk carrier size range
- Mini Bulk Carrier ,'Handysize','Handymax', 'Panamax",Capesize' , Suezmax,Very Large Bulk Carrier ,Seawaymax ,Malaccamax ,Setouchmax ,Dunkirkmax ,Kamsarmax ,Newcastlemax etc.
Bulk carriers come in all sizes, from the smallest ships of only a few hundred tons deadweight to the largest of over 360,000 tons, 340 metres or more in length, 63 metres in beam and with draughts of 23 metres.....
Our detail pages illustrated many safety aspects of Bulk carrier
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Operation of sea going bulk carriers involved numerous hazards . Careful planning and exercising due caution for all critical shipboard matters are important . This site is a quick reference to international shipping community with guidance and information on the loading and discharging of modern bulk carriers so as to remain within the limitations as specified by the classification society.
It is vital to reduce the likelihood of over-stressing the ship's structure and also complying with all essential safety measures for a safe passage at sea. Our detail pages contain various bulk carrier related topics that might be useful for people working on board and those who working ashore in the terminal. For any remarks please Contact us
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