Көлемі көп жүк тасымалдау кемелері

Ship made to transport unpackaged bulk cargo

A bulk carrier or bulker is a merchant ship specially designed to transport unpackaged bulk cargo—such as grain, coal, ore, steel coils, and cement—in its cargo holds. Since the first specialized bulk carrier was built in 1852, economic forces have led to increased size and sophistication of these ships. Today's bulk carriers are specially designed to maximize capacity, safety, efficiency, and durability. Today, bulk carriers make up 21 percent of the world's merchant fleets, and they range in size from single hold mini bulk carriers to mammoth ore ships able to carry 400,000 metric tons of deadweight (DWT). A number of specialized designs exist: some can unload their own cargo, some depend on port facilities for unloading, and some even package the cargo as it is loaded. Over half of all bulk carriers have Greek, Japanese, or Chinese owners, and more than a quarter are registered in Panama. South Korea is the largest single builder of bulk carriers, and 82 percent of these ships were built in Asia. On bulk carriers, crews are involved in operation, management, and maintenance of the vessel, taking care of safety, navigation, maintenance, and cargo care, in accordance with international maritime legislation. Crews can range in size from three people on the smallest ships to over 30 on the largest. Cargo loading operations vary in complexity, and loading and discharging of cargo can take several days. Bulk carriers can be gearless (dependent upon terminal equipment) or geared (having cranes integral to the vessel). Bulk cargo can be very dense, corrosive, or abrasive. This can present safety problems that can threaten a ship: problems such as cargo shifting, spontaneous combustion, and cargo saturation. The use of old ships that have corrosion problems—as well as the bulk carriers' large hatchways—have been linked to a spate of bulk carrier sinkings in the 1990s. These large hatchways, important for efficient cargo handling, can allow the entry of large volumes of water in storms and accelerate sinking once a vessel has listed or heeled. New international regulations have since been introduced to improve ship design and inspection and to streamline the process for crews to abandon ship.

The term bulk carrier has been defined in varying ways. As of 1999, the International Convention for the Safety of Life at Sea defines a bulk carrier as "a ship constructed with a single deck, top side tanks and hopper side tanks in cargo spaces and intended to primarily carry dry cargo in bulk; an ore carrier; or a combination carrier." Most classification societies use a broader definition, by which a bulk carrier is any ship that carries dry unpackaged goods. The terms "VLOC", "VLBC", "ULOC", and "ULBC" for very large and ultra large ore and bulk carriers were adapted from the supertanker designations very large crude carrier and ultra large crude carrier.

Before specialized bulk carriers were developed, shippers had two methods to move bulk goods by ship. In the first method, longshoremen loaded the cargo into sacks, stacked the sacks onto pallets, and put the pallets into the cargo hold with a crane. These methods were slow and labor intensive. As with the container ship, the problem of efficient loading and unloading has driven the evolution of the bulk carrier. Specialized bulk carriers began to appear as steam powered ships became more popular. The first steam ship recognized as a bulk carrier was the British collier John Bowes, built in 1852. She featured a metal hull, a steam engine, and a ballasting system which used seawater instead of sandbags. The first bulk carriers with diesel propulsion began to appear in 1911.—and most of this trade was coastal. However, on the Great Lakes, bulk carriers hauled vast amounts of iron ore from Minnesota and Michigan's northern mines to the steel mills. In 1929, 73 million tons of iron ore was transported on the Lakes, and an almost equal amount of coal, limestone, and other products were also moved. Two defining characteristics of bulk carriers were already emerging: the double bottom, which was adopted in 1890, In this period, Great Lakes freighters increased in size, to maximize economies of scale, and self unloaders became more common to cut turnaround time. The thousand footers of the Great Lakes fleets, built in the 1970s, were among the longest ships afloat, and, in 1979, a record 214 million tons of bulk cargo were moved on the Great Lakes.

+General Bulk Carrier Types Illustration DescriptionGeared bulk carriers are typically in the handysize to handymax size range although there are a small number of geared panamax vessels, like all bulk carriers they feature a series of holds covered by prominent hatch covers. They have cranes, derricks or conveyors that allow them to load or discharge cargo in ports without shore based equipment. This gives geared bulk carriers flexibility in the cargoes they can carry and the routes they can travel. (Photo: A typical geared handysize bulk carrier. )Combined carriers are designed to transport both liquid and dry bulk cargoes. If both are carried simultaneously, they are segregated in separate holds and tanks. Combined carriers require special design and are expensive. They were prevalent in the 1970s, but their numbers have dwindled since 1990. (Photo: The oil pipeline and dry bulk hold aboard Maya. )Gearless carriers are bulk carriers without cranes or conveyors. These ships depend on shore based equipment at their ports of call for loading and discharging. They range across all sizes, the larger bulk carriers (VLOCs) can only dock at the largest ports, some of these are designed with a single port to port trade in mind. The use of gearless bulk carriers avoids the costs of installing, operating, and maintaining cranes. (Photo: Berge Athen, a 225,000 ton gearless bulk carrier. )Self dischargers are bulk carriers with conveyor belts, or with the use of an excavator that is fitted on a traverse running over the vessel's entire hatch, and that is able to move sideways as well. This allows them to discharge their cargo quickly and efficiently. (Photo: John B. Aird a self discharging lake freighter. )Lakers are the bulk carriers prominent on the Great Lakes, often identifiable by having a forward house that helps in transiting locks. Operating in fresh water, these ships suffer much less corrosion damage and have a much longer lifespan than saltwater ships. As of 2005, there were 98 lakers of or over.

The world's bulk transport has reached immense proportions: in 2005, 1.7 billion metric tons of coal, iron ore, grain, bauxite, and phosphate was transported by ship. Today, the world's bulk carrier fleet includes 6,225 ships of over 10,000 DWT, and represent 40% of all ships in terms of tonnage and 39.4% in terms of vessels. Including smaller ships, bulk carriers have a total combined capacity of almost 346 million DWT. Combined carriers are a very small portion of the fleet, representing less than 3% of this capacity. As of 2005, the average bulk carrier was just over 13 years old. All of the 98 bulk carriers registered in the Great Lakes trade are over 20 years old and the oldest still sailing in 2009, the St. Mary's Challenger, was 106 years old.

As of 2005, the United States Maritime Administration counted 6,225 bulk carriers of or greater worldwide. More bulk carriers are registered in Panama, with 1,703 ships, more than any four other flag states combined. These three nations account for over 53% of the world's fleet. The Fednav Group in Canada operates a fleet of over 80 bulk carriers, including two designed to work in Arctic ice. Croatia's Atlantska Plovidba d. d. has a fleet of 14 bulk carriers. The H. Vogemann Group in Hamburg, Germany operates a fleet of 19 bulk carriers. Portline in Portugal, owns 10 bulk carriers. Dampskibsselskabet Torm in Denmark and Elcano in Spain also own notable bulk carrier fleets. Other companies specialize in mini bulk carrier operations: England's Stephenson Clarke Shipping Limited owns a fleet of eight mini bulk carriers and five small Handysize bulk carriers, and Cornships Management and Agency Inc. in Turkey owns a fleet of seven mini bulk carriers.

Asian companies dominate the construction of bulk carriers. Of the world's 6,225 bulk carriers, almost 62% were built in Japan by shipyards such as Oshima Shipbuilding and Sanoyas Hishino Meisho.

Generally, ships are removed from the fleet by going through a process known as ship breaking or scrapping. Ship owners and buyers negotiate scrap prices based on factors such as the ship's empty weight (called light ton displacement or LDT) and prices in the scrap metal market. In 1998, almost 700 ships were scrapped in places like Alang, India and Chittagong, Bangladesh. Half a million deadweight tons worth of bulk carriers were scrapped in 2004, accounting for 4.7% of the year's scrapping. During the 1990s, bulk carriers were involved in an alarming number of shipwrecks. This led ship owners to commission a study seeking to explain the effect of various factors on the crew's effectiveness and competence. The study showed that crew performance aboard bulk carriers was the lowest of all groups studied. Deck officers and stevedores oversee the operations. Occasionally loading errors are made that cause a ship to capsize or break in half at the pier. The loading method used depends on both the cargo and the equipment available on the ship and on the dock. In the least advanced ports, cargo can be loaded with shovels or bags poured from the hatch cover. This system is being replaced with faster, less labor intensive methods. Double articulation cranes, which can load at a rate of 1,000 tons per hour, represent a widely used method, Start up and shutdown procedures with conveyor belts, though, are complicated and require time to carry out. The immense size of cargo holds and the tendency of cargoes to be physically irritating add to the difficulty of cleaning the holds. When the holds are clean, the process of loading begins. It is crucial to keep the cargo level during loading in order to maintain stability. Extra precautions are taken, such as adding longitudinal divisions and securing wood atop the cargo.

A hatch or hatchway is the opening at the top of a cargo hold. The mechanical devices which allow hatches to be opened and closed are called hatch cover. In general, hatch covers are between 45% and 60% of the ship's breadth, or beam, and 57% to 67% of the length of the holds. Newer vessels have hydraulic operated metal hatch covers that can often be operated by one person. The Load Line Conference of 1966 imposed a requirement that hatch covers be able to withstand load of 1.74 tons/m2 due to sea water, and a minimum scantling of 6 mm for the tops of the hatch covers. The International Association of Classification Societies then increased this strength standard by creating its Unified Requirement S21 in 1998. This standard requires that the pressure due to sea water be calculated as a function of freeboard and speed, especially for hatch covers located on the forward portion of the ship. Some manufacturers have preferred high tensile steel recently in order to reduce the tare weight. However, the use of high tensile steel for longitudinal and transverse reinforcements can reduce the hull's rigidity and resistance to corrosion. Double hulls have become popular in the past ten years. One of the advantages of the double hull is to make room to place all the structural elements in the sides, removing them from the holds. This increases the volume of the holds, and simplifies their structure which helps in loading, unloading, and cleaning. Double sides also improve a ship's capacity for ballasting, which is useful when carrying light goods: the ship may have to increase its draft for stability or seakeeping reasons, which is done by adding ballast water. A recent design, called Hy Con, seeks to combine the strengths of single hull and double hull construction. Short for Hybrid Configuration, this design doubles the forward most and rear most holds and leaves the others single hulled. This approach increases the ship's solidity at key points, while reducing the overall tare weight. Since the adoption of double hull has been more of an economic than a purely architectural decision, some argue that double sided ships receive fewer comprehensive surveys and suffer more from hidden corrosion. In spite of opposition, double hulls became a requirement for Panamax and Capesize vessels in 2005. Freighters are in continual danger of "breaking their backs" and thus longitudinal strength is a primary architectural concern. A naval architect uses the correlation between longitudinal strength and a set of hull thicknesses called scantlings to manage problems of longitudinal strength and stresses. A ship's hull is composed of individual parts called members. The set of dimensions of these members is called the ship's scantlings.

The 1980s and 1990s were a very unsafe time for bulk carriers. Many bulk carriers sank during this time; 99 were lost between 1990 and 1997 alone. These regulations required the upper ballast tanks designed in a manner to prevent shifting. They also required cargoes to be leveled, or trimmed, using excavators in the holds. The practice of trimming reduces the amount of the cargo's surface area in contact with air which has a useful side effect: reducing the chances of spontaneous combustion in cargoes such as coal, iron, and metal shavings. When very fine concretes and aggregates mix with water, the mud created at the bottom of the hold shifts easily and can produce a free surface effect.

In 1990 alone, 20 bulk carriers sank, taking with them 94 crewmen. In 1991, 24 bulk carriers sank, killing 154. This level of loss focused attention on the safety aspects of bulk carriers, and a great deal was learned. The American Bureau of Shipping concluded that the losses were "directly traceable to failure of the cargo hold structure"
Sea water enters the forward hatch, due to a large wave, a poor seal, corrosion, etc. Advanced methods of loading were not foreseen when the ships were designed. While the new processes are more efficient, loading is more difficult to control (it can take over an hour just to halt the operation), occasionally resulting in overloading the ship. These unexpected shocks, over time, can damage the hull's structural integrity. The new rules adopted in the 1997 annexes to the SOLAS convention focused on problems such as reinforcing bulkheads and the longitudinal frame, more stringent inspections (with a particular focus on corrosion) and routine in port inspections.

Since December 2004, Panamax and Capesize bulk carriers have been required to carry free fall lifeboats located on the stern, behind the deckhouse. One argument against the use of free fall lifeboats is that the evacuees require "some degree of physical mobility, even fitness" to enter and launch the boat. Also, injuries have occurred during launches, for example, in the case of incorrectly secured safety belts. In December 2002, Chapter XII of the SOLAS convention was amended to require the installation of high level water alarms and monitoring systems on all bulk carriers. This safety measure quickly alerts watch standers on the bridge and in the engine room in case of flooding in the holds. In cases of catastrophic flooding, these detectors could speed the process of abandoning ship.