Part B Text Study

Cargo Ships

Structures of ships

Ships are the conveyances running at sea and there are large-sized and small-sized ships. Different ships have different handling operations, either vertical or horizontal loading, discharge, and stowage, and different equipment and requirements of the cargo on board. Although there are many types of ships, the structures of these ships are almost the same. Simply speaking, hull and machinery are the two main parts of a ship. The hull is the shell including the superstructure, and most often, at least with larger vessels, divided into sections:holds or tanks. The machinery includes engines, auxiliary equipment serving electrical installations, etc. For a user of shipping services, the type of machinery is primarily of interest in the way it influences the cost of operating a vessel.1

The foremost part is called the bow and the rearmost part is called stern. When standing in and facing the bow, the left-hand side is called port side and the right-hand side is called the starboard side. Waterline is an imaginary line circumscribing the hull that matches the surface of the water when the hull is not moving. Midships is the midpoint of the load waterline (LWL), and it is halfway from the forward-most point on the waterline to the rear-most point on the waterline. Beam or breadth (B) is the width of the hull; depth (D) is the vertical distance from the bottom of the hull to the uppermost edge at the side; draft (d) or (T) is the vertical distance from the bottom of the hull to the waterline; and freeboard (FB) is the difference between depth and draft.

Hull is the outer shell of ships, which is riveted or electrically welded with armor plates. Frame is the total of all kinds of material that supports the shell. It is divided into two parts:longitudinal material and horizontal material. The longitudinal material includes keel, base framework, and side framework. And the horizontal material includes rib, ship girder, and cabin side. Deck is the armor plates paved on ship girder, and divides the ship body into upper floor, middle floor, and lower floor. The number of deck floors of large ship may reach 6 or 7. It is used to reinforce ship framework. Also, with the constructed several deck floors, it is useful for distributing loads and carrying cargoes. Holds and tanks are the various spaces below board: forepeak, sternward cabin, cargo cabin, machine cabin, and boiler cabin, etc. Superstructure is the buildings on the board. It is for sailor's living and working use, and also for marine store. It is composed of forecabin, sternward room, and bridge. All permanent housing above the main deck is known as superstructure. At the fore end is the forecastle and at the back end is the poop. The space between the holds and the bottom of the hull contains double bottom tanks. These are used for ballast water and fuel. The main deck covers the cargo spaces or holds. There are openings cut in the deck, and these openings are the hatches, one to each hold. Ships use either cranes or derricks to lift the cargo into the hold and discharge it.

Types of ships in light of transport purposes of cargoes and passengers

1. Liners and tramps. Vessels designed to transport cargo and/or passengers are called merchant ships. They may be classified as liners or tramps. A liner carries cargoes between two fixed destinations. Her sailing schedule has been prearranged—she has a fixed homeport, port of destination and port(s) of call (POC), and fixed estimated time of arrival (ETA) and estimated time of departure (ETD). A liner vessel is allowed to carry up to 12 passengers.Freighters that carry cargoes according to schedules that are not fixed are called tramps. Homeports, ports of destination, POCs, ETA, and ETD differ with every voyage. A tramp is not allowed to carry any passengers. Merchant ships may carry general cargoes, bulk cargoes, refrigerated cargoes, heavy cargoes, timber, and many more.

2. General cargo ships. General cargoes are cargoes that have been packed in crates, boxes or bags, or cargo coming in pieces (unpacked cargo items), and are loaded and discharged by the vessel's own derricks or by shore based cranes. The conventional general cargo ships have several tween decks, so that the cargoes for the various destinations can be reached and discharged without having to remove cargo for other destinations first. The general cargo ships are becoming obsolete since general cargoes are more and more transported by container vessels.

3. Bulk carriers. Bulk cargo is unpacked cargo of one commodity. Dry bulk cargo such as grain, ore, and fertilizers is carried in specially designed vessels with holds that have been divided into compartments by longitudinal and transverse separations, so that the ship's stability will not be affected by a full cargo. The holds of these ships are often constructed in such a way that they are self-trimming; this means that the surface of the cargo is constantly made equal by special pumps in rolling circumstances or when the vessel has a list. Dry bulk cargo is loaded and discharged by cranes with grabs or by pumps. Liquid cargoes such as crude oil, petroleum, and edible oils are carried in tankers, for example in very large crude carriers (VLCCs), chemical tankers, such as liquefied petroleum gas (LPG) carriers or liquefied natural gas (LNG) carriers. Product tankers are small tankers that carry different sorts of oils. For safety reasons, tankers must be fitted with double bottoms. These spaces also provide storage for fuel, lubricating oil and water. Tankers are divided into compartments by longitudinal and transverse bulkhead. Cofferdams are empty spaces between the tanks and in the double bottom. They serve as separations to prevent liquids from leaking from one tank into the other. Cofferdams often serve as pump-rooms. Pumps for loading and discharging the cargo may be installed in these compartments. Tankers are often loaded and discharged in the offing by means of flexible pipes. This system of wet bulk handling reduces the number of laydays.

4. Container ships. Cargo that has been containerized is carried by container ships. Containers are most often measured in TEUs and are stowed in a cellular arrangement in rows, bays, and tiers. The rows run abeam, or athwart ship; the bays run fore to aft and the tiers are horizontal layers. The three-figure code on each container refers to this stowage system. Thus, each container can easily be found. Container ships are sometimes equipped with their own gantry cranes that load and discharge the containers. Container ships may carry general cargoes, liquid cargoes, or refrigerated cargoes. The main advantages of carrying cargoes in containers are short laytime because of efficient and rapid cargo handling, few stevedores required, less pilferage because of cargoes being stored in locked containers.

5. Ro/Ro ships. On a Ro/Ro ship, cargoes are rolled on and rolled off by lorries or trailers. The great advantage of this system is that no cargo handling equipment is required. The loaded vehicles are driven aboard via ramps through special stern and bow doors and are properly secured for the passage. Upon arrival in the port of discharge, the vehicles are released and driven ashore to their destinations.

6. Coasters. A coaster carries cargo along the coast or on sea-voyages. Trans-Atlantic voyages are quite common. A coaster is of limited length and tonnage. Her engine room is situated aft. Often there are no tween decks and the cargo spaces have no obstacles so that a variety of cargo can be handled. Hatches are very broad and cover most of the main deck surface. Because of her limited length, she will hardly experience any problems related to longitudinal stresses. However, due to the broad hatchways, transverse strengthenings are necessary to avoid difficulties caused by transverse stresses.

7. Refrigerated cargo vessels (Reefers). Refrigerated cargo vessels are ships that carry perishable cargoes, such as meat or fruit. These cargoes require cooling and must be stored in spaces that have precise temperature and humidity controls during the voyage. Reefers, as these ships are also called, are equipped with refrigerating plants.

8. Lash vessels. Lash stands for Lighter Aboard Ship. A Lash vessel, also referred to as a seabee, has a main deck that is flat and without any obstacles. A lighter is a container that floats in the water. The containers may be hoisted on board by the vessel's own heavy derricks that stack them on board. Another way of loading the containers on board is by submerging the vessel first (for this she must be equipped with a powerful pumping system), then have tugs or push boats tow or push the lighters over the lash vessel, after which the vessel will emerge again and will pick up the lighters.

9. Heavy load vessels. Heavy load vessels have been designed to lift and carry extremely heavy cargo on the main deck. Their most prominent features are very heavy derricks (booms), masts and lifting blocks. Their cargoes, such as drilling platforms, engines, yachts, trains, derelicts, and wrecks, are loaded onto the main deck, which is flat and free from any obstacles. A special way of loading and carrying heavy cargo is performed by submerging the ship and has the cargo module float over it. She must be equipped with a powerful pumping system. After pumping the ship empty, the vessel will emerge again and will pick up the cargo.

10. Timber carriers. Timber is a kind of raw material from which wood products are manufactured. Vessels that carry timber can easily be recognized by their tall derricks. A timber carrier has been designed in such a way that she can carry a tall deck cargo. Her Plimsoll Mark is provided with a special timber load line that indicates the maximum draft to which she is allowed to be loaded under certain circumstances and in different seasons.

11. Multipurpose vessels. Cargo ships that carry both general cargo, bulk cargo, and containerized cargo are called multipurpose or multiloads vessels. These ships are equipped with a variety of cargo handling gears to load and discharge the different types of cargoes. An OBO-ship has been designed to carry oil/bulk/ore. She has been subdivided in such a way that oil can be carried in the largest compartments and ore can be carried in the smaller compartments.

12. Passenger ships. Passenger ships, such as cross-Channel ferries, have been designed to carry passengers and their vehicles on a prearranged route. Their main features are more or less the same as the features of the Ro/Ro vessels. Cruise ships have been especially designed to carry holidaymakers.

Types of ships in compliance with the number of decks equipped

1. Single deck vessels. Single deck vessels have one continuous deck. Easy access with one hatch for each hold means economical loading and discharge. Many single deck vessels have very large hatches, and some are known as self-trimmers because of provisions for the cargo to flow into all corners of the hold. This reduces loading costs and time spent in ports.The most suitable cargoes for single deck vessels are heavy bulk cargoes, such as coal, grain, and iron ore. However, these vessels also carry such light cargoes as timber which can be stowed on deck as well as below. Single deck vessels are not suitable for general cargoes since there are few means of separating cargo tiers and lots.

2. Tween deck vessels. The tween deck vessels have additional decks (tween decks) below the main deck, all running the full length of the ship. A vessel with tween decks is suitable for general cargo, because the cargo space is divided into separate tiers, and the decks eliminate risks of cargo damage by preventing too much weight to be put on the cargo at the bottom.

3. Shelter deck vessels. Shelter deck vessels have an additional deck above the main deck, that is, a shelter deck. The advantage of the shelter is that it provides more under-deck space for carrying light cargoes. There are two types of shelter deck vessels, the closed and the open. The difference relates to the measurement of the ship. For new tonnage, the difference has been abolished through changes in the measurement rules.

4. Specialized cargo carrying vessels. In addition to traditional single deck, also called full scantling ships, and tween and shelter deckers, there exists a multitude of specialized cargo carrying vessels. These include gas carriers, wood carriers, refrigerated ships, oil tankers, container ships, and Ro/Ro vessels. Most special ships are, however, variations of the basic designs. The differences are mainly relate to the loading and discharge methods and equipment and the requirements of the cargo while it is on board.2

Ship measurements

Ship measurements determine the cargo capacity of a single vessel and (in combination with speed) also the transport capacity of a service. Ships are measured for a variety of purposes, for example, cargo capacity in terms of cubic capacity; cargo capacity in terms of weight capacity; navigation, such as the draught of canals and ports; dues in ports and canals;and the freight rates payable. Some of these measurements will be important for shippers' choice of vessels. Generally, it is convenient to distinguish between volume and weight measurements in relation to the ship and the cargo carried.

1. Volume measurements. The word ton in shipping can denote both weight and capacity (volume), and the term tonnage can indicate many different measures as shown in Figure 2.1. The tonnage of a ship is not a weight, but a volume, thus tonnage and ton cannot be confused. Gross tonnage (GT) and net tonnage (NT) are two ways of volume measurement. These two tonnages were defined by the International Convention on Tonnage Measurement of Ships, 1969, adopted by the IMO in 1969 and came into force in 1982. Since then, GT and NT have replaced gross registered tonnage (GRT) and net registered tonnage (NRT) respectively.3Gross tonnage is calculated based on the moulded volume of all enclosed spaces of the ship, thus is the total internal volume of a ship, including the engine room and other non-cargo spaces as well. Most of the maritime regulations such as SOLAS and MARPOL are applicable to ships based on their GTs. Net tonnage on the other hand, is calculated based on the moulded volume of all cargo spaces of the ship, thus is the volume of only the cargo carrying spaces on the ship, which determines the earning capability of the ship. Most of the port and anchorage dues are applicable to ships based on their NTs. Net tonnage shall not be taken as less than 30 percent of the gross tonnage. Neither GT nor NT should be confused with measures of weight such as deadweight tonnage or displacement, and GT and NT should not be confused with Suez Canal Tonnage (SCT) which uses a slightly different formula to calculate the toll for transiting the canal. The cargo capacity of a ship, in volume, is rather measured in grain capacity or bale capacity (BC), depending on the cargo.These measurements of the cubic capacity only relate to the cargo holds, and are normally given in cubic feet. They indicate how many cubic feet of cargo may be loaded into the ship. Some commercial ship registers indicate grain and bale capacities in cubic meters. The grain capacity, also named grain space or bulk capacity, is the complete capacity of the ship's cargo spaces and includes hatchways. Measurements are taken from the tank top (floor of the holds) to the underside of the deck plating and to the outside of the ship frames. The grain capacity is the capacity available for cargo shipped in bulk, which is free to flow between the frames and beams. The bale capacity, also referred to as bale space, is the total amount of under deck capacity available for packed cargo which may not be stowed between frames. Thus the bale capacity will always be less than the grain capacity. For a container ship, the appropriate measure of size is the number of containers it can carry, namely, measured in TEUs.

2. Weight measurements. The weight of the cargo will often be an important limitation to the volume that may be loaded. Deadweight tonnage (DWT or dwt) and displacement tonnage (DT) are two ways of weight measurement. The deadweight tonnage indicates the weight of cargoes, water, stores, fuel, etc. which the ship may carry. International conventions deal with safety aspects of shipping. The load line convention regulates the safe depth to which ships may be loaded. The classification societies will authorize the marking of the ship indicating this. The deadweight tonnage varies with different trades or geographical areas. The load line is different for different conditions. For example, a ship is permitted to draw less water (load less cargo) during winter, and similarly, more may be loaded into the ship if she runs in tropical waters or in fresh waters. The deadweight tonnage is thus a figure which is of importance when calculating how much cargo could be taken into a ship. The weight of bunkers, water, and stores necessary to provide for crew and maintenance must be deducted from the deadweight tonnage to find the cargo carrying capability in weight tons. The cargo which may be loaded is therefore always somewhat less than the deadweight tonnage. The deadweight tonnage is a useful measure if heavy cargo is loaded. If the cargo is light, the ship may be full before the load line has reached the waterline. The limiting factor will, in that case, be the volume of the cargo, not its weight. Displacement tonnage of a ship is another weight measure which is used occasionally and has little or no commercial use. Displacement denotes the weight of water displaced by a ship and is the actual total weight of the ship.4Like deadweight tonnage, displacement tonnage is often expressed in long tons or in metric tons. Displacement light and displacement loaded indicate displacement unloaded and fully loaded respectively. Light displacement tonnage is the actual weight of the ship when afloat with no cargo, fresh water, stores, fuel, passengers, etc. on board, and loaded displacement tonnage is the actual weight of the ship and cargo. Deadweight tonnage is the displacement at any loaded condition minus the lightship weight, thus it becomes the difference between loaded and light displacements.5

Notes

1. Simply speaking, hull and machinery are the two main parts of a ship. The hull is the shell including the superstructure, and most often, at least with larger vessels, divided into sections: holds or tanks. The machinery includes engines, auxiliary equipment serving electrical installations, etc. For a user of shipping services, the type of machinery is primarily of interest in the way it influences the cost of operating a vessel.

简单而言，船体和机械是船上的两个主要组成部分。船体是指包括上部结构在内的船的外壳，它通常（至少对大船来说）又可分隔成货舱或油舱。机械包括发动机、为电气装置服务的辅助设备等。航运业务的客户主要会考虑不同类型的机械对船舶营运成本的影响。

2. In addition to traditional single deck, also called full scantling ships, and tween and shelter deckers, there exists a multitude of specialized cargo carrying vessels. These include gas carriers, wood carriers, refrigerated ships, oil tankers, container ships and Ro/Ro vessels. Most special ships are, however, variations of the basic designs. The differences mainly relate to the loading and discharge methods and equipment and the requirements of the cargo while it is on board.

除了传统的单层甲板船（也称为全实船）、二层甲板船和遮蔽甲板船以外，还有众多的特种货物运载船舶，包括气体运输船、木材运输船、冷藏货运输船、油轮、集装箱船和滚装船。然而，大多数特种货船在基本结构上存在差异，主要取决于货物在船上的不同装卸方式、所需的不同装卸设备和理舱要求。

3. Gross tonnage (GT) and net tonnage (NT) are two ways of volume measurement.These two tonnages were defined by the International Convention on Tonnage Measurement of Ships, 1969, adopted by the IMO in 1969 and came into force in 1982. Since then, GT and NT have replaced gross registered tonnage (GRT) and net registered tonnage (NRT) respectively.

总吨位与净吨位是容积丈量的两种方式。这两种吨位是由国际海事组织在1969年制定并于1982年生效的《1969年国际船舶吨位丈量公约》中规定的。自此公约生效之日起，总吨位与净吨位分别取代了总登记吨位与净登记吨位。

4. Displacement tonnage of a ship is another weight measure which is used occasionally and has little or no commercial use. Displacement denotes the weight of water displaced by a ship and is the actual total weight of the ship.

船舶的排水量吨位是偶尔用到的另一个重量丈量单位，很少或没有商业价值。排水量表示船舶在水中所排开水的重量，也就是船舶自身的实际总重量。

5. Displacement light and displacement loaded indicate displacement unloaded and fully loaded respectively. Light displacement tonnage is the actual weight of the ship when afloat with no cargo, fresh water, stores, fuel, passengers, etc. on board, and loaded displacement tonnage is the actual weight of the ship and cargo. Deadweight tonnage is the displacement at any loaded condition minus the lightship weight, thus it becomes the difference between loaded and light displacements.

空船排水量和满载排水量分别指未装载时和满载时的船舶排水量。空船排水量吨位是船舶未装载货物、淡水、物料、燃料、旅客等时的船舶实际重量，而满载排水量吨位是船舶与货物的实际重量。载重吨位是满载排水量减去空船排水量，即应是满载排水量与空船排水量之间的差额。

Comprehension Enhancement

Decide whether the following statements are true or false and try to correct the false ones.

( ) 1. Freeboard is the vertical distance from the bottom of the hull to the waterline.

( ) 2. The longitudinal material of a ship includes keel, base framework, side framework, rib, and cabin side.

( ) 3. Dry cargo ships have tanks, and liquid cargo ships have holds.

( ) 4. Neither the liners nor the tramps are allowed to carry any passengers.

( ) 5. The tween deck vessel is suitable for general cargoes, while the single deck vessel is fit for bulk cargoes.

( ) 6. Horizontal loading and vertical loading are used in tween deck vessels.

( ) 7. Measurement by volume and measurement by weight are two ways of ship measurements.

( ) 8. Bale capacity is larger than grain capacity.

( ) 9. A vessel is allowed to draw more water during winter.

( ) 10. The deadweight tonnage is closely connected with the loaded displacement and light displacement.