It is crucial to learn the various ways of expressing a ship’s size and dimensions so that one ship can be compared against another or the suitability of a ship for a suitable trade may be assessed.
These are the actual weights of the ship and its cargo.
Light Displacement Tonnage (LDT): is the actual weight of the ship as built and commissioned excluding fuel, stores, crew etc. Light Displacement Tonnage (LDT) is of limited commercial importance except when a ship is irrevocably being sold for scrapping. Then, Light Displacement Tonnage (LDT) specifies the weight of metal that the shipbreaker is acquiring. Light Displacement Tonnage (LDT) is also used in draft survey calculations.
Total Displacement Tonnage (TDT): is the Light Displacement Tonnage (LDT) plus the weight of all fuel, stores, lubricants, crews, and everything else that makes the ship ready to go to sea. The weight of all fuel, stores, lubricants, crews, etc. are known collectively as “constants” and would total on an average size vessel of about 50,000 DWAT about 3,000 tons. Total Displacement Tonnage (TDT) is used for describing the size of military ships.
Deadweight Cargo Capacity (DWCC): the weight of cargo that can be carried by the ship when fully loaded to the summer load-line.
Deadweight All Told (DWAT): the total weight of a fully-loaded ship i.e. Deadweight Cargo Capacity (DWCC) plus total displacement.
Ship Pseudo Tonnages
These two measurements (Gross Tonnage and Net Tonnage) are called ‘tonnages’, however, Gross Tonnage and Net Tonnage are cubic measurements based on an international formula (International Tonnage Convention) for comparing the overall size of ships. Gross Tonnage and Net Tonnage are commonly used by ports and statutory organizations as the basis of levying dues or taxes on ships.
Gross Tonnage (GT): the internal cubic measurement of all the enclosed spaces within the ship’s hull and superstructure. Calculated to a formula one GT is a little less than 3 Cubic Meter. Gross Tonnage (GT) is a convenient way of measuring the total bulk of the ship and therefore is often used to express passenger ships and ferries.
Net Tonnage (NT): the Gross Tonnage (GT) less those spaces such as engine room and crew accommodation that cannot be utilized for commercial and revenue-earning purposes.
Ship Measurements are the critical dimensions of the ship which must be recognized to decide whether the ship can safely enter locks, canals, docks, etc.
Length Over All (LOA): the length of the ship from the foremost point on the bow to the most aft point on the stern.
Beam: the overall width of the ship.
Moulded Depth: the height of the ship from the bottom of the keel to the top of the main deck.
Draft (Draught): the distance from the waterline to the bottom of the keel. Draft (Draught) determines the minimum depth of water the ship needs to be afloat.
Air Draft: the distance from the water line to the highest point on the ship’s superstructure, commonly the top of the mast. Air Draft is critical when making passage under bridges or cross river power cables etc.
Ship Cargo Measurements and Capacities
Grain Cubic Capacity: the measurement in cubic meters or cubic feet of the internal capacity of all cargo spaces when they are loaded with a free-flowing cargo such as bulk grain. Grain Cubic Capacity measurement includes such spaces as the recess between the frames of the ship’s hull.
Bale Cubic Capacity: the measurement in cubic meters or cubic feet of the internal capacity of all accessible cargo spaces if the cargo spaces (holds) are full of baled cargo. The smaller spaces and recesses are excluded from Bale Cubic Capacity.
Lane Metres: Roll on-Roll off (Ro-Ro) ships have their cargo spaces divided into lanes in which vehicles are stowed one behind the other. Lane Metres is the total length of all the lanes in meters. Lane Metres is used to describe the cargo capacity of the ship.
TEU (Twenty-Foot Equivalent Unit): regularly container ships are expressed in terms of the number of containers they can carry. TEU (Twenty-Foot Equivalent Unit) is the common way of referring to a container ship’s size.
In day-to-day dealings with ships, three (3) different types of plans are encountered:
- General Arrangement (GA) Plans
- Capacity Plans
- Stowage Plans
General Arrangement (GA) Plans: present the main parts of the ship from a side view as well as from above for each deck. Regularly, General Arrangement (GA) Plans include one or more cross-sections. Simplified General Arrangement (GA) Plans are used in some of the descriptions of ships that follow. Additionally, General Arrangement (GA) Plans show the load-line and the ship displacement scale. Ship Displacement Scale illustrates the distance by which the ship will sink into the water for each tonne loaded on board.
Capacity Plans: similar to General Arrangement (GA) Plans but expressly illustrate full details of the hatches, cargo-carrying spaces (holds), bunker, ballast, and freshwater tanks.
Stowage Plans: illustrate where each parcel of cargo is placed in the ship holds and the orientation of the ports. Stowage Plans are crucial for the stability of the ships.
Basic Ship Layout
The ship hull includes steel frames covered with steel plates. The hull is divided at intervals into compartments that are separated by watertight bulkheads. Ordinarily, the first compartment in the bow comprises a water tank (forepeak tank) and a storage area (forecastle – fo’csle) because this compartment is not a suitable shape for carrying cargo. The next compartments are the cargo holds which may number from one to eight, depending on the size and type of ship. Traditionally, the ship’s cargo holds are numbered for reference from bow to stern. Each cargo hold is accessed through a hatch which is an opening in the main or weather deck. In tween-deck ships, there is an intermediate decks in the holds. Modern ships are equipped with cranes or gantry-cranes for cargo handling. Between the floor of the hold (ceiling) and the outer hull of the ship is a space named the double bottom. Double bottom is used for the storage of fuel, water, or ballast. Modern ships carry fuel or ballast in wing tanks. Wing tanks are between the hold and the side of the ship. The engine room is at the aft of the holds. The engine room comprises the main engine and auxiliary engines. The above deck over the engine room is the accommodation for the crew members and storage spaces. The propeller shaft runs from the engine room through the stern to the propeller which is in front of the rudder. Each ship is earmarked a load-line mark which indicates the maximum draft to which the ship can be loaded. A ship can be loaded to a deeper draft with safety in more moderate weather, different marks are allocated to various seasons and also to allow for loading in freshwater which is less buoyant than saltwater. Draft marks are painted on the ship’s hull at the bow, stern, and amidships by the load-line.
Today, the remarkable majority of ships are powered by diesel engines. Modern ships are dual powered by LNG-diesel engines. Ships are fitted with the fuel preparation equipment, allowing ships to burn low-cost residual Intermediate Fuel Oil (IFO) bunker fuels efficiently and without harm to the engines. Marine Diesel Oil (MDO) or a blend of Intermediate Fuel Oil (IFO) is used to power the auxiliary engines and also the main engine when the ship is entering, leaving port or while maneuvering in confined waters. The response of more former engine design to a change of throttle position is very slow when burning Intermediate Fuel Oil (IFO) bunkers. This may affect the safety of the ship when an instantaneous response by the engine is required. Therefore, the fuel is switched from Intermediate Fuel Oil (IFO) to Marine Diesel Oil (MDO) for instantaneous response.
Ships are employed either as liners or as tramps. Liner ships trade according to a schedule, between designated ports or areas. Liner ships’ cargoes are made up of various consignments from numerous shippers, usually manufactured or semi-manufactured goods. In liner shipping, freight rates are customarily published in a tariff and may alter according to the commodity. In liner shipping, the trading area defines the type of ship which may be a container ship, a Ro-Ro, or a combination of two types. Today, instead of general-purpose ships, modern MPP (Multi-Purpose Ships) are used in liner trades. In liner shipping, the standard document covering the contract of carriage will be a Bill of Lading (B/L). Tramp ships trades where the business demands it. Commonly, tramp ships carry one commodity or one commodity by different grades. Frequently, tramp ships carry raw materials, and there is commonly only one shipper. In tramp shipping, the contract of carriage is a Charter-Party. In tramp shipping, charterers may prefer a Voyage Charter basis and pay Freight per ton of cargo for an agreed quantity from port A to port B. Alternatively, charterers may prefer a Time Charter basis and pay Hire per day for the use of the ship for an agreed trip or period which can be merely weeks, months, or years. The rate of Freight or Hire is freely negotiated between charterers and shipowners. The rate of the Freight or Hire level will depend upon the strength or weakness of the shipping market at the time of signing the contract.
There are three (3) main types of ships:
- Dry Cargo Ships
- Miscellaneous Ships
1- Dry Cargo Ships: are planned to transport dry, non-liquid cargoes. Dry Cargo Ships are sub-divided into:
- a- Bulk Carriers
- b- Multipurpose Ships
- c- Container Ships
- d- Ro-Ro Ships (Roll-on/Roll-off Ships
- e- Refrigerated Ships (Reefers)
a- Bulk Carriers: are the simple transportation boxes of the oceans. Bulk Carriers range in size from the smallest coaster of about 250 DWT up to the largest ore carriers of 400,000 DWT. Commonly, bulk carriers have unrestricted holds with large hatches to provide for fast loading and discharging of cargo. Bulk carriers are essentially designed for the carriage of bulk cargoes, such as ores, grains, coal, fertilizers, etc. Consequently, bulk carriers’ holds are built to be self-trimming.
Self-trimming ships’ cargo hold is shaped in such a way that when loaded into the holds the cargo trims itself evenly over the area of the hold without resorting to expensive manual labor to achieve this. Before-mentioned even distribution is necessary for two reasons. The first reason is to assure the highest utilization of the ship’s cargo holds. When the ship is loaded through a small hatch, the cargo would adopt a conical shape. The shape of that cone would be dictated by the natural angle of repose of the material concerned. The angle of repose varies broadly from commodity to commodity such as bulk cement, sugar, lentils, etc. The point of a cone of cargo protruding through the hatchway long before the hold is full. The second reason for trimming the cargo across the whole of the hold is one of safety. In a ship’s cargo hold, even distribution of cargo is vital not only to assure that the ship steams on an even keel but also to avoid uneven stresses in the structure of the ship. Consequently, self-trimmer ships require the most spacious hatch size commensurate with safe construction. Therefore, the loading machine spread the cargo evenly and so in charter parties, a clause obliging the shipper to ensure that the cargo is spout trimmed. Furthermore, self-trimming describe the angle between the vertical side of the ship and the bottom of the hold. Self-trimming does not solely refer to the loading of a ship because grabs are regularly used to discharge ships. Therefore, grabs are not able to reach right into the angle between the vertical side of the ship and the bottom of the hold. Modern bulk carriers are erected with a sloping section that is reaching fore and aft for the whole length of the hold. The sloping steel plates trim the cargo into the square of the hatch within reach of the grab, so minimizing the hand shoveling. Additionally, the sloping sections are utilized for ballast spaces.
Angle of Repose: when loading a bulk carrier, different materials also have different stability. If the cone of bulk cargo is left un-trimmed, the cone of bulk cargo quickly collapses. If the cone of bulk cargo simply settled down to a level surface, all well and good but if it did its settling when the ship was heeling to one side then the ship could assume a dangerous list. Not only is this another reason for the cargo to be at least spout trimmed at loading port but for some commodities, it does not end there. Some bulk cargoes such as grain, tend to slide about almost like a fluid. Therefore, even swift buffeting could cause a serious list even if the cargo had been leveled carefully at the time of loading. In the old days, the bulk cargo shifting problem was overcome by the use of shifting boards. Shifting boards are vertical wooden partitions that divide cargo holds into several smaller holds what would otherwise be one large free surface. Shifting boards prevent cargo shifting that causes a list. In the old grain charter parties, particularly in the short-sea trades, reference is found to the shippers having to provide up to 10% of a grain cargo in bags for safe stowage. As an alternative to shifting boards, the bagged cargo would be laid on top of the bulk to stop it shifting. Modern bulk carriers approach the angle of repose problem differently by shaping the hold to decrease the free surface at the top of the cargo. The sloping steel plates are constructed between the deck and the side of the ship. The aforementioned shape has the effect of diminishing the free surface within which the fluid-like action can take place. Additionally, these sections are utilized for ballast water when required and the ability to put some ballast above the waterline instead of all of it in the bottom of the ship makes for a much more comfortable ballast passage. During the ballast passage, if all the ballast weight is at the bottom of the ship, a pendulum effect is generated when the ship confronts any kind of heavy weather. Hence, crew members refer to such a condition as the ship being ‘very stiff’ that is not only uncomfortable but also generates critical stresses in the ship’s framework. On the other hand, if there is abundant weight at the wing tanks of the ship during ballast voyage, the ship’s rolling shifts become excessive and the crew members refer to such a condition as the ship being ‘very tender’.
Types of Bulk Carriers by Size:
- Mini Bulk Carrier (3,000 DWT – 10,000 DWT)
- Handysize Bulk Carrier (10,000 DWT – 35,000 DWT)
- Handymax Bulk Carrier (35,000 DWT – 50,000 DWT)
- Supramax Bulk Carrier (50,000 DWT – 60,000 DWT)
- Ultramax Bulk Carrier (60,000 DWT – 65,000 DWT)
- Panamax Bulk Carrier (65,000 DWT – 85,000 DWT)
- Post-Panamax Bulk Carrier (85,000 DWT – 110,000 DWT)
- Capesize Bulk Carrier (110,000 DWT – 200,000 DWT)
- Very Large Bulk Carrier (200,000 DWT – 400,000 DWT)
Furthermore, bulk carriers are sub-categorized according to port or area restrictions such as Seawaymax, Malaccamax, Setouchmax, Dunkirkmax, Kamsarmax, Newcastlemax.
On medium and small bulk carriers, cranes improve flexibility by equipping ships to trade to places where shore facilities are not adequate.
Modern handysize, handymax, supramax, and ultramax bulk carriers are outfitted with cranes. Panamax and post-panamax bulk carriers seldom have their cranes as such bulk carriers tend to trade between advanced ports where loading is by shore gantry cranes with purpose-built devices such as spouts and discharge is by grabs or some other equipment designed for rapid unloading. In some dedicated trades bulk carriers are fitted with conveyor systems, so-called self-unloader bulk carriers.
Ore Carriers are purpose-built bulk carriers for only the iron ore trades. Regular bulk-carriers are built with enough cubic capacity to carry cargoes such as grain and coal which require at least 45 cubic feet per ton weight of cargo. This is far too much space for a heavy commodity like iron ore. Not only does a dense material like iron ore, only occupying the bottom half of the holds make a normal bulk carrier very ‘stiff’ but with a bulk-carrier one has simply built far more ship than is required for iron ore trade. There is no point in wasting all that steel providing space that will never be utilized.
Combination Carriers: some shipowners find the bulk-carrier too limited in a few types of trades, therefore the naval architects designed various variations of bulk carriers. A small amount of space is required for iron ore which could allow for a substantial amount of additional capacity and still be within more or less the same overall dimensions as a bulk carrier. Consequently, that spare space was designed as tankage and so the Ore/Oil Carrier was formed. Ore/Oil Carrier allows the shipowner to operate in whichever trade gives the best return. Additionally, Ore/Oil Carrier decrease the ballast passage, by loading one way with iron ore and then only a short ballast run top load another way with oil, or vice versa. Later on, naval architects designed the OBO(Ore/Bulk/Oil) Carrier.
Con-Bulker (Container/Bulk Carrier) was designed and built as a combination carrier. However, the consequent sophistication of the container trades has resulted in limited use of Con-Bulker (Container/Bulk Carrier) today.
Laker Ship (Lake-Fitted Bulk Carrier): bulk carrier capable of trading into the Canadian-USA Great Lakes where there is a beam restriction in the St. Lawrence Seaway locks of 23.15 meters and a draft restriction of 26 feet in Fresh Water. About 30,000 DWT partly loaded because of the draft limitation to about 19,000 DWT.
b- Multipurpose Ships: are the modern replacements of the traditional Cargo Ships. Multipurpose Ships are designed to be able to take bulk cargo, bagged cargo, containers, and general cargo with equal ease and, if necessary, at the same time. Generally, Multipurpose Ships are 5,000 DWT up to 25,000 DWT and have two decks (tween-decker). Multipurpose Ships have large hatches and are equipped with cranes to lift containers and heavy cargoes. Lately, Multipurpose Ships have been replaced by Container Ships and Ro-Ro Ships.
c- Container Ships: are designed to carry containers only. Container Ships’ holds are cellular (vertical frames, or guides) into which the containers are slotted. Commonly, Container Ships can handle containers of 20 or 40 feet in length. The size of the Container Ships is expressed by the number of TEU (Twenty-Foot Equivalent Units) she can carry. Most small-sized Container Ships are self-sustained (cargo gear on board to load and discharge containers). Large Container Ships provide electric power outlets for refrigerator-containers. Extremely specialized Container Ships for trades where there is a high demand for chilled cargo are equipped with central refrigeration machinery which delivers cooled air to insulated containers through porthole’ in the units although this system is now being phased out. Container Ships are simply open hold ships which mean that the hatches give access to the whole of the hold-area. In Container Ships, the cell guides are constructed in the holds and no lashings are required below decks. Small Container Ships’ hatch covers of the holds are either slab or pontoon type and are fitted out to carry containers. Below deck of Container Ships, the containers are secured by the cellular arrangement but on the hatch covers, containers must be lashed to prevent movement. The modern deep-sea gearless Container Ships transport between 3,000 TEU – 23,000 TEU. The hatchless Container Ships are erected with cell guides that are extended above the main deck level so that on-deck lashing is also unnecessary. In some Container Ship design, there is also a heightened and streamlined foc’sle (fore-castle) with a wave breaking device designed to keep sea-water away from the main deck of the ship. In both Container Ship designs, the aim is to avoid the extra labor and delay involved in removing and replacing hatch covers as well as the tiresome securing of the containers carried on deck. Today, most of the general cargo is moved in containers. One of the most significant accomplishments of containerization is the efficiency of cargo operations by drastically reducing the cost of handling and transportation. There are two main trades in the container shipping market: East-West and North-South. In container shipping, China has the biggest volume in (Twenty-Foot Equivalent Units) lifts annually. The size of all other merchant ships are commonly described in DWT (Deadweight Tons). However, the capacity of container ships is customarily expressed in terms of the number of containers she can carry. Standard container sizes are either 20 feet or 40 feet long, so the capacity of container ships is expressed in 20 TEU (Twenty-Foot Equivalent Units), or 40 FEU (Forty-Foot Equivalent Units). 20 TEU (Twenty-Foot Equivalent Units) is used to present the container ship’s container carrying capacity. Each container space is called a slot. Smaller Container Ships are used as Feeder Container Ships, feeding the hinterland around major container terminals with loaded containers inbound from abroad, before feeding containers for export back to the container terminal on the return route. Feeder Container Ships serve less sophisticated container ports. Therefore, Feeder Container Ships may well be geared (gantry cranes), enabling Feeder Container Ships to load and to discharge containers with their shipboard equipment.
d- Ro-Ro Ships (Roll-on/Roll-off Ships): are suitable solely for cargo which can be driven on/off the ship, such as cars, lorries, and cargo on trailers (road trailers, mafi trailers). The size of a Ro-Ro Ships (Roll-on/Roll-off Ships) is measured in lane meters, which indicate the total length of the marked parking lanes available on board. The size of the entrance ramp of Ro-Ro Ships (Roll-on/Roll-off Ships), its length, width, height of the openings leading into the hull, and the total weight it can carry is also important. Additionally, so-called Pure Car Carriers (PCC) fall into this category.
Ro-Ro Ships (Roll-on/Roll-off Ships) Access Equipment
Ramps and Bow-Stern Doors: unique features of Ro-Ro Ships (Roll-on/Roll-off Ships) are their ramps. Ramps are employed externally to dispatch wheeled vehicles between quay and ship. Additionally, inside the Ro-Ro Ships (Roll-on/Roll-off Ships), ramps provide access from deck to deck. Ro-Ro Ships’ (Roll-on/Roll-off Ships) external ramps has three (3) types:
- Axial Bow and Stern Ramps
- Angled Quarter Ramps
- Slewing Ramps
Ro-Ro Ships’ (Roll-on/Roll-off Ships) internal ramps can either be fixed or moveable, serving two or more decks.
The axial stern ramp can also serve as a stern door where the ramp is short. Alternatively, when the axial ramp is long then a separate watertight door is used, closing before the ramp being raised.
Bow openings provide access to cargo spaces through the forward end of the ship and there are two (2) types commonly in use:
- Bow Visors
- Bow Doors
1- Bow Visor: is a portion of the ship’s bow, connected at the weather deck level with hinges, and is lifted upwards when the entry is required. The separate inner watertight door is fitted along with an axial ramp.
2- Bow Doors: twin bow clamshell doors are fitted in the plating around the stem and are hinged to open outwards from the center-line. Bow Doors operation, sealing, and fastening systems are similar to that of a bow visor. Additionally, Bow Doors have an internal watertight door and axial ramp.
Ro-Ro Ships’ (Roll-on/Roll-off Ships) Internal Ramps and Lifts
Less space is wasted when a ship is fitted with a moveable ramp. Alternatively, elevators or lifts are erected for shifting vehicles from one deck to another. The advantages of elevators over ramps are that elevators require less internal space. However, the disadvantages of elevators over ramps, elevators are more complex in way of electric and mechanical equipment and hydraulics. If elevators are too close, maneuvering space is limited. Additionally, unlike ramps, elevators break down and suspend the operation.
Types of Ship Elevators:
- Wire Operated Elevator
- Chain Operated Elevator
- Scissor Lifts Elevator
Side Loaders: are located in some Ro-Ro Ships (Roll-on/Roll-off Ships) and Side Loaders’ purpose is to increase the main cargo accesses. Side doors are most practical on ships when their draft remains fairly constant. Hence, side doors are at the quay level. There are numerous designs of side doors and the side door design depends on the type of ship and cargo.
e- Refrigerated Ships (Reefers): are very specialized ships. Refrigerated Ships (Reefers) have two or more decks. Refrigerated Ships (Reefers) are ocean-going deep-freezers. Refrigerated Ships’ (Reefers) holds are insulated and have a comprehensive compressor system with which Refrigerated Ships (Reefers) keep the temperature in the holds at the required level. In Refrigerated Ships (Reefers) trade, different cargoes requiring different temperatures. Refrigerated Ships (Reefers) are customarily very fast ships (around 23 knots), therefore reducing the transit time for the frozen or chilled cargoes. Additionally, Refrigerated Ships (Reefers) have small hatches and cargo gear designed to operate speedily, so limiting the time the cargo is exposed to the weather. The size of a Refrigerated Ships (Reefers) is normally expressed by the volume of the ship’s holds expressed in cubic feet or cubic meters.
2- Tankers: comprises any ship designed to carry liquid cargoes and ranges from the tiniest tank barge up to the ULCC (Ultra Large Crude Carriers). Tankers transport crude oil but also outfitted to transport clean petroleum products (refined or semi-refined) or a wide variety of other liquid cargoes. In describing oil cargoes the term dirty refers to crude oil cargoes and clean refers to refined or semi-refined petroleum products. Petroleum spirit, kerosene, etc. are naturally described as clean whilst products at the other end of the refining scale, such as heavy fuel oil, are referred to as dirty. A crude carrier only carries a quite limited number of grades of oil. However, clean products or chemical tankers might well have the capability of carrying a large number of different products at one time. This parceling of petroleum product cargoes is a traditional feature, especially of chemical tankers, designed to carry several different, and often incompatible liquids carried in separate tanks. Parceling demands a complex pumping and pipework system to prevent the intermingling of cargoes. Many liquid chemicals react with steel, therefore chemical tankers’ tanks are constructed of stainless steel or coated with special paints such as epoxy or even with a rubber. Liquid cargoes such as liquid sulfur, hydrochloric acid, vegetable oils, wine are now carried in bulk, therefore the range of carrying capabilities of chemical tankers has to be wide. Furthermore, LPG (Liquid Petroleum Gas) and the LNG (Liquid Natural Gas) carriers are placed into the tanker category. All tankers are equipped with pumps by which tankers discharge their cargoes. Additionally, tankers are also equipped with an advanced cargo tank cleaning machinery, because tanks need detailed cleaning. In oil tankers, to circumvent the risk of explosion it is important to decrease the oxygen and the oil vapor content of the tanks before cleaning the tanks. Decreasing the oxygen and the oil vapor content of the tanks is done by pumping Inert Gas (the exhaust gasses from the main engine) into the tanks. Modern crude oil tankers are equipped with a Crude Oil Wash system which also eliminates the need to dispose of large quantities of dirty ballast. In chemical tankers, tank cleaning can be even more complex. Some tankers are equipped with cargo heating coils, required when the cargoes become too viscous to pump or even solidify at ambient temperatures. Tankers are equipped with a Hose Crane for handling the loading and discharging hoses. Aframax tankers are tankers that are built just under 80,000 DWT. Aframax tankers origin go back to a council established at the behest of the major oil companies called The London Tanker Brokers Panel which periodically calculated Average Freight Rate Assessments (AFRA). These tanker rates were used for a variety of purposes even including long-term contracts in which the parties agreed to relate the tanker freight rate to the current AFRA in some way. One category of size for which an AFRA was calculated was 45,000 DWT – 79,999 DWT and there was a big drop in rate after that for the 80,000 DWT – 159,999 DWT size. Consequently, prudent shipowners ordered tankers built of around 80,000 DWT to ensure that, their tankers did not exceed 79,999 DWT. The London Tanker Brokers Panel still exists but is now independent of the oil companies. The London Tanker Brokers Panel calculates AFRAs commercially for anyone requesting to use the service. Suezmax tankers are less than about 150,000 DWT and capable of transiting the Suez Canal. VLCC (Very Large Crude Carrier) is a crude oil tanker of between about 200,000 DWT – 300,000 DWT. ULCC (Ultra Large Crude Carrier) is a crude oil tanker over about 300,000 DWT.
3- Miscellaneous Ships: encompasses everything else that floats except warships and private yachts.
Tugs: ranges from the deep ocean-going salvage tugs which are also used to tow oil rigs around the world, to the small harbor tugs. The power of tugs is expressed by the Brake Horse Power (BHP) or by the Bollard Pull (BP).
Oil Rigs: used in off-shore oil fields. Oil Rigs are customarily divided into two categories, drilling and production platforms.
Off-Shore Ships: have a large flat cargo carrying platform aft built particularly to service oil rigs. The more powerful Off-Shore Ships are called Anchor Handling Ships.
Cruise Ships (Passenger Liners): are designed with short 7-14 day trips with as many ports of call as possible. Cruise Ships have a particularly shallow draft, which enables them to enter or get as close as possible to as many exotic ports as possible.
Ferry: is designed to utilize between the same two ports as quickly as possible. Ferries are almost all Ro-Ro Ships (Roll-on/Roll-off Ships) and are designed for the fast loading and unloading of the passengers, cars, and lorries. Ferries range in size from the super ferries down to the cross-river or harbor ferry.
Deciding Size of a Ship
Calculated on the cost per ton-mile basis, by far the cheapest form of moving cargoes is by sea. The larger the ship, the cheaper the carrying cost per ton will be. Consequently, the shipowner wants to buy the largest possible ship to be able to secure the benefit of the economy of size. However, there are two limitations. Firstly, the shipowner wants a ship that is as flexible as possible. In other words, shipowner wants a ship that can enter and operate in as many ports as possible, the majority of ports in the world have some kind of draft restrictions and infrastructure restrictions which will reduce the dimension of ships. Secondly, due to trade patterns, shippers of the cargo is only able to ship their cargoes in certain restricted sizes. Therefore, while a VLCC (Very Large Crude Carrier) might be the ideal article for shipping crude oil from Saudi Arabia to Japan, it would be unlikely to be used for carrying oil from Amsterdam to London. Likewise, 23,000 TEU container ships are employed on the Far East-USA trade but not on intra-Mediterranean routes. As result, a shipowner wishes to acquire the largest possible ship commensurate with a forecasted trading pattern.
After deciding on type, size, and trade, the shipowner must then contemplate how the ship will be managed. The role of the ship manager is to translate the shipowner’s ideas into reality so that the ship can execute the tasks set by the shipowner efficiently, safely, and profitably. Ship Management is either carried out by the shipowner’s organization (In-House Ship Management), or an independent organization is employed under contract (Third-Party Ship Management). In either case, the Ship Management’s duties are similar.
Ship Management’s duties encompass registration and documentation of the ship as required by national and international authorities. Ship Management’s duties incorporate crewing, victualling, stores, spare parts, maintenance, and repairs. Ship Management arranges the insurance and the handling of claims and recoveries. Ship Management appoints surveyors and a host of other tasks intended to keep the ship running properly. In sum, it is the ship manager’s responsibility to ensure that the ship is “tight, staunch and strong, and in every way fitted for the voyage”.
Ship’s Cargo Handling Equipment
Derrick: is the most simplistic form of cargo handling equipment erected on board of a ship. Derrick was developed from the spars of sailing ships as a means of lifting and transferring cargo from ship to quay and vice versa. Derrick is a mast and a swinging boom which allows a load to be lifted and moved sideways. Derricks have essentially been replaced by cranes or gantries on modern ships. Modern derrick designs are:
- Hallen Derrick
- Velle Derrick
- Stuelcken Derrick
Cranes: after the late 1960s more ships began to operate with cranes. In the beginning, cranes were pricey compared with derricks. Furthermore, cranes were slower to operate. Cranes’ capacity and outreach were limited and cranes required very experienced drivers. With the increase in the carriage of unitized cargo, the practical value of the cranes’ accurate spotting ability became more obvious. Consequently cranes, often having a capacity of 25 – 40 tonnes SWL (Safe Working Load) and sufficient outreach to service two holds as well as overside, are now generally encountered on many ships. Cranes are installed between two hatches, so can operate on two hatches.
Gantry Cranes: some types of bulk carriers, container ships, ro-ro ships are equipped with traveling gantry cranes which straddle the full width of the ship and move along the weather deck on rails situated outboard of the hatch coamings. Gantry gantries can only be productively operated in full form ships with a wide parallel body. The hoist can be slewed to port and starboard and plumb over any part of the area under the gantry and with the gantry being able to move fore and aft, all of the weather deck can be utilized for stowing cargo. Large container ships are normally handled by shore terminal equipment, but gantry cranes can be seen infrequently either in large ships as an interim measure while port facilities are still being developed or in smaller container ships when operating to less developed ports. Gantry cranes are installed on LASH (Lighter Aboard Ship) Ships which are designed to combine large ocean-going mother ships with craft small enough to reach restricted berths.
Ship cranes and gantry cranes are not the only equipment installed to facilitate discharge. With the greater specialization of ships for particular commodities or trades, a range of highly specific systems have been designed to discharge bulk cargoes into dedicated shore installations such as conveyor-belt systems, elevators, and suction systems.