10/9/2015Devron S. Newman - GSK 1 General Ship Knowledge Unit 3: Ship Types ML 301.1(3.0)

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General Ship Knowledge Unit 3: Ship Types ML 301.1(3.0)

Lessons in Unit 3 – Ship TypesLesson 1: Bulk Carriers and Tankers

Lesson 2: General Cargo, Container and Ro/Ro vessels.

Lesson 3: Specialized vessels (lumber ships; passenger ships; reefers and car carriers)

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M/V Charles Martin; built 1983; DWT 37,604;tons GT 24,877 tons

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Lesson 1: Bulk Carriers and Tankers

Bulk carriers are single deck vessels and generally have

5 to 9 hatches equipped with sliding hatch covers.

They have double bottom tanks with the tank top rising

outwards to the ship’s side to form hoppers. Wing tanks

are provided on either side which are used as ballast

tanks as well as for loading grain cargo sometimes.

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Lesson 1: Bulk Carriers and Tankers

One or two holds may be designated as ballast holds to carry water ballast if required for stability purposes in rough weather. The machinery spaces and accommodation are aft and the cargo space configuration depending on the types of cargoes; for example iron ore carriers have different hold and ballast tanks configuration.

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M/V “Berge Stahl”Transports iron ore from Brazil to Rotterdam.Length 343m; Beam 63m; Draft 25mDWT 365,000 tonsTakes 4 to 5 days for unloading

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Deep Sea Bulk Carrier - gearless

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Geared bulk carrier

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Loading/Discharging Dry Bulk Cargo

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A large bulker in the seaway

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Hatch covers and cranes in secured position

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Lesson 1: Bulk Carriers and Tankers

Bulk carriers normally carry single commodity for the single shipper at prevailing freight rates agreed between the owner and the shipper. On long hauls there is considerable reduction in the per ton-mile cost of transportation.

Bulk carriers today typically range from 20,000 to 300,000 tonnes deadweight with speeds from 13 to 16 knots.

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Lesson 1: Bulk Carriers and Tankers

For commercial purposes the bulk carriers have been

categorized as:

VLBC above 200,000DWT

Cape size 130,000 – 150,000DWT

Panamax 75,000 – 80,000DWT

Handymax 30,000 – 47,000DWT

Handy size 20,000 – 30,000DWT

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Bulker M/V Selendang Ayu

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Lesson 1: Bulk Carriers and TankersTankers: Vessels carrying liquid cargoes in bulk are termed astankers. They carry dirty oil (crude), clean oils (refined petroleumproducts); chemicals; liquefied gases.Tankers have long hulls with small freeboard. These ships have

singlebottom under the cargo tanks and the engine room is aft of the cargotanks. The cargo space is divided into tanks with transverse andlongitudinal bulkheads. The longitudinal bulkhead safeguardagainst free surface effect and sloshing. Cargo tanks are separatedby cofferdams to prevent leakage into water tanks and machineryspace. Because of the fire hazard associated with oils and its vapour,effective separation from the accommodation and machineryspace is of paramount importance.

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Jahre Viking – world’s largest ship ULCC1504 ft long; 226 ft. wide

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Crude Oil Tanker

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Profile of a Crude Oil carrier

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A section of the tank arrangement

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Lesson 1: Bulk Carriers and Tankers

The aft cofferdam is used as the pump room which has pumps for discharge and transfer of cargo. For commercial purposes tankers have been categorized as:

ULCC > 400,000DWT VLCC 200,000 – 400,000DWT Suezmax up to 145,000 DWT Medium range 45,000 – 70,000DWT General purpose up to 30,000DWT

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Lesson 1: Bulk Carriers and Tankers

The biggest hazard associated with tankers is that of fire and explosion.

Product tankers: These are used for transporting refined oil products. They range from about 40,000 – 50,000DWT and more than one type of product can be carried simultaneously.

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Crude Oil Tanker

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Gas Carriers Gas carriers range in capacity from the

small pressurised tankers of between 500 and 6,000 m3 for shipment of propane, butane and the chemical gases at ambient temperature up to the fully insulated or refrigerated seagoing tankers of over 100,000 m3 capacity for the transport of LNG and LPG. Between those two distinct types is a third tanker type – semi pressurised gas carrier.

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LNG Carrier

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Profiles

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Gas carriers

A nominal 3/8-in.-thick primary membrane fabricated of stainless steel or Invar. Note that the latter, an alloy containing 36% nickel and 64% iron, has a very low coefficient of thermal expansion. 

A nominal 3/8-in.-thick secondary membrane of alloy steel separated from the primary membrane by about a foot of perlite insulation. Perlite is a naturally occurring, lightweight volcanic glass. 

Another foot or so of perlite separates the secondary membrane from the nominal 1-in.-thick inner hull.

The outer hull (1 to 1½ in. steel plate) forms a ballast tank with the inner hull. The inner and outer hulls are separated by a distance of about 8 to 10 ft.

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Gas Carriers

These very flexible tankers are able to carry many cargoes in a fully refrigerated condition at atmospheric pressure or at temperatures corresponding to carriage pressure of between five and nine bar. The movement of liquefied gases by waterways is now a mature industry, served by a fleet of many tankers, a network of export and import terminals and a wealth of knowledge and experience on the part of various people involved.

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Gas Carriers A feature almost unique to the gas carrier is

that the cargo is kept under positive pressure to prevent air entering the cargo system. This means that only cargo liquid and cargo vapour are present in the cargo tank and flammable atmospheres cannot develop.

Furthermore all gas carriers utilise closed cargo systems when loading or discharging, with no venting of vapour being allowed to the atmosphere.

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Boil Off Gas

 Neither type of storage system is fully effective and, the gas cargo boils off at the rate of around 0.15 per cent per day. Ordinarily this would be considered a negative factor, but for the fact that most LNG ships are designed to make use of this tendency and are equipped with gas turbine engines that are mostly fuelled by the Boil Off Gas (BOG). For this reason LNG carriers only need to take on bunkers for auxiliary engines and for running the boilers for the turbines in port.

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Cross Sectional Diagram

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Gas carriers In the LNG trade, provision is always

made for the use of a vapour return line between tanker and shore to pass vapour displaced by the cargo transfer. In the LPG trade this is not always the case as, under normal circumstances during loading, reliquefaction is used to retain vapour on board. By these means cargo release to the atmosphere is virtually eliminated and the risk of vapour ignition is minimised.

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Gas carriers

Gas carriers are divided into two main groups.

Liquefied Petroleum Gas (LPG) Carriers, which are designed to carry mainly butane, propane, butadiene, propylene, vinyl chloride monomer (VCM) and are able to carry anhydrous ammonia.

Liquefied Natural Gas (LNG) Carriers, which are designed to carry liquefied natural gas (which is mostly methane).

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Gas Carriers

Gas carriers are classed in three types based on hazard potential:

i) type 1G, designed to carry the most hazardous cargoes

ii) type 2G , designed to carry cargoes having a lesser degree of hazard

iii) type 3G, designed to carry cargoes of the least hazardous nature.

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Gas Carriers

Gas carrier typesAll gas cargoes are transported in liquid form and, because of their physical and chemical properties, they are carried either at:- pressures greater than atmospheric, or at- temperatures below ambient, or a combination of both.Therefore, gas carriers are generally grouped as follows:

i) Fully Pressurised

ii) semi-pressurised and refrigerated

iii) fully refrigerated

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Gas carriers

LNG is mainly methane and ethane. LNG ships carry their cargo at -161°C, at a relative density of approximately 0.600 with a volume contraction ratio of 1 in 600. LNG cargo is carried at ambient pressure.

LPG is mainly propane and butane. LPG ships carry their cargo at -42°C, at a relative density of approximately 0.500 with a volume contraction ratio of 1 in 300. LPG cargo may be carried under pressure.

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Gas Carriers

The cargo tank construction of LNG and LPG ships can be of (a) prismatic design (b) membrane design or (c) spherical design. Materials used for these cargo tanks can be aluminium, balsa wood, plywood, invar or nickel steel, stainless steel, with pearlite and polyurethane foam.

Because of the demand for insulation at these extremely low cargo temperatures, the first cost of these specialised ships are extremely high. A very high standard of workmanship is required for the building of these types of vessel.

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Gas carriers

Their capacity ranges from 75000 to 138000m3 of gas, their LBPs up to 280 m and their Br. Mld from 25 to 46 m. When fully loaded, their CB can be 0.660 up to 0.680 with service speed in the range of 16–20.75 kt. They are fine-form vessels .

Gas carriers must comply with the standards set by the Gas Codes or national rules, and with all safety and pollution requirements common to other tankers.

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Gas carriers

Safety features inherent in the tanker design requirements have helped in the safety of these tankers. Equipment requirements for gas carriers include temp and pressure monitoring, gas detection and cargo tank liquid level indicators, all of which are provided with alarms and ancillary instrumentation. The variation of equipment as fitted can make the gas carrier one of the most sophisticated tankers afloat today.

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Gas carriers

There is much variation in the design, construction and operation of gas carriers due to the variety of cargoes carried and the number of cargo containment systems utilized. Cargo containment systems may be of the independent tanks (pressurized, semi-pressurized or fully refrigerated) or of the membrane type.

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Lesson 1: Bulk Carriers and Tankers

Gas carriers (LNG & LPG carriers) These vessels carry gases that are liquefied. The volume after liquefaction could be as much as 600 times less than in the gaseous state. Liquefaction can be achieved by increasing pressure or reducing the temperature or a combination of both.

LPG consisting mainly of propane, butane, propylene, butylene was carried in pressurized vessels prior to 1959. Present day vessels carry the gas at a temperature of -50° C. The tanks are cylindrical, placed horizontally or of prismatic construction with insulation sprayed on the inner hull.

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Pressurised LPG Carrier

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LPG Carrier “Ocean Primus”

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Lesson 1: Bulk Carriers and Tankers

Natural gas has a much lower critical temperature and much higher critical pressure. The LNG is therefore carried at a temperature below -160° C. The tanks are either spherical free-standing with domes visible from the deck. The very low temperature of the LNG poses a problem of brittle fracture.

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LNG Carrier

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Picture of a LNG Carrier

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Cross–section of a LNG Carrier with Membrane Tank

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Lesson 1: Bulk Carriers and Tankers Chemical carriers: These purpose-built tankers were constructed from about 1954. Chemicals carried in bulk are either derivatives of crude oil, coal tar, vegetable oils and fats or are heavy chemicals like sulphuric, nitric, phosphoric acids and caustic soda. The problems associated with the carriage of chemicals are pollution and safety hazards. The operation and construction of these vessels are governed by the Bulk Chemical (BCH) Code.

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Chemical Tankers

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View of pipelines on deck

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Lesson 2: General Cargo, Container and Ro/Ro Vessels

General cargo vessels carry cargoes of finished products, raw material, construction material, chemicals in packaged form, heavy machinery items etc. These vessels fall into two categories – liner and tramp. These terms are associated with the trade rather than the actual vessel type. Their sizes range from 10,000 – 20,000DWT and normally operate at speeds of 15 – 20 knots. They have double bottom tanks that are used for storage of fuel carriage of ballast water.

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General Cargo vessel

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General cargo being loaded

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General Cargo, Container and Ro/Ro Vessels

The hull is divided by transverse bulkheads to form holds, typically four to six. The engine room is located aft of the cargo holds. The holds may be further divided by one or two ‘tween decks with hatchways that will allow cargo to be loaded or unloaded into the compartment. General cargo vessels may have one or two refrigerated holds to carry refrigerated cargo and deep tanks for carrying small parcels of edible oil, or non-hazardous liquid chemicals.

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General Cargo, Container and Ro/Ro Vessels

Over the years the equipment fitted to general cargo vessels have changed to facilitate better cargo handling. For example derricks and hatch covers have changed to cranes and more sophiscated hatch covers.

The concept of unitization i.e. pre-slung cargo and palletisation has reduced break-bulk handling, reduced handling time and improved stowage, security and safety of the cargo.

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Cars loaded in a general cargo ship

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Heavy Lift Ship with the “USS Cole”

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Heavy Lift vessel with 275t cranes

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Heavy Lift cargo being loaded

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General Cargo, Container and Ro/Ro Vessels

Container ships: A container is an extended form of unit load in transportation. The popularity and dominance of containerized transportation nearly wiped out the break-bulk transportation business due to the fast turnaround time associated with this mode of transportation.

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Feeder container ship

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Medium-sized container ship

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Large purpose built container ship

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Container ship in port

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Container Ship

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Container Ship

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Container ship cargo hold

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General Cargo, Container and Ro/Ro Vessels

Containerization is one of the units of modal and multimodal transportation in door-to-door or floor-to-floor service. The first container ship was a converted tanker the S/S “Maxton”which carried 58 containers in April 1956. But it was not until 1966 that the first container service crossed the Atlantic ocean.

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General Cargo, Container and Ro/Ro Vessels

Container vessels are classified as first generation – those carrying less than 1000 TEUs and second generation – those carrying more than 1000 TEUs while fourth generation have capacities of 4,000 to 5,000TEUs. These ships have speeds of 18 to 25 knots. They may have their own cargo handling equipment or may be gearless.

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General Cargo, Container and Ro/Ro Vessels

The trend today is for big container ships to call on ports with shore cranes. The latest design of these ships is the ones without hatch covers.

Types of containers vessels are:a. Fully containerised vesselsb. Partial containerised vessels c. Convertible container vesselsd. Combi-container vesselse. Feeder container vessels

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Ro/Ro Vessels

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Stern ramp of a car carrier

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Container cargo on a Ro/Ro Ship

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The Generations of Container Ships

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Lashing Bridge on a Container Ship

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Lesson 3: Specialized VesselsPassenger ship

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Modern Cruise Ship

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Specialized Vessels

Car Carriers: designed to carry only cars; also called pure car carriers (PCC). They have multi-deck construction and can accommodate large numbers of cars (up to 6,000). Cars are handled in a drive-on drive-off basis. The hull has a box type profile and their speeds are up to 20 knots.

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Car carrier

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Ferries

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Specialized Vessels

Lumber carrier: The constructional features are similar to the bulk carriers of small size with double bottom tanks and top side tanks. They have their own cargo handling equipment. The loading of logs, lumber or timber is inside the holds as well as on deck. Special regulations are to be followed for ensuring that the ship’s stability is intact. Chips carriers carry wood chips in their holds. Because of the high stowage factor of wood chips, the vessels have large depth and small draft.

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Wood Chip carrier

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Specialized Vessels

Refrigerated Cargo Ships: These ships haveconstructional features of a general cargo ship with four or five holds divided vertically by two or three ‘tweendecks. The holds are insulated to maintain lowtemperatures down to -30 C. They have their own cargohandling equipment. Their speed s are relatively highand usually range between 20 -23 knots.

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Reefer

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Reefer Showing Side Doors

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Specialized Vessels Heavy Lifters: Most of the general cargo ships have cargo handling equipment to handle cargo weighing up to 100 tonnes. However, the heavy lifters have equipment to handle single pieces of cargo weighing up to 1,000 tonnes. The heavy lift cargoes a are carried along with the general cargoes as and when available. The strength and stability along with spec ial securing arrangements for heavy cargoes are given special consideration.

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Elements of a Ship

The HullMaterial: The hull is usually constructed from steel plates welded together. The steel may be mild or high tensile steel which is categorised into several grades according to the chemical and physical properties.

Typical structures: Bow part; Fore part; Mid ship; Aft part; Stern part

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Elements of a Ship

Propeller: There are several kinds of propulsion devices in addition to the known screw propeller. There are fixed pitch and controllable pitch propellers.

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Elements of a Ship

Steering Gears: Rudder, a device which is used to turn the ship and a hydraulic system integrated with the rudder which facilitates the steering of the vessel.

Fittings on Deck; Mooring devices (anchors; winches; capstans; windlass)

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Elements of a Ship

Cargo Handling Devices: These are the main outfittings for a cargo ship. There are many different types of cargo handling gear depending on the type of ship.

Navigation Bridge: This is where the navigating of the vessel takes place. All the navigational instruments and systems are located here.

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