CATEGORIES OF CARGO AND TYPES OF SHIPS

1. UNIT 1 CATEGORIES OF CARGO AND TYPES Categories of Cargo
and Types of Ships
OF SHIPS
Structure
1.1 Introduction
Objectives
1.2 Categories of Cargoes
1.2.1 Bulk Solid
1.2.2 Bulk Liquids
1.2.3 Unitized Cargo
1.2.4 Heavy Lifts
1.2.5 Deck Cargoes
1.2.6 Refrigerated Cargoes
1.2.7 Ro-Ro
1.2.8 Gases
1.2.9 Chemicals
1.3 Types of Ships
1.3.1 General Cargo Ships
1.3.2 Bulk Carriers
1.3.3 Oil Tankers
1.3.4 Container
1.3.5 Pure Car Carrier
1.3.6 Chemical Tanker
1.3.7 Ro-Ro Ships
1.3.8 LPG/LNG
1.3.9 Reefer Ships
1.3.10 Heavy Lift Ships
1.4 Summary
1.5 Answers to SAQs
1.1 INTRODUCTION
Movement is an essential component of life. Right from the beginning of civilization,
humans have been moving from place to place in search of food, for a living and for
exchanging goods.
Modern life is so complex that one has to depend on others. The same is true of countries
as well. No country today can prosper without the cooperation and assistance of others.
This requires movement of goods and materials between countries. Trade provides us
with our necessities and also adds to amenities and comfort of life.
Transport is a system in which passengers and goods are carried from one place to
another. Waterways are the cheapest means of transport and are most suitable for
carrying heavy and bulky goods.
Objectives
After going through this unit, you should be able to
• explain the various categories of cargoes carried by the ships, and
• familiarize yourself with the various types of ships which are used to
transport different categories of cargoes or goods.
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2. Cargo Handling
and Stowage 1.2 CATEGORIES OF CARGOES
Ninety per cent of the world trade is seaborne i.e. handled by ships. An estimated 50,000
ships carry more than 2500 million tones of cargo in and out of the ports of the world.
The main reason for this is that the producing countries are not the major consumers of
the commodities they produce.
Iron ore is produced by Australia, India, Brazil and Nigeria but the steel and steel
products are manufactured by Japan, Korea and the European Countries, Lamb and Beef
produced in Australia, New Zealand and Argentina is consumed in Europe and USA.
Two thirds of the world shipments of grain cargoes is made by USA through the U.S.
Gulf Ports and consumers are developing countries and sometimes even China and
Russia.
Similarly, oil produced by the OPEC Countries finds its way to countries all over the
world.
Let us try to categories these cargoes.
1.2.1 Bulk Solid
Large volumes of homogeneous (uniform) cargo which lies loose in the holds
(compartments) of the ship, i.e. it is not bagged or confined in any specific way other
than that imposed by the ship’s design.
Examples: Coal, Mineral ores (iron, aluminium), Concentrates (refined ores), Grain,
Sugar, etc.
1.2.2 Bulk Liquids
Large volumes of cargoes in liquid state, which are carried loose in the compartments of
a ship.
Examples: Unrefined crude oil, Refined products of crude oil (aviation spirits, gasoline,
gas oil and lubricating oils)
1.2.3 Unitized Cargo
A number of “small sized” items which are made up into one unit of standard size.
Examples: Pallets, Containers.
1.2.4 Heavy Lifts
Heavy loads which are carried on ships as one piece. Present day heavy loads consist of
semi submersible oil rigs, Jack up oil rigs, etc.
Examples: Boilers, Railway Engines (weighing about 100 tons), machinery for factories,
equipment for heavy industries and other cargoes weighing about 700 to 1000 tons.
1.2.5 Deck Cargoes
Cargoes which are carried on the main deck of the ship, instead of being carried inside
the ship, due to its nature, size, shape, etc.
Examples: Timber, Project cargo, some dangerous cargoes, heavy lift cargoes.
1.2.6 Refrigerated Cargoes
Cargoes carried in specially insulated holds or compartments to maintain the controlled
temperature required to prevent the deterioration of the products carried.
Examples: Meat, Fruit, Vegetables, Dairy products.
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3. 1.2.7 Ro-Ro Categories of Cargo
and Types of Ships
Roll on-Roll off cargo which is motorized or wheeled on board the ship, being
transferred from deck to deck using ramps and elevators.
Examples: Cars, Trucks, Trailers.
1.2.8 Gases
Liquefied Natural Gas (L.N.G.): These cargoes are liquified by cooling in shore
installation and then transported by ships with elaborate insulation of their tanks capable
of maintaining very low temperatures (as low as −161o C) required to prevent the liquid
cargo vaporizing.
Liquefied Petroleum Gas (L.P.G.): These cargoes are liquified using pressure. They are
then transported in spherical tanks on board ships which are able to maintain this
pressure and therefore the liquid state.
1.2.9 Chemicals
Cargoes which are generally carried in liquid form in bulk in specially built tanks and
which pose danger to personnel handling them.
Examples: Acids, Alkalis, Mineral Oils, etc.
SAQ 1
(a) What is the difference between LPG and LNG?
(b) What is the difference between Ro-Ro and unitized cargoes?
(c) Differentiate between oil cargoes and chemicals.
(d) Write some major cargoes being shipped by sea and which countries are
exporting these cargoes?
1.3 TYPES OF SHIPS
In the last chapter we have seen that the cargoes may be in solid liquid, or gaseous form.
They may require to be carried under controlled temperatures or may require specialized
containers. To carry liquid cargoes in ships which are constructed for carriage of dry
cargoes, is unthinkable.
Ships are, therefore, now constructed for the type of cargo and the type of trade that she
will undertake.
1.3.1 General Cargo Ships
Until ships started to be built to carry specific and specialized cargoes, all ships were
simply general cargo ships, i.e. built to carry all types of cargoes e.g. drums of asphalt or
caustic soda, cases of machinery, boxes or cartons containing ebarings or electronic
goods, Radios, Transistors, steel plates, paper rolls, cases of Tea, Bags of coffee seeds
etc. General cargo ship’s holds were further compartmentalised by one or two decks
under the main deck so that different types of cargo carried by these ships could be
separately stowed. The role of the general cargo vessel began to wane with the arrival of
big size bulk carriers and tankers, but the decline of these general cargo vessels has
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4. Cargo Handling accelerated since the advent of containerisation (in the 1960s). Not only are container
and Stowage ships able to carry greater volumes of cargo in standarised cargo containers, the time
spent in loading and discharging has been dramatically reduced. Where a general cargo
vessel may take 3 - 4 days to load or discharge, a container ship can achieve the same in a
matter of hours. Although general cargo vessels still remain in operation they are
generally small in size, are not suitable for containers, or operating on coast and Inland
waters.
Figure 1.1
SAQ 2
(a) What are the principal advantages of a container ship over general cargo
ship?
(b) In which way was it possible to separate the cargo on a general cargo
vessel?
1.3.2 Bulk Carriers
Bulk carriers are the great work horses of the shipping world, carrying raw dry cargoes
such as coal, iron ore, grain, sulphur, scrap metal in their huge cavernous holds. All the
time of writing this unit there is a huge demand for these vessels, driven by the
extraordinary expansion of the Chinese economy. Recently imports of iron ore into China
have boosted the earnings of bulk carrier owners.
The vessels in the top row are called a geared bulk carriers, so called because they carry
its own cargo cranes – very useful when visiting ports which do not have shore cargo
handling equipment.
The vessel in the bottom row are a gearless bulk carriers. These ships do not have its
own cargo handling gear and hence dependent on shore side cargo loading and
discharging equipment. They are normally much bigger in size than the geared bulk
carriers.
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5. Categories of Cargo
and Types of Ships
Figure 1.2
Bulkers range from about 20,000 Deadweight tons (handy size) through the medium size
(Panamax) vessels of upto 80,000 DWT, to the giant (cape size) vessels of over 200,000
DWT. Due to the rough use that these vessels are put to, their life-expectancy is less than
it would be for say, a container ship. The decade of 90’s witnessed a number of bulk
carrier accidents but the problem is now well under control.
Figure 1.3
SAQ 3
(a) What are the advantages of gearless bulk carrier over a geared bulk
carrier?
(b) Why is the life of a bulk carrier considered less than that of a
container vessel?
(c) Why is a cape size vessel called “Cape Size”?
1.3.3 Oil Tankers
Tankers are designed to carry liquid cargoes (not just oil). Oil tankers come in two basic
types, the crude carrier, which carries crude oil, and the clean products tanker, which
carries the refined products, such as petrol, gasoline, aviation fuel, kerosene and paraffin.
Tankers range in all sizes, from the small bunkering tanker (used for refuelling larger
vessels) of 1000 DWT tons to the real giants: the VLCC (Very Large Crude Carrier) of
between 2-300,000 DWT and the ULCC (Ultra Large Crude Carrier) of upto
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6. Cargo Handling 500,000 DWT. Product carriers are smaller in size but product carriers of over 100,000
and Stowage DWT are already operational.
Figure 1.4
It should be remembered that over 60% of the worlds oil is transported by these tankers,
and over 99% of that arrives safely without causing pollution. Most oil pollution seen on
beaches comes from the engine rooms of vessels (of all types) and not necessarily from
the cargo tanks of tankers.
HANDYSIZE TANKER = 20,000 – 30,000 DWT
HANDYMAX TANKER = approx. 45,000 DWT
PANAMAX TANKER = approx. 79,000 DWT
AFRAMAX TANKER = between 79,000 – 120,000 DWT
SUEZMAX TANKER = between 120,000 – 180,000 DWT
V.L.C.C. TANKER = between 200,000 – 300,000 DWT
U.L.C.C. TANKER = over 300,000 DWT
Handy Size Panamax Size
Aframax Size Suexmax Size
U.L.C.C. Size
V.L.C.C. Size
Figure 1.5
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7. SAQ 4 Categories of Cargo
and Types of Ships
(a) What is the difference between cargoes carried by VLCC and those by
Product Carriers?
(b) Suezmax tanker size just a few years ago was less than 100,000 DWT. Why
has it now gone above 120,000 DWT?
1.3.4 Container
The Containership or Boxship is the great success story of the last 40 years. General
cargo was historically carried in dry cargo vessels, without any particular specialization.
Cargo loading and unloading was always a slow, labourious task, due to the varying
shapes, sizes, weights and fragility of the numerous cargoes being carried on any one
vessel. The idea of standardizing the carrying box, or container at 20 feet long was a
breakthrough that allowed for vessels to be designed to carry these standard sized boxes,
and for dockside equipment also to be designed to lift, stack and store these specific
shapes.
In 1937, a New Jersey truck driver named Malcolm McLean, sitting in his truck at the
New Jersey Docks suddenly had a novel idea. Instead of large numbers of stevedores
having to manually load cargo, why not create a standard shaped box into which goods
can be handled in a standard way. His idea took 20 years before the first container transit
was undertaken (with his own money, because no ship owners would listen to his idea).
In 1969 Malcolm McLean retired as a multi-millionaire !!!
Figure 1.6
So, from a ‘back of the fag-packet’ idea was born the container ship. Initially, these were
small vessels of up to 10,000 DWT, carrying no more than a few hundred TEU (Twenty
foot Equivalent Units), but have grown in size as the success and economies of these
vessels have become more obvious. Today’s container ships are being built to take 9,500
T.E.U., with plans afoot to build 10-12,000 TEU ships.
As well as the Twenty foot container, many goods need larger boxes, so there is a larger
standard sized container, the FEU (Forty Foot Equivalent Unit). On board a modern
containership, the complex method of loading the TEU and FEU in an order that will
facilitate offloading at the other end is now largely computerised. These vessels are built
for speed, and can reach upwards of 28 knots, moving cargoes around the globe.
Through transport or inter-modal transport means that these containers can be offloaded
from a ship, and rapidly loaded onto trains or onto container lorries for onward transport
to the place of delivery.
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8. Cargo Handling SAQ 5
and Stowage
(a) What is the size of the largest Road Transport Container?
(b) Who first conceived the idea of a container?
(c) What are the advantages of a container ship over a general cargo ship?
1.3.5 Pure Car Carrier
Pure Car Carrier is a ship designed to carry cars in different compartments of the ship.
Some ships are designed to carry cars in some compartments and trucks in other
compartments. They are now known as Pure Car and Truck Carriers (PCTCs).
Figure 1.7
1.3.6 Chemical Tanker
They range in size and construction but one thing is common for them all. We are very
much dependent upon the products they carry every day. Find out how we get ourselves
toothpaste, cooking oil, plastic, paint, perfume, wine and spirits.
A chemical tanker is like an oil tanker but with more number of and smaller tanks. Some
vessels have up to 56 tanks. The tanks are specially equipped to handle many types of
cargo. Here are some examples of the cargo they carry and the problems they face:
Vodka: In order to ship this in a sober manner, the tanks must be perfectly clean. The
tanks have highly efficient washing machines to make this possible. Highly skilled (and
cheerful?) surveyors are actually tasting the product during loading and discharging to
ensure the customer is not left with a bad taste in their mouth.
Vinyl Acetate is used for making plastics. Unfortunately this stuff has a tendency to
make plastic on its own when you least expect it. This is called polymerization and you
can probably imagine what it would look like if these things get out of hands! To avoid
any mishap another chemical is mixed into the tank to slow down this process, the so-
called inhibitor.
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9. Toluene Di Isocyanate is used to make your bed-mattress porous and thus nice and Categories of Cargo
comfortable. TDI reacts violently when exposed to air. In order to avoid anything crazy and Types of Ships
from happening (explosions, etc.) the tanks are filled with nitrogen gas before loading to
get rid of the air inside. Still wonder why these mattresses are so expensive?
Acetic Anhydride is very popular with the security-police in regime ruled countries. It
makes tear gas. To avoid the same fate as many courageous civic rights fighters, the crew
must wear masks or ‘diving gear’ when handling this product. Fortunately most of this
stuff are used for the common good.
Soya Oil, what would French fries be without it? This is shipped in large quantity on
tankers. It freezes very easily so the tankers are equipped with heating coils keeping the
oil on a temperature of 40-60oC.
Rubber: Did you know that rubber is liquid and transported on tankers before turned
into tyres, etc.? Now you know!
Acrylates have a pleasant smell but only if you have only one drop of it. On the other
hand, filling 20,00,000 litres of it into a tanker soon makes your nose start begging for
mercy! It is common to turn off the air condition system on tanker vessels when handling
this grade. This saves the ship from smelling (...) later. Acrylates are used for toilet
articles, perfumes, foodstuff, etc.
Propylene Oxide is sometimes added into Jet Fuel to get a better burn. So when loading
this into a tank and many others, just remember that smoking is strictly prohibited and,
believe me, dangerous for your health.
Tanker constructed, equipped, classed and certified to carry any chemical listed in
Chapter 17 of the International Chemical Code (ICC) and classed as A, B, C or D in
Annex II to MARPOL 73/78 can usually also carry petroleum products and the products
listed in chapter 18 of the ICC.
SAQ 6
(a) What is the main difference between chemical and oil tanker?
(b) Describe polymerization and what precaution is taken to slow down same?
1.3.7 Ro-Ro Ships
The Ro-Ro, or more fully the Roll on-roll off vessel, come in a number of shapes and
sizes, but generally in two types; the passenger ro-ro and the Cargo ro-ro.
Passenger ro-ros have become common sights wherever people want to travel over water
with their vehicles. It is probably the only type of cargo vessel that most people have
travelled on. Usually a rear door (but sometimes a bow door) allows for vehicles to be
driven on and off, stored on the car deck below the passenger accommodation areas.
The cargo ro-ro is less ‘plush’ than the passenger type, as these vessels are designed for
the carriage of commercial vehicles where luxurious passenger accommodation is not a
primary consideration. Considerable concerns have been expressed over the bow-door
type of ro-ro design. The HERALD OF FREE ENTERPRISE was one such vessel, where
the practice of sailing before the bow door was fully closed had been allowed to develop.
Tragically, on leaving Zeebrugge, the folly of this practice led to the disaster that claimed
nearly 200 lives. If water is allowed to enter the car deck, the stability of the whole vessel
can be rapidly affected. It is estimated that it only needs small amount of water over the
whole car deck, for the vessel to become very unstable.
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10. Cargo Handling
and Stowage
Figure 1.8
The ESTONIA was another such vessel where, in a storm, the shield over the bow door
was ripped off. Once water penetrated the car deck the vessel began to turn over and sink.
SAQ 7
(a) What types of cargoes are carried by Ro-Ro ships?
(b) Describe the advantages of Ro-Ro ships.
1.3.8 Liquefied Petroleum Gas/Liquefied Natural Gas Carrier
Natural gas has 600 times the volume of LNG.
The LNG carrier (Liquefied Natural Gas) and its cousin the LPG carrier
(Liquefied Petroleum Gas) are products of the late twentieth century. LNG and LPG are
the preferred fuel types of certain countries for their industrial power needs. Japan is one
such country, and so LNG needs to be transported to Japan, but is not the easiest of
cargoes to be transported. In its natural state, LNG is a gas, so to transport it, it needs to
be either pressurized into a liquefied form, or kept as a liquid by reducing the
temperature (simple application of Boyle’s Law in physics!).
The shape of the LNG Carrier is quite unmistakable, with the shape of the Moss tanks
(which are like enormous spherical thermos flasks !) visible along the deck, which has
led to the nickname of ‘Dinosaur Eggs Carriers’.
Obviously, the carriage of an explosive gas – kept at below freezing temperatures as an
unstable liquid presents a very dangerous cargo, yet it is for this very fact, that LNG
Carriers have about the best safety record of all maritime vessels. Only the best officers
and crews are employed on these vessels, and the vessels themselves are maintained
meticulously, and renewed frequently. There have been accidents involving LNG/LPG
carriers, but where such events have occurred, the crews or salvors have so far,
successfully managed to vent off the cargo into the atmosphere, thus rendering the lethal
cargo harmless.
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11. Categories of Cargo
and Types of Ships
Figure 1.9: Liquefied Natural Gas (LNG)
Propane, butane, or propane-butane mixtures derived from crude oil refining or
natural gas fractionation. For convenience of transportation, these gases are
liquefied through pressurization.
Figure 1.10: Liquefied Petroleum Gas (LPG)
SAQ 8
Describe the types of Cargoes carried by LPG and LNG ships?
1.3.9 Reefer Ships
In the year 1880 there was an important breakthrough, when 400 frozen carcases were
carried safely by sea using a simple ship refrigeration plant to keep them hard-frozen on a
two month voyage from Australia to the United Kingdom. This had huge implications,
both for the consumers, who were able to source their produce from across the world, and
to the producer countries like Australia and New Zealand, which were permitted by
seagoing refrigeration to develop their main export markets.
Since these beginnings, the ‘reefer’ trades have hugely expanded to handle all forms of
fresh food, with substantial quantities of meat, fish, dairy produce, bananas, citrus and
other fruits criss-crossing the world in specialised refrigerated ships. Cargoes are carried
either frozen, chilled, cooled or increasingly at controlled temperatures that can be varied
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12. Cargo Handling to ensure that the produce reaches the market at its optimum condition, often ripening on
and Stowage the voyage.
Figure 1.11
Reefer ships are effectively large refrigerators, heavily insulated with modern glass fibre
or similarly efficient insulation, shuttered with bright metal that prevents taint and is easy
to clean. They are ships that tend to be divided into many more spaces than conventional
dry cargo ships, with several tweendecks and even locker spaces, so that different
commodities can be separated and carried, if required, at different temperatures. Below
decks a reefer ship resembles a large modern warehouse, and cargo is usually carried and
handled in palletised form, moved about on conveyors or by electric fork lift trucks.
Some cargo, such as bananas, is often handled through doors in the ship’s side.
Cleanliness and the maintenance of optimum temperatures are the pre-requisites.
Modern refrigeration plant works with environmentally kind refrigerants such as R-22
and is largely automated. Air is cooled in a brine cooling system by screw compressors
and cold air ducted to the cargo spaces. They can usually carry refrigerated containers on
deck. A large reefer ship might typically offer about 500,000 cubic feet of refrigerated
space, and be capable of loading 250 containers on deck.
Reefers operate seasonally, but because there is a heavy trade between the hemispheres,
can hopefully find employment. In recent years, too much new construction has led to
over tonnage. The specialist reefer ships, which are generally operated as tramps rather
than in the liner trades, are seeing their cargo base increasingly attacked by large
container ships, which are offering more slots for refrigerated boxes. Indeed the largest
reefer capacity in a single ship is not on a ‘traditional’ reefer, but aboard a large container
ship.
Reefer containers are either fitted with their individual refrigeration units which can be
plugged in to the ship’s electrical power source, or, less usually, with apertures for ducted
cold air. With the increase in exotic food cargoes, special containers have been devised
that can tailor the internal atmosphere to the precise requirement of the foodstuffs.
1.3.10 Heavy Lift Ships
Heavy loads were first carried on conventional cargo ships, either handled by a port
floating crane, or by the ship’s “jumbo” derrick which would make short work of loads
like boilers or railway engines, up to about 100 tonnes. But manufacturers, who liked to
ship their products in one piece, rather than expensively assembling them on-site, were
constantly building heavier and heavier items, and a small specialist sector of the
shipping industry has developed to carry these very heavy and awkward loads.
Problems lie in the risk of the ship becoming unstable when the weight is taken by the
cranes or derricks, and a range of strategies have been developed to deal with this. While
some ships merely use ballast water to counterbalance the weight of a load as it is lifted
off the wharf, others put great hydraulic feet onto the dock, or hang water-filled weights
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13. on the offshore side of the ship. Some ships have a couple of giant 300 ton cranes which Categories of Cargo
can lift 600 tons in tandem. and Types of Ships
Figure 1.12
Other ships are built to roll cargo off and on the stern, across a huge reinforced ramp,
while others in the specialist fleet are effectively powered floating docks, which can be
ballasted down to let a heavy load be floated aboard, and gently grounded as the ballast is
pumped out and the ship rises. Several damaged warships, have been carried home in one
of these dock-ships, a far less risky operation than an ocean tow.
From the 100 ton railway engine, this sector can find ships available that will take loads
such as oilfield modules or chemical plant of 3,000 tons and above. The offshore industry
and various massive industrial projects such as refineries or chemical works has
encouraged a growing heavy lift sector, and this has grown considerably. The ships have
to be naturally robust, but the crew are required to be real experts, with a whole range of
unusual skills that they have to learn. They are experts in hydraulics, and jacking, cutting
and welding. If you want to see a real logistics challenge, look at a heavy lifter carrying
three or four giant container cranes, already assembled and ready to roll ashore.
The crew will have to prepare the ship for the heavy or unusually dimensioned load, load
the cargo in a way that will avoid stressing the structure of the vessel while maintaining
the stability. Then they will have the complex job of securing the load to make sure it
does not shift in a seaway, often welding it down. On arrival the crew will perform the
operation in reverse, often having to reinforce the wharf to ensure that their precious
cargo does not fall through the decking. They have been known to build ramps and
breakwaters, to protect the discharge; even roadways to speed the cargo on its way.
There is no sign that there is any diminution in the quantities of heavy lifts offering-quite
the reverse as planners try and get this sort of inconvenient freight off the roads.
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14. Cargo Handling
and Stowage 1.4 SUMMARY
Cargoes may be of various categories, viz. bulk solid, bulk liquid, unitized cargo, heavy
lifts, deck cargoes, refrigerated cargoes, Ro-Ro, gases, and chemicals.
General Cargo chips, bulk carriers, oil tankers, container, pure car carrier, chemical
tanker, Ro-Ro ships, reefer ships, and heavy ships are deployed to carry different types of
cargoes.
Bulk carriers are the great work horses of the shipping world. They carry dry cargoes
such as coal, iron ore, grain, sulphur and scrap metals.
Oil tankers are specifically designed to carry liquid cargoes. Pure car carriers carry cars,
while chemical tankers are designed to carry different chemicals. Reefer ships are
effectively large refrigerators, heavily insulated with modern glass fiber. Ships are also
designed and built to carry heavy lifts.
1.5 ANSWERS TO SAQs
For answers to SAQs, please see the relevant text.
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