A gas carrier (or gas tanker) is a ship designed to transport LPG, LNG or liquefied chemical gases in bulk.

1. GAS CARRIER
Gas carriers are ships that are specially designed to transport gas. This ship type is considered to
be more technically advanced than Bulker and Tankers. Most ships of this type are built at yards
in Korea or Japan as they have the experience and proven track record.
A gas carrier (or gas tanker) is a ship designed to transport LPG, LNG or liquefied chemical
gases in bulk.
Principle type and design characteristics of modern liquefied gas carriers :
Gas carriers range in capacity from the small pressurized 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 – semipressurised gas carrier.
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.
Gas carriers have certain features common with other tankers used for the carriage of bulk
liquids such as oil and chemical tankers.
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.
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.
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).

2. Gas carriers are classedin three types based on hazard potential:
i) type 1G, designed to carry the most hazardous cargoes
ii) type 2G and 2PG, designed to carry cargoes having a lesser degree of hazard
iii) type 3G, designed to carry cargoes of the least hazardous nature.
Gas carrier types
All gas cargoes are transported in liquid form (ie they are not carried as a gas in its vapour 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
Note. These grouping names are more prevalently used when discussing the classes and types of
LPG carriers rather than LNG carriers.
In principle, the design is ‘a box within a box that is separated by a void space’, similar in effect
to the principle of a flask. Gas Carriers can be split into two distinct groups. One is the liquefied
natural gas (LNG) carrier. The other is the liquefied petroleum gas (LPG) carrier.
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.
The cargo tank construction of LNG and LPG ships can be of
(a) prismatic design
(b) membrane design
(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.

3. 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.
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.
The safety features inherent in the tanker design requirements have helped considerably in the
safety of these tankers. Equipment requirements for gas carriers include temperature 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.
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.
OIL TANKER
A tanker (or tank ship or tankship) is a merchant vessel designed to
transport liquids or gases in bulk. Major types of tankship include the oil tanker, the chemical
tanker, and gas carrier.
Out of the sheer need to transport “black gold” from remote areas of extraction to locations
where they could be refined and become of significant importance, the creative ideas of an early
oil miner found their feet and developed into a work of invention.
And a mighty marine masterpiece was born — the oil tanker ship.
An oil tanker ship is a large ship that moves oil across the globe. The size is dependent on the
quantity of oil they carry and whether they travel through inland or coastal routes. With 2 million
metric tons of oil each year, their importance in the oil industry cannot be overestimated.
Due to their colossal size, they offer a simple and cheap approach to transporting oil over long
distances, providing a huge platform for big corporations to maximize their profit.
The advancement that was achieved by their emergence has never been relegated to the
background. However, they‘ve caused serious issues too—the percentage of the most disastrous
ecological calamities abounded because of their emergence on waterways cleaning equipment.
The first type of these ships was built in 1860s with wind-powered sail, which, subsequently,
were replaced with steam engines. This was the ingenuity and product of the Palmer

4. Shipbuilding and Iron Company, and was named Vaderland. Then, oil makers in Pennsylvania
had their hands full with the utilization of badges; a large ship tugged by an alternate boat. They
are usually unpowered.
Zoroaster was the name of the first oil tanker built and designed by Ludvig Nobel of Sweden in
1878. Ludvig and his sibling were at the helm of affairs at Branobel—a huge oil organization in
the 1870s.
Oil tanker capacity
Oil tanker capacity is estimated based on their convey limit in dead weight (DWT), which is the
total weight of a ship (including the load, crew, provisions, etc.) excluding the weight of the ship
if unloaded.
Oil tanker capacities based on deadweight are as follows:
Panamax
With an oil tanker size of 500,000 barrels, these tankers sure command a measure of respect in
this industry. They are regarded as the largest vessel that travels through the Panama Canal.
A crude oil tanker of this sort weighs up to 70,000 dead weight tons (a crude oil tanker is one of
the two types of oil tankers that move raw unrefined oil from where it is pumped out of the earth
to where they will be refined).
Aframax
Their weight ranges from 70,000 to 120,000 dead weight tons, with a capacity of 750,000 barrels
of oil. In the Average Freight Rate Assessment tanker system (AFRA), they are the largest
tankers. AFRA is a standard used for contract terms with well-defined ship capacity tanker
explosion.
Suezmax
This is the largest tanker passing the Suez Canal with the range of deadweight tons from 120,000
to 200,000 and 1,000,000 barrels of oil.
Very large crude carrier (VLCC)
Their weight extends from 200,000 to 325,000 dead weight tons; used mainly in the
Mediterranean Sea, the North Sea, and near West Africa, with an approximate capacity of
2,000,000 barrels of oil.
Ultra large crude carrier (ULCC)
It is also known as ULCC. The weight extends from 325,000 to 550,000 dead weight tons. Their
capacity is up to 4,000,000 barrels of oil and they are used in the Persian Gulf to European and
American to Asia.

5. Classification of tankers on the basis of their types
Oil tankers
They are tankers that convey oil and its by-products. The products also include petrol, gasoline,
kerosene, paraffin.
The subdivisions of this category are as follows:
Product tankers: They’re used for transportation of petroleum-based chemicals
Crude tankers: They’re specifically used for transportation of crude oil from point of extraction
to the point where it is refined.
LNG carrier
These ships are deployed for the transportation of LNG (Liquefied Natural Gas). Care and
precautionary measures are taken due to the delicate nature of the materials they carry.
Oil chemical tanker
These tankers transport chemicals of various types. Their design allows for consistent
maintenance. They are usually coated for ease of identification of chemicals to be transported.
Slurry tankers
Slurry is a word for the material that does not dissolve in water. They’re used as fertilizers and
moved by these tankers to the areas of importance.
Hydrogen tankers
They find their importance in the transportation of liquefied hydrogen gas.
Juice tankers
These tankers are meant for carrying orange juice in mass quantities. Other fruit juice carriers are
also available.
Wine
Transportation of wine these days can be done in sleek tankers of these types to the areas of
intended use.
ITB (Integrated Tug Barges)
They are mainly used in the eastern coast of the US; basically, the tug and the barge are
combined into a single cargo carrying unit.
As oil tankers ply the waterways, it has become imperative that their activities be put under
control to ensure that safety procedures are absolutely complied with on board ships and at
terminals. To this end, a safety guide meant to regulate the activities of vessels and terminals was
published in 1978 and referred to as the International Safety Guide for Oil Tankers and
Terminals (ISGOTT)

6. This guide provides operational advice to personnel involved in the activities of oil tankers and
terminal operations. They include guidance, operational safety, better handling crude oil and
petroleum products on tankers and at terminals.
ISGOTT is a combination of a petroleum tanker safety guide, international oil tanker safety
guide, and terminal safety guide, published by the International Chamber of Shipping (ICS) and
the Oil Companies International Marine Forum (OCIMF) respectively. Severally publications
have been in the public domain since 1978.
This safety guide also extends to oil supertankers (VLCC) with capacities well over 250,000
DWT. These ships are capable of taking on 2,000,000 barrels of oil per 318,000 metric tons.
A barrel of oil
Questions such as “how many gallons make a barrel and how many barrels in a tanker?” will
continue to generate so much fuss until things are put into perspective.
A barrel of oil is actually a unit of volume. In the US and Canada, one barrel contains 42 gallons
of crude oil.
Today’s supertankers, on the average, can hold 2 million barrels or 84 million gallons of crude
oil and petroleum products.
And according to the California Energy Commission, each crude oil barrel contains products
such as:
 Finished motor Gasoline (51.4%)
 Jet fuel (12.3%)
 Still gas (5.4%)
 Distillate fuel oil (15.3%)
 Marketable coke (5.0%)
 Liquid refinery gas (2.8%)
 Residual fuel oil (3.3%)
 Asphalt and road oil (1.7%)
 Lubricant (0.9%)
 Other refined products (1.5%)
Oil tanker operational safety measures and general precautions
Oil tanker operation is a serious business in any part of the world and involves numerous
complexities, and careful measures have to be taken into consideration to ensure safety on board.
They are as follows:
 Restrictions on smoking, burning, and naked light activities on board of vessels.
 Smoking prohibited in designated area when gas freeing and purging is in place
 Hand gas lighters strictly prohibited but safety matches are allowed within the designated
smoking area.
 Permanent notices at entrance points and exits.

7.  Strict control over the use of portable stoves and cooking appliances. Before their use,
porthole and doors are closed and absence of hydrogen gas is confirmed.
 At berth, gallery stoves are prohibited.
 Electric heaters must be used at designated points only.
 In areas, in which inflammable gas may be present, equipment like portable radios,
electronic calculators are not used except for those of sealed-in type.
 Personnel must be properly dressed when entering the cargo deck area and wear personal
protective equipment.
 Visitors on board are guided by notices at entrance points and allowed in upon
presentation of ID.
 Visitors are not allowed to access the cargo area or even the deck unless escorted by
vessel personnel.
 Combustible materials are stored in a well-ventilated area to avoid accumulation of
inflammable gases—saw dust, oily rages, etc.
Oil tanker engine
Oil tanker engines are designed to power tankers carrying enormous amount of oil. For example,
the largest oil tanker in the world—Jahre Viking, formally Seawise Giant,—with oil tanker
dimensions measuring 1,504 feet (458.46m) as the oil tanker length; 266 feet as the width, and
oil tanker weight of 564,650 DWT, carries up to 4,000,000 barrels of oil.
Tankers of this type are powered by very big engines, a typical example is the world’s biggest
engine called Wartsila-sulzer RTA-96-c used to power super oil tankers and container ships, with
dimensions measuring 89 feet long and 44 feet wide, and manufactured by Aioi Works in Japan.
The configurations of the cylinders are in these orders: 6, 8, 10, 12 feet and 2 inches. Each of the
cylinders has a diameter of 3 feet 2 inches and a stroke of 8 feet and 2 inches.
The weight of the 12 cylinders is 2,000 metric tons with 90,000 horse power and a fuel economy
of 53,244 HP at 100 Revs per minute.
This engine is regarded as the most powerful, and the fact that it operates at a slower rate, which
is 20 times less than a 2.0 liter car engine makes it an added advantage to its life when at the
middle of the sea with 100,000 tons of oil.
If the low speed is considered from the perspective of the power output, it’s a win-win situation
when it comes to fuel consumption. The extraordinary fuel economy in the 14-cylinder type is
too good to be true—it displaces 25,480 liters (1.56 million cubic inches burn only 1, 6660
gallons of crude oil per hour).
This colossal moving structure will continue to remain relevant in this industry, even if we use
the chock full of opportunities it offers for years to come.