What are Tanker Ships?

What are Tanker Ships?

Liquid Cargo is shipped in specialised vessels called tankers, which can be of different kinds, depending on the cargo type. It might be crude oil, LPG, alcoholic beverages like wine, hydrogen-based organic compounds, chemicals, juices and even liquefied gaseous substances.

Modern tankers are equipped with advanced technologies and come in different sizes and capacities. They range from small self-propelled barges to ultra-large crude carriers. About 35% of the world’s merchant ships are tankers.

Different kinds of tanker ships provide the appropriate transportation facility for liquefied freight. Some of the longest vessels in the world today are also tanker ships.

The IMO (International Maritime Organisation) stipulates the construction and technical structuring of tanker ships. These stipulations were amended periodically to ensure that safety aspects were met.

Tanker Size and classes

The size of tankers is measured in DWT, i.e. Dead Weight Tons, and as per size, they are classified as follows:

• Seawaymax
• Panamax
• Aframax
• Suezmax
• VLCC (Very large crude carrier)
• ULCC (Ultra-large crude carrier)

Tanker product and classes

Tankers can transport any liquefied material in bulk. Based on the material they carry, they are classified as follows:

• Asphalt/Bitumen Carriers
• Bunker Tankers Crude Oil Tankers
• LNG/LPG Tankers
• Product Tankers
• Chemical Tankers
• Other Tankers

Famous tankers

TI Class Tankers

Biggest oil tankers in the world (now scrapped)

Tanker Vessels: An Elucidation

As specified earlier, different variances of liquefied freight necessitate the use of different kinds of tanker vessels. Tanker ships are mainly classified on the basis of the type of cargo and size of the vessel. Some of the most commonly used tankers are:

• Crude Oil tanker
• Chemical tanker
• Product tanker
• Gas tanker

Crude Oil Tankers

Tanker vessels used for oil transportation through marine channels are referred to as oil tanker ships. The term ‘oil tankers’ is a broad term that covers not only crude oil tankers but also vessels used in the transit of distilled and processed rock oil.

Deadweight tonnage (DWT) determines the maximum capacitance of oil tanker ships. The classification of these tanker ships, therefore, is directly proportional to their DWTs /size.

Product Tankers

Vessels that help transport distilled rock oil, gasoline, petrol, and all petroleum-based organic compounds from their distilling units to the dispersion centres are referred to as product tankers.

Product tankers are specially designed due to the cargo they carry. Stainless steel is used to construct their cargo tanks, and they have corrugated bulkheads, complex piping systems, and deep well pumps.

They are of different types-

• MR type (Medium range)
• LRI type (Large Range 1)
• LRII type (Large Range 2)

The MR Type has a standard deadweight tonnage of 25,000 to 60,000, the LRI Type has 55,000 to 80,000, and the LRII type has 80,000 to 160,000.

Chemical Tankers

As the name suggests, chemical tankers carry industrial chemicals like caustic soda, sulphuric acid, etc., which are dangerous and pose a pollution threat. Chemical tankers are designed with stainless steel and specially coated tanks for safety reasons. 

Chemical tankers can accommodate different chemicals simultaneously since they have many smaller cargo tankers and piping systems that allow the subdivision of onboard systems so that different cargo can be loaded and discharged without being contaminated. They are a vital part of the industrial supply chain. 

Gas Carriers

These ships transport LPG or LNG used for heating, cooking, electricity generation and other industrial applications. Gas Carriers enable the distribution of these energy sources to customers around the world, which offers additional security to the global market.

History Of Tankers

In late 1861, Elizabeth Watts sailed a vessel carrying 224 tons of petroleum to England. The tanker industry was set up in about 1886, and specialised vessels were developed to transport oil worldwide.

The 2700-ton GLUCKAUF of Britain was the world’s first true oil tanker, with separate tanks for the oil built into its hull. It was the first ship to have oil compartments in which oil could be directly pumped, whereas earlier oil had been shipped in drums or barrels. The Glukauf is the tanker whose design we follow to this day.

Americans invented the tank steamship to carry oil in bulk; an enterprising Yankee demonstrated this fact. He stated that oil can be pumped directly through the pipeline to the steamship, and it can safely be transported across the oceans. This will reduce the cost of multiple barrels, as in one tanker, more oil can be transported.

But until 1950, it still made vessels to carry oil only instead of other liquefied freights.

Their significant achievement at the time was their fleet of 16000 DWTs, which is still in use. After the middle of the 20th century, tankers carrying all types of liquids and with larger sizes (VLCCs and ULCCs) came into existence.

In 1990, double-hull designs became more popular.

Other innovations of the 21st century did not work for modifying tankers but to ensure safety. Standards were set by IMO (International Maritime Organisation) to ensure the safer design of tanker ships.

Classification of Tankers

Based on the above principle, the tanker ships are mainly classified into:

• Suezmax
• Panamax
• Aframax
• Very Large Crude Carrier (VLCC)
• Handymax
• Capesize
• Ultra Large Crude Carrier (ULCC)
• Handy

ULCCs, or Ultra Large Crude Carriers, are the biggest oil tanker vessels currently in operation, with DWTs ranging to a maximum of about five hundred and fifty thousand tonnes.

The second biggest crude and product tanker vessel types in operation are the VLCCs or Very Large Crude Carriers. These vessels’ variances have a maximum DWT of slightly over three hundred thousand tonnes.

Find out more about VLCC and ULCC Vessels

Crude oil tankers and product tankers are also classified on the basis of the important international water conduits in which they can gain easy entryway. These vessels include:

The tanker vessels built to pass through the Panama and Suez Canal are referred to as Panamax and Suezmax vessels. The former vessels have DWTs up to eighty thousand tonnes, while the latter ships have DWTs ranging to about two hundred thousand tonnes.

After both canals underwent expansion, higher-capacity tankers were built to pass through them. These vessels are known as post-Panamax and post-Suezmax vessels.

Aframax tanker ships have DWTs up to slightly over 100,000 tonnes, and these tanker types can gain entryway to almost all harbour facilities across the world.

Find out more about Panamax and Aframax Tankers

Read here for an extensive classification of tanker ships

Gas tankers are specially built tankers which are used to carry liquefied natural gas (LNG) and liquefied petroleum gas (LPG).

Operational Procedure

The tanker operation should be well-planned and documented before actual execution. Each person present on the tanker and terminal should be familiar with the details of the plan, which should be modified before execution after proper consultations and formal recording of the changes.

Following are the operations which are executed on tanker ship transportation:

1. Setting of Lines and Valves
2. Pressure Valve Operations
3. Proper handling of generated pressure surges
4. Proper checking of Butterfly and Non-Return (Check) Valves
5. Loading Procedures
6. Discharging Procedures
7. Pipeline and Hose Clearing after all Cargo Operations

Loading Operation 

First, the tanker vessel’s owner/operator or charger issues the loading order. Before loading, the leakage of hose couplings should be checked. Tank lids are closed, and the tank riser is placed in the loading position.

Lower the ullage meter to its lowest position. Shut the suction and discharge valves. Connect the ship’s terminal lines and manifold through hoses.

After adequately checking the ship for all pre-loading operations, the ship indicates to the terminal that it is safe to open the loading valves now and start loading.

Actual loading operations are listed as:

1. Loading should be started slowly to ensure that all connections are oil-tight and there is no static accumulation. Supervise the pump room. If the oil is flowing overboard through sea chests, ask for immediate shutdown. Take samples of oil being loaded to check its temperature.

2. After checking, the speed of loading of oil may be increased to its maximum allowable rate.

3. The moorings, towing wire, etc., should be regularly supervised, and the loading speed should not exceed the maximum allowable rate. The tank valve is closed as soon as the ullage reaches its calculated level.

4. The speed must be minimised near the end of loading to diminish the chances of overtopping or overflow.

5. First, close the shore valve and then the manifold valves. The tank valves should be closed last. After closing all the valves, empty the drip tray hoses and loading arms before disconnecting them from the manifold. Blind flanges are inserted in the manifold valves after disconnecting the loading arms from them, and all the main and cross-over valves are closed.

Discharging Operation 

1. The ship’s or terminal representative or cargo inspector should take details of the ullage, density, and temperature of the freight loaded. This will help the receiver calculate the quantity of cargo before discharge.

2. Then, connect the hoses to the tank and open the tank ventilators. Free the pump room from gas and open the necessary valves.

3. Throughout the discharge procedure, keep the pump room ventilators running. Open the necessary cargo lines and terminal valves. Start the inert gas and let the pumps stand by until the discharging is about to start.

4. Open the short gate valve and ship manifold valves and start discharging. The safety measures and precautions to be taken during discharging are the same as in loading operations.

5. When discharging starts, the liquid level is at its highest value, and the discharging speed can be increased. However, when the liquid level is low, the discharge speed should be lowered to the minimum allowable draining rate.

6. If a grumbling sound can be heard from the tank outside, it implies that the tank is nearly dry. The drain wing should be familiar with the location of all the tanker’s suction valves. After draining the tanker completely, tank dips are taken in the presence of a terminal inspector.

7. Remove all the connections and drain the hoses and loading arms completely.

Tanker vessels are indispensable in the maritime domain. Thanks to technological advancements in their structural and constructional facets, their utility has become even more applicable and viable in the ever-growing field of maritime liquefied cargo transportation.

Tanker Market Study

According to the latest BIMCO report on the tanker shipping market, the supply-demand balance could tighten in 2024 and 2025. Fleet growth is low, and shipping distances are increasing due to the Red Sea Crisis. 

The ships are forced to avoid the Suez Canal and travel through the Cape of Good Hope route. An increase in the number of new tanker ships contracted will propel tanker fleet growth in 2025.

Crude tanker growth will be in the Suezmax and Aframax segments, estimated to grow by 2.8% to 4.2% until the end of 2025. VLCC capacity is said to increase by just 0.5%.

According to BIMCO, the product tanker fleet’s capacity will increase by 6.2% between 2023 and 2025. The fastest-growing segments are LR2s and MRs, with 13.9% and 5.3%, respectively.

You may also like to read:

• Panamax and Aframax Tankers: Oil Tankers with a Difference
• Different Types of Tankers: Extensive Classification of Tanker Ships
• What Are Gas Tanker Ships – Everything You Wanted To Know
• LNG Tankers – Different Types And Dangers Involved
• What were T-2 Tanker Ships?

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About Author

Zahra is an alumna of Miranda House, University of Delhi. She is an avid writer, possessing immaculate research and editing skills. Author of several academic papers, she has also worked as a freelance writer, producing many technical, creative and marketing pieces. A true aesthete at heart, she loves books a little more than anything else.

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