Ever wondered how liquid and gaseous cargo is transported around the global trade routes? Well, they are transported across sea routes with the help of special type of vessels called tankers. This article will take you deeper into the fascinating tanker shipping sector, which is responsible for the global energy trade.
What Are Tanker Ships?
Vessels that simplify the transport and supply of mass quantities of liquified and gaseous cargo are referred to as tanker vessels. Cargo like organic compounds, chemicals, fuels, hydrocarbons (LNG, LPG and more) juices and even alcoholic beverages are transported via tanker ships. Tankers range in size from vessels of a few hundred tons like vessels for servicing small coastal settlements and harbors to several hundred thousand tons of long-range haulers.
Also Read: Types of Ships: Ultimate Guide
History of Tanker Ships
The Introduction of tanker ships date back to the 1800s when the era of industrial boom was gathering momentum slowly, before the late 19th century, technology simply did not support the idea of carrying bulk liquids and gases or selling them in the market. The first tanker ships were used for the transfer of refined fuel in bulk from refineries to the consumers by the oil industry. The very first oil tanker ship in the world, Zoroaster was the first one to carry liquid cargo in tanks contrary to the idea of transporting liquid cargo like oil in casks and drums which were very unsafe and time-consuming. In 1861, a vessel carrying 224 tons of petroleum was navigated to England by Elizabeth Watts and it was the first cargo-carrying liquified material. The 2,700 ton GLUCKAUF was the first tanker which had separate tanks built into it’s hull for oil. The benchmark size of a tanker at that time was around 16,000 DWT. Slowly over the decades, the tanker population evolved into Very Large Crude Carriers (VLCCs) and Ultra Large Crude Carriers (ULCCs).
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Classification of Tanker Ships
Tankers can be largely classified based upon their types, their purpose, the vessel’s hull type and the size of the vessel. Let us now look at each type of tanker ships based upon these factors.
On the Basis on type, tankers can be classified into:
- Oil Tankers
- Gas Tankers
- Chemical Tankers
1. Oil Tankers
An Oil Tanker is designed to carry crude oil, petrol, gasoline products in bulk. Their size range from 55,000 DWT to VLCCs over 300,000 DWT. Oil tankers are indulged in carrying products ranging from crude oil to refined products. Oil tankers are primarily divided into product tankers and crude tankers.
Product tankers, as the name suggests are used to carry various petroleum based products, mainly refined oil of various grades. They are coated with epoxy in order to protect the cargo from chemicals and ease of tank cleaning.
Crude tankers are specifically used for the transportation of crude oil to the refineries from the crude oil extraction site, where the oil is refined to various grades and the products are extracted and distributed.
2. Gas Tankers
Gas tankers are equipped with the most cutting edge technology and they are used to transport compressed gases in bulk. They are mostly built in the advanced shipyards of Japan or Korea.
Gas Tankers can be further classified into
- Fully Pressurized Ships
- Semi-Pressurized Ships
- Ethylene Ships
- Fully Refrigerated LPG Ships
- LNG Ships
Fully Pressurized Ships
These type of tankers have tanks made up of carbon steel with a design pressure of 18 barg in ‘C Type’ where there are no thermal insulations. They are usually small in size because of the design pressure and the weight of the tanks. The cargo can be directly transferred by the compressors or pumps.
Having a design similar to the construction of fully pressurized ships, these vessels have a maximum working pressure of 5-7 bars. They are popular in the coastal areas of Mediterranean and Northern Europe.
These types of vessels are built to carry all type of cargo but also have special facilities to carry Chemical Gases or LPG’s. They have Type C pressure tanks having capacities of around 1000 – 1200 cubic meters. Thermal Insulation and liquefaction are fitted on this variant of gas tankers.
Fully Refrigerated LPG Ships
They have tanks constructed in a prismatic shape made up of 3.5% which makes them suitable cargo at extremely cold temperatures ranging to -48 degrees centigrade.
These are vessels that carry Liquified Natural Gas (LNG) and require to be handled and looked after owing to the precious cargo that they carry. They have a cargo capacity between 125000 m3 to 135000 m3. Around 193 LNG tankers are currently under operation worldwide. These carry LNG in their boiling temperature (-162 degree centigrade) and are fitted with independent cargo or membrane tanks. These vessels typically have a lifespan of around 20-25 years.
These tankers can be further classified into four categories in terms of the cargo containment system.
Moss (Spherical-Type A)
The Norwegian company, Moss Maritime have designed the system and thus this system has been named after them. Most of these vessels have 4-5 tanks which have a operating pressure of 22kPa or 3.2psi, that can be increased if needed.
IHI (Prismatic-Type B)
Designed by Ishikawajima-Harima Heavy Industries, these self-supporting prismatic Type B tank has been employed only in two vessels in order to cater to the problem of sloshing over the membrane in LNG Carrier tanks and sustain internal accidental damage due to equipment releases.
TGZ MARK III
These type of membranes are designed by Technigaz and consists of waffles, the primary barrier is made up of stainless steel of 12mm thickness. The secondary membrane is followed by a primary insulation which is a new secondary insulation all of which are supported by the vessel’s structure from the outside.
Made up of a material called Invar and designed by Gaztransport into primary and secondary membranes, these tanks have no thermal contraction. Here the plywood boxes are filled with perlite for insulation and flushed with nitrogen gas.
CS1 refers to the combined system no.1 which is designed by Gaztransport and Technigaz. The primary barrier is made up of Invar and the secondary is constructed out of Triplex. Only 3 vessels are made using this membrane system by 1 shipyard.
3. Chemical Tankers
Ranging in sizes from 5000 DWT to 35000 DWT, these type of tankers are used to transport various types of liquid chemicals. They are designed specifically to maintain consistency and the size of these vessels is smaller compared to oil tankers due to the size restriction of ports and shore facilities and specialized nature of the cargo. The tanks in these vessels are often coated with Phenolic epoxy or zinc paint or stainless steel based on what type of chemicals they carry.
They can be further classified into three types
These types of tankers carry very hazardous cargo and can pose very serious environmental and safety hazards if there is leakage so maximum preventive measures are taken to prevent that from happening.
These tankers carry moderately contagious cargo and require significant preventive measures.
Products with amply severe safety and environmental hazards require lower preventive measures when compared to TYPE 1 and TYPE 2 are carried by these tankers.
Based on their purpose, tanker ships are classified into the following:
Slurry Tankers carry waste materials and all those materials that do not dissolve in water. These type of vessels are used to carry frittered products like fertilizers to places where they are put to productive use.
These tankers, as the name suggests are used for the bulk transportation of Liquified Hydrogen gas. Kawasaki Heavy Industries was the first one to design a hydrogen tanker.
As per the naming, these tankers are designed and fitted to carry mass quantity of juices namely fresh or concentrated. These tankers are occupied with preservation plants and temperature control systems which help to keep the cargo fresh at all times.
As the name suggests, these tankers are specially designed to carry wine from the place of production to the final destinations.
On the basis of their hull type, tankers can be classified into the following:
Single Hull Tankers
As the name suggests, only one outer layer runs around the structure of the vessels making it prone to leaking ballast thus making it a threat to marine environment.
Double Hull Tankers
Double hull tankers have a double layer of watertight protection all around the vessels. The gap between the hulls is used as ballast tanks for maintaining stability.
Based upon their sizes, tankers can be classified into the following:
- Small Range (Product) Tanker: 10,000 to 60,000 tons DWT.
- Panamax Tanker: 60,000 to 78,000 tons DWT.
- Aframax (Average Freight Rate Assessment) Tanker: 80,000 to 1,20,000 tons DWT.
- Suezmax Tanker: 1,20,000 to 2,00,000 tons DWT.
- VLCC (Very Large Crude Carrier): 2,00,000 to 3,20,000 DWT.
- ULCC (Ultra Large Crude Carrier): 3,20,000 to 5,50,000 DWT.
Small Range (Product) Tankers: These vessels carry cargos of refined petroleum products over relatively shorter distances, such as from Europe to the U.S. East Coast.
Panamax Tankers: The tankers that can operate in the Panama Canal is known as the Panamax tankers.
Aframax Tankers: Mainly used in China, Black Sea and the Mediterranean, these tankers weigh in around 80,000 to 120,000 DWT.
Suezmax Tankers: The tankers that can operate in through the Suez Canal are called Suezmax
VLCC: Very Large Crude Carriers or VLCCs are tankers having a cargo carrying capacity of 25,00,00 tons.
ULCC: Ultra Large Crude Carriers or ULCCs are the ones which have a hauling capacity of up-to 50,00,00 tons.
Working of Tanker Ships
Much like that of the bulk carriers or container ships, tanker ships too, are work on the basic principle of demand and supply.
Let us assume that there exists an importer, the one who wishes to receive a certain quantity of liquified or gaseous cargo. This requirement is fulfilled by an exporter, who will be selling and thereby sending the required liquified or gaseous cargo to the importer. This transaction is fulfilled by tanker ships, where exporters send liquified or gaseous cargoes to various of importers around the world through tankers.
Before loading cargo, the shipowner (or operator) enters into a detailed agreement which is called a charter. There are several types of charters which exist in the tanker shipping sector. Some of which are called bareboat charters, spot charters and time charters.
Design of Tanker Ships
The general arrangement of a tanker is given below. The cargo oil tanks are similar sized so as to maintain balance and symmetry and each are designed depending on the total expected DWT of the ship. The main deck is usually laden with a network of pipelines which make possible the loading and the unloading of cargo.
The signature design of a tanker ship is the bulbous bow, that is used for increasing the power efficiency of the ship. The design can be classified into three types.
The Delta type bulb has more volume concentrated at the lower half, than the upper half. This property makes it advantageous to be used in ships that have frequent changes in waterline, as more concentration of bulb volume at the lower portion ensures bulb immersion for a larger range of waterlines and loading conditions.
The O-type bulb has maximum volume concentrated at the center. This is used for most ships that require a cylindrical bow shape, for example – Tankers.
The Nabla type bulb is almost shaped like that of a tear-drop, with more volume concentrated at the top. This shape of bulb is preferred in ships that are to be equipped with exceptional sea-keeping abilities, for example – warships.
Future of Tanker Ships
Tankers today are an integral part of global trade and the fleet of merchant vessels and still enjoys a big position in the operational part of the maritime sector. With the industrial boom all over the world and the demand of goods soaring everyday with introduction of new technologies, tankers have experienced an unimaginable increase in sizes in the past few decades. With the introduction of new laws and rules set up by MARPOL, the shipping industry is being revolutionized to be at par with the wave of 3Ds that is being followed; Decarbonization, Digitalization and Diversification. The abatement of SOx and NOx compounds has forced several shipping companies to set up goals and plans for going green and aiming for net-zero carbon emissions from ships by 2050. Companies like A.P. Moller – Maersk are aiming to do it by 2040. This calls for the use of alternative fuels for shipping which have no harmful emissions when burnt. Fuels such as methanol, Liquified Natural Gas (LNG), Liquified Biogas, Methanol, Hydrogen.
With ever-increasing population and the demand soaring by the day, the supply and demand of good will continue to soar. Tanker ship’s demand will continue to remain unchanged owing to the increase in global import / export and the longevity of these vessels. The capacities of refineries across the middle east are increasing and with emerging number of petroleum reserves in the US and Asia, the trading lanes of tankers are expected to prosper more. No doubt tankers will continue to be a part of this global merchant fleet for decades to come.