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  • Writer's pictureSarah Whiteford

What is a Tanker Ship?

Tankers are vessels that carry liquefied freight. This can be anything from rock oils to alcoholic beverages, including liquefied oil products. We're going to focus mainly on petroleum and natural gas products and the tankers that transport them.

Sirius Star - Image Credit: Wikipedia

When did people start using tankers to transport liquid cargo?

As crude oil became a popular source of energy in the 1850s, a new method was needed to transport “black gold” from where it was found to where it was used. In the 1860s, oil tankers were built that were powered by wind sails. Early tankers were filled by pouring oil into holds and then shipped from America to Britain. Later, 40 gallon barrels were used but were heavy at 64 pounds empty. This was expensive as they were only used once, and they tended to leak. In Russia, this resulted in about half the cost petroleum production being the barrels themselves!

According to HowStuffWorks, not long after “1873, the Palmers Shipbuilding & Iron Company assembled the first steam-driven oil tanker, named the Vaderland.” In 1878, the first modern oil tanker was built by Ludvig Nobel in Sweden. Ludvig and Robert Nobel, brothers of Alfred Nobel of the Nobel Prize, ran Branobel, a large oil company at that time. The Zoroaster held 246 metric tons of kerosene in two iron tanks joined with pipes. In 1883, tanker design improved dramatically, using multiple, divided holds to all but eliminate the free surface effect, where oil could slosh back and forth and capsize a ship.

Heather Knutsen - Image Credit: Marine Insight

What types of oil tankers are there?

Crude tankers and product tankers are the two basic categories of oil tankers. As you might expect, crude tankers transport crude oil that has not yet been processed. These are the larger of the two, and as we’ll cover later, can be absolutely massive. Product tankers transport oil products that have been already been refined and are ready to be sold. They are smaller and built to carry substances like gasoline from a refinery to the consuming market. Oil tankers are the most efficient way to transport petroleum products outside of a pipeline, with transport costs averaging about $0.02 to $0.03 per gallon.

Tanker ships can be used for other purposes than simply transportation: they can be built as replenishment oilers to refill ships at sea. If they become uneconomical to operate, they can be used as floating storage vessels.

What are some of the common terms used to describe oil tankers?

  • Double hull – this is a two hull design with one hull inside the other. This is a now mandatory design that helps to prevent oil spills in case of an accident.

  • DWT or Deadweight Tonnage – a measurement in metric tons of the maximum load of cargo.

  • OBO – Ore-bulk-oil carriers are set up to transport oil and then transport a material like iron ore on the return trip.

Tanker Ship Chart - Image Credit: EIA

Tanker sizes:

  • General Purpose tanker – 10,000-24,999 DWT

  • Medium Range tanker – 25,000-44,999 DWT

  • LR1 (Long Range 1) – 45,000-79,999 DWT

  • LR2 (Long Range 2) – 80,000-159,999 DWT

  • VLCC (Very Large Crude Carrier) – 160,000-319,999 DWT

  • ULCC (Ultra Large Crude Carrier) – 320,000-549,999 DWT

What is a Supertanker?

ULCCs and some VLCCs are classified as Supertankers. With capacities of over 250,000 DWT, they can hold 2,000,000 barrels of oil. These ships cannot even enter ports at full weight, and have to unload some of their cargo offshore. Their large size also means they spend a lot of time at sea, sometimes 70 days at a time. Long routes with huge amounts of oil makes these ships a tempting target for pirates. In 2008, a pirate attack on a large supertanker brought attention to this danger. After this incident, crews were issued guidelines for avoiding and foiling attacks while minimizing the chances of an encounter before it happens.

Supertanker – Image Credit: Freight Waves

What about gases?

Gas tankers are different from crude or product tankers since they are built to transport gases. They are more specialized and more cutting-edge than their oil carrying cousins. There are four main types of gas tanker:

  1. Fully pressurized ships carrying pressurized gas at ambient temperature. Since gases are transported at air temp, they have no insulation or refrigeration systems. They are usually smaller ships due to the design pressure and weight of the tanks.

  2. Semi-pressurized can carry substances at a maximum pressure of about 5-7 bar. Due to their flexibility in working with a wide variety of cargo, these are very popular with owners and operators.

  3. Ethylene ships are set up with the same Type C pressure tanks of the fully pressurized ships, but with added thermal insulation and liquefaction.

  4. LNG ships carry liquefied natural gas at temperatures as low as -160°C. The tanks are heavily insulated to reduce the amount evaporation or “boil-off”, although some ships are powered from the boil off from the cargo. LNG ships are of double-hull design and have four to five large LNG tanks to hold the gas. According to Energy Education, “In addition to these ships being advanced in the way that they hold the LNG, they are also equipped with advanced gas and fire detection and suppression systems to ensure that even a small leak would trigger a response.”

LNG Ship - Image Credit:

Are tankers safe?

After the Valdez oil spill in 1989, stricter standards have been implemented on tanker ships. The Valdez ran aground and spilled 11,000,000 gallons of oil in Alaska’s Prince William Sound. New standards arose quickly after that incident, with the most significant change being supertankers switching from single-hull to double-hull design. Double hull was the required standard by 2010 and single hull designs were completely phased out. Even smaller tankers above 20,000 DWT are installed with inert gas systems. These systems pump gas from the ship’s boiler flue into empty and partially filled tanks, making the air almost impossible to ignite.

Why do we need tankers?

Tankers allow the transport of oil all over the world, giving mobility and power to billions of people. They started with a simple sailing ship tanker in the 1950s and we currently have tankers that are 333 meters long (over 1000 feet)! They transport crude oil, products, LNG, and all types of liquids all around the world to places where only ships can go. Oil tankers have also been the subject of some serious spills, and therefore are heavily regulated to be safer with better double hull designs, fire response and prevention systems, and other technology. As long as we need to transport liquids over long distances, there will be tanker ships.

Happy Fun Fact Friday!


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