What Is a Tanker Ship?

One of the most important typologies of ships that have helped improve our daily lives and commodities is the tanker ship.

Tankers ship represents part of one of the most important technology evolution that man has ever made. The continuing evolution and improvement for these ships have developed ships that can carry different types of bulk liquid cargoes.

Nowadays, tanker ships are the main marine responsible for carrying liquid cargoes, and they do it by carrying an incredible quantity of oil each year.

What is a taker ship? Although several definitions can be attributed to the tankers ships, the USCG (United States Coast Guard) defines a tank vessel as a vessel constructed or adapted primarily to carry, or that carries, oil or hazardous material in bulk cargo or cargo residues.

Then making further distinctions between a tank ship and tank barge, defining a tank ship as a ship self-propelled, and a tank barge if it hasn’t any means of propulsion.

Before diving more into details about the characteristics of tankers ships is good practice to take a look at the history and evolution of that beautiful ships.

History of tanker ships

The first tanker ships that have ever sailed on the sea was the Elizabeth Watt that sailed for England in 1861, carrying 224 tons of petroleum. So anyway, we should consider that she was the first ship that carried bulk liquid cargo on the sea, but she wasn’t the first truly tanker ship.

In fact, the first ship that was built for the specific role of serving as tanker ships arrived after some years.

The Gluckauf can be considered the first tanker ship built to carry liquid cargo.

With the passing of the years, the number of tanker ships was significantly increasing, thanks to technological advancements, particularly after the invention of the diesel engine used rather than coal systems as propulsion.

1950 until nowadays 

In the 1950 years, the dimension of tanker ships was already reaching 16.000 tons. Still, the essential evolution and boom of size arrive in the middle of the 20th Century, thanks to the increase in demand for the motor car.

The dimension after this incredible demand increase until reaching 30,000 tons. And that size can be defined as limited because of restriction on the passing of the Suez Canal.

What determinate the increase of the tanker ship size was the closure of the Suez Canal. In fact, due to the longer voyage that the ships were obliged to do, the tanker owner started to build bigger tanker ships to have more margin of revenue.

1959 the Tanker ship Universe Apollo become the biggest tanker ships, with a deadweight of 114,356. After that ship, the world of tanker ships continues to grow until reaching incredible sizes, as we will see during the next part of the article.

Tanker ships Construction Evolution

Single hull Construction Tanker ship

The first type of tanker ships was built by using a single hull, making use of a longitudinal system. The bulkhead section’s main configuration of a tanker ships was provided by using twin longitudinal bulkheads, creating a 3 tanks configuration athwartships in the vessel: a centre tank and a set of wing tanks.

This configuration was wieldy used and implemented with success; the only problem was during the tank cleaning operations, resulting in more difficulty.

Double hull construction tanker ship

In late 1960, pushed by political and environmental pressure, the owners of tanker ships had to shift from single-hull construction to double hull constructions.

In particular, one event has determinate this important change, and it was the grounding of a single hull tanker ship Exxon Valdez in 1989.

What is a double hull design?

The double hull design is a type of design used by tankers ships that consist of using 2 pieces of steel, inner and outer hulls, to separate the cargo area from the sea to minimize oil outflow in case of collision or shell damage.

Classification of tanker ships

Tanker vessels are classified according to the type of cargo that they will carriers routinely over many voyages.

The classification of tanker vessels is summarized in three main categories:

1. Crude-oil carriers

2. Product carriers

Clean (gasoline, jet, diesel, etc.)

Dirty (black oils—residual fuel oils, vacuum gas oils, asphalt, etc.)

3.Parcel carriers (chemical/speciality cargoes, etc.)

Anyway, the one mentioned before is not the only classification made on the tanker ships; there is a more common classification called the deadweight tonnage.

Classification of Tankers according to Deadweight Tonnage

CategoryTonnage RangeTrade
Handy/Coastal/Parcel/Barge5,0000 to 35,000 dwtProduct/parcel
Medium35,000 to 160,000 dwtProduct/ crude oil
VLCCs (very-large crude carrier)160,000 to 300,000 fwtCrude Oil
ULCCs (ultra-large crude carrier)300,000 dwt and aboveCrude Oil

As you can see on the table, Tankers ships can reach incredible dimensions; to give you a clearer idea about length and breadth, I decided to list the biggest tankers ships that were present and served during the past years.

Biggest tankers ships ever built.

Seawise Giant.

The first and most giant ships that were ever build was the Seawise Giant.

The seawise giant characteristics are scary; she was 414m in length, with a displacement of 657.019 tonnes and a draft of 24.6m.

Due to her incredible dimension, it wasn’t possible to navigate through the Suez Canal and Panama canal as well.

Loading operation for a tanker ship

The loading operations in a tanker ship and the discharging operation can be considered the most crucial part that the crew on board should take care of.

Usually, before loading the cargo into a tank, some necessary checks must be performed from the personnel on board.

These are:

  • know the unit weight of cargo 
  • Know the amount of space that cargo will occupy

But this is not all. Because once the cargo is loaded into a tank, it is necessary to determine the effectively loaded quantity into the tank.

And the last step, at the discharge port recalculating the exact quantity onboard before discharging it.

For more details, take a look at the loading operation for a tanker ship

Discharge operation for a tanker ship

The discharge phase for a tanker ship is crucial; when preparing to discharge, the pumps should be slowly filled at a maximum 10%, and in particular, the initial flow should be controlled and slowly open.

Some point that must be checked during the discharge operation are:

  • the IGS is operating normally
  • cargo is being received by the reception facility
  • cargo is only being discharged from the
  • appropriate tanks
  • levels are not changing significantly in the
  • cargo oil tanks that are not being discharged
  • the engine room has confirmed that the pump
  • speed can be increased
  • control or pump valves are fully open
  • pump suction gauges are steady and indicate
  • the appropriate pressure for the static suction
  • Pump discharge gauges are matched.
  • There are no cargo leaks in the system

The importance of cargo measurement on tanker ship

We often mentioned that calculation is made during the loading and discharging phase related of cargo liquid for tanker ships.

To understand the importance deeply that having an accurate estimation of cargo into the tank has is important to know how the tanker ship market works.

What is the purpose of tanker ships?

The purpose of tanker ships is to carry bulk liquid cargo, which earns and gives revenue for the vessels owners.

To make it most efficiently and accurate on the measurements of the cargo on board is fundamental.

How is cargo measured on board of tanker ship?

To maximise the accuracy during the loading and discharging operation, the measurement is conducted by physical gauging, temperature, and sampling.

How is the cargo purchase?

In general, there is three main part involved during the transportation of bulk liquid cargoes, these are:

  1. Charterer
  2. Master
  3. Terminal

The charterer is the figure that is usually a figure that has arranged to purchase the cargo from a supplier at a loading port.

Then the Terminal has the responsibility to supply the vessel with the amount of cargo ordered by the charterer. The quantity delivered is then listed on a bill of lading or a certificate of quantity.

The figure of the master of the ship enters the game once the cargo is on the ship’s tank, and his crew start the measurements.

If the discrepancy between the cargo assigned on the bill of landing and the effective cargo loading onboard is minimum, the master will sign it without any problem.

Opposite case in case the volumes declared has a large discrepancy. In that case, the master usually signs the bill of lading under protest, noting the disparity between the 2 values.

Cargo piping systems

As tanker ships mainly deal with liquid cargo, the piping systems are an important part of any tank vessel. The main purpose of piping systems inside tanker ships is to provide the path for liquid flow to and from the cargo tanks.

In facts, due to the important role that the piping system has onboard this ship, the person responsible for dealing with the piping systems must be familiar with that to avoid any possibility of oil spilling.

The general approach to classified and give an order to the piping system onboard ships is the one to divide the piping system by locations, in particular: 

• Bottom Piping

• Deck piping

• Pump Room piping


I hope that this article gives you a clearer idea about the tanker ship and why it is so important. Many others things may be analyzed about tankers ships, and this is what we will do in the upcoming articles