Oil Tankers: All You Need to Know

They are the largest moving objects ever built; their fleet carries over 100 million tons of oil in a single day. They are targets in war and targeted by environmentalists; they are an essential life line to industrialized nations around the globe. They are Oil Tankers.

Longer than most skyscrapers are tall they are steel giants carrying the earths most valuable commodity oil. Oil tankers transport over half of the 80 million barrels of oil the world consumes on a daily basis. The United States is the biggest consumer of oil but in only produces one third of what it consumes and the rest is imported from around the world.

Classification of Oil Tankers

Oil Tankers come in a range of sizes and are classified by their DWT or dead weight tonnage which is the tankers weight when fully loaded. The 5 dominant classes are named as:

1] Panamax {750 feet ,60000 DWT}

2] Aframax {850 feet,100000 DWT}

3] Suezmax {899 feet,150000 DWT}

4] VLCC i.e. Very Large Crude Carriers {1099feet,280000 DWT}                                                                        

5] ULCC i.e. Ultra Large Crude Carriers {1237 feet,410000 DWT}

The latter two are more commonly referred to as Super Tankers. In some cases, a tankers classification name also specifies the region in which it can safely operate when fully loaded. For example, a Panamax is the largest tanker that can safely pass through the Panama Canal whereas the Suezmax is the largest tanker that can pass through the Suez Canal.

Types of Oil Tankers
Types of Oil Tankers

Constructional Properties of Oil Tankers

The only purpose of the oil tanker is to carry oil lots and lots of oil and the intent is seen in the tankers design. Beneath the steel skin of the tankers there are a series of tanks subdivided by bulkheads. In a large size oil tankers tanks are generally divided into three compartments that extend the width of the hull and as many as forty compartments that extend the length of the hull. The main reason for this division is to avoid spilling and provide stability to the cargo. After the cargo tanks at the stern of the ship is a lone tower known as the super structure which consists of all the necessary control room and crew accommodations. The remainder of the deck consists of an array of pipes used to transport oil in or out of the compartments below.

Side view of Oil Tanker

Most product tankers and costal tankers are small in size and are single hull that is they do not have a double bottom. However recent MARPOL (Marine Pollution) Rules require tankers over 120m length to be double hulled irrespective of the type pf cargo.  Due to the additional environmental risk involved in operating single hulled tankers they are banned from carrying heavy grade oil to and from European ports. Panamax, Aframax, Suezmax, VLCC and ULCC tankers, all of them are double hulled. The primary reason of providing double hull in tankers is to prevent the contact of oil with the external environment in case of any breach in the structure of the hull. Because of having that extra layer, it is difficult for the oil to leak resulting in a smaller number of spills.

Since Oil Tankers operate at a low speed, of about 12 to 14 knots they are run by large slow speed marine diesel engines as there are no space constraints. These engines provide more shaft efficiency and gear box losses are highly reduced as the RPM of the engine is same as that of the propeller.

In-Build systems in Oil Tankers

Oil tankers have various systems for various operations, some of them are listed below:

Cargo Oil Heating System: Crude oil is heavy and becomes thick and sluggish in cold environment which hamper the flow oil in pipes during discharge. So, a cargo oil heating system is installed to maintain the suitable temperature and viscosity of the oil.

Cargo Tank Venting System: Cargo oil tanks are never fully filled in order to allow space for oil vapour. These vapour are highly inflammable, so a proper venting system is used which allows to vapours to escape from closed spaces and prevent accumulation.

Overflow Control System: In order to ensure that the level of oil in the tank does not exceed the design head this system uses a level and pressure cascade control. In case of any spill, spill valves and high-level alarms are connected to the system to take action.

Inert Gas System: In case of any accumulation of oil vapor there is a chance of a potential fire situation. Vacant spaces between the free surface of the cargo oil and the top plating of the tank is kept inert in order to prevent potential fire situation. This is done by supplying and regulating inert gas in cargo oil tanks, the space above the oil surface is ensured to be completely occupied by inert gas. Common gases used are Argon and Carbon Dioxide.

Fire Fighting System: This is the most vital system on board for the safety of the oil tanker and is designed as per MARPOL rules. Fire hoses, extinguishers and sprinklers are distributed along the ship’s length and breadth for all access points. There is a CO2 bottle room just above the engine room to allow flooding of CO2 in case of engine room fire.

Fun Fact: Tech giant Samsung is one of the largest ship builders in the world. Samsung Heavy Industries Co., Ltd is a core subsidiary of the Samsung group and is one of the ‘Big Three’ shipbuilders in South Korea.

Salient Features of Oil Tankers

As soon as an oil tanker leaves the port it becomes a self-sufficient floating city capable of producing all of its own electricity. Oil tankers have huge generating units which generate electricity to keep all the equipment and systems working. A VLCC requires only a single 30000 horse power diesel engine for power. The propulsion system comprises of a single propeller and rudder which has the capacity to move a fully loaded VLCC at the speed of 15 knots. Crude Oil in a container is offloaded by the help of huge steel pipes which extend to the length of the tankers center compartments. When the vessel is ready for discharge hydraulic pumps are employed which create vacuum inside the steel pipes. There are various navigation systems present in order to guide the ship from bad weather. For the entertainment purposes of the crew present on the tanker there is a gym, recreational room and a bar present in order to avoid boredom and have healthy physical and mental state. Some of them are also equiped with complete set of musical instruments onboard.

The history tankers date back to thousands of years ago when oil was transported in barrels. Since then, there has been a large number of changes in the design and an increased efficiency over the years.

15 thoughts on “Oil Tankers: All You Need to Know”

  1. I am lucky to read your article on Oil Tankers. I was impressed with how well written and researched the article proved to be. It has enhanced my knowledge on the subject, and created a desire to know more.
    I am looking forward to your future work which I hope will be on the same subject.
    Well done, keep writing, this is just the beginning for greater laurels ahead!

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