Oil tanker
A crude oil tanker is designed to carry large amounts of non-refined oil in bulk around the world. Sizes can be up to 550.000 GT. There are various sizes of oil tankers, such as:
10.000–24.999 DWT: General Purpose tanker
25.000–44.999 DWT: Medium Range tanker
45.000–79.999 DWT: Large Range 1
80.000–159.999 DWT: Large Range 2
160.000–319.999 DWT: Very Large Crude Carrier
320.000–549.999 DWT: Ultra Large Crude Carrier
The hull design is an important component of the structure of an oil tanker. Nowadays there are two types of hulls in existence; the double hull tanker and a hybrid of both.
The double hull construction became mandatory for tankers with cargo capacities larger than 5000 tons, which are built after 1993. This means that after 2015 no single hull tankers will be in service anymore, while for the carriage of heavy grade oils, this requirement applies from 2010. A ballast tank usually separates the double hull with a space of approximately 2-3 meters. This means that in the cases of minor grounding or minor collision, oil release is unlikely.
The inert gas plant:
To protect the oil tanker from explosions, an inert gas plant is installed. This keeps oxygen levels below 8% in all ‘empty’ cargo tank spaces by ‘filling’ them with carbon dioxide and nitrogen to prevent formation of explosive/flammable vapour mixtures with air. This is required for oil tankers > 20.000 DWT.
The Fuel tanks:
Just as any other ship, a crude oil tanker needs fuel. Most of the tankers use slow running two-stroke engines that can cope with very heavy fuels. These fuels are located in bunker tanks situated in wing tanks near the engine room. On newer ships these wing tanks are protected external impact damage by void spaces or ballast tanks.
The Cargo tanks:
Each oil tanker is divided into several cargo tanks. Each tank is restricted to a maximum size related to the size of the tanker. Accordingly, the oil tanker will not spill all of its cargo on any single impact while such sub-division gives extra strength to the vessel’s hull. The cargo of oil tankers could be crude oil or products such as fuel oils.
The maximum tank size of a centre tank is 50.000 MT (Metric ton), while for the more vulnerable wing tank it is 30.000 MT.
