Reference
Crude Carriers
The largest tankers afloat. What it carries, how it is built and the limits that define the class.
- Cargo gear
- Self-discharging by cargo pump
- Capacity measured in
- Deadweight tonnes (DWT); cargo in barrels
- Typical size
- From about 80,000 DWT to over 320,000 DWT
- Cargo type
- Crude oil
About crude carriers
Tankers moving crude oil from producing regions to refineries, and the largest merchant ships in service by cargo weight.
Sizes carry their own market names: Aframax, Suezmax, VLCC — Very Large Crude Carrier, around 300,000 DWT — and ULCC above that. The names refer to trade routes and canal constraints rather than to any formal standard.
Because crude does not need the tank coatings that refined products do, these ships are built for volume rather than cargo flexibility. The largest often load and discharge offshore, since few ports have the depth to take them alongside.
What it carries
How it is built
- VLCCs and ULCCs are the sizes most used on long-haul crude routes, carrying roughly 200,000 to 400,000 tonnes.
- Aframax and Suezmax sit below them, and are chosen where the route runs through a narrow waterway or the terminal cannot take a larger ship.
- A double hull — cargo tanks separated from the sea by ballast space on the sides and bottom — mandatory under MARPOL for oil tankers.
- Cargo divided between several tanks, with longitudinal and transverse bulkheads limiting the free surface effect of liquid movement.
- An inert gas system that keeps tank atmospheres below the oxygen level at which the vapour space could ignite.
- Cargo pumps and a fixed pipeline system with a manifold amidships, so the ship discharges its own cargo.
- Heating coils in tanks intended for cargo that must stay warm enough to pump.
Why it is used
- Moves very large volumes of liquid with no packaging at all.
- The ship discharges itself, so terminals need pipework and storage rather than heavy lifting equipment.
- Segregated tanks allow several grades to travel on the same voyage without mixing.
What to check before fixing
- Tank cleaning between cargoes takes time and cost, and the previous cargoes carried determine what may be loaded next.
- Vetting inspections by oil majors govern which ships are acceptable, over and above class and flag requirements.
- Pollution liability is severe, and both the ship and the terminal operate under strict transfer procedures.
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