Sea cargo reference
Tanker Market
Liquid cargo, split by what is in the tanks. The notes below cover the cargo, the way the hull is arranged, and the limit that puts a ship in this class.
- Ship's gear
- Self-discharging by cargo pump
- How capacity is counted
- Deadweight tonnes (DWT), cargo volume in cubic metres or barrels
- Usual size
- From under 10,000 to over 300,000 DWT
- Cargo type
- Bulk liquids and gases
The tanker market
These ships carry liquid in bulk. The market splits them by the liquid, not only by hull size. Crude, refined products, chemicals, liquefied gas and asphalt each need a different ship.
The shared layout is a double hull, cargo split across separate tanks, inert gas that keeps the vapour space below the oxygen level that would let it ignite, and the ship's own pumps and manifold so it can discharge without shore cranes.
The five tanker types further down differ in coating and tank build, in how the tanks are washed between cargoes, and in the rules they trade under.
Cargo on board
How the hull is arranged
- A double hull keeps cargo tanks off the sea, with ballast space on the sides and bottom. MARPOL requires this on oil tankers.
- The cargo sits in several tanks. Longitudinal and transverse bulkheads limit how far the liquid can slosh.
- An inert gas system holds the tank atmosphere below the oxygen level at which the vapour could catch fire.
- Cargo pumps and a fixed pipeline meet a manifold amidships, so the ship pumps its own cargo ashore.
- Tanks for cargo that must stay warm enough to pump carry heating coils.
Why this trade uses it
- Large volumes of liquid move with no packaging.
- The ship pumps itself out, so a terminal needs pipes and tanks rather than heavy cranes.
- Separate tanks let several grades travel on one voyage without mixing.
Settle these points before you fix
- Washing tanks between cargoes costs time and money. What the ship carried last decides what it may load next.
- Oil majors vet ships on top of class and flag rules, and that vetting decides who will take the ship.
- Pollution liability is heavy. Ship and terminal both follow strict transfer rules.