(i) Segregated Ballast Tanks (SBT): dedicated ballast tanks that are completely separated from the cargo oil and the cargo oil piping system, used only for ballast. They are required by MARPOL to provide adequate ballast capacity without carrying ballast in cargo tanks, so that the cargo tanks are not contaminated and the risk of oil pollution from ballast discharge is eliminated. SBTs are located in protective positions (see iii) and are arranged so that the ship can operate safely in ballast.

(ii) Clean Ballast Tanks (CBT): cargo tanks that have been cleaned and are used for ballast, but which are not dedicated; they are only used for ballast after the tanks have been cleaned to a standard such that the ballast water is clean (oil content below the discharge limit). CBT is an alternative to SBT permitted for existing tankers, but the tanks must be cleaned and the ballast water must meet the discharge criteria.

(iii) Protective Locations (PL): the requirement that the segregated ballast tanks and other spaces be located so that, in the event of a collision or grounding, the cargo tanks are protected from damage and the outflow of oil is minimised. The SBTs are placed in the wing and bottom regions (protective locations) so that they absorb the impact of a collision or grounding, reducing the risk of cargo tank rupture and oil spillage.

COW is a method of cleaning cargo tanks using the crude oil itself. During discharge, high-pressure crude oil is sprayed from fixed washing machines (rotating nozzles) onto the tank walls and bottom, dissolving and washing the clinging oil and sludge back into the cargo being discharged. The washing is carried out in a sequence with the discharge, and the washings are collected in a slop tank. The system uses the ship's cargo pumps and a dedicated COW piping system with fixed washing machines, and is operated under a COW manual and safety procedures (inert gas, gas-free checks).

(ii) Advantages of Crude Oil Washing.

• Reduces the amount of oil left in the tank (better stripping), so more cargo is discharged and less sludge remains.
• Reduces the need for water washing, so less oily water is produced and the risk of pollution is reduced.
• Reduces corrosion of the tank structure (less water and sludge in contact with the steel).
• Reduces the time and cost of tank cleaning.
• Improves the safety of tank entry (less gas and sludge).
• Reduces the amount of slop and the need for slop disposal.