Cofferdam and Drain Tanks
What do you mean by cofferdam?
To avoid the mixing of two different liquids a void space/empty space is provided between two tanks. This prevents any accidental intermixing of two different liquids due to leaking.
What is stuffing drain tank?
Stuffing box oil can be re-used because the oil is not contaminated. Whatever oil from crank case is scrapped by the stuffing box from piston rod; it is drained to the stuffing drain tank.
What is scavenge drain tank/dirty tank?
Whatever waste oil produced in the scavenge spaces or present in the scavenge spaces is drained to scavenge drain tank.
The oil present in the scavenge space is mainly from the cylinder lubrication drained along with the unburned carbon particles which are present due to the blow past of the piston rings. This oil cannot be re-used so it is called dirty oil.
The scavenge drain oil is mainly burned in the incinerator which is present in the ship to burn the wast sludge and oils which cannot be used.
In next article we can see the MIDDLE PLATFORM of the engine room .