Ullage
Meaning
Ullage is the empty space between the surface of the liquid cargo and the top of the tank, measured to work out how much cargo is on board.
Ullage explained
Tankers measure ullage in each tank with fixed or portable gauges, then convert it to volume using the tank's calibration tables and to weight using temperature and density. Ship figures are compared with shore figures to check for losses.
Ullage space also lets the cargo expand as its temperature changes.
Related terms
Remaining on board
Remaining on board (ROB) is cargo left in a tanker's tanks after discharge; on-board quantity (OBQ) is residue already in the tanks before loading.
Cargo shortage
A cargo shortage is a difference between loaded and discharged quantities; many tanker charters let charterers deduct losses above 0.5%.
Vessel experience factor
The vessel experience factor (VEF) is the average ratio between a ship's measured cargo figures and shore figures, used to correct ship quantities.