Draft survey

A draft survey determines the weight of bulk cargo loaded or discharged by measuring the ship’s displacement before and after. The surveyor reads the six draft marks, corrects for trim, list, hull deformation (hog or sag), and water density, and reads the hydrostatic tables to get displacement, then deducts ballast, fuel, fresh water, and constants to isolate the cargo weight. Done carefully the method is accurate to within a fraction of a percent, which is why it is the accepted basis for bulk cargo quantity disputes.