Work out draft survey quantity instantly with clear inputs, formula shown and shareable results.
A draft survey measures cargo by weighing the ship: displacement after loading minus displacement before, corrected for dock water density and adjusted for any change in bunkers, fresh water and stores. It is the accepted method for bulk cargoes where weighing ashore is impractical.
Draft survey
Cargo = (final - initial displacement) x density correction - change in deductibles
Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.
Typically 0.3-0.5% on a full cargo when carried out carefully in calm water. Trim, list, hog and sag corrections all matter.
The hydrostatic tables assume 1.025 t/m3. Brackish or fresh dock water changes the mass represented by the same displaced volume.