A draft survey is a calculation of the weight of cargo loaded or unloaded to or from a ship from measurents of changes in its displacement. The technique is based on

Archimedes' principle Archimedes' principle (also spelled Archimedes's principle) states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces. Archimedes' ...

. The procedure is standardized by the

United Nations Economic Commission for Europe The United Nations Economic Commission for Europe (ECE or UNECE) is one of the five regional commissions under the jurisdiction of the United Nations Economic and Social Council. It was established in order to promote economic cooperation and ...

for the measurement of coal cargoes.

Procedure

The draft survey is performed by reading the ship's

draft Draft, The Draft, or Draught may refer to: Watercraft dimensions * Draft (hull), the distance from waterline to keel of a vessel * Draft (sail), degree of curvature in a sail * Air draft, distance from waterline to the highest point on a vesse ...

on the draft markings at six standard points on the hull: forward, midships and aft on both

port and starboard Port and starboard are nautical terms for watercraft and aircraft, referring respectively to the left and right sides of the vessel, when aboard and facing the bow (front). Vessels with bilateral symmetry have left and right halves which are ...

sides. Corrections for factors such as trim, water density and non-cargo weight changes are made before calculating the cargo weight change.

References

{{reflist Measurement Nautical terminology