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Draft Survey
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Draft Survey

When shipping containers and project cargo, the weight can be determined relatively easily by weighing the individual containers or individual goods. When loading bulk cargo, determining the total weight is somewhat more difficult. 

The following are used:

  • Weighbridges to determine the mass of each individual truck transporting the bulk goods.
  • Conveyor belt carts that record the weight of the load while the goods are being loaded.
  • Draft Survey: Here, according to the Archimedes principle, the weight of the cargo is determined based on the changed draft of the ship.

Weighbridges and conveyor belt cars are not available in every port. However, determining a ship's draft is possible anywhere and at any time. 

How does a draft survey work?

  • Determination of water density and water temperature.
  • Sounding of the ballast and bunker tanks and calculating the individual masses.
  • Reading the draft at six points.
  • Determination of trim.
  • Determination of the deflection of the ship (hogging/sagging).
  • Determination of ship weight before loading.
  • After loading, the weight of the ship is determined in the same way.
  • Determination of the difference in weight before and after loading.

The weight of the load determined according to the Archimedes principle can be determined with an accuracy of ±0.5%.

In comparison, the accuracy of weighbridges is between 0.5% – 1.0% and that of conveyor belt vehicles between 0.125% – 0.5%.