Supervision of Quantity
ESTABLISHING QUANTITY OF CARGO LOADED OR DISCHARGED. Methods of weighing bulk cargoes ashore, draft survey procedures, reasons for unexpected results.
Shorebased methods of weighing. THE QUANTITY of cargo loaded aboard a bulk carrier can be measured in a variety of ways. The only method which directly involves the ship's personnel is the draft survey, but before considering this method in detail it is worth giving brief consideration to methods which may be used ashore. An understanding of these methods will help in assessing their reliability.
Electronic weighing of cargo on conveyor belt:
The most common method of weighing used at modern loading terminals is the belt scale. This device continuously weighs the material on a selected length of the loading conveyor belt and multiplies this instantaneous weight value by the belt speed. The signal thus obtained is at all times proportional to the rate of material flow on the belt. Some commercial belt scales rely on magneto-elastic load cells. These devices rely upon the fact that the magnetic characteristics of steel are affected by mechanical stress.
The accuracy of a belt scale depends largely on the design of the conveyor and the way it is maintained. Provided that the conveyor conforms to specified basic requirements for design and operation, an accuracy of better than