The deadweight scale can be of great assistance in estimating the weight of cargo loaded or discharge.
For example, if Draft before loading = 14´ 6˝ Draft after loading = 29´ 0˝ It can be seen from the scale that the deadweight has increased from 5,000 to about 15,000 tons, or 10,000 tons has been loaded. Of course, the density of the water, any stores or bunkers loaded, list and any hogging or sagging would have to be taken into account.
Furthermore, if this method of assessing cargo deadweight loaded is to form the basis of a freight payment or claim, then it will need to be done by an independent draft surveyor.
The deadweight scale. Note that the Tons Per Inch immersion, or TPI, is the number of tons that must be loaded or discharged at that draft to alter the draft 1 inch. Note: TPC = 0.4 x TPI. Assuming you can only read the draft accurately to within an inch, the TPI gives an indication of the accuracy of the draft survey.