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From: Sailor
Location: Great Lakes
email:
Remote Name: 65.95.247.112
Date: 01.31.06
Time: 04:23:22 PM
Cargo tonnage calculations on the ship are usually done by the 1st Mate after loading is finished. He compares the draft marks on the hull to a table of figures for which gives the ships displacement for each draft; usually in 1 inch increments. Once he knows the total displacement of the loaded ship he subtracts the weight of the ship (called the lightship displacement) from the total. He then subtracts the 'deductibles'. These are things like fuel, fresh water, any remaining ballast, the crew & stores, etc. The remaining tonnage is the total weight of the cargo. There are a couple of other small calculations to take into account hog/sag as well as water density calculations (i.e. salt water). The mate then compares his figures with the dock's figures which is stated on the Bill of Lading. If the difference is significant there may be an independant survey done from a third party to double check the tonnage load.