NETTONNAGE
Net tonnage
Net tonnage is a dimensionless index calculated from the total moulded volume of the ship's cargo spaces by using a mathematical formula. Defined in The International Convention on Tonnage Measurement of Ships that was adopted by the International Maritime Organization in 1969, the net tonnage replaced the earlier net register tonnage which denoted the volume of the ship's revenue-earning spaces in "register tons", units of volume equal to . Net tonnage is used to calculate the port duties and should not be taken as less than 30 per cent of the ship's gross tonnage.The above text is a snippet from Wikipedia: Net tonnage
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