Tonnage's a measure of the size or cargo capacity of a ship. The term derives from the taxation paid on tuns of wine, and was later used in reference to the weight of a ship's cargo; however, in modern maritime usage, "tonnage" specifically refers to a calculation of the volume or cargo volume of a ship. The term's still sometimes incorrectly used to refer to the weight of a loaded or empty vessel. Measurement of tonnage can be less than straightforward, not least because it's used to assess fee… (More on Tonnage)