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Gross Tonnage

A unitless measure of a vessel's enclosed internal volume, used for regulatory classification and licensing.

Gross Tonnage (GT) is a unitless measure of a vessel's total enclosed internal volume, calculated by a formula defined in the International Convention on Tonnage Measurement of Ships. Despite the word "tonnage," it is not a weight — it is a dimensionless number derived from volume.

Gross tonnage is used to determine: - Which USCG Master's license level a captain needs to command the vessel. - Regulatory classifications (GT > 100, GT > 200, GT > 500 each trigger different rules). - Port fees, canal tolls, and registration charges — most of which scale with GT.

A 50-foot yacht might have a GT of 15-25; a 100-foot motor yacht might have a GT of 80-120; a 200-foot superyacht commonly exceeds GT 500.

Examples

  • A 100-ton Master license authorizes operation of vessels up to 100 GT.
  • A vessel over 200 GT triggers additional USCG inspection and crewing requirements.

Related Terms

Masters License—A tiered USCG license authorizing a captain to operate an inspected passenger vessel, sized by vessel tonnage.Displacement—The weight of water a vessel displaces when floating, equal to the total weight of the vessel and its contents.Mega Yacht—An informal term for a large private yacht, typically 80-200 feet, with a professional crew.Superyacht—A private yacht typically 200 feet (60 meters) and larger, with a full professional crew and high-end interior.

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