What is net tonnage?

Net Tonnage is an important measurement used in the USCG vessel documentation process. It is a measure of a vessel’s internal volume, calculated as a function of its length, breadth and moulded depth (the vertical distance between the uppermost deck to the lowest point of the hull or keel).

Essentially, it is used to calculate the total load-carrying capacity of a boat.

This figure has several implications for US vessel documentation; firstly, it determines how much cargo a vessel can safely carry and thus affects which taxes may apply; secondly, it can influence which waters can be navigated with that particular type and size of boat; lastly, it also has bearing on issues such as marine pollution ratings. As such, it is essential to accurately calculate and record a vessel’s net tonnage when applying for USCG documentation.

Vessels that measure over five net tons and are wholly owned by a citizen of the United States are eligible for documentation. As a “rule of thumb,” vessels that are 25 feet in length or longer almost invariably measure five net tons.

Law 67.105 describes more about tonnage and dimension requirements.