Net tonnage is used in the United States to determine eligibility for registering boats with
the federal government. It is a nonlinear unit derived from the total volume of a ship's cargo space as well as some
dimensionless factors. Net tonnage is not a measure of the weight of the ship or its cargo, and should not be confused
with terms such as deadweight tonnage or displacement. Net tonnage is also used to determine the amount of money that
can be charged to a ship for using a port's facilities.