Duty of Tonnage Law and Legal Definition
Duty of tonnage refers to a charge imposed on a commercial vessel for entering, remaining in, or leaving a port. Duty of tonnage may apply only to vessels of a particular class, or of not less than a particular size, or to vessels of a particular construction. So, it may apply only to vessels engaged in a particular trade, or the vessels which are liable to it may be ascertained by any rule of discrimination which the state may choose to adopt. A duty of tonnage is as much a tax as a duty on imports or exports. [Johnson v. Drummond, 61 Va. 419 (Va. 1871)].
Therefore, duty on tonnage is a tax on a vessel because a vessel is the only vehicle of commerce on the high seas. Hence, in effect, duty of tonnage is a tax on commerce.