Code of Federal Regulations Title 46. Shipping § 46.69.107 Gross and net register tonnage

(a) The vessel's gross register tonnage is the sum of the following tonnages, less the tonnages of certain spaces exempt under § 69.117:

(b) The vessel's net register tonnage is the gross register tonnage less deductions under §§ 69.119 and 69.121.

(c) The authorized measurement organization must issue a U.S. Tonnage Certificate as evidence of a vessel's measurement under this subpart, which must also indicate the vessel's measurement under the Convention Measurement System in subpart B of this part, if applicable. There is no requirement to maintain the U.S. Tonnage Certificate on board the vessel.