Section 69.161 - Gross and net register tonnages(a)Gross register tonnage means the tonnage of a vessel, less certain spaces exempt under § 69.169 , and is the sum of the following: (1) Under-deck tonnage (§ 69.163 ).(2) Between-deck tonnage (§ 69.165 )(3) Superstructure tonnage (§ 69.167 )(4) Excess hatchway tonnage (§ 69.115 )(5) Tonnage of framed-in propelling machinery spaces included in calculating gross register tonnage (§ 69.121(d)(1) ).(b)Net register tonnage means 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.CGD 87-015b, 54 FR 37657, Sept. 12, 1989, as amended by USCG-2011-0522, 81 FR 18731, Mar. 31, 2016