Gross register tonnage
(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)).