Section 69.65 - Calculation of volumes(a) Volumes V and Vc used in calculating gross tonnage ITC and net tonnage ITC, respectively, must be measured and calculated according to accepted naval architectural practices for the spaces concerned.(b) Measurements must be taken, regardless of the fitting of insulation or the like, to the inner side of the shell or structural boundary plating in vessels constructed of metal, and to the outer surface of the shell or to the inner side of structural boundary surfaces in all other vessels.USCG-2011-0522, 81 FR 18722 , Mar. 31, 2016 USCG-2011-0522, 81 FR 18722, 3/31/2016