46 C.F.R. § 171.072
When doing calculations to show compliance with § 171.070, the following uniform average permeabilities must be assumed:
(b) 60 percent in the following spaces:
[CGD 79-023, 48 FR 51017, Nov. 4, 1983, as amended by USCG-2014-0688, 79 FR 58287, Sept. 29, 2014]