46 CFR § 153.231 - Type II system.
A type II containment system must meet the following requirements:
(b) Except as allowed in §§ 153.7 and 153.235 -
(1) It may be no closer to the tankship's shell than 76 cm (approx. 29.9 in.); and
(2) It may not be located in any part of the tankship subject to the damage described in Table 172.135 of this chapter for Grounding Penetration, Vertical extent from the baseline upward.