Section 155.120 - Equivalents(a) For ships required to be surveyed under § 151.17 of this chapter, the Commandant may, upon receipt of a written request, allow any fitting, material, appliance or apparatus to be fitted in a ship as an alternative to that required by both MARPOL 73/78 and subpart B of this part if such fitting, material, appliance, or apparatus is at least as effective as that required by subpart B. Substitution of operational methods to control the discharge of oil in place of those design and construction features prescribed by MARPOL 73/78 that are also prescribed by subpart B of this part is not allowed.(b) Any equivalent to a feature prescribed by MARPOL 73/78 that is authorized for a ship having an IOPP Certificate is noted on that Certificate.(c) For tank vessels required to have overfill devices installed under parts 155 and 156 of this chapter, the Commandant may, upon receipt of a written request, allow any fitting, material, appliance, or apparatus to be fitted in a tank vessel as an alternative to the required overfill device(s) that are specified in these parts if the proposed alternative device is at least as effective as that required in the regulations.CGD 75-124a, 48 FR 45714, Oct. 6, 1983, as amended by CGD 90-071a, 59 FR 53290, Oct. 21, 1994