Section 157.160 - Tanks: Ballasting and crude oil washing(a) The owner, operator, and master of a tank vessel under § 157.10(e) shall ensure that: (1) Ballast water is carried in a cargo tank only as allowed under § 157.35 ;(2) For oil cargo residue control, at least 25 percent of the cargo tanks are crude oil washed before each ballast voyage and that each cargo tank is crude oil washed at least once every fourth time crude oil is discharged from the tank, but no tank need be crude oil washed more than once during each 120 day period;(3) Ballast water in a cargo tank that is crude oil washed but not water rinsed during or after the most recent discharge of crude oil from that tank is discharged in accordance with § 157.37(a) ; and(4) Cargo tanks are not crude oil washed during a ballast voyage.(b) The owner, operator, and master of a tank vessel having a COW system under § 157.10a(a)(2) or § 157.10c(b)(2) shall ensure that-(1) Ballast water is carried only in a cargo tank that is crude oil washed during or after the most recent discharge of crude oil from that tank;(2) Before each ballast voyage a sufficient number of cargo tanks have been crude oil washed during or after the most recent discharge of crude oil from those tanks to allow ballast water to be carried in cargo tanks:(i) With a total capacity to meet the draft and trim requirements in § 157.10a(d) ; and(ii) For the vessel's trading pattern and expected weather conditions;(3) For oil cargo residue control, at least 25 percent of the cargo tanks not used for carrying ballast water under paragraph (b)(2)(i) of this section are crude oil washed before each ballast voyage, and that each cargo tank is crude oil washed at least once every fourth time crude oil is discharged from the tank, but no tank need be crude oil washed more than once during each 120 day period;(4) Cargo tanks are not crude oil washed during a ballast voyage; and(5) Ballast water in a cargo tank that is crude oil washed but not water rinsed during or after the most recent discharge of crude oil from that tank is discharged in accordance with § 157.37(a) .CGD 77-058b, 45 FR 43709, June 30, 1980, as amended by CGD 82-28, 50 FR 11628, Mar. 22, 1985; USCG-2000-7641, 66 FR 55573, Nov. 2, 2001