Section 15.520 - [Effective until 1/17/2025] Mobile offshore drilling units (MODUs)(a) The requirements in this section for MODUs supplement other requirements in this part.(b) The OCMI determines the minimum number of officers and crew (including lifeboatmen) required for the safe operation of inspected MODUs. In addition to other factors listed in this part, the specialized nature of the MODU is considered in determining the specific manning levels.(c) A license or officer endorsement on an MMC as offshore installation manager (OIM), barge supervisor (BS), or ballast control operator (BCO) authorizes service only on MODUs. A license or endorsement as OIM is restricted to the MODU type and mode of operation specified on the credential.(d) When underway, a self-propelled MODU, other than a drillship, must be under the command of an individual who holds a license as master endorsed as OIM, or an MMC endorsed as master and OIM. When not underway, such a vessel must be under the command of an individual holding the appropriate OIM credential.(e) A drillship must be under the command of an individual who holds a license or MMC officer endorsement as master. When a drillship is on location, or is maintaining its position with a dynamic positioning system, the individual in command must hold a license as master endorsed as OIM or an MMC with master and OIM officer endorsements.(f) A non-self-propelled MODU must be under the command of an individual who holds a license or MMC officer endorsement as OIM.(g) An individual serving as mate on a self-propelled surface unit when underway, other than a drillship, must hold an appropriate license, or an MMC endorsed as mate and BS or BCO. When not underway, such a vessel may substitute an individual holding the appropriate BS or BCO endorsement for the mate, if permitted by the cognizant OCMI.(h) An individual holding a license or MMC officer endorsement as BS is required on a non-self-propelled surface unit other than a drillship.(i) An individual holding a license or MMC officer endorsement as BS may serve as BCO.(j) The OCMI issuing the MODU's COI may authorize the substitution of chief or assistant engineer (MODU) for chief or assistant engineer, respectively, on self-propelled or propulsion-assisted surface units, except drillships. The OCMI may also authorize the substitution of assistant engineer (MODU) for assistant engineer on drillships.(k) Requirements in this part concerning radar observers do not apply to non-self-propelled MODUs.(l) A surface MODU underway or on location, when afloat and equipped with a ballast control room, must have that ballast control room manned by an individual holding a license or MMC officer endorsement authorizing service as BCO.USCG-2004-17914, 78 FR 78003 , Dec. 24, 2013