46 CFR 15.520: Credential and manning rules for MODUs
Last reviewed: October 14, 2026
This section adds manning and credential requirements for mobile offshore drilling units (MODUs). It sets which MMC endorsements the person in command must hold, and requires Barge Supervisor or Ballast Control Operator endorsements in certain cases. The OCMI decides minimum manning for inspected MODUs.
Applies toMODUs, including self-propelled, non-self-propelled and drillship units, and the officers and crew who serve on them.
What it says
The OCMI determines the minimum number of officers and crew, including Lifeboat Operators, needed for safe operation of inspected MODUs.
46 CFR 15.520(b)“The OCMI determines the minimum number of officers and crew (including Lifeboat Operators) required for the safe operation of inspected MODUs.”
An OIM, BS or BCO officer endorsement authorizes service only on MODUs, and an OIM endorsement is restricted to the MODU type and mode of operation specified on the credential.
46 CFR 15.520(c)“An endorsement as OIM is restricted to the MODU type and mode of operation specified on the credential.”
When underway, a self-propelled MODU other than a drillship must be under the command of an individual who holds an MMC endorsed as Master and OIM.
46 CFR 15.520(d)“When underway, a self-propelled MODU, other than a drillship, must be under the command of an individual who holds an MMC endorsed as Master and OIM.”
A drillship must be commanded by an individual holding a Master officer endorsement. On location, or when maintaining position with a dynamic positioning system, that individual must hold both Master and OIM officer endorsements.
46 CFR 15.520(e)“When a drillship is on location, or is maintaining its position with a dynamic positioning system, the individual in command must hold an MMC with Master and OIM officer endorsements.”
A non-self-propelled MODU must be under the command of an individual who holds an MMC officer endorsement as OIM.
46 CFR 15.520(f)“A non-self-propelled MODU must be under the command of an individual who holds an MMC officer endorsement as OIM.”
An individual holding a BS officer endorsement is required on a non-self-propelled surface unit other than a drillship.
46 CFR 15.520(h)“An individual holding an MMC officer endorsement as BS is required on a non-self-propelled surface unit other than a drillship.”
A surface MODU that is underway or on location, afloat, and equipped with a ballast control room must have that room manned by an individual with an MMC officer endorsement authorizing service as BCO.
46 CFR 15.520(l)“must have that ballast control room manned by an individual holding an MMC officer endorsement authorizing service as BCO.”
Common questions
Who determines manning levels on an inspected MODU?
The OCMI determines the minimum number of officers and crew for safe operation of inspected MODUs. The OCMI also considers the specialized nature of the MODU.
“The OCMI determines the minimum number of officers and crew (including Lifeboat Operators) required for the safe operation of inspected MODUs.”
Can a Barge Supervisor serve as Ballast Control Operator on a MODU?
Yes. An individual holding an MMC officer endorsement as BS may serve as BCO.
“An individual holding an MMC officer endorsement as BS may serve as BCO.”
Do Radar Observer requirements apply to non-self-propelled MODUs?
No. Requirements in this part concerning Radar Observers do not apply to non-self-propelled MODUs.
“Requirements in this part concerning Radar Observers do not apply to non-self-propelled MODUs.”
Who must command a drillship?
A drillship must be under the command of an individual who holds an MMC officer endorsement as Master. On location or when using dynamic positioning to hold position, that individual must also hold an OIM endorsement.
“A drillship must be under the command of an individual who holds an MMC officer endorsement as Master.”
The text of 46 CFR 15.520
Electronic Code of Federal Regulations (eCFR), current as of April 16, 2026 · Read it on eCFR
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 Lifeboat Operators) 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) An officer endorsement on an MMC as Offshore Installation Manager (OIM), Barge Supervisor (BS), or Ballast Control Operator (BCO) authorizes service only on MODUs. An 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 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 an 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 an MMC with Master and OIM officer endorsements.
(f) A non-self-propelled MODU must be under the command of an individual who holds an 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 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 an MMC officer endorsement as BS is required on a non-self-propelled surface unit other than a drillship.
(i) An individual holding an 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 an MMC officer endorsement authorizing service as BCO.
The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of April 16, 2026. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.