Outer Continental Shelf National Center of Expertise (OCSNCOE)

MODU Frequently Asked Questions (FAQs)

Please find  answers to commonly asked questions related to Mobile Offshore Drilling Units below.

Answers in this FAQ section are not a substitute for applicable legal requirements, nor are they rules (however, some questions may have an answer that comes directly from existing regulation or policy). The answers are not intended to require or impose legally binding requirements on any party. Answers provided represent the OCSNCOE’s current thinking, after researching existing regulations and policy, as well as consultation with Coast Guard Subject Matter Experts. These answers are intended to assist industry, mariners, the public, the Coast Guard and other regulators in applying statutory and regulatory requirements. When available, the FAQ will direct the reader to the official documents, such as the Federal Register, the Code of Federal Regulations or NVICs and policies. The answers provided are subject to change with regulatory or policy updates.

Regulatory Requirements

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Foreign flagged MODUs choosing to comply with the "Option A" requirements of 33 CFR 143.207(a) must comply with the design and equipment requirements of 46 CFR Part 108, as applicable to the build date of the MODU. 46 CFR Subchapters F & J are not applicable as the paths to those subchapters are located in 46 CFR Part 107 (§107.231(a)), to which Option A MODUs are not subject. 46 CFR Subchapter S applies as the path to that subchapter is located at 46 CFR 108.301.

Option A MODUs will also typically comply with the operating requirements of 46 CFR 109, per 33 CFR 146.205(a).

Regulatory paths:
33 CFR 143.207(a) > 46 CFR Part 108 (including requirements of 46 CFR Subchapter S, via §108.301)
33 CFR 146.205(a) > 46 CFR Part 109

Additional regulatory guidance:
CG Marine Safety Manual (MSM) Vol II, Section G, Chapters 1 & 3

Note that with the cancellation of NVIC 3-88, there is no regulatory guidance allowing the use of NVIC 4-78 (46 CFR 109, Appendix A) for Option A MODUs.

Yes, if the foreign flagged MODU was issued an initial COC prior to June 25, 2014.

On June 25, 2014 NVIC 3-88 was cancelled and the Marine Safety Manual (MSM) Volume II, Section G was updated. With this update, NVIC 4-78 became applicable to foreign flagged MODUs only if it had previously held a U.S. Coast Guard Certificate of Inspection issued under 46 CFR Subchapter “I”.

NVIC 4-78 applies to existing U.S. Flagged Mobile Offshore Drilling Units (MODUs) and existing foreign flagged units that meet specific prerequisites as further discussed below. The NVIC is included as Appendix A to 46 CFR Part 109.

Existing units” are defined as units contracted for which are to be constructed and delivered prior to January 1, 1981.

NVIC 4-78 was historically applied to existing foreign flagged MODUs choosing to be inspected under 33 CFR 143.207(a) and 33 CFR 146.205(a), also known as Option “A”. This provision was found in paragraph 3.B.2 of Enclosure (1) to NVIC 3-88, CH-1. Much of the NVIC 3-88, CH-1 content was incorporated into Marine Safety Manual (MSM), Volume II, CH-1, Section G, Chapter 3 (MSM II.G.3) on June 25, 2014 and NVIC 3-88, CH-1 was cancelled at that time.

Current guidance found at MSM, Volume II.G.3.B.1.b (page G3-9) states Existing MODUs – All existing units will be inspected as in the above paragraph. However, units contracted for before January 3, 1979, and issued a Certificate of Inspection (COI) under 46 Subchapter I [emphasis added] may continue to meet the requirements in force at the time of the COI issuance but must also meet the applicable requirements of 46 Subchapter I-A as specified in Navigation and Vessel Inspection Circular, “Inspection and Certification of Existing Mobile Offshore Drilling Units” (Appendix A of 46 CFR Part 109) until the unit is rebuilt. After a rebuild, the unit must meet the requirements of 46 CFR Subchapter I-A. The definition for REBUILT can be found in 33 CFR 140.10.”

While NVIC 3-88, CH-1 allowed all existing units to utilize Appendix A (NVIC 4-78) of 46 CFR 109, the verbiage was modified with incorporation into the MSM to only allow the use of Appendix A by foreign flagged MODUs that were previously an existing U.S. flagged MODU that had been issued a COI under 46 Subchapter I. If a foreign flagged MODU does not meet these prerequisites, the unit can be examined under Option “A”, but cannot utilize 46 CFR 109 Appendix A (NVIC 4-78) and would have to use 46 CFR Parts 108 and 109 that are applicable to the build date(s) of the MODU.

See the following flowchart for 46 CFR 109, Appendix A applicability. Note that pdf files are available for the NVIC 4-78 Flowchart or the NVIC 4-78 Flowchart Print Version (click on the names).

NVIC 4-78 Flowchart


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Is the number of lifeboatmen based on the total number of lifeboats onboard or on the number of lifeboats needed for 100% coverage of persons onboard (POB), since these types of units are required to maintain redundancy in lifeboat capacity?

Short answer: It is based on 100% coverage (but could vary/be increased by the Flag State Administration). Let’s take a further look…

Foreign-flagged units are pretty straightforward in that the Safe Manning Document sets the number of lifeboatmen required by the Administration. Many administrations base this off of the total number of lifeboats onboard.

Let’s look at some of the applicable cites to see the intent/how the minimum number would be determined:
2009 MODU 14.10.5 requires certificated persons to be placed in command AND second-in-command of EACH lifeboat. Based on this cite, each lifeboat is required to have 2 lifeboatmen (note that this is not based on the capacity of the lifeboat, but is a straight 2-per lifeboat requirement). A typical drillship example with 6 lifeboats provided, 3 on each side (100% POB coverage on each side), would need 12 lifeboatmen based on the wording in this cite. The majority of Administrations choose to use the formula of 2 lifeboatmen multiplied by the total number of lifeboats to obtain the required number of lifeboatmen to list on their Minimum Safe Manning documents.

But wait, 2009 MODU 14.10.4 requires sufficient certificated persons onboard to launch and operate the survival craft TO WHICH PERSONNEL ARE ASSIGNED. 2009 MODU 14.10.5 works in concert with 14.10.4. This puts an interesting twist to our ‘typical’ drill ship example, and the station bill will need to be consulted to determine the appropriate number of lifeboatmen based on the boats to be used. A typical drillship meets the design and equipment requirements of 100% capacity on each side (2009 MODU 10.3.1) with 3 lifeboats on each side, but common practice across the industry is to assign personnel to the 4 fwd lifeboats as their primary abandonment location/station.

Some examples of lifeboatmen numbers that would meet the intent in our drillship example, in accordance with 2009 MODU 14.10.4 & 14.10.5:
   • 3 lifeboats assigned (100% POB coverage), port or starboard boats (depending on scenario) = 6 lifeboatmen required
   • 4 fwd lifeboats assigned (exceeds 100% POB coverage, but personnel are assigned to 4 boats) = 8 lifeboatmen required

2014 SOLAS III/10.4 helps to check the intent and is a little clearer than the MODU Codes, as it uses “each survival craft to be used” in the certificated person(s) requirement.

Essentially, an Administration that requires 12 lifeboatmen would cover most any muster/abandonment assignments scenario on our typical drillship example. If an Administration requires only 6 lifeboatmen on our example, the station bill/abandonment station assignments should reflect that arrangement (6 lifeboatmen wouldn’t be sufficient if the 4 fwd boats were being utilized).

Note: If an Administration requires more lifeboatmen than the station bill/boat assignments require, the number stipulated on the Minimum Safe Manning document MUST be adhered to. If the station bill/boat assignments require more than the Administration stipulates, the required number set forth in the applicable MODU code must be complied with.

1989 MODU 14.9.5 and 14.9.4 are the same as the 2009 MODU cites discussed above.

The MODU Code (1979) does not specifically address the requirement related to manning of survival craft and the requirement will be stipulated by the Administration on the Minimum Safe Manning document. Note that ‘emergency procedures’ are located within Chapter 10 of the 79 Code, compared to Chapter 14 of the 89 & 09 Codes.

U.S. requirements follow a similar approach for MODUs. 46 CFR 109.323(c) requires a person to be placed in charge of each survival craft TO BE USED. §323(c)(1) requires them to be trained/certificated for those duties and §323(c)(2) requires the second-in-command for lifeboats permitted to carry MORE THAN 40 persons (41 POB and higher). Note that the biggest difference is that the lifeboat capacity determines when the second lifeboatman is required.

As supplementary guidance to the regulations, CG Marine Safety Manual Vol III/B.2.B.2.f discusses lifeboatmen and when/how many are required and uses the statement “each survival craft to be used” as well. This specific MSM cite is for mechanically-propelled vessels of 100 GRT or more, but is referenced as footnote 15 in B.2.O.1 (MODU sample manning).

Conclusion: Both IMO and U.S. requirements are aimed at providing lifeboatmen for the boats needed to accommodate evacuation of the persons onboard (100% of POB capacity), not providing lifeboatmen coverage for the redundant boats.

Navigational Aids

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A MODU operating on DP and attached to the seabed is considered underway, not making way, and restricted in the ability to maneuver.

Lighting configuration:Restricted Maneuverability - Underway, not making way
   - Three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white.

Note that masthead lights, sidelights and sternlight are NOT required, as the MODU is not making way and anchor lights are NOT required, as the MODU is not considered as “anchored”.

Day shape configuration:
   - Three shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond.

See the follow-on question below, where additional lights and shapes may be required.

Are there additional navigation light requirements that apply to a MODU operating on dynamic positioning (DP), while obstructions exist in addition to the drilling equipment (e.g. ROV ops, subsea ops with the heave-compensated crane, etc.)?

Yes. Due to additional operations where obstructions exist to one side, the MODU may indicate the sides on which other vessels may and may not pass.

Lighting configuration:Restricted Maneuverability with obstructions - Underway, not making way
   - Restricted maneuverability lighting as described above (drilling only), PLUS;
   - Two all-round red lights in a vertical line to indicate the side on which the obstruction exists; and
   - Two all-round green lights in a vertical line to indicate the side on which another vessel may pass.

Day shape configuration:
   - Restricted maneuverability shapes as described above (drilling only), PLUS;
   - Two balls in a vertical line to indicate the side on which the obstruction exists; and
   - Two diamonds in a vertical line to indicate the side on which another vessel may pass.

MODU navigation lighting is also discussed on the USCG Navigation Center’s FAQ page by clicking here.

Short Answer:


Long Answer:

Note: This answer is based on conventional incandescent-type light assemblies. Manufacturer’s instructions should be consulted for LED lanterns or retrofits to ensure compliance with advertised/intended characteristics and range.

Part 1: Leveling

The “ridges” of the Fresnel lens found on obstruction lights serve a very important purpose. These ridges condense the light to the center of the lens and send out a type of light beam to meet the required range.

If the light is not level the focal plane will either be above or below the vessel. Either condition could reduce the required range, resulting in non-compliance with regulations and not meeting charted characteristics. See the graphical depiction below.

Graphic depicting focal planes of level and non-level aids to navigation lanterns

The leveling of the lantern can be checked via the built-in bubble levels of some lanterns or with the method displayed below (utilized by U.S. Coast Guard short-range aids to navigation technicians).

Graphic depicting how to verify the leveling of an aids to navigation lantern

Part 2: Focusing

There is another issue, especially on larger lights, that has to do with the “focus” of the light. For the light to be in focus, the lamp needs to be lined up with the center of the Fresnel lens. To check this, there are sighting marks (an “O” and “X” pair or two “X” pair) marked at 180° increments on the outside of the lens. When looking through the “O” to the “X” on the opposite side (180°) of the lens, the lamp should fall between the two sighting marks with the sighting marks aligned. The most common issue with the focus on certain model lights is when the bracket for the lamp changer mounts is installed upside down, which moves the lamp out of the focal plane of the lens.

The graphic below illustrates how to verify that a lantern is properly focused.

Graphic depicting how to verify the focusing of an aids to navigation lantern

Financial Responsibility

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Short answer:
Fixed OCS Facilities and FOFs are required to demonstrate OSFR and MODUs are required to carry a COFR for a tank vessel or a non-tank vessel based on its operation.

Further discussion:
The requirements for an OSFR are found in 30 CFR 553 and the requirements for a COFR are found in 33 CFR 138.

This is based on 30 CFR 553.10:
(a) This part applies to any COF [Covered offshore facility] on any lease or permit issued or on any RUE [Right-of-use and easement] granted under the OCSLA or applicable State law.
(b) For a pipeline COF that extends onto land, this part applies to that portion of the pipeline lying seaward of the first accessible flow shut-off device on land.

Covered Offshore Facility (COF) in 30 CFR 553.3 means a facility:
(1) That includes any structure and all its components (including wells completed at the structure and the associated pipelines), equipment, pipeline or device (other than a vessel or other than a pipeline or deepwater port licensed under the Deepwater Port Act of 1974 (33 U.S.C. 1501 et seq.)) used for exploring for, drilling for, or producing oil or for transporting oil from such facilities. This includes a well drilled from a mobile offshore drilling unit (MODU) and the associated riser and well control equipment from the moment a drill shaft or other device first touches the seabed for purposes of exploring for, drilling for, or producing oil but it does not include the MODU; and…,

33 CFR 138.15(b) states:
For the purposes of financial responsibility under OPA 90, a mobile offshore drilling unit is treated as a tank vessel when it is being used as an offshore facility and there is a discharge, or substantial threat of a discharge, of oil on or above the surface of the water. A mobile offshore drilling unit is treated as a vessel other than a tank vessel when it is not being used as an offshore facility,

33 CFR 138.230(d) states:
Offshore facilities. The OPA 90 limit of liability or offshore facilities other than deepwater ports, including for any offshore pipelines, is set forth at 30 CFR 553.702.

OSFR and COFR Applicability
  Oil Spill Financial Responsibility Certificate of Financial Responsibility
Mobile Offshore Drilling Unit No Yes
Floating OCS Facility Yes No
Fixed OCS Facility Yes No