Who Needs a Merchant Mariner Credential (MMC)? Exact Conditions for MMC Requirements

Overview

This article explains the specific conditions under which an individual must hold a Merchant Mariner Credential (MMC), as defined by the U.S. Coast Guard (USCG). The MMC is a foundational credential required for many maritime positions, especially those performing safety-sensitive or operational duties aboard U.S. vessels. Understanding who needs one—and who doesn’t—is critical for maintaining regulatory compliance and avoiding enforcement action under 46 CFR Part 10 and Part 15.

What Is a Merchant Mariner Credential (MMC)?

A Merchant Mariner Credential (MMC) is a credential issued by the USCG that serves as a mariner’s license, certificate of registry, and merchant mariner document combined into one. It is required for individuals working in specific roles on commercial vessels and is used to verify that a mariner is qualified and authorized to serve in their position.

Who Is Required to Hold an MMC?

An individual must hold an MMC if they meet any of the following conditions:

1. Serving on U.S. Vessels Subject to Inspection

If the vessel is subject to USCG inspection under 46 U.S.C. Chapter 33, then all crewmembers who:

• Perform safety-sensitive duties, stand watch, or

• Operate machinery or systems vital to the vessel’s navigation or safety

must hold an MMC.
Examples include:

• Deck officers

• Engineers

• Tankermen

• Able Seamen (ABs)

• Ordinary Seamen (OSs)

• Stewards and cooks on inspected passenger vessels

2. Serving on Vessels Required by Law to Be Operated by Licensed Individuals

If a vessel’s operation requires a licensed or certified officer (e.g., a Master or Mate), then those individuals are required to have the appropriate MMC endorsements.

3. Performing Duties Requiring STCW Certification

If a mariner is serving on a seagoing vessel of 200 GRT or more on international voyages, and:

• Performs watchstanding, engine room, or safety functions, or

• Requires STCW (Standards of Training, Certification, and Watchkeeping for Seafarers) credentials

They must hold an MMC with STCW endorsements.

4. Serving as Part of the Regular Crew on Certain Uninspected Vessels

While uninspected vessels (e.g., some commercial fishing vessels) typically do not require MMCs, there are exceptions:

• Crew operating towing vessels, especially on navigable waters

• Individuals working on offshore supply vessels, passenger vessels, or oil spill response vessels

• Mariners employed in positions that directly affect the vessel’s safe operation

In these cases, an MMC may be required even if the vessel is uninspected.

5. Serving on Certain Recreational Vessels When Carrying Passengers for Hire

If a vessel is recreational but is used to carry passengers for hire, and:

• The operator is required to hold a USCG license (e.g., OUPV “six-pack” license),
  Then the mariner must have an MMC with the appropriate credential.

Who Is Not Required to Hold an MMC?

An MMC is not required for individuals who:

• Are serving on uninspected recreational vessels not engaged in commercial service

• Are volunteers on certain educational or non-profit vessels (with USCG approval)

• Are only performing maintenance, catering, or support work not directly connected to vessel operations or safety

• Serve solely as passengers

However, these individuals must not engage in any duties that contribute to the operation or navigation of the vessel.

Summary Table: MMC Requirement by Role & Vessel Type

*Note: Some uninspected fishing or towing vessels may still require MMCs based on service area, role, or job duties.

Regulatory References

• 46 CFR Part 10 – Licensing and Certification of Mariners

• 46 CFR Part 15 – Manning Requirements

• Merchant Mariner Credential Center – USCG

• 46 U.S.C. § 8701 et seq. – Seamen Credential Requirements

Last updated: May 15, 2025 (reflects USCG regulations in effect as of this date).