- What the National Master 500/1600 GL and Inland Credential Actually Is
- Who Governs It and Where the Exam Content Comes From
- How the Exam Modules Are Organized
- Great Lakes and Inland vs. Inland-Only: Side by Side
- The Six Content Areas in Detail
- What Counts as an Extra Module and What Does Not
- Who Pursues This Endorsement and Where It Is Used
- How Your Own Module List Gets Decided
- A Route-Aware Preparation Sequence
- Frequently Asked Questions
- NM51GI here means National Master 500/1600 GL and Inland, a U.S. Coast Guard mariner credential.
- The National Maritime Center (NMC) publishes the exam modules under scope GLI03.
- Great Lakes and Inland routes use six modules: Q100, Q320, Q321, Q322, Q323 and Q324.
- Inland-only routes use five: Q100 or Q300, plus Q320 through Q323. Q324 is omitted.
What the National Master 500/1600 GL and Inland Credential Actually Is
NM51GI refers to the National Master 500/1600 GL and Inland endorsement, a U.S. Coast Guard mariner credential for masters of vessels operating on the Great Lakes and inland waters. The tonnage shorthand, 500/1600, points to the gross-register-ton thresholds associated with this grade of master's license. The "GL and Inland" portion describes the geographic route: Great Lakes plus inland waters, or inland waters alone for a restricted route.
This is not a vendor certification or an IT credential, and it has nothing in common with the other credentials that happen to share a similar-looking acronym. It is a federal maritime endorsement, and the examination content comes from the agency that issues it. If you are trying to untangle the terminology first, the site has short explainers on what NM51GI is and what NM51GI stands for.
Who Governs It and Where the Exam Content Comes From
The governing body is the United States Coast Guard National Maritime Center. The NMC publishes examination modules and topic matrices openly, which matters for candidates: the scope of what you may be tested on is not a secret. The relevant scope for this endorsement is labeled GLI03, covering Master of vessels under 500/1600 gross register tons on Great Lakes and Inland routes.
The published material this article draws on includes the NMC's Great Lakes and Inland endorsements page, the GLI03 module page for Master under 500/1600 GRT (modules Q323 and Q326 are referenced there), and the deck and engineering examination guide. That guide is the published regulations-effective document dated March 24, 2014, with the relevant reference at section 2.1.2.2, printed page 25. It is not a newly issued 2026 blueprint, although current indexed NMC matrices corroborate the same module headings. Treat it as the issuer's published structure, and always confirm against the live NMC pages before you commit to a study plan.
How the Exam Modules Are Organized
Instead of one monolithic test, the NMC divides the examination into numbered modules, each identified by a Q-code. A candidate sits the modules that apply to the endorsement and route being sought. For the full original route, the exact sets are:
- Great Lakes and Inland: Q100, Q320, Q321, Q322, Q323, Q324 (6 modules)
- Inland: Q100 or Q300, Q320, Q321, Q322, Q323 (5 modules)
Two details trip people up. First, Q100 and Q300 are alternatives, not companions. Q100 covers Rules of the Road for both Inland and International waters, while Q300 is the Inland-only Rules module that applies to the restricted route. You do not sit both as simultaneous requirements. Second, Q324 (Great Lakes Topics) appears only on the Great Lakes and Inland route. That single module is the difference between a six-group and a five-group preparation plan.
The six groups also should not be read as "six exams" for every applicant. The number of groups is a way of organizing preparation. How many modules you personally sit depends on your route, on whether you hold a prior endorsement, and on what the NMC assigns you.
Great Lakes and Inland vs. Inland-Only: Side by Side
| Module | Subject | Great Lakes and Inland | Inland |
|---|---|---|---|
| Q100 | Rules of the Road: Inland and International | Yes | Alternative to Q300 |
| Q300 | Rules of the Road: Inland only | No | Alternative to Q100 |
| Q320 | Deck General | Yes | Yes |
| Q321 | Deck Safety | Yes | Yes |
| Q322 | Navigation General: Great Lakes and Inland | Yes | Yes |
| Q323 | Navigation Problems: Chart Plot | Yes | Yes |
| Q324 | Great Lakes Topics | Yes | Omitted |
| Total modules | 6 | 5 |
Notice what the table prevents you from doing: you cannot reach "six" on the inland route by double-counting the two Rules modules, and you cannot drop Great Lakes Topics from the Great Lakes route and still call it a full-route plan. The count is route-specific. For a deeper walk through each area, see the complete guide to the NM51GI content areas.
The Six Content Areas in Detail
Domain 1: Rules of the Road, Inland and International (Q100)
The Rules module is the navigation rulebook every master must carry in their head. Q100 spans both Inland and International rules; Inland-only candidates may take Q300 instead.
- Know which rule set governs which waters, since that boundary drives the Q100 versus Q300 choice
- Right-of-way, lights, shapes and sound signals are recall-heavy and reward repetition
- Where a COLREGS limitation applies to an Inland route, the guide lists Q100 separately
Domain 2: Deck General (Q320)
Deck General covers the working knowledge of a vessel and its operation on deck, the practical seamanship foundation that sits under the more specialized modules.
- Treat it as the broad base: topics here recur in later modules
- Expect applied, operational thinking rather than pure memorization
Domain 3: Deck Safety (Q321)
Deck Safety addresses the safety obligations that fall on a master: how the vessel, crew and equipment are kept safe and what is required of the person in command.
- Safety content is regulation-anchored, so precision matters
- Pair this with Deck General, since the two overlap in practice
Domain 4: Navigation General, Great Lakes and Inland (Q322)
Q322 is the theory-and-method module for navigation on these routes, the conceptual counterpart to the hands-on plotting module that follows it.
- This is the module where route specifics (Great Lakes versus inland rivers and canals) start to matter
- Alternative Navigation General modules must never be counted together as simultaneous requirements
Domain 5: Navigation Problems, Chart Plot (Q323)
Q323 is the chart-work module. You work problems on a chart, which makes it a skills test rather than a recall test.
- Plan on real chart time with the actual tools, not just reading about plotting
- Q323 is also referenced on the GLI03 module page for Master under 500/1600 GRT
Domain 6: Great Lakes Topics (Q324), Great Lakes-and-Inland Route Only
Q324 is the module that distinguishes the Great Lakes route. The published topic matrices for Q324 include:
- Piloting and compass error
- Meteorology and oceanography
- Maneuvering and handling, including ice
- Stability, construction and damage control
- Cargo handling
That topic list shows why Great Lakes candidates need a longer runway. Weather, ice and large-vessel handling are not afterthoughts on open lake water, and this module treats them accordingly. If you want the difficulty picture before you plan, read how hard the NM51GI exam is.
What Counts as an Extra Module and What Does Not
The NMC publishes additional modules that sit beside the full-route sets, and it is easy to mistake them for extra requirements on top of the six or five. They are not additional full-original-exam domains.
- Q326, Navigation and Deck General/Safety, is a separate module used in a towing-to-Master-under-500 raise-of-grade situation. It is not part of the standard full-route set.
- Inland-to-Great-Lakes-and-Inland route extensions are listed separately in the guide, centered on Q324, and on Q100 where a COLREGS limitation applies.
- Upgrade, raise-of-grade and route-extension modules are separate pathways, not extra domains stacked onto the original six.
Who Pursues This Endorsement and Where It Is Used
A master's endorsement on Great Lakes and inland waters is a working credential for people who command vessels, or who intend to, on those waterways. Mariners who commonly pursue it come from:
- Towing and barge operations moving cargo along rivers, canals and the Great Lakes
- Passenger and excursion vessel operations on inland and lake waters
- Mariners advancing a deck career from mate or towing roles toward command
- Operators who started on an inland-only route and want to extend onto the Great Lakes
The route extension path is worth planning around deliberately. An inland-only endorsement is a narrower license; adding Great Lakes privileges means Q324 enters the picture. For the job side of the story, see NM51GI jobs, and for earnings context see the NM51GI salary guide. This article deliberately avoids quoting wage figures, since none are established in the issuer's published structure.
How Your Own Module List Gets Decided
The most important practical fact in this whole article is this: the NMC determines the individual's assigned modules. The module tables above describe the published full-route sets, but your personal list is set by your application and your existing credentials, and it is communicated through your approval to test.
That means the correct workflow is:
- Confirm your target endorsement and route (Great Lakes and Inland, or Inland only).
- Submit your application through the NMC process and receive your approval to test.
- Read the modules listed on that approval; those are your actual requirements.
- Build your study plan around that list, not around a generic count.
Eligibility and sea-service questions belong to a different layer of the process; the site covers them in NM51GI requirements. Fees and scheduling are likewise governed by the issuer and can change, which is why this article does not state current dollar amounts; check the cost breakdown and exam dates pages alongside the NMC's own notices.
A Route-Aware Preparation Sequence
Rather than a generic weekly template, sequence your work by how the modules depend on each other. A Great Lakes and Inland candidate might order the work like this, adjusting to the modules on the actual approval to test:
Rules of the Road (Q100 or Q300)
- Start here: Rules knowledge underpins collision-avoidance reasoning in later navigation work
- Confirm which Rules module your approval lists before studying the wrong rule set
Deck General and Deck Safety (Q320, Q321)
- Study the two together, since their subject matter overlaps in practice
Navigation General, then Chart Plot (Q322, Q323)
- Learn the method in Q322 before drilling plotting problems in Q323
- Schedule hands-on chart time, as this is a skills module
Great Lakes Topics (Q324), if on your route
- Give meteorology, ice handling and stability extra time, as they are the broadest topics
For a fuller method, the NM51GI study guide goes deeper, and the cheat sheet is useful for a final-pass review. When you are ready to test your recall under realistic conditions, the NM51GI practice test site offers route-aware practice, and you can start with the main practice tests to find your weak modules. This site is independent exam prep; it does not reproduce sample questions from the issuer and is not endorsed by the Coast Guard or the NMC.
Frequently Asked Questions
The United States Coast Guard National Maritime Center governs the endorsement and publishes its examination modules and topic matrices under scope GLI03.
The published full-route set for Great Lakes and Inland is six modules: Q100, Q320, Q321, Q322, Q323 and Q324. Your individual list is whatever the NMC assigns on your approval to test.
The Inland route omits Q324, Great Lakes Topics. It uses Q100 or Q300 for Rules of the Road, plus Q320, Q321, Q322 and Q323. Q100 and Q300 are alternatives, never both.
No. Q326, Navigation and Deck General/Safety, is a separate module tied to a towing-to-Master-under-500 raise-of-grade pathway. It is not an additional domain stacked onto the full original route.
No. The issuer's published structure does not establish a population pass rate, a single overall question count, or current fees here. Check the NMC directly for current fees, and see the site's pages on pass rate and passing score for what can and cannot be said.