NM51GI Exam Domains 2026: Complete Guide to All 6 Content Areas

How the NM51GI Modules Are Organized

Candidates searching for the "NM51GI exam domains" often expect a tidy blueprint with percentage weights and a single question count. The National Maritime Center does not publish that for this credential, and it would be a mistake to invent one. What the NMC does publish, openly, is a set of examination modules and the topic matrices that sit behind them. This guide organizes those modules into six route-aware preparation groups so you can plan your study time intelligently.

Those groups are unweighted. Nothing in the published material tells us that one module counts for a larger share of your outcome than another, so treat each one as something you must clear on its own terms. If you want the broader picture before diving into individual modules, start with What Is NM51GI? and the explanation of what NM51GI stands for.

Route Math: Six Groups, Five Groups, and Why the Count Varies

The headline number of "six content areas" is accurate only for one route. Here is how the full-route module sets break down:

Two details trip people up. First, the Inland route omits Q324, the Great Lakes Topics module, which is why it has five rather than six. Second, Q100 and Q300 are alternatives for the Rules of the Road requirement. Q100 covers Inland and International rules, while Q300 is the Inland-only alternative for a restricted route. Counting both would double-count Rules and manufacture an apparent sixth module that does not exist on the Inland route.

The number of groups is also not a universal count of examinations for every applicant. Your individual module assignments come from the NMC, and the right reference is the approval to test you receive, not a blog post (this one included). For eligibility and the paperwork that precedes testing, see NM51GI Requirements: Eligibility, Prerequisites & How to Qualify.

Domain 1: Rules of the Road (Q100 / Q300)

Rules modules reward precision. A candidate who knows the general idea of right-of-way but cannot distinguish an Inland rule from its International counterpart will struggle. Because the Great Lakes and Inland endorsement spans both regimes, build a side-by-side comparison of where the two rule sets diverge and drill from it. Our NM51GI cheat sheet is a handy place to consolidate those differences once you have worked them out yourself.

Remember the either/or logic: on the Inland route you prepare for Q100 or Q300 according to what your approval specifies, not both.

Domain 2: Deck General (Q320)

Because Q320 appears on both route sets, there is no scenario in which you can skip it based on route choice. Candidates who come from towing backgrounds sometimes assume their hands-on experience carries them here, but the module is written to test documented knowledge. Compare your day-to-day habits against the published topics and fill any gaps deliberately. The difficulty profile is discussed more fully in How Hard Is the NM51GI Exam?

Domain 3: Deck Safety (Q321)

A useful habit is to keep a running list of any topic that feels like it could belong to either Q320 or Q321 and then check it against the matrices. The modules are separate, and a topic's home module tells you where it will be examined.

Domain 4: Navigation General: Great Lakes and Inland (Q322)

One of the most common mistakes in published module discussions is treating alternative Navigation General modules as simultaneous requirements. They are not. If your approval lists Q322, that is the Navigation General module on your plate. Anything else you read about is relevant only if your own approval says so.

Domain 5: Navigation Problems: Chart Plot (Q323)

Domain 6: Great Lakes Topics (Q324)

Those published topics are broad, and several of them reward real-world context. Ice handling and Great Lakes weather behavior are not intuitive for someone whose experience is entirely on rivers or protected inland waters. If you are pursuing the full Great Lakes and Inland route, give Q324 its own study block and do not treat it as a bolt-on. Whether this extra module pays off for your career is a separate question explored in Is the NM51GI Certification Worth It? and the employment picture in NM51GI Jobs.

A caution on framing: do not describe Q324 as an "unpublished scope." The NMC publishes the module and its topic matrix. The preparation challenge is breadth, not secrecy.

What Is Not a Domain: Q326 and Route Extensions

Several modules show up in the NMC materials that are easy to mistake for additional domains. They are not part of the six.

If you already hold an Inland endorsement and want to extend to the Great Lakes, your path is a route extension, and the NMC lists the relevant modules (Q324, plus Q100 where a COLREGS limitation applies) as a separate set. That is a different situation from sitting a full original exam. Likewise, a candidate raising grade from towing to Master under 500 may be assigned Q326. Mixing these into the six-domain count produces a number that matches nobody's real exam plan.

Sequencing Your Preparation Around Your Route

Because the modules differ in character, the order in which you tackle them matters more than any generic study method. A sensible NM51GI-specific sequence looks like this:

For broader pacing ideas that fit around work schedules, see the NM51GI Study Guide, and when you are ready to test your recall under realistic conditions, use the NM51GI practice tests. If you want to understand scoring before you sit, read about the NM51GI passing score and check testing windows and scheduling. Cost questions are answered in the certification cost breakdown; note that this guide does not state current fees, since they are not established here.

Frequently Asked Questions

For related background, see NM51GI Certification and the overview of what the data shows on pass rates, and when you want to put your preparation to the test, head to the main practice test site.