- What NM51GI Actually Refers To
- Who Issues It and What It Authorizes
- The Module Map: Six Groups, Two Routes
- Walking Through Each Domain
- Modules You Should Never Add Together
- Your Approval Decides Your Modules
- Sequencing the Modules Over Your Prep Weeks
- Where This Credential Gets Used
- Frequently Asked Questions
- NM51GI here means National Master 500/1600 GL and Inland, a mariner credential issued through the U.S. Coast Guard National Maritime Center.
- The Great Lakes and Inland full route uses six modules: Q100, Q320, Q321, Q322, Q323 and Q324.
- The Inland route has five modules: Q100 or Q300, plus Q320, Q321, Q322 and Q323. Q324 is omitted.
- Q100 and Q300 are alternatives. Never count them together as simultaneous requirements.
What NM51GI Actually Refers To
Search for "NM51GI" and you may land on material about unrelated credentials, because several programs share similar-looking codes. On this site, the term means one thing only: National Master 500/1600 GL and Inland (NM51GI). It is a deck-officer credential for mariners who aim to serve as master of vessels on the Great Lakes and inland waters, within the tonnage ranges the title describes.
If you have already read our entries on the NM51GI meaning or what NM51GI stands for, this article goes one level deeper. It focuses on the structure of the examination modules, because that is where candidates most often get confused.
Who Issues It and What It Authorizes
The governing body is the United States Coast Guard National Maritime Center (NMC). The NMC publishes the examination modules and topic matrices for Great Lakes and Inland endorsements on its public site. Nothing about the scope is secret: the module headings, the topic lists and the route-by-route groupings are all published by the issuer.
The relevant examination scope is designated GLI03, covering the master endorsement for vessels of less than 500 and 1,600 gross register tons on the Great Lakes and Inland route. The published examination guide places this reference at section 2.1.2.2, printed page 25.
The Module Map: Six Groups, Two Routes
The most important thing to understand about NM51GI is that its examination content is organized as modules, each identified by a Q-code. Which modules apply to you depends on your route. The table below shows the exact module sets published for the full-route endorsements.
| Route | Module set | Count |
|---|---|---|
| Great Lakes and Inland | Q100, Q320, Q321, Q322, Q323, Q324 | 6 modules |
| Inland | Q100 or Q300, Q320, Q321, Q322, Q323 | 5 modules |
Notice the two differences. First, the Inland route omits Q324, the Great Lakes Topics module, so it has five groups rather than six. Second, on the Inland route the Rules of the Road requirement can be met by Q100 or Q300, and these are alternatives rather than a pair.
In this article series, those module headings are treated as unweighted, route-aware preparation groups. The packet behind this guide does not establish percentage weightings, a single overall question count, a single overall duration, current fees or a population pass rate, so you will not find invented figures here. For deeper coverage, see our complete guide to the NM51GI exam domains.
Walking Through Each Domain
Domain 1: Rules of the Road
Rules of the Road: Inland and International (Q100)
This module covers collision-avoidance rules. Q100 addresses both Inland and International rules, while Q300 is the Inland-only alternative for the restricted route.
- Know which rule set governs which waters, because the boundary matters in practice.
- Expect to apply rules to vessel situations such as meeting, crossing and overtaking.
- If a COLREGS limitation applies to your endorsement, Q100 is the module the published guide lists for it.
Domain 2: Deck General
Deck General (Q320)
Q320 is a general seamanship and vessel-operations module. It forms part of both the Great Lakes and Inland route and the Inland route.
- Treat it as a foundation module; later navigation and safety questions assume you are comfortable with its vocabulary.
Domain 3: Deck Safety
Deck Safety (Q321)
Q321 addresses safety on deck and aboard the vessel. Like Q320, it appears in both route sets.
- Study it alongside Deck General, since the two modules often reinforce each other's content.
Domain 4: Navigation General
Navigation General: Great Lakes and Inland (Q322)
Q322 is the navigation theory module for the Great Lakes and Inland scope. It sits in both route sets.
- This is a concept module. It builds the reasoning you will then use in the chart-plotting module.
Domain 5: Navigation Problems
Navigation Problems: Chart Plot (Q323)
Q323 is the hands-on chart-plotting module. It appears on both routes and is the one where careful, repeatable working habits matter most.
- Practice plotting under time pressure, because accuracy and speed develop together.
Domain 6: Great Lakes Topics
Great Lakes Topics (Q324), Great Lakes-and-Inland route only
Q324 is the module that distinguishes the Great Lakes route from the Inland route. The published topic list for it includes:
- Piloting
- Compass error
- Meteorology and oceanography
- Maneuvering and handling, including ice
- Stability, construction and damage control
- Cargo handling
If you are on the Inland route, Q324 does not apply to you, and you should not spend study hours on it. If you are on the Great Lakes and Inland route, it is a full module that deserves dedicated time, particularly the ice-handling and meteorology topics, which have no counterpart in the other modules.
Modules You Should Never Add Together
A common mistake is adding up every Q-code on the NMC pages and concluding that the exam is some larger number of tests than it is. Several rules prevent that error.
- Q100 and Q300 are alternatives. Alternative Rules modules are never simultaneous requirements.
- Do not hide the Great Lakes module by double-counting Rules. The Great Lakes and Inland route has six groups because Q324 is included, not because Rules was counted twice.
- Raise-of-grade modules are separate. Q326, Navigation and Deck General/Safety, is a distinct module for the towing-to-Master-under-500 raise of grade. It is not an additional domain of the full original examination.
- Route-extension modules are separate. The guide lists Inland-to-Great Lakes/Inland content (Q324, and Q100 where a COLREGS limitation applies) separately from the original full-route sets.
Your Approval Decides Your Modules
The authoritative answer to "which modules must I take?" is the NMC's decision on your individual application, shown in your approval to test. Whatever a study guide, forum thread or this article implies, the modules named in your own approval are the ones you must sit.
That is why the application stage matters so much. Before you build a plan, read our breakdown of NM51GI requirements and eligibility so you understand what the NMC will look for. Fee and scheduling mechanics are also handled by the issuer, and current amounts can change, so confirm them directly rather than relying on any secondhand figure. Our certification cost overview explains the categories of expense to expect, and the exam dates and scheduling article covers how testing windows work in general terms.
Sequencing the Modules Over Your Prep Weeks
Because the modules build on each other, the order you study them in matters more than the total hours. This is the one place where a schedule helps, and it is tied directly to the module structure. The example below assumes the six-module Great Lakes and Inland route; Inland candidates simply drop the Q324 week.
Rules of the Road (Q100 or Q300)
- Start here because rules vocabulary appears everywhere else.
- Confirm from your approval whether Q100 or Q300 applies.
Deck General and Deck Safety (Q320, Q321)
- Study these together; their content overlaps.
Navigation General (Q322)
- Build the theory before you start plotting.
Chart Plot (Q323)
- Repeat plotting exercises until your method is consistent.
Great Lakes Topics (Q324)
- Reserve this week only if your route includes Great Lakes.
- Give extra attention to ice handling and meteorology.
For a fuller method, see our NM51GI study guide, and when you are ready to test your recall, the NM51GI practice tests let you drill each domain on its own. If you want a compact refresher near exam day, the one-page cheat sheet is built for that.
Where This Credential Gets Used
A master endorsement for the Great Lakes and Inland scope is relevant to operators of vessels on those waters. That includes commercial operators on the Lakes and on rivers and other inland waterways. Rather than quote hiring figures that this packet does not establish, we point you to the dedicated articles: NM51GI jobs covers the kinds of roles the credential supports, and the salary guide and ROI analysis discuss compensation and value in qualitative terms.
If you are weighing difficulty, the difficulty guide explains why the chart-plot module and the Great Lakes topics tend to demand the most deliberate practice. And if you are asking about outcomes, our pages on pass rate and passing score are candid about what is and is not publicly established.
Key Takeaway
Before you open a single study resource, find your approval to test and write down the exact Q-codes on it. Then study only those modules, in the order that builds knowledge: rules, deck, navigation theory, chart plot, then Great Lakes topics if applicable.
Frequently Asked Questions
It refers to National Master 500/1600 GL and Inland (NM51GI), a mariner credential associated with the U.S. Coast Guard National Maritime Center. It does not refer to any other credential that happens to share the acronym.
Six: Q100, Q320, Q321, Q322, Q323 and Q324. The Inland route has five, using Q100 or Q300 for Rules, plus Q320, Q321, Q322 and Q323, with Q324 omitted.
No. Q100 and Q300 are alternatives for the Rules requirement, so they should never be counted as simultaneous requirements. Your approval to test shows which one applies to you.
No. Q326, Navigation and Deck General/Safety, is a separate module for the raise of grade from towing to Master under 500. Upgrade, raise-of-grade and route-extension modules are not additional domains of the full original examination.
No. The published material used here does not establish percentage weightings, a single overall question count or duration, current fees or a population pass rate, so none are stated. Confirm any such details with the NMC. For general background, see what the NM51GI certification is.