- NM51GI here means National Master 500/1600 GL and Inland, a U.S. Coast Guard mariner credential.
- The Great Lakes and Inland route uses six modules: Q100, Q320, Q321, Q322, Q323 and Q324.
- The Inland route has five modules because it omits Q324 Great Lakes Topics.
- Q100 and Q300 are alternative Rules of the Road modules, never simultaneous requirements.
Understanding the NM51GI Label
Key Takeaways
- NM51GI here means National Master 500/1600 GL and Inland, a U.S. Coast Guard mariner credential.
- The Great Lakes and Inland route uses six modules: Q100, Q320, Q321, Q322, Q323 and Q324.
- The Inland route has five modules because it omits Q324 Great Lakes Topics.
- Q100 and Q300 are alternative Rules of the Road modules, never simultaneous requirements.
- The National Maritime Center assigns your actual modules in your approval to test.
What the Label Actually Refers To
NM51GI Exam Prep is built around one specific credential: National Master 500/1600 GL and Inland. It is a mariner endorsement issued under the authority of the United States Coast Guard, and the examination work behind it is administered through the Coast Guard's National Maritime Center (NMC). If you arrived here wondering whether the string "NM51GI" points to a medical code, a software product or some other certification, the answer on this site is no. Everything here concerns the deck officer exam path for masters of vessels in the 500 and 1600 gross register ton range operating on the Great Lakes and inland waters.
For a quick orientation to related terminology, you can also read What Is NM51GI? and What Does NM51GI Stand For?. This article focuses on the practical meaning: what the name tells you about the credential, the waters it covers and the examination modules a candidate may face.
Decoding "500/1600 GL and Inland"
Each element of the title carries information about the endorsement.
National Master
"Master" is the top deck-officer position aboard a vessel, the person with ultimate responsibility for the ship, crew and cargo. "National" signals that the endorsement is issued under U.S. domestic rules rather than the international STCW framework.
500/1600
The numbers refer to gross register tonnage (GRT) tiers. The title pairs a 500 GRT tier with a 1600 GRT tier, and the NMC examination page for this path is titled around "Master LT 500/1600 GRT" with module references Q323 and Q326. Your specific tonnage limitation depends on the endorsement you are seeking and the sea service you can document, so treat the NMC and the regulations as the authority rather than relying on the shorthand alone.
GL and Inland
"GL" stands for Great Lakes, and "Inland" refers to inland waters. The combined route is broader than an inland-only endorsement, which is why it carries an extra examination module covering Great Lakes topics. The distinction matters for exam planning and is explained in the route comparison below.
Who Governs It: The National Maritime Center
The governing body is the United States Coast Guard National Maritime Center. The NMC publishes examination modules and topic matrices publicly, which means the scope of what you will be tested on is not a secret. The published sources reviewed for this article include the NMC's Great Lakes and Inland endorsements page, the GLI03 page covering Master LT 500/1600 GRT (Q323 and Q326), and the NMC deck and engineering examination guide.
One important caveat: the deck and engineering guide referenced here is the published regulations-effective document dated March 24, 2014, not a newly issued 2026 blueprint. Current indexed NMC matrices corroborate the module headings, but candidates should always confirm current details directly with the NMC. For eligibility questions, see NM51GI Requirements, and for the broader credential picture, NM51GI Certification.
The Published Examination Modules
The NMC organizes this path as GLI03, and the full-route module list is built from a handful of coded modules. This site groups them into route-aware preparation domains. These are not weighted percentages, and no overall question count or exam duration is established in the published materials reviewed, so any claim of a single universal exam length should be treated skeptically.
Domain 1: Rules of the Road (Q100, or Q300 for Inland-only)
Q100 covers Rules of the Road: Inland and International. Q300 is the inland-only alternative that applies on the restricted route. Where a COLREGS limitation applies, the guide lists Q100 separately.
- Q100 and Q300 are alternatives, not a combined requirement
- Know which one your approval to test assigns
Domain 2: Deck General (Q320)
The broad seamanship and vessel-operations foundation for a deck officer.
Domain 3: Deck Safety (Q321)
Safety-focused deck knowledge expected of a master.
Domain 4: Navigation General: Great Lakes and Inland (Q322)
General navigation knowledge tailored to the Great Lakes and inland route.
Domain 5: Navigation Problems: Chart Plot (Q323)
Applied chart-plotting problems. This is a hands-on skill module rather than pure recall.
Domain 6: Great Lakes Topics (Q324)
Applies to the Great Lakes-and-Inland route only. Published Q324 topics include piloting, compass error, meteorology and oceanography, maneuvering and handling including ice, stability, construction and damage control, and cargo handling.
For a deeper walk through each area, see NM51GI Exam Domains: Complete Guide to All 6 Content Areas.
Great Lakes and Inland vs. Inland-Only
The single most useful thing to grasp about the NM51GI name is how the route changes the module count. The two full-route sets are laid out below.
| Route | Modules | Count |
|---|---|---|
| Great Lakes and Inland | Q100, Q320, Q321, Q322, Q323, Q324 | 6 |
| Inland | Q100 OR Q300, Q320, Q321, Q322, Q323 | 5 |
The difference is Q324. Great Lakes Topics exists only on the Great Lakes-and-Inland route, so the Inland route has five modules while the combined route has six.
Raise-of-grade and route-extension modules
Some modules sit outside the full-original-exam picture. Q326, Navigation and Deck General/Safety, is a separate towing-to-Master-under-500 raise-of-grade module. The guide also lists Inland-to-GL/Inland extension modules (Q324, and Q100 where a COLREGS limitation applies) separately. These upgrade and extension modules should not be read as additional domains in a full original exam. If you already hold a related endorsement, your required modules may look quite different from a first-time applicant's.
Common Misreadings to Avoid
- "There are six exams for everyone." Six is the full Great Lakes and Inland route. The Inland route has five, and upgrade candidates may have fewer or different modules.
- "The percentages are published." The NMC publishes modules and topic matrices, but this packet establishes no percentage weights. This site treats the domains as unweighted preparation groups.
- "The numbers are fixed facts." Question counts, durations, current fees and population pass rates are not established by the sources reviewed here. Treat anything stated confidently without a source with caution, and see NM51GI Pass Rate and NM51GI Passing Score for how to think about those questions.
- "This site speaks for the Coast Guard." It does not. Preparation materials here are independent, and no issuer endorsement is implied. Your authoritative instructions come from the NMC.
Key Takeaway
Before you buy any study material, get your approval to test from the NMC and read the exact module list on it. That document, not a generic exam description, defines what you must pass.
Sequencing Your Preparation by Module
Because the route determines the module list, plan around your own approval. A reasonable ordering for a Great Lakes and Inland candidate is to start with skill-heavy material first, since chart plotting rewards repeated practice, then layer in the knowledge-heavy modules.
Navigation Problems: Chart Plot (Q323)
- Begin plotting practice immediately, because accuracy comes from repetition
- Pair with Navigation General (Q322) concepts
Rules of the Road and Deck modules
- Confirm whether Q100 or Q300 applies to you
- Work through Deck General (Q320) and Deck Safety (Q321)
Great Lakes Topics (Q324), if on your list
- Review piloting, compass error, meteorology, ice handling, stability and cargo handling
- Skip this only if your route is Inland-only
For a fuller plan, the NM51GI Study Guide and the NM51GI Cheat Sheet cover review structure, and you can test yourself on the main NM51GI practice test site. If you are weighing the investment, the certification cost breakdown and ROI analysis are good next reads, and the practice tests help you gauge readiness before you schedule.
Frequently Asked Questions
It refers to National Master 500/1600 GL and Inland, a U.S. Coast Guard mariner credential whose examination work is handled through the 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 because it omits Q324 and uses Q100 or Q300 for Rules of the Road.
No. They are alternative Rules of the Road modules. Q300 is the inland-only alternative, and your approval to test determines which applies to you.
No. Q326, Navigation and Deck General/Safety, is a separate towing-to-Master-under-500 raise-of-grade module, not an additional domain of a full original exam.
The National Maritime Center assigns them individually. Use your actual approval to test as the authoritative list, and confirm any current details such as fees directly with the NMC.
In short, the name NM51GI encodes a master's endorsement, a tonnage range and a water route, and each of those choices shapes the modules you will sit. For related explainers, see What Does NM51GI Stand For? and NM51GI Meaning.