USCG 100-Ton Captain License Exam: What to Expect

The USCG Master 100 Gross Tons license is the workhorse credential of the commercial passenger vessel industry. It's what powers the whale watch captain, the sailing school skipper, the small ferry operator, and the charter boat master. If you're running inspected vessels or need to go beyond the six-passenger OUPV limit, the 100-ton is where you step up.

The exam is more demanding than the 6-pack, with more modules and deeper technical content. Here's a complete guide to what's actually tested, how many questions you'll face, and how to prepare without burning yourself out.

What the 100-Ton Credential Covers

The Master of Vessels of Not More than 100 Gross Tons (commonly shortened to Master 100 GT or "100-ton") is governed by 46 CFR Part 11, Subpart B. It authorizes you to serve as master of inspected vessels — Subchapter T passenger vessels, inspected fishing vessels, small towing vessels — up to 100 gross tons on near coastal or inland routes.

The credential is issued by the USCG NMC (National Maritime Center) in Martinsburg, WV, which processes all U.S. merchant mariner credential (MMC) applications. The exam itself is administered at an NMC-approved Regional Exam Center.

Sea Service Requirements

Before you sit for the exam, you need sea service documented in a USCG-acceptable logbook:

• 720 days total sea service (12 months on deck)
• At least 360 days on near coastal waters if applying for the near coastal route endorsement
• At least 90 days as operator or in charge of the deck watch on vessels of at least 50 GRT

This is the most common application bottleneck. The "in charge of the deck watch" days often require a supervisor's sign-off or a letter from a vessel operator attesting to your watchstanding duties. Start documenting this carefully from day one.

Exam Module Breakdown

The Master 100 GT near coastal exam comprises multiple modules. The NMC tests each module separately, and you must score 70% or higher on each module independently — there's no averaging across modules.

| Module | Question Count | |--------|---------------| | Rules of the Road | 50 questions | | Deck General | 100 questions | | Navigation General | 100 questions | | Chart Plotting | 9 problems (plotted exercises) | | Safety | variable |

Note: NMC module structures can be combined or separated depending on the testing center and whether you've passed individual modules from a prior application. Check with your REC for your specific exam plan.

What Each Module Tests

Rules of the Road (50 questions, 70% to pass)

Full COLREGS 1972 and U.S. Inland Rules — all 38 rules. This module goes deeper than the OUPV version. Expect:

• Lights and shapes for every vessel type, including pilot vessels, vessels not under command, RAM vessels, constrained-by-draft, seaplanes on the water, and WIG craft
• Every sound signal: fog, maneuvering, distress, answers to distress
• Traffic separation scheme rules (COLREGS Rule 10) and how they interact with overtaking and crossing rules
• Narrow channel conduct, including the rights of vessels proceeding downbound on the Mississippi River system
• Bends and anchorage areas — when and how to sound signals

This module trips up candidates who know the rules in general but haven't drilled the precise exceptions. Know exactly where COLREGS and Inland diverge.

Deck General (100 questions, 70% to pass)

Seamanship, stability, and cargo handling. At the 100-ton level, stability gets real:

• GM (metacentric height) and how it affects vessel motion — the difference between stiff and tender vessels
• Free surface effect — how tank partitioning affects GM
• Stability letters and load lines — understanding what the stability booklet is telling you
• Anchoring: scope calculation, anchor gear types, working with two anchors
• Fire and damage control: classes of fire, appropriate extinguishing agents, flooding and freeboard calculations
• Towing: tow length, bridle configuration, snatching a line, emergency towing procedures
• Weather: reading synoptic charts, identifying fronts, tropical cyclone behavior, sea state prediction

Chapman Piloting, Seamanship & Small Boat Handling is worth reading cover to cover for this module. It's the standard reference.

Navigation General (100 questions, 70% to pass)

Deeper into navigation than the 6-pack. Expect:

• Compass correction: variation, deviation, deviation tables — converting between magnetic and compass bearings in both directions
• Current sailing: set and drift, course made good, speed made good, leeway
• Tidal calculations using tide and tidal current tables
• Running fix, cross-bearing fix, distance off by vertical angle, distance off at change of bearing
• Electronic navigation: GPS error characteristics, RAIM, DGPS
• LORAN (legacy — still appears on some question banks)
• Introduction to celestial: solving for LOP from sun sight, Nautical Almanac use, assumed position

For navigation, Dutton's Nautical Navigation (15th ed) is the canonical reference. Get it and use it. The NMC question bank pulls directly from the concepts in this book.

Chart Plotting (9 problems, 70% to pass)

Nine plotted problems on NOAA paper charts — compass work, distance calculation, ETA problems, current vector diagrams, and position fixing. You bring your own plotting equipment: parallel rules or rolling plotter, dividers, and a pencil.

Practice on actual charts. The problem types are predictable but the mechanical skill requires repetition. The most common errors:

• Forgetting to apply variation when converting between true and compass
• Applying deviation in the wrong direction
• Arithmetic errors in time/speed/distance calculations

Work through at least 50 plotted problems before test day.

The Application Process

Submit your application to the NMC via their online MMLD (Mariner Licensing and Documentation) system. Required documents typically include:

• Sea service record signed by vessel master(s)
• Proof of U.S. citizenship (passport or birth certificate)
• USCG-approved physical (CG-719K) signed by a licensed physician
• Drug test through a USCG-approved MRO conducted within the past 12 months
• CPR/first aid certification
• References (for first-time applicants)

Processing times vary — plan for 60-90 days. Once approved, you'll receive an authorization-to-test letter and can schedule your exam at a Regional Exam Center.

A Study Schedule That Works

12 weeks out: Start with the Rules of the Road. Read all 38 rules twice without taking notes. Then get a copy of the NMC question bank (available through approved schools or prep programs) and start working Rules of the Road questions only.

10 weeks out: Add Deck General. Focus first on stability — it's the hardest conceptual section and needs the most time. Read Chapman chapters on stability and seamanship.

8 weeks out: Add Navigation General. Start with compass correction (it's mechanical and predictable) before moving into current sailing and celestial.

6 weeks out: Begin chart plotting exercises. Daily practice until problems feel automatic.

4 weeks out: Full-length timed practice exams by module. Identify weak areas and drill them specifically.

2 weeks out: Review only — no new concepts. Reinforce what you know. Sleep well before exam day.

Practice with Binnacle School

The 100-ton exam is passable on the first attempt with structured practice — but the question bank is large and the concepts stack. [Binnacle School](/school) gives you exam-format practice sessions organized by module and topic, so you can drill Rules of the Road separately from Deck General and know your exact weak spots before test day.

Start practicing for your Master 100 GT exam →

Binnacle AI is not affiliated with the U.S. Coast Guard or the NMC. Exam module structures and question counts reflect current NMC guidance as of 2026 — confirm at uscg.mil/nmc before scheduling your exam. This article is informational, not legal or licensing advice.