0.1 About the Master Less Than 100 GRT Credential

What Master Less Than 100 GRT Means

The Master of self-propelled vessels of less than 100 gross register tons (GRT) — commonly called Master 100, Master 100-Ton, or Master LT 100 GRT — is a U.S. Coast Guard deck officer credential issued on a Merchant Mariner Credential (MMC). It authorizes you to serve as master (the person in command) of self-propelled vessels whose gross tonnage is under 100 GRT, on the route endorsed on your license (Near Coastal, Great Lakes & Inland, or Inland).

This is not a recreational boating card and not a simple "captain's license" slogan. It is a federal officer endorsement under Title 46 of the Code of Federal Regulations (CFR), with the Near Coastal original path governed principally by 46 CFR 11.428. Holding it means the Coast Guard has evaluated your identity, citizenship, sea service, medical fitness, drug testing, security screening, and professional knowledge, and found you qualified to take legal responsibility for a vessel and everyone aboard.

Gross tonnage here is regulatory vessel measurement, not the weight of the boat on a scale and not simply "how many passengers it seats." A vessel can look small and still approach or exceed 100 GRT, or look large and measure under 100 GRT depending on enclosed volume and measurement rules. Your authority as Master 100 stops at vessels less than 100 GRT unless you hold a higher tonnage endorsement.

Why operators pursue Master 100

Most candidates need Master 100 because they want to work for hire on vessels that go beyond the uninspected passenger vessel limit. Typical commercial platforms include:

• Charter and head boats running fishing, diving, or sightseeing trips for groups larger than six
• Small ferries and water taxis operating under inspection
• Dinner boats and harbor cruise vessels
• Whale-watch and eco-tour boats
• Other inspected small passenger vessels listed on a Certificate of Inspection (COI)

Once a vessel is inspected and carries more than six passengers, the master generally must hold an appropriate Master endorsement for the vessel's tonnage and route — not an OUPV. That commercial step-up is the central career reason Master 100 exists.

Master 100 vs OUPV (Six-Pack)

The Operator of Uninspected Passenger Vessels (OUPV) endorsement is widely known as the six-pack. OUPV authorizes operation of uninspected passenger vessels carrying six or fewer passengers for hire. It is the right credential for many bare-bones charter boats that never cross into inspected-vessel territory.

Master 100 is the next professional tier for small commercial passenger operations:

A practical rule of thumb used throughout the industry: if the boat runs under a COI and carries more than six passengers, plan on Master, not OUPV. Moving from OUPV to Master 100 on the same route is a common raise-of-grade (ROG) path; the exam load is smaller than the full original ONC06 set (covered in Section 0.4).

Do not confuse "I can drive a 100-foot boat recreationally" with Master 100 authority. Recreational operation of your own vessel is a different legal regime. Master 100 is about commercial service under Coast Guard manning and inspection rules.

Routes: Near Coastal, Great Lakes & Inland, Inland

Route is as important as tonnage. The endorsement states where you may serve as master. The three route packages you will see for Master LT 100 GRT are:

1. Near Coastal (NC) — ocean waters not more than 200 miles offshore (the classic "outside" small-passenger route along coasts and to nearby islands, within the NC definition).
2. Great Lakes & Inland — the Great Lakes system plus inland waters as defined for that endorsement.
3. Inland — inland waters only (rivers, lakes, bays, and sounds as defined for the Inland route).

Master 100 is not issued as an Oceans Master 100. Unlimited or oceans-range master authority for higher-tonnage or oceans service is a different endorsement ladder (higher tonnage, different sea service, different exams). If your goal is deep-ocean commercial command far beyond Near Coastal limits, Master LT 100 GRT is the wrong target credential; if your goal is coastal charters, head boats, small ferries, dinner boats, and similar COI vessels under 100 GRT, it is exactly the right one.

When you apply, you must match sea service location to the route you want. Days earned only on restricted inland waters will not, by themselves, support a full Near Coastal original path without the ocean/NC/Great Lakes component required by regulation (see Section 0.2).

NMC Exam Code ONC06 and 46 CFR 11.428

The National Maritime Center (NMC) catalogs officer exams by code. For original Master Less Than 100 GRT Near Coastal, the operative code is ONC06. That code tells Regional Exam Centers (RECs) and approved schools which module set you must pass (Rules of the Road, Deck General, Deck Safety, Navigation General Near Coastal, and Chart Plot). Section 0.4 lists every module number, question count, and passing percentage.

The regulatory home for the Near Coastal Master LT 100 path is 46 CFR 11.428. That section sets service, route, and examination expectations for the endorsement. Tonnage breakpoints that control whether your sea service supports 100 GRT, 50 GRT, or 25 GRT authority live primarily in 46 CFR 11.422 and are calculated in Section 0.2.

Who this study guide is for

This guide is written for candidates preparing for ONC06 (original Master NC LT 100) or the raise-of-grade modules from OUPV Near Coastal to Master Near Coastal. You may already hold OUPV, or you may be coming straight from deck service toward an original Master. Either way, you need the same professional core: COLREGS and Inland Rules at 90%, deck seamanship and safety at 70%, near-coastal navigation at 70%, and chart plot at 90%.

Scope of authority vs day-to-day command

Holding Master 100 does not automatically make every vessel under 100 GRT legal for you to run tomorrow. You still need:

• A vessel whose tonnage and route fit your endorsement
• Proper manning as required by the COI or applicable rules
• Required documents, drills, and equipment for that vessel class
• Company policies, insurance, and state/local requirements that may exceed federal minimums

The license is the Coast Guard's permission to serve in the master billet when the vessel and voyage match your MMC. It is the legal foundation of commercial command on the small-passenger fleet this guide targets.

Key vocabulary to lock in now

• GRT (gross register tons): regulatory measure of enclosed volume used for licensing limits
• COI (Certificate of Inspection): Coast Guard document for inspected vessels stating routes, passengers, manning, and equipment
• OUPV: Operator of Uninspected Passenger Vessels; six or fewer passengers for hire
• MMC: Merchant Mariner Credential — the booklet that carries officer and rating endorsements
• NMC: National Maritime Center — national credentialing and exam authority
• REC: Regional Exam Center — where modular exams are administered
• ONC06: exam code for original Master LT 100 GRT Near Coastal
• 46 CFR 11.428: primary rule for Master LT 100 Near Coastal path

Master the difference between OUPV six-pack and Master on a COI vessel, know your route limits, and remember that ONC06 under 46 CFR 11.428 is the formal path this entire study guide prepares you to pass.