What Master 100 unlocks
Master 100 GRT lets you operate USCG-inspected passenger vessels (Subchapter T or K) within the route and 100 GRT tonnage limit on the MMC. Whale-watch boats, dinner cruises, larger fishing party boats, and ferries can fall under this credential. Without a Master endorsement, the OUPV lane is capped at six passengers for hire on an uninspected vessel.
Sea-service requirements by route
Master less than 100 GRT is route-specific. The Near-Coastal route requires 720 days of deck-department service on ocean, near-coastal, or Great Lakes waters; inland-water service may substitute for up to 360 of those days. The Great Lakes/Inland route starts from 360 total days, and Great Lakes authority requires 90 days on Great Lakes waters. Current NMC checklists also apply a recency screen of 90 days in the past 7 years.
How the 100 GRT limit is calculated
The Coast Guard does not award 100 GRT just because the course or page says Master 100. Under 46 CFR 11.422, the tonnage limit is based on the size of vessels in your qualifying service. The current NMC Near-Coastal checklist shows the 100 GRT limit at either 180 days on vessels of 51 GRT or above, or 360 days on vessels of 34 GRT or above. The Great Lakes/Inland checklist uses 90 days on 51+ GRT or 180 days on 34+ GRT because that route has a 360-day base requirement. If your boat-size history is smaller, the endorsement may be issued at 50 or 25 GRT instead.
Exam differences vs OUPV
All four OUPV modules plus a Plotting (chart-work) module and a tightened General module on regulations. The Plotting module is the new ground for OUPV upgraders — running fixes, set & drift, danger bearings, magnetic variation/deviation. Pass mark on Plotting is 90%.
Before scheduling, compare the Master modules against the USCG captain's license exam format guide so the ATT letter, pass marks, and retest window are not a surprise.
Endorsements
Optional add-ons are route- and service-specific. For sail or auxiliary sail authority, 46 CFR 11.428 requires 12 months of sail or auxiliary-sail service on the Near-Coastal route, while 46 CFR 11.455 requires 6 months for Great Lakes/Inland. Commercial Assistance Towing is different from a towing-vessel officer endorsement: under 46 CFR 11.482, an OUPV, Mate, or Master needs an Assistance Towing endorsement to perform assistance towing unless an exception applies, and the add-on is earned by passing a written exam or completing a Coast Guard-approved course — not by a blanket six-month tow-service requirement. The authority still stays inside the scope of the underlying MMC.