0.2 Eligibility, Sea Service & Tonnage Calculations

Baseline Eligibility

Before the National Maritime Center will evaluate you for Master of self-propelled vessels less than 100 GRT, you must clear non-negotiable personal requirements. For the Near Coastal original path under 46 CFR 11.428, lock in these foundations:

• Age: at least 19 years old
• Citizenship: U.S. citizen (officer endorsements requiring citizenship follow this rule; do not assume permanent residency is enough for this master path)
• Identity and security: TWIC and security screening as part of the MMC process (Section 0.3)
• Medical fitness: valid Coast Guard medical certificate
• Chemical testing: drug test meeting Coast Guard timing rules
• Sea service: documented 720 days in the deck department meeting route and tonnage rules below

Sea service is almost always the long pole. Age and citizenship are binary gates; sea service is a multi-year construction project that must be proved on paper with sea service letters, discharges, or other accepted evidence.

The 720-Day Deck Service Rule (46 CFR 11.428)

For original Master LT 100 Near Coastal, you need 720 days of service in the deck department on vessels operating on Ocean, Near Coastal, or Great Lakes waters. That is roughly two years of full-time deck time if you work continuously — longer if you work seasonal charters.

Inland substitution

Not all of those 720 days must be "outside." Regulation allows inland service to substitute for up to 360 days of the 720. In other words:

If you have 400 inland days and 320 ocean/NC/Great Lakes days, you do not meet the rule: only 360 inland days can count, and 320 outside days leave you short of 720. If you have 360 inland + 360 NC, you meet the day-count structure (tonnage still must be checked separately).

Recency

You also need recency: 90 days of qualifying service within the past 7 years. Old career time from a decade ago does not fully substitute for recent deck experience. If your last commercial deck hitch was eight years ago, plan a return to sea before you apply.

Engine-department credit

Some engine-room time can help, but only a little. Engine-department service may credit up to 90 days toward the sea-service total. Do not build an application that assumes all engine time counts as deck time; the 90-day ceiling is a hard planning number. Prefer clean deck letters whenever possible.

What "deck department" means in practice

Deck service includes work as master, mate, able seaman, ordinary seaman, deckhand, and similar ratings whose primary duties are navigation, lookout, line handling, cargo/passenger handling on deck, and watchstanding related to vessel operation. Pure hospitality, galley-only, or shoreside admin roles generally do not count as deck service even if they occur on a boat. Your sea service letter should state position, vessel name and official number, tonnage, waters, dates, and days so evaluators can apply 11.428 and 11.422 without guessing.

Tonnage Calculations (46 CFR 11.422)

Having 720 days is not enough if those days were only on tiny vessels. Tonnage of the vessels on which you served determines whether NMC will issue 100 GRT, 50 GRT, or 25 GRT authority on the master endorsement. The breakpoints that matter for Master LT 100 planning are:

Target: 100 GRT authority

To obtain 100 GRT on the Master endorsement, your service must include either:

• 180 days on vessels of 51 GRT or greater, or
• 360 days on vessels of 34 GRT or greater

Lower tonnage breakpoints (50 GRT and 25 GRT)

If you cannot meet the 100 GRT vessel-day thresholds, 46 CFR 11.422 still allows lower tonnage limits (commonly discussed as 50 GRT and 25 GRT breakpoints) based on the size of vessels in your record. A 50 GRT or 25 GRT Master is still a Master endorsement, but your command authority stops at that tonnage. Many candidates intentionally seek time on ≥51 GRT inspected passenger vessels or large enough commercial craft so the first MMC already shows Master 100, not Master 25.

Worked planning examples

Example A — clean 100 GRT path: 400 days deck on 60 GRT head boats (NC) + 320 days deck on 40 GRT inland dinner boats. Outside/NC days exceed 360; inland substitution under 360 is fine for the 720 structure. Vessel days ≥51 GRT already exceed 180 → supports 100 GRT.

Example B — 34 GRT alternative: 360 days on 35 GRT NC charter boats + 360 days inland on 20 GRT vessels. The 360 days on ≥34 GRT can support 100 GRT tonnage if the rest of 11.428 is met — even though you never sailed a 51 GRT hull.

Example C — short on tonnage: 720 days entirely on 18–22 GRT six-pack boats. Day count and route may be fine for a master exam path, but tonnage service is too light for 100 GRT; expect a lower tonnage limit unless you add larger-vessel time.

Always record GRT (or GT as accepted) from the vessel's documentation or COI on every sea service letter. "About 50 feet" is not a tonnage figure.

Optional Endorsements and Special Paths

Sail or auxiliary sail

If you will master sail or aux-sail commercial vessels, you may need sail or auxiliary sail endorsements in addition to power Master authority. Those typically require additional sail service and may involve extra exam modules. Do not assume power Master 100 alone covers commercial sailing passenger operations.

Assistance towing

Assistance towing is a common add-on for captains who tow disabled recreational vessels for hire. It is optional relative to base Master 100 but required for that specific service. Plan the extra service and any exam module if towing is part of your business model.

Mate on inspected vessels ≥200 GRT → Master 100

A valuable raise path: a mariner holding Mate on inspected vessels of 200 GRT or more may obtain Master 100 on the same route without an additional exam, still paying applicable evaluation and issuance fees. That path recognizes that mate service on larger inspected vessels already proves a professional deck standard. If you already hold that mate endorsement, confirm current NMC checklist language before scheduling unnecessary modules.

Raise of grade from OUPV

Mariners who already hold OUPV Near Coastal commonly raise grade to Master Near Coastal LT 100 with a reduced exam set (module Q165 at 70% — see Section 0.4) once sea service and tonnage for Master are met. OUPV service still must be documented carefully; the six-pack time may count toward days, but tonnage of the vessels still controls 100 vs 50 vs 25 GRT.

Application Checklist MCP-FM-NMC5-15

When you are ready to package the application, use the Coast Guard National Maritime Center checklist MCP-FM-NMC5-15 dated September 15, 2025 (or the current superseding revision if NMC later replaces it). That checklist is the evaluator's roadmap for original Master LT 100 packages. It aligns required forms, TWIC, medical, drug test, first aid/CPR or Basic Training, sea service evidence, fees, and photo/identity items so you do not mail a half-complete package.

Pre-application self-audit

1. Confirm age ≥ 19 and U.S. citizenship documents.
2. Tally deck days by water body: Ocean/NC/Great Lakes vs inland; ensure ≥360 outside if using max inland substitution.
3. Confirm 90 recency days in the last 7 years.
4. Cap any engine credit at 90 days.
5. Run tonnage math for 100 vs 50 vs 25 GRT under 11.422.
6. Decide optional sail / aux sail / assistance towing.
7. Gather sea service letters with vessel GRT, official numbers, and signatures.
8. Walk MCP-FM-NMC5-15 line by line before submitting through the MMC/ASAP process described next.

Sea service is won or lost on specificity. Vague letters force RFEs (requests for evidence) and months of delay. Build the record as if a skeptical evaluator will reconstruct every day — because that is exactly what happens.