How to Get a Sea Service Letter for the NMC: Format, Required Fields, and Employer Tips
A sea service letter with a single missing field — vessel official number, gross tonnage, exact route — will cause your application to be returned with a deficiency. Here is what every letter must include and how to get it right.
Updated May 2026 · 8 min read
Why the Letter Format Matters
Sea service letters are the primary evidence the NMC uses to verify that you have completed the sea service requirements for the endorsement you are applying for. The examiner at the NMC is checking specific fields — vessel tonnage, route, position, and dates — against the 46 CFR requirements for your target endorsement.
If any required field is missing or ambiguous, the NMC will issue a deficiency letter and return your application for correction. This typically adds 6–10 weeks to your processing time while you go back to the employer to get a corrected letter.
Required Fields in Every Sea Service Letter
Under 46 CFR Part 10, a sea service letter must document the following for each vessel:
Vessel name
M/V Pacific Star
Full official vessel name as documented with the USCG. Include any prefix (M/V, F/V, S/S).
USCG Official Number (or IMO Number for foreign vessels)
Official No. 1234567
This is the most commonly missing field. Found on the vessel documentation certificate (CG-1270). Not the state registration number — the USCG official number. For foreign vessels, the IMO number is acceptable.
Gross Tonnage (GT)
Gross Tonnage: 85 GT
Must match the vessel's document. Use Gross Tons (GT), not Net Tons or Displacement Tons. For tonnage-based endorsements, this is critical.
Route / Waters
Near Coastal, Gulf of Mexico
Must correspond to a USCG route designation: Inland, Near Coastal, Oceans, Great Lakes, or Western Rivers. For some endorsements, the specific ocean or region matters.
Your position / capacity
Captain / Master
Your actual role aboard: Master, Mate, Chief Mate, AB, Deckhand, Engineer, etc. Must match what you are claiming for endorsement credit.
Dates of service — start and end
January 15, 2024 – September 30, 2025
Exact dates. Month, day, and year for both start and end dates.
Total days of service
Total: 210 days
Total qualifying sea days for the period. Some employers use calendar days; some use shift days or underway days. Confirm which method the employer is using — underway days may be fewer than calendar days.
Employer signature
Signed by HR Director or company officer
Must be signed by an authorized representative of the employer. A company letterhead with printed name but no signature is not acceptable.
Recommended But Not Required
Including the following strengthens the letter and reduces the chance of follow-up questions from the NMC:
- Propulsion type (motor, sail, steam) — relevant for some engine endorsements
- Service area specifics (e.g., Hawaiian waters, Gulf of Mexico, Pacific Ocean)
- Contact phone and email for the signatory — the NMC can clarify questions without returning your packet
- Company letterhead (the letter will look official and clear)
How to Ask Your Employer for the Letter
Most maritime employers are familiar with sea service letters — this is routine. Give the HR department or your captain the above list of required fields and ask them to write the letter on company letterhead.
If the employer is unfamiliar or resistant, explaining that the letter is required by the US Coast Guard for federal credential application usually resolves any hesitation. The letter is not a legal document that creates liability for the employer — it is a factual statement of employment.
For older or defunct employers
If the employer no longer exists or you cannot contact them, the NMC may accept notarized personal affidavits for sea service in some circumstances. This is not a guaranteed substitute and adds processing time. The NMC may also cross-reference voyage logs, Coast Guard inspection records, and vessel documentation to verify service. Consult the NMC directly if you are in this situation.
Finding the USCG Official Number
The USCG Official Number appears on the vessel's Certificate of Documentation (CG-1270). If you do not have the CG-1270, you can look up any documented vessel by name at the USCG MVID (Marine Information for Safety and Law Enforcement) database. Many maritime attorneys and USCG licensing consultants also maintain access to this database.
For vessels documented with individual states rather than the USCG (common for smaller vessels), there may not be a USCG Official Number. In this case, use the state registration number and clearly note that it is a state-documented vessel. The NMC examiner will verify tonnage through other means.
Using AI to Verify Your Letters
BinnacleCrew's sea-service log includes an AI letter parser. Upload a photo or scan of your sea service letter and the AI will extract all fields — vessel name, official number, gross tonnage, route, position, dates, and days — and flag any missing required information before you mail your packet.
It also adds the entry to your sea service log automatically, so you can track total qualifying days toward any endorsement without manual entry.
Pro feature. AI extracts fields and flags missing data. Free tier available.
What a Good Letter Looks Like
[Company Letterhead]
May 15, 2026
To Whom It May Concern:
This letter confirms the sea service of John A. Mariner aboard the following vessel in the capacity listed below:
Vessel Name: M/V Pacific Star
USCG Official Number: 1234567
Gross Tonnage: 85 GT
Route: Near Coastal, Pacific Coast
Capacity: Captain / Master
Dates of Service: January 15, 2024 – September 30, 2025
Total Days of Service: 210 days
If you have questions, please contact our HR department at (808) 555-0100.
Sincerely,
Jane Smith
HR Director, Pacific Charter Company
[Signature]