How to Document Sea Service for a USCG Merchant Mariner Credential (CG-719S, Sea Service Letters, and What Counts as a Day)
Sea service is the backbone of almost every Coast Guard merchant mariner credential (MMC) application. It is also one of the most common reasons applications stall. When the National Maritime Center (NMC) can't credit your time, you get an "Awaiting Information" (AI) letter, and your application sits until you fix it.
This guide walks through what the regulations and the NMC's own published guidance say about documenting sea service, with a focus on OUPV ("six-pack") and Master less than 100 GRT applicants. Every rule below is linked to its source at the bottom of the page.
Not legal advice. Pilot House Prep is an independent prep aid. We are not affiliated with the U.S. Coast Guard or the National Maritime Center. The Coast Guard alone decides how your service is credited. Always check the current regulations and NMC guidance before you file.
What counts as sea service?
According to the NMC's sea service guide, a day of sea service is any day you served on a vessel in an assigned position in the deck or engineering department, not as a passenger. Handling lines, standing lookout, steering, and other navigation or propulsion duties all count. Recreational, commercial, and military time can all qualify.
The same NMC guidance notes that:
- Sea service generally counts from the day you turn 16. Under 46 CFR 11.201(c)(5), experience before age 16 is generally not creditable, with rare case-by-case exceptions.
- Sea service never expires and can be reused for later endorsements.
- Keeping copies of your records is your job. The Coast Guard doesn't hold them for you.
What counts as a "day"?
This is where many applicants get tripped up. The rules are in 46 CFR 10.107 (definitions) and 46 CFR 10.232(h):
- The standard day is 8 hours of watchstanding or day-working, not counting overtime.
- On vessels under 100 GRT, a day is still considered 8 hours unless the Coast Guard decides the vessel's operating schedule makes that inappropriate, and in no case less than 4 hours. The NMC guide puts it plainly: on vessels under 100 GRT, a full day of credit requires 4 or more hours, and days with less than 4 hours never earn credit.
- A month is 30 days, and a year is 360 days for service requirements (46 CFR 10.107).
- 12-hour days earn 1.5 days of credit only in specific cases. The vessel has to be authorized to run a two-watch system under 46 U.S.C. 8104 and 46 CFR 15.705. On most vessels, hours past 8 earn nothing extra. If a letter claims 12-hour days, NMC guidance says it must state that the vessel's Certificate of Inspection (COI) authorizes a two-watch system, and the COI must actually authorize it.
How many days do I need? (OUPV and Master less than 100 GRT)
These are the minimum service totals for original endorsements under 46 CFR Part 11. Day counts use the 30-day month and 360-day year above.
| Endorsement | Minimum service | Route-specific requirement | Rule |
|---|---|---|---|
| OUPV, near-coastal | 12 months (360 days) operating vessels | At least 3 months (90 days) on ocean or near-coastal waters | 46 CFR 11.467(c) |
| OUPV, Great Lakes and inland | 12 months on Great Lakes or inland waters | At least 3 months (90 days) on the Great Lakes | 46 CFR 11.467(d) |
| OUPV, inland | 12 months (360 days) operating vessels | None | 46 CFR 11.467(e) |
| Master, near-coastal, less than 100 GRT | 2 years (720 days) in the deck department on ocean or near-coastal waters | Great Lakes and inland service can substitute for up to 1 year | 46 CFR 11.428(a) |
| Master, Great Lakes and inland, less than 100 GRT | 1 year (360 days) of deck service | 3 months on the Great Lakes for Great Lakes authority | 46 CFR 11.455(a) |
| Master, inland, less than 100 GRT | 1 year (360 days) on any waters | None | 46 CFR 11.457(a) |
There are two more rules to plan around:
- Recent service. For a national officer endorsement, you generally need at least 3 months of service within the 3 years before you apply, on vessels of appropriate tonnage or horsepower (46 CFR 11.201(c)(1)). This is why NMC asks sea service letters for officer endorsements to break out days served within 3 years of the letter's date.
- Tonnage depends on your boats. Master endorsements under 200 GRT are issued at 25, 50, 100, or 200 GRT. The limit is based on the tonnage of the vessels you actually served on (46 CFR 11.422). If more than 75% of your time was on vessels of 5 GRT or less, the endorsement is automatically limited to under 25 GRT. Without the vessel's GRT, you can't get credit toward anything above 25 GRT, so record it (or the boat's measurements, below) for every vessel.
Route credit also matters. For ocean and near-coastal endorsements, Great Lakes time counts day-for-day up to 100% of required service, and other inland time counts day-for-day for up to 50% (46 CFR 10.232(b)).
Which document do I use?
The base rule is 46 CFR 10.232(a). The Coast Guard accepts certificates of discharge, service letters, and other official documents signed by the owner, operator, Master, or Chief Engineer, and it must be satisfied the evidence is authentic.
Vessels under 200 GRT: the CG-719S or an equivalent letter
For smaller vessels, you can use the Small Vessel Sea Service Form (CG-719S). You can also send a letter with all the same information. Key points from the form and NMC's instructions:
- One form per vessel. If one form claims several boats, it will be rejected.
- One form covers at most 5 years. Use more forms for longer periods.
- Give the official number or state registration number. Never make one up. NMC warns that invented numbers get the form rejected.
- Give the gross tons. If you don't know the GRT, give length, width, and depth. All three are needed.
- List the propulsion type (motor, sail, auxiliary sail, and so on). Sail endorsements require service on sail or auxiliary sail vessels.
- "Served as" must be a real position in the deck, engine, or steward department. "Owner" isn't a position. If you list two departments without splitting your time, NMC divides the time equally between them.
- Describe the waters, for example "Chesapeake Bay" or "Atlantic Ocean, within 20 nm." Unless your description supports Great Lakes or near-coastal credit, the time is treated as inland.
- Write days month by month. Fill in each month and year individually, with no arrows or lines. Make sure box 1 (total days) equals the sum of the months and the sum of boxes 2–4 (Great Lakes, inland, near-coastal).
- Average hours underway must be at least 4 for credit.
Owners vs. non-owners
This is one of the biggest differences between applicants:
- If you own the vessel, you may attest to your own service, but you must include proof of ownership (46 CFR 10.232(a)(4)). NMC lists acceptable proof as a title, state registration, Certificate of Documentation, proof of insurance that clearly identifies the vessel, or bills of sale. Photos are not proof of ownership. If a corporation owns the boat, include proof that you own the company, such as articles of incorporation.
- If you don't own the vessel, you can't attest to your own time, even if you were the captain. An owner, operator, or another master (or other credentialed person) has to sign the attestation section and give an address and phone number.
Employer sea service letters (any size vessel; required over 200 GRT)
For vessels over 200 GRT, use a discharge, an official letter, or other official records, such as service logs or discharge books from marine companies. Someone other than you must sign them. Per NMC's general sea service letter instructions, a letter should:
- Be on company or vessel letterhead, and be dated. If you're still aboard, NMC uses the letter date as your service end date.
- For each vessel, list the name, official number, vessel type, propulsion, tonnage, horsepower (when applicable), start and end dates, and number of underway days.
- For officer endorsements, break out the days served within 3 years of the letter date. For renewals and Tankerman endorsements, use 5 years.
- State whether the days were 8-hour or 12-hour. If they were 12-hour, attest that the COI authorizes a two-watch system.
- Include your position and the route where you served (46 CFR 10.232(a)(2)).
Military service is documented differently. The rule asks for an official transcript of sea service or a history of assignments, and a DD-214 is not acceptable (46 CFR 10.232(d)(1)).
Common reasons sea service gets kicked back
NMC's own "common errors" lists and NMC-published AI summaries keep pointing to the same problems:
- The letter is unsigned or undated, or doesn't say what waters the service was on.
- Math errors on the CG-719S, where the totals don't add up.
- Missing proof of ownership when the owner attests.
- The applicant signs as their own attesting witness on a boat they don't own.
- Overlapping days: the same dates are claimed on two vessels, or more days are claimed than the month has.
- Days are blank or shown with arrows instead of written month by month.
- Missing GRT or measurements, or the vessel's number is missing or made up.
- Near-coastal or Great Lakes days claimed without a matching written description of the waters.
- Not enough service, or not enough recent service, for the endorsement requested.
A quick pre-filing checklist
- Use one CG-719S per vessel, with each form covering 5 years or less.
- Give the real official or state number, plus GRT or all three measurements.
- List a real position (not "owner"), with time split if you served in more than one department.
- Write days for each month, check the totals, and make sure no dates overlap across vessels.
- Describe the waters in words that match your route breakdown.
- Sign it yourself, and get a third-party attestation with an address and phone, or include proof of ownership.
- Make sure letters are on letterhead, dated, signed, and include the 3-year breakdown.
- Check that your totals meet the endorsement minimum, including the 90 recent days.
FAQ
Can I count time on my own recreational boat? Yes, recreational time can count. If you own the boat, you can sign for your own service, but you must include proof of ownership, such as a title, registration, Certificate of Documentation, insurance that identifies the vessel, or a bill of sale.
I was the captain, but I don't own the boat. Can I sign my own CG-719S? No. NMC guidance says a non-owner can't attest to their own service, even as master. The owner, operator, or another master has to sign and give their contact details.
Do short trips count? On vessels under 100 GRT, a day needs at least 4 hours underway to be credited. Days under 4 hours earn no credit.
Does a 12-hour day count as 1.5 days? Only on vessels authorized to run a two-watch system under 46 U.S.C. 8104 and 46 CFR 15.705, and the letter must say so. On most small passenger and recreational boats, a long day is still one day.
Does old sea service expire? NMC says sea service never expires. However, officer endorsements generally also require 3 months of service within the 3 years before you apply.
Is a DD-214 enough for military sea time? No. The regulation requires an official transcript of sea service or a history of assignments.
Want a second set of eyes before you file?
Our team is building Pilot House Prep, a pre-filing check for OUPV and Master 25/50/100-ton original packets. It flags common sea service and packet mistakes, like the ones above, before you send anything to the NMC. We don't file for you and we can't guarantee approval, but we can help you catch the easy-to-miss errors first.