OS to AB

Hello everyone,

I have a question and have gotten many answers, but all have left me to confusion:

I recently submitted for a 100-ton captain/mate.
Currently working aboard a tugboat for 6 months.

I was told by a captain that I was able to upgrade my OS to an AB, (his words) “since I’ve already taken the 100 ton class and passed, the AB is pretty much the same test and seatime”.

I called the coastguard and spoke with a couple receptionists and was told I needed to complete the lifeboatman, as well as the Marlinspike seamanship practical, then to sent an amendment email. At the same time, the school is telling me “no way the AB test is different”.

So I’m a bit confused as to whether im able to upgrade it to an AB special or not. Im signed up for a lifeboatman class a couple weeks from now.

Honestly, I could use some clarification. Thank you guys


Unless things have changed, the lifeboat and marlinspike are practical AB tests that are not required for the 100 ton which only consists of a written exam.

Yes, I am trying to upgrade it from OS to AB and was told I technically have already done the testing portion of the AB in the 100 ton class I took.

I’m currently working deck and trying to move up the ranks

Lifeboatman is a separate endorsement, and is required for AB, see 46 CFR 12.401(c)(6). Marlinspike seamanship is a practical test, also required for AB. See 46 CFR 12.405(c).

Does that school have an AB course they are trying to sell you? You can see sample exams for both on the NMC website and make your own comparison.

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Yes they are

You have the sea time to get AB. Get approved to test by the coast guard, then pay $100 to test. Gets you three attempts at the test. If you fail three times, which with due diligence you probably wont, then the classes are around $1000 and 4- 5 days long. If needed, while you’re there add RFPNW and VPDSD. Get to know the checklists and CFR’s. Ive found many older mariners spout off rumors and their experience when the requirements and tests were different. And calling the coast guard is often like speaking to a lawyer they’ll be vague and talk out of both sides of their mouth.

AB checklist:

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Probably not the best advice at this point. Better to find out if it will be needed where you will work first, then spending tome and money on something not needed. Also, if you need RFPNW, you will also need Basic Training, another week and $1,000. Better to find out if you need any of that before spending a lot of time and money. If you’re working on a tug, there is a good chance that STCW endorsements are not needed, either because the tug operates inland, or because it is less than 200 GRT and only operates on dopmestic voyages.


Yes, be a company man. Don’t get bare minimum basic training, don’t get rfpew so you set yourself up for able seafarer. Just corner yourself as an inland tugboat deckhand.

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One never knows what opportunities will come knocking in the future. Be prepared.

What are you going to make with 100 ton?

There are now AB jobs that pay over $500 a day.

Take a class to get Lifeboatman (with lifeboats for ships). Don’t waste your money on a Restricted Lifeboatman (with only life rafts.)

If you need an exam, just go take it at the USCG. Brush up on rules of the road. Just wing it on everything else. You’ll do fine.

The Marlinspike demonstration is a joke. You only need to know how to tie about a dozen knots. You don’t need to know when to use which knot for what application, or how to untie a knot after it’s been under strain. You’ll take an everybody passes “class” for that.

If you are a young guy with many years of work ahead of you, go ahead and invest in RFPNW and BT classes.


I think your captain may have meant that if you can pass the 100t exam, you can easily pass the AB exam.



Your question has a couple of options to consider. As an AB you are in a support role, as a 100-ton Mate you are considered as the vessel’s operator, and as the Master you are considered Management. The Coast Guard regulations separate license and endorsements into two schemes, National (domestic) and STCW standards. There are employment opportunities in both schemes.

With that said, the testing for Able Seaman and 100-ton Master is different. Here is my recap of your questions and this topic.

(1) As a National AB, you need to test for Lifeboat(Q445) or Limited Lifeboatman (Q447) endorsement which also requires a demonstration of lowering and recovery of a lifeboat. This is usually completed by taking a USCG Approved Lifeboatman course. See Lifeboatman Checklist, Deck Engineering Guide on page 36, and NMC webpage Sample Exams Deck Ratings for Lifeboatman. I recommend taking the Lifeboat course. This course will also satisfy the STCW Proficiency in Survival Craft, but you will need the 5-day Basic Training Course to have it placed on your MMC.

(2) Next is taking a two-module National Able Seaman Examination. Module A, (Q450), will have 50 questions - 70% pass, relating to subjects on watchstanding as a lookout, i.e., points, bearing drift, and helmsman duties, Helm commands, Navigation General Subjects, Buoyage, and ROR as they apply to being a lookout.

Module B (Q451) Deck General /Safety will have 50 questions - 70% pass, subjects relating to deck nomenclature, knots, blocks and tackles, deck equipment, and deck safety subjects, i.e., firefighting, and lifesaving equipment. See Able Seaman Checklist and Deck Engineering Guide on page 36 and NMC webpage Sample Exams Deck Ratings for Able Seaman.

(3) Then is the Marlinspike Seamanship (knots and splicing) Demonstration. See Deck Engineering Guide on page 37.

National AB Qualifications as per 46 CFR 12.403

  1. A National AB Special starts with 360 days sea time, it does not have a tonnage requirement.
  2. A National AB Limited is 540 days but requires sea time on vessels over 100-ton.
  3. A National AB Unlimited is 1080 days but there is no tonnage requirement. Your sea service needs to be Oceans, Near Coastal or Great Lakes time.

International Deep-Sea Sailing
If you are going to sail oceans, then you will need to complete STCW Courses and Assessments for the position, you wish to sail under. Note: 46 CFR 11.201 “requires that an applicant for STCW must hold the appropriate National Endorsement.”

STCW Deck Endorsements Qualifications as per 46 CFR 12.603.
Prerequisite for STCW endorsements requires completing a USCG Approved Basic Training course.
In this case, a National AB would need to complete the STCW demonstration assessments found in NVIC 06-14 RFPNW and NVIC 14-14 Able Seafarer-Deck. See STCW Rating Checklist for RFPNW and Able Seafarer-Deck.

Shipboard assessments are free assessments and are signed off by a shipboard authorized assessor. An alternative is you can attend a USCG Approved School, at a cost. Ensure the following (1) you meet the sea time requirements found in the STCW Checklist or NVIC 19-14 (2) pay close attention to vessel requirements in each NVICs and (3) the assessor meets the qualifications as outline in the appropriate NVIC. i.e., assessor for both RFPNW and Able Seafarer should have at least 1 year of experience as OICNW on vessels of at least 200 GRT or 500 GT NVIC 19-14. Assessments must be complete shipboard assessments prior to December 31, 2023 and submitted by June 30, 2024 to take advantage of Qualified Assessor Extension policy. See Qualified Assessor Extension Update 082521.

Hope this helps

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