Deck Rating AB or OSDeck Rating AB or OS. You need an AB or OS to work as deckhand on seagoing vessels greater than 100 GRT.

Deck Rating AB or OS

There are two deck rating AB or OS. That is to say Able Seaman, or Ordinary Seaman. To clarify, these are MMC National Ratings. And they are required to work as deck crew on seagoing vessels over 100 GRT. This article you will define which deck rating is best for you.

It must be stated that: Master is not the same as AB. While the Master has the knowledge and skills of the AB. Unless your MMC says AB, you cannot legally hold the position of AB. However, the same experience used for one can be used for the other.

Deck Rating AB

The AB is an experienced sailor. That is to say, getting an AB requires sea time. And, in addition, knowledge of seamanship terms and skills. Lastly, the AB must also be skilled in sea survival. Including the operation of survival craft. That is to say, the AB must have a Lifeboatman, or Lifeboatman-limited rating.

Lifeboatman Checklist >>

AB Ratings

There are six AB ratings. Because, all AB exams are the same, upgrading is based on sea time only.

Firstly, AB Unlimited is the top rating. In short, this AB needs 3-years sea time, and can work on any size or type of vessel.

Secondly, AB Limited is the next lower rating. In short, this AB needs 1.5-years sea time, and can work on any type of vessel less than 1600 GRT. For example: smaller ships around 200-feet.

Thirdly, AB Special is next under limited. This AB needs 1-year of sea time, and can work on any type of vessel less than 500 GRT. For example, most any tugboat.

The remaining ABs are lessor ratings. Because, they are for one vessel type only. And, in addition, each requires only 180-days sea time.

OSV (AB Offshore Supply Vessel), for oil industry vessels.

Fishing (AB Fishing), for fishing industry vessels.

Sail (AB Sail), for sail or auxiliary sail vessels.

AB Checklist >>

Columbia Pacific (ColPac) Maritime offers a 5-day ($700) AB course. However, we do not offer Lifeboatman courses. For Lifeboatman we recommend the following schools. Both offer AB courses too.

Compass Courses in Edmonds, Washington.

Seafarers Worldwide in Anacortes, Washington.

Deck Rating AB or OS: Ordinary (OS)

Ordinary Seaman (OS) is an entry level rating. That is to say, it is a beginners rating. Therefore no experience is required. Follow these steps to get an OS.


Firstly, enroll in the TWIC program. Most important, save and email the receipt with the application.

2. Physical Exam – short form

Secondly, complete form 719KE, Application for a Medical Certificate Short Form. Most important, READ and FOLLOW the instructions.

3. DOT / USCG Drug Screening

Thirdly, get a drug screening. Form 719P DOT/USCG Drug Screening.

4. Pay the fees

Fourthly, pay the Coast Guard fees at the Gov.Pay website. There are two fees for a total of $140. This is a $95 evaluation fee, and a $45 issuance fee. Most important, save and email the receipt with the application.

5. MMC Application form

Fifthly, complete form 719B Application for a Merchant Mariner Credential. Most important, READ and FOLLOW the instructions.

In Section II check the box for a the original issue of an entry level rating. And then write in OS as the description.

6. Email to an REC

Lastly, scan and email this to a US Coast Guard Regional Exam Center (REC).

Email Instructions


The OS is the beginner rating. While the AB is for experienced sailors. In contrast, Master is NOT the same as AB. You must have an AB to work as an AB. In summary, the career mariner without an AB will miss may great employment options.

Always read and follow the instructions. And then, if you have any questions, please contact us. Above all, our business is helping mariners. However, selling courses is what we do to stay in business.