Able Seaman (AB) Ratings: USCG Requirements, Sea Service, and Upgrade Path
AB is the workhorse endorsement for unlicensed deck crew. There are five AB ratings, each with different sea service requirements and route authorizations. Here is the full breakdown and how each builds toward officer endorsements.
Updated May 2026 · 9 min read
What Is an Able Seaman Endorsement
The Able Seaman endorsement is a rating endorsement on your MMC that certifies you as qualified unlicensed deck crew. Unlike an officer endorsement (Master, Mate), AB is a rating — it qualifies you to work as a crew member, not as the person in command.
AB is required by law on vessels of 100 GT or more on ocean or near coastal voyages of more than 600 miles (46 USC 8702). On smaller vessels and charter operations, the employer may still require AB as a minimum credential for deck crew.
For mariners building toward officer endorsements, AB sea service counts toward the sea service requirements for Mate and Master licenses — you are getting credit for the same hours you work.
The Five AB Ratings
AB Unlimited
46 CFR 12.401Sea service
1,080 days on deck of ocean or near coastal vessels
STCW
STCW Basic Safety Training (BST) required for ocean vessels
Who uses this
The highest AB rating. Qualifies for any vessel type, any route. Required by most shipping companies for experienced unlicensed deck crew. Path to Mate Unlimited.
AB Special
46 CFR 12.403Sea service
360 days on deck on vessels operating on near coastal or inland waters
STCW
BST required for near coastal operations
Who uses this
Works on vessels 100 GT and above on near coastal and inland waters. Cannot serve on ocean-going vessels. Common for tugboat, barge, and coastal ferry crew.
AB OSV (Offshore Supply Vessel)
46 CFR 12.405Sea service
180 days on offshore supply vessels or similar near coastal vessels
STCW
BST required
Who uses this
Specific to offshore supply vessel operations. Used in Gulf of Mexico oil field support. Often combined with STCW and tankerman endorsements for offshore sector.
AB Sail
46 CFR 12.407Sea service
360 days on sailing vessels, at least 180 days on ocean or near coastal waters
STCW
BST required for ocean vessels
Who uses this
Specific to sailing vessels. Used on tall ships, charter sailboats, ocean racing support. Limited commercial demand but required for some tall ship and sailing charter operations.
AB Limited
46 CFR 12.409Sea service
180 days on deck of vessels on inland waters or Great Lakes
STCW
Not required for inland-only operations
Who uses this
Entry-level AB rating for inland and Great Lakes vessels. Common starting point for river mariners and Lake boat crew. Cannot serve on near coastal or ocean-going vessels.
AB Application Requirements
Applying for an AB endorsement follows the same CG-719B packet process as any MMC application. In addition to the standard requirements (physical, drug test, TWIC), you need:
- Sea service letters documenting the required days, route, and capacity (deck crew)
- STCW Basic Safety Training certificate (for AB Special, AB Unlimited, AB OSV, AB Sail)
- Proof of watchstanding service (AB Unlimited requires 180 days as helmsman or lookout, documented in sea service letters)
AB to Officer: How Sea Service Credits Forward
The sea service you accumulate as AB on deck directly satisfies the sea service requirements for officer endorsements. Specifically:
- AB sea service on vessels under 100 GT counts toward OUPV and Master 100 GT requirements
- AB sea service on vessels 100–500 GT counts toward Mate and Master 500 GT requirements
- AB Unlimited service on ocean-going vessels of 500 GT+ counts toward Mate Unlimited and Master Unlimited pathway
The key is that sea service letters must document the vessel size (GT), route, and your position accurately. "Deckhand" and "AB" may be used interchangeably by employers, but the NMC evaluates the actual duties — make sure letters describe your actual role.
BinnacleCrew shows your progress toward AB and officer endorsements simultaneously.