USCG AB and QMED Exam Domain Review

Why Domain Mapping Matters

The U.S. Coast Guard National Maritime Center (NMC) issues two separate merchant mariner credentials relevant to this program: the Able Seaman (AB) endorsement and the Qualified Member of the Engine Department (QMED) endorsement. Although both credentials require a working knowledge of safety and MARPOL pollution prevention, their core exam content is distinct. Knowing exactly which topics belong to which credential saves study time and prevents the common mistake of over-preparing in one area while leaving gaps in another.

This lesson maps each credential's exam domains, gives you practice across all four main content stations, and helps you build a targeted self-study plan.

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Part A: AB Exam Domains

COLREGS and Inland Rules of the Road form the backbone of AB deck knowledge. The International Regulations for Preventing Collisions at Sea (COLREGS) and the U.S. Inland Rules govern how vessels maneuver, display lights and shapes, and use sound signals. Expect questions on stand-on and give-way responsibilities, crossing, meeting, and overtaking situations, as well as the specific light configurations for various vessel types (fishing, towing, not under command, restricted in ability to maneuver). Read the rules carefully — small wording differences between Inland and COLREGS matter on the exam.

Basic Seamanship and Marlinespike covers rope types and construction, knot and splice selection, block-and-tackle mechanical advantage, and line handling at the dock. You should know safe working load concepts and when synthetic versus natural fiber line is appropriate. Never stand in the bight of a line under load — snap-back injuries are a leading cause of deck fatalities.

Deck Watchkeeping tests your understanding of lookout duties, helm orders, compass error, and proper log entries. Questions often ask you to identify who has the conn, what information must be recorded in the deck log, and how to relieve a watch properly.

Anchoring and Mooring includes scope calculation (the ratio of rode length to water depth plus freeboard), anchor types and holding power, and mooring line arrangement. Understanding why adequate scope improves holding — and why too little scope causes dragging — is frequently tested.

Cargo Handling Terminology focuses on definitions: deadweight, displacement, draft, freeboard, load line marks, and terms like dunnage and broken stowage. Stability fundamentals round out this domain: you should understand the relationship among center of gravity (G), center of buoyancy (B), and metacenter (M), and what a positive GM means for vessel safety.

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Part B: QMED Exam Domains

Engine-Room Watchkeeping parallels deck watchkeeping but below decks. Questions address watch relief procedures, equipment log rounds, alarm response, and reporting to the engineer of the watch. Safe practice requires following lockout/tagout (LOTO) procedures before working on any energized or pressurized system — confirm the energy source is isolated, tagged, and tested before starting maintenance.

Auxiliary Machinery is a broad domain covering pumps (centrifugal, positive displacement, reciprocating), air compressors, and heat exchangers. You should know the difference between centrifugal and positive-displacement pump operating characteristics, what priming means and why centrifugal pumps require it, and how a shell-and-tube heat exchanger transfers heat between two fluid streams without mixing them.

Basic Electrical Theory tests Ohm's Law, series and parallel circuit behavior, reading a simple electrical diagram, and identifying common shipboard electrical safety hazards. Always wear appropriate PPE — insulated gloves and safety glasses — when working near energized electrical panels, and follow LOTO before opening any electrical enclosure for maintenance.

Fuel and Lubrication Systems covers fuel oil treatment (settling, purifying, clarifying), viscosity requirements, and the function of lube oil filters and coolers. Understanding why correct viscosity protects bearing surfaces is a common question type.

MARPOL Pollution Prevention applies to both credentials but is heavily tested on QMED. MARPOL Annex I covers oil and oily mixtures from machinery spaces; Annex V covers garbage. Know that the Oil Record Book must be maintained and that overboard discharge of oily water from machinery spaces is prohibited inside special areas and generally limited to 15 parts per million (ppm) outside special areas when using an approved oily water separator. Garbage discharge restrictions under Annex V depend on distance from shore and garbage type — plastics are prohibited from discharge anywhere.

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Reading the Question Stem Correctly

Many students lose points by misreading the credential context in the question stem. Watch for phrases like "as AB on watch" or "as QMED standing watch in the engine room" — these signal which credential's rules apply. If a stem asks about a light configuration for a towing vessel, that is an AB/COLREGS question. If it asks about centrifugal pump priming, that is a QMED question. Practice sorting question stems before choosing an answer; the domain routing is itself a test skill.

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Scoring and Remediation

You must reach 70% or better on at least three of the four station sets to meet the lesson check. If your COLREGS station falls below 70%, you will complete a Rules of the Road chart exercise before the next lesson. Use your gap-tracking sheet to record station scores alongside your earlier self-assessment data. Identify your top three weak topics per credential — this list drives your study between now and the credentialing exams.