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100+ Free Assistant Engineer OSV Practice Questions

Prepare for the USCG Assistant Engineer of Offshore Supply Vessels (OSE02) exam with instant access — no signup required.

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Key Facts: Assistant Engineer OSV Exam

OSE02

NMC Exam Code

USCG NMC Assistant Engineer-OSV exam page

4

Modules on motor original path (Q650, Q652, Q653, Q654)

USCG Deck & Engineering Guide / NMC OSE02

70

Multiple-choice questions per module

USCG NMC OSE02 module structure

70%

Minimum passing score per module

USCG NMC engineering exam standard

280

Total questions on four-module motor original path

4 × 70 questions (Q650/Q652/Q653/Q654)

3 yr / 18 mo QMED

Unlimited HP service (or 1-year approved training)

46 CFR 11.555(a)

$240

Typical original lower-level fees (eval + exam + issuance)

46 CFR 10.219

No exam

Increase in scope AE-OSV 4,000 HP → unlimited HP

USCG Deck & Engineering Guide

15 ppm

Machinery-space oily bilge discharge limit via OWS

MARPOL Annex I / 33 CFR

OSE02 is the USCG National Maritime Center examination for Assistant Engineer of Offshore Supply Vessels. The motor original path is four modules (Q650 Motor Plants, Q652 General Subjects, Q653 Engineering Safety & Environmental Protection, Q654 Electrical/Electronic/Control Engineering), each 70 questions at 70% to pass—about 280 questions total. Service under 46 CFR 11.555: unlimited HP requires 3 years engineroom with 18 months QMED (or a 1-year approved training program); less than 4,000 HP requires 2 years/1 year QMED; less than 1,000 HP requires 1 year/6 months QMED. Increasing scope from AE-OSV 4,000 HP to unlimited HP needs no further exam per the Deck & Engineering Guide. Typical original lower-level fees are about $240 ($100 evaluation + $95 exam + $45 issuance) under 46 CFR 10.219.

Sample Assistant Engineer OSV Practice Questions

Try these sample questions to test your Assistant Engineer OSV exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1The flywheel on a marine diesel engine is fitted mainly to:
A.Drive the lube-oil pump directly at all engine speeds
B.Store rotational energy so the crankshaft turns smoothly between power strokes
C.Fan cooling air across the crankcase sump
D.Set the maximum fuel rack position at full load
Explanation: A diesel delivers torque in pulses — one power stroke per cylinder per cycle — so crankshaft speed would surge and fall within every revolution. The flywheel's inertia carries the shaft through the non-firing strokes, holding cyclic speed variation within design limits, and it also carries the turning-gear teeth and timing marks.
2What is the chief function of scavenging in a two-stroke-cycle marine diesel engine?
A.To inject fuel at the correct crank angle
B.To remove burned exhaust gases and replace them with fresh air
C.To circulate lube oil to the wrist pin
D.To cool the fuel injector tip between firings
Explanation: Scavenging uses pressurized fresh air to push burned gases out of the cylinder and fill it with clean air for the next charge, since a two-stroke has no separate exhaust stroke.
3A marine diesel engine governor is best described as a device that:
A.Limits maximum cylinder firing pressure
B.Automatically adjusts fuel rack position to maintain a set engine speed under varying load
C.Controls jacket cooling water temperature
D.Times the opening of the exhaust valves
Explanation: The governor senses engine speed and repositions the fuel control rack to add or reduce fuel, holding the selected speed as load changes.
4The main function of a diesel fuel injection pump is to:
A.Separate water from the fuel before it reaches the day tank
B.Deliver a measured quantity of fuel at high pressure to the injector at the correct crank angle
C.Cool the injector nozzle tip between injections
D.Regulate jacket-water flow through the cylinder head
Explanation: The injection pump has three jobs: it meters the fuel quantity called for by the rack, raises it to the pressure the nozzle needs to atomize it, and delivers it at the crank angle fixed by the cam. Metering, pressure, and timing together determine how that cylinder burns.
5On a marine diesel, the primary purpose of fuel injection timing is:
A.To control engine cooling water temperature
B.To regulate scavenge air volume
C.To set the crank angle at which fuel begins to burn so combustion peaks shortly after top dead center
D.To set lube oil pressure to the main bearings
Explanation: Injection timing fixes the crank position where fuel injection (and combustion) begins; correct timing places peak cylinder pressure just after TDC for useful work without excessive stress.
6A diesel will not start when starting air is admitted, although air pressure is normal. The most likely cause is that the:
A.Cooling water expansion tank is low
B.Turning gear is still engaged
C.Fuel oil viscosity is too high for the day tank heater setting
D.Crankcase oil level is slightly above the high mark
Explanation: If the turning (jacking) gear is left engaged it locks the engine mechanically and prevents rotation on starting air; interlocks normally block air admission, so engaged gear or a failed interlock is the classic cause.
7The primary purpose of a turbocharger on a marine diesel is to:
A.Reduce jacket water temperature
B.Supply pressurized charge air so more fuel can be burned and power increased
C.Filter fuel oil before the injectors
D.Drive the lube oil pump at all speeds
Explanation: A turbocharger uses exhaust energy to compress intake air, increasing mass of oxygen in the cylinder so more fuel can be burned and power density rises.
8Blue-grey exhaust smoke from a diesel engine most often indicates:
A.Incomplete combustion of fuel (overfueling)
B.Burning of lubricating oil in the combustion space
C.Coolant leaking into the combustion chamber
D.Normal full-load operation
Explanation: Blue or blue-grey smoke typically indicates lubricating oil is reaching the combustion chamber through worn rings, valve guides, or over-lubrication.
9What is the principal reason a closed diesel jacket cooling system uses treated fresh water rather than raw seawater in the engine jackets?
A.Fresh water freezes at a higher temperature
B.Treated fresh water reduces corrosion and scale inside the engine and allows controlled temperature regulation
C.Seawater cannot remove heat from a diesel
D.Fresh water has a much lower specific heat than seawater
Explanation: A closed freshwater loop with corrosion inhibitors protects cylinder liners, heads, and coolers from seawater corrosion and scale; a heat exchanger then rejects heat to seawater.
10If mean effective pressure (MEP) is 150 psi and the engine has a piston area of 100 in² with a stroke of 1 ft, the indicated work per power stroke is approximately:
A.150 ft-lbf
B.1,500 ft-lbf
C.15,000 ft-lbf
D.150,000 ft-lbf
Explanation: Indicated work ≈ MEP × area × stroke = 150 lbf/in² × 100 in² × 1 ft = 15,000 ft-lbf per power stroke.

About the Assistant Engineer OSV Exam

The USCG Assistant Engineer-OSV endorsement (NMC exam code OSE02) authorizes service as an assistant engineer officer on offshore supply vessels within the horsepower and route limits of the Merchant Mariner Credential. Under 46 CFR 11.555, unlimited-propulsion-power candidates need three years of engineroom service including 18 months as QMED (or equivalent), or one year in an approved Assistant Engineer-OSV training program; reduced service applies for less than 4,000 HP and less than 1,000 HP tiers. The original motor examination is delivered as four multiple-choice modules—Q650 Motor Plants, Q652 General Subjects, Q653 Engineering Safety & Environmental Protection, and Q654 Electricity, Electronics & Control Engineering—each 70 questions with a 70 percent passing score. Content emphasizes diesel propulsion common to OSV/workboat service, electrical generation and motor control, MARPOL and firefighting safety, and shipboard auxiliaries such as pumps, hydraulics, refrigeration, and steering gear.

Assessment

Modular REC battery under exam code OSE02. Motor original: Q650, Q652, Q653, Q654. Each module independently graded at 70%. REC rules commonly allow up to 3.5 hours per module, with a minimum of two modules per day when multiple remain, completed on consecutive days within the same business week. Engine candidates receive 46 CFR Parts 1–199 and 33 CFR Parts 1–199 as room references.

Time Limit

Up to 3.5 hours per module

Passing Score

70% on each module

Exam Fee

$95 exam fee; about $240 typical original lower-level total ($100 evaluation + $95 exam + $45 issuance) (U.S. Coast Guard National Maritime Center (NMC) / Regional Exam Centers)

Assistant Engineer OSV Exam Content Outline

35%

Motor Plants (Q650)

Diesel cycle fundamentals, two-stroke vs four-stroke marine engines, fuel injection and timing, turbocharging and scavenging, governors and speed control, cooling and lubrication systems, starting-air safety, main and auxiliary engines, and motor-plant casualty recognition including oil-mist and crankcase events

25%

Electricity, Electronics & Control (Q654)

Ohm's law and power calculations, three-phase generation, paralleling and load sharing, motors and controllers, ground detection on insulated systems, batteries, transformers and rectifiers, basic electronics and automatic control, and electrical casualty response

20%

Engineering Safety & Environmental (Q653)

Fire triangle and fire classes, fixed CO2 total-flooding and foam systems, SCBA and enclosed-space entry, damage control and dewatering, MARPOL Annex I 15 ppm bilge discharge via OWS, Oil Record Book, OPA 90 awareness, sewage/MSD basics, and hazardous materials/SDS

20%

General Subjects (Q652)

Centrifugal and positive-displacement pumps, NPSH and cavitation, hydraulics and steering gear, refrigeration and air conditioning, heat exchangers and zinc anodes, fuel and lube oil purifiers, sewage systems, valves and piping, compressors, and engineer watchkeeping duties

How to Pass the Assistant Engineer OSV Exam

What You Need to Know

  • Passing score: 70% on each module
  • Assessment: Modular REC battery under exam code OSE02. Motor original: Q650, Q652, Q653, Q654. Each module independently graded at 70%. REC rules commonly allow up to 3.5 hours per module, with a minimum of two modules per day when multiple remain, completed on consecutive days within the same business week. Engine candidates receive 46 CFR Parts 1–199 and 33 CFR Parts 1–199 as room references.
  • Time limit: Up to 3.5 hours per module
  • Exam fee: $95 exam fee; about $240 typical original lower-level total ($100 evaluation + $95 exam + $45 issuance)

Keys to Passing

  • Work through all 100 available questions
  • Review every answer and explanation
  • Track weak areas and revisit them
  • Use our AI tutor for tough concepts

Assistant Engineer OSV Study Tips from Top Performers

1Treat each module as a separate 70-question test at 70% — drill motor, electrical, safety/environmental, and general subjects as independent passes
2For motor plants, master scavenging vs turbocharging, fuel viscosity control, cylinder lubrication, starting-air safety, and oil-mist detector/crankcase explosion response
3Memorize environmental limits engineers are tested on: 15 ppm machinery-space bilge discharge via OWS, Oil Record Book entries, and basic MARPOL Annex structure
4For electrical, drill Ohm's law, three-phase line vs phase voltage (√3), generator paralleling conditions, reverse-power protection, and ground detection on ungrounded systems
5Practice pump NPSH/cavitation, positive-displacement relief valves, hydraulic steering gear failures, and refrigeration superheat/TXV basics for general subjects
6Know fire classes and that CO2 total-flooding requires the space evacuated, sealed, and ventilation secured before release
7Review 46 CFR 11.555 service tiers so you apply for the correct horsepower limitation and understand the no-exam increase-in-scope path from 4,000 HP to unlimited
8Simulate 3.5-hour module pacing with timed 70-question blocks before your REC appointment

Frequently Asked Questions

What is the USCG Assistant Engineer-OSV exam?

It is the National Maritime Center modular knowledge examination (exam code OSE02) for the Assistant Engineer of Offshore Supply Vessels national endorsement. The motor original path covers modules Q650, Q652, Q653, and Q654.

How many questions and what is the pass mark?

Each module has 70 multiple-choice questions and requires a minimum of 70% to pass. The four-module motor original path totals 280 questions.

Which modules does a motor (diesel) candidate take?

Motor original candidates take Q650 Motor Plants, Q652 General Subjects, Q653 Engineering Safety & Environmental Protection, and Q654 Electricity, Electronics & Control Engineering.

What sea service is required under 46 CFR 11.555?

Unlimited propulsion power: three years of engineroom service with at least 18 months as QMED or equivalent, or one year in an approved Assistant Engineer-OSV training program. Less than 4,000 HP/3,000 kW: two years engineroom with one year as QMED. Less than 1,000 HP/750 kW: one year engineroom with six months as QMED.

Do I need another exam to go from AE-OSV 4,000 HP to unlimited HP?

Per the Deck & Engineering Guide for the administration of merchant marine examinations, increasing scope from Assistant Engineer-OSV 4,000 HP to unlimited HP does not require a further professional examination once service and other credentialing requirements are met.

What are the typical fees?

For an original lower-level officer endorsement, 46 CFR 10.219 lists $100 evaluation, $95 examination, and $45 issuance (about $240 total). Fees are paid electronically (Pay.gov) through the NMC process; always confirm the current schedule.

How long do I get per module?

NMC administration guidance commonly allows up to 3.5 hours per module. When multiple modules remain, RECs typically require a minimum of two modules per day, completed on consecutive days within the same business week.

Is this practice bank an official exam simulation?

No. It is a free English multiple-choice study aid covering OSE02 topic areas for Assistant Engineer-OSV. Official exams are administered by the Coast Guard at Regional Exam Centers using current NMC banks.