You are assigned to an OSV fitted with main propulsion diesel engines operating on the cycle represented in the polar timing diagram shown in the illustration. When do the exhaust valves open and close respectively?

The exhaust valves open at 55o before bottom dead center on the power stroke. The exhaust valves close at 85o after top dead center on the intake stroke.

The exhaust valves open at bottom dead center at the beginning of the exhaust stroke. The exhaust valves close at top dead center at the end of the exhaust stroke.

The exhaust valves open at 55o before bottom dead center on the power stroke. The exhaust valves close at 85o after top dead center on the intake stroke.

The exhaust valves open at top dead center at the end of the exhaust stroke. The exhaust valves close at bottom dead center at the beginning of the exhaust stroke.

The exhaust valves open at 85o after top dead center on the intake stroke. The exhaust valves close at 55o before bottom dead center on the power stroke.

You are assigned as an engineer on an offshore platform supply vessel using main propulsion engines of the type shown in the illustration. What statement represents the procedure for inspection of the upper cylinder liner bore while in place inside the engine?

With the particular piston positioned at BDC and the corresponding air box handhold cover removed, inspect the upper liner bore through the scavenging air ports.

With the particular piston positioned at TDC and the corresponding oil pan handhold cover removed, inspect the upper liner bore through the scavenging air ports.

With the particular piston positioned at TDC and the corresponding air box handhold cover removed, inspect the upper liner bore through the scavenging air ports.

With the particular piston positioned at BDC and the corresponding oil pan handhold cover removed, inspect the upper liner bore through the scavenging air ports.

You are analyzing the data used for trend analysis for one of the main propulsion diesel engines on the ship- docking tug to which you are assigned. The cylinder exhaust temperature of one of the cylinders is significantly lower than the others. When analyzing compression and firing pressure data, however, the numbers are within the normal range for this particular cylinder. What condition would produce these results?

Excessive carbon build-up on exhaust pyrometer probe of affected cylinder

Leaking fuel injector needle valve for affected cylinder

Leaking exhaust valve on affected cylinder

Excessive carbon build-up on air inlet ports or valves of affected cylinder

Excessive carbon build-up on exhaust pyrometer probe of affected cylinder

You are analyzing the data used for trend analysis for a two-stroke main propulsion diesel engine on your general-purpose supply vessel. Although the engine has yet to experience a safety shutdown on high crankcase pressure, over time the crankcase pressure (which normally runs in a vacuum) has gradually become less negative. Which of the following failures would most likely be responsible for this condition?

Leaking crankcase handhold cover

Dribbling injector needle valve

In a closed-loop process control system, what is meant by the integral mode of control?

It is a control mode that produces a control action that is proportional to the accumulation of error over time.

It is a control mode that produces a control action that is proportional to the rate at which the error is changing.

It is a control mode that produces a control action that is proportional to the error.

It is a control mode that produces a control action that is proportional to the gain.

It is a control mode that produces a control action that is proportional to the accumulation of error over time.

Assuming valve "A" is correctly aligned in the no-flow position as shown with the system in operation, which of the following statements is true?

Valve "D" would normally open before valve "B".

The fixed delivery pump would be stopped automatically by a pressure switch.

Valve "D" would normally open before valve "B".

Valve "B" would be open before valve "D".

Your vessel has run aground and upon taking fuel oil tank soundings, you find that a fuel tank level has increased. You therefore should suspect __________.

a crack in the hull portion of the fuel tank

contamination from the salt water flushing system

a crack in the hull portion of the fuel tank

Progressive flooding in the engine room may be minimized by securing watertight boundaries and __________.

pumping out flooded compartments

transferring reserve feed water

pumping out flooded compartments

In a compartment that has been completely flooded with water, the greatest pressure will be exerted __________.

along the bottom of any bulkhead

at a point that is one-third from the bottom of the bulkhead

at the vertical center of the bulkhead

along the bottom of any bulkhead

Kapok life jackets require proper care and should NOT be __________.

stowed near open flame or where smoking is permitted

used as seats, pillows, or foot rests

Assuming the alternator shown in figure "A" of the illustration is equipped with a diode plate as configured in figure "D", what is the purpose of the diode plate? Illustration EL-0037

It rectifies exciter armature AC to DC for rotating main field excitation and eliminates the need for brushes.

It inverts exciter armature DC to AC for rotating main field excitation, but does not eliminate the need for brushes. .

It rectifies exciter armature AC to DC for rotating main field excitation, but does not eliminate the need for brushes..

It rectifies exciter armature AC to DC for rotating main field excitation and eliminates the need for brushes.

It inverts exciter armature DC to AC for rotating main field excitation and eliminates the need for brushes.

In preparation for paralleling generators, if the US built, US Flag vessel electric plant condition is as shown by graph "A", what would be the rotational status of the synchronizing lamps as shown in circuit "B"?

Revolve slowly in the fast direction

Revolve rapidly in the slow direction

Revolve slowly in the slow direction

Revolve slowly in the fast direction

What is the correct methodology to prevent shaft currents in an alternator?

Insulating EITHER the outboard bearing shell OR the outboard bearing pedestal.

Insulating BOTH the inboard AND outboard bearing shells.

Insulating BOTH the inboard AND outboard bearing pedestals.

Insulating EITHER the inboard bearing shell OR the inboard bearing pedestal.

Insulating EITHER the outboard bearing shell OR the outboard bearing pedestal.

To prevent shaft currents in an alternator, the outboard bearing shell or outboard bearing pedestal is insulated. If the methodology used is the insulated bearing pedestal, how is the pedestal insulation evaluated?

Measuring the resistance between the bearing pedestal and the bearing bedplate of a disassembled machine with a 500-Volt megohmmeter.

Measuring the resistance between the bearing pedestal and the bearing bedplate of an assembled machine with a 500-Volt megohmmeter.

Measuring the resistance between the bearing pedestal and the bearing bedplate of a disassembled machine with a digital multimeter setup as an ohmmeter.

Measuring the resistance between the bearing pedestal and the bearing bedplate of an assembled machine with a digital multimeter setup as an ohmmeter.

Measuring the resistance between the bearing pedestal and the bearing bedplate of a disassembled machine with a 500-Volt megohmmeter.

OSV – Chief Engineer Practice Test

What is on the OSV – Chief Engineer exam

Module	Questions	Illustrations	Practice
Q680 Motor Plants	69	19	Practice →
Q682 General Subjects	70	11	Practice →
Q683 Engineering Safety & Environmental Protection	69	4	Practice →
Q684 Electrical - Electronic - Control Engineering	70	23	Practice →
Total	278	57

Most modules require 70 percent to pass; Rules of the Road modules require 90 percent.

Q680 · 69 questions · 19 illustrations

Motor Plants

All Motor Plants and Auxiliary Boilers questions Sit Q680 timed

1. You are assigned to an OSV fitted with main propulsion diesel engines operating on the cycle represented in the polar timing diagram shown in the illustration....
2. You are assigned to an OSV fitted with main propulsion diesel engines operating on the cycle represented in the polar timing diagram shown in the illustration....
3. You are assigned as an engineer on an offshore platform supply vessel using main propulsion engines of the type shown in the illustration. What statement repres...
4. You are analyzing the data used for trend analysis for one of the main propulsion diesel engines on the ship- docking tug to which you are assigned. The cylinde...
5. You are analyzing the data used for trend analysis for a two-stroke main propulsion diesel engine on your general-purpose supply vessel. Although the engine has...

Showing the first 5 of 69. Start at question 1 and use Next to work through the module →

Q682 · 70 questions · 11 illustrations

General Subjects

All General Subjects questions Sit Q682 timed

Showing the first 5 of 70. Start at question 1 and use Next to work through the module →

Q683 · 69 questions · 4 illustrations

Engineering Safety & Environmental Protection

All Engineering Safety questions Sit Q683 timed

Showing the first 5 of 69. Start at question 1 and use Next to work through the module →

Q684 · 70 questions · 23 illustrations

Electrical - Electronic - Control Engineering

All Electricity questions Sit Q684 timed

Showing the first 5 of 70. Start at question 1 and use Next to work through the module →

OSV – Chief Engineer exam FAQ

Q How many questions are on the OSV – Chief Engineer exam?

The National Maritime Center's 2026 sample examination for OSV – Chief Engineer has 278 questions across 4 modules: Q680 Motor Plants (69 questions), Q682 General Subjects (70 questions), Q683 Engineering Safety & Environmental Protection (69 questions) and Q684 Electrical - Electronic - Control Engineering (70 questions). Every one is multiple choice with four answers, and you can practice all of them on this page.

Q What modules are on the OSV – Chief Engineer exam?

The modules are Q680 Motor Plants (69 questions), Q682 General Subjects (70 questions), Q683 Engineering Safety & Environmental Protection (69 questions) and Q684 Electrical - Electronic - Control Engineering (70 questions). Each module is graded separately, so you need to pass every one to pass the exam.

Q What score do I need to pass the OSV – Chief Engineer exam?

Most USCG exam modules require 70 percent to pass; Rules of the Road modules, where they apply, require 90 percent. Check the specific requirements for your endorsement with the National Maritime Center.

Q Are these the real questions?

Yes. They are the questions on the National Maritime Center's published 2026 sample examination for OSV – Chief Engineer (modules Q680–Q684), matched to our bank of released U.S. Coast Guard exam questions. The exam you sit draws from the same pools.

Q Can I take a timed OSV – Chief Engineer practice exam?

Yes. Subscribers can sit any module as an official sample exam in its published order, timed or untimed, with answers revealed at the end. Free accounts can build one 10-question practice exam and answer questions on every module page.

Other engine practice tests

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