USCG Merchant Mariner Credential (MMC) Exam — Questions and Answers

Question 1: What is an 'Aqueous Film-Forming Foam' (AFFF) used for aboard vessels?

Suppressing Class A cargo fires
Suppressing flammable liquid (Class B) fires, especially oil fires (Correct answer)
Fighting fires in cook galley areas
Electrical equipment fires

Correct answer: Suppressing flammable liquid (Class B) fires, especially oil fires

AFFF creates a film over flammable liquid surfaces that seals off fuel vapors and cools the surface, making it highly effective for Class B oil and fuel fires common on vessels.

Question 2: Which firefighting agent is most effective for a Class A (ordinary combustibles) fire?

Water (Correct answer)
Dry chemical
CO2
Foam

Correct answer: Water

Water is the most effective agent for Class A fires involving ordinary combustibles such as wood, paper, and cloth because it cools the burning material below its ignition temperature.

Question 3: A vessel is considered to be 'not under command' when she is?

Unable to maneuver as required by the rules due to exceptional circumstances (Correct answer)
Towing another vessel
Operating in restricted visibility
Anchored in a fairway

Correct answer: Unable to maneuver as required by the rules due to exceptional circumstances

COLREGS Rule 3 defines a vessel not under command as one that through exceptional circumstances is unable to maneuver as required and cannot keep out of the way of another vessel.

Question 4: What does a single prolonged blast of a vessel's whistle indicate in restricted visibility?

A vessel at anchor
A vessel underway and making way (Correct answer)
A vessel aground
A vessel towing

Correct answer: A vessel underway and making way

Under COLREGS Rule 35, a power-driven vessel underway and making way shall sound one prolonged blast at intervals of not more than 2 minutes.

Question 5: A vessel observing a sudden shift in wind direction and a rapid pressure drop should?

Increase speed and head for open water
Signal nearby vessels with one prolonged blast
Log the observation and continue passage
Prepare for severe weather and consider altering course (Correct answer)

Correct answer: Prepare for severe weather and consider altering course

A sudden wind shift combined with rapid pressure drop are classic precursors to severe weather, requiring immediate preparation and possible course alteration for safety.

Question 6: What weather phenomenon is indicated by a halo around the sun or moon?

Clear skies for 48 hours
Fog approaching within 12 hours
A high pressure system building
Precipitation likely within 24–48 hours (Correct answer)

Correct answer: Precipitation likely within 24–48 hours

A halo around the sun or moon is caused by ice crystals in cirrus clouds, which often precede a warm front and indicate rain within 24–48 hours.

Question 7: What vessel identifier is automatically transmitted when a DSC distress alert is sent?

The master's license number
The vessel's call sign
The vessel's MMSI number (Correct answer)
The vessel's IMO number

Correct answer: The vessel's MMSI number

A DSC distress alert automatically transmits the vessel's unique 9-digit MMSI number along with the nature of distress and GPS position when connected.

Question 8: A crew member finds an oil spill on the main deck near the fuel manifold. What is the FIRST action to take?

Contain the spill, notify the officer on watch, and prevent ignition sources (Correct answer)
Immediately hose the spill overboard
Apply dispersant chemicals without authorization
Log the spill and wait for the next watch

Correct answer: Contain the spill, notify the officer on watch, and prevent ignition sources

The first actions for a deck oil spill are containment to prevent spread, immediate notification of the officer on watch, and elimination of ignition sources to prevent fire.

Question 9: What is the purpose of the fire main system aboard a vessel?

To distribute seawater under pressure to fire hoses and hydrants throughout the vessel (Correct answer)
To supply fresh water to the crew
To cool the engine room machinery
To supply water to the sprinkler system only

Correct answer: To distribute seawater under pressure to fire hoses and hydrants throughout the vessel

The fire main is a dedicated piping system that distributes pressurized seawater from fire pumps to fire hydrants, hoses, and nozzles throughout the vessel for firefighting use.

Question 10: What is the Act to Prevent Pollution from Ships (APPS) the U.S. implementing legislation for?

The Refuse Act
The Oil Pollution Act of 1990
MARPOL — the International Convention for the Prevention of Pollution from Ships (Correct answer)
The Clean Water Act

Correct answer: MARPOL — the International Convention for the Prevention of Pollution from Ships

The Act to Prevent Pollution from Ships (APPS) is the U.S. federal law that implements MARPOL, making violations of its discharge standards punishable under U.S. law.

Question 11: What is the purpose of 'snap-back zones' marked on a vessel's deck?

Areas where crew must stay during bunkering
Safe standing areas during cargo operations
Designated zones for heaving lines to be coiled
Areas crew must avoid standing in due to the recoil path of mooring lines under tension (Correct answer)

Correct answer: Areas crew must avoid standing in due to the recoil path of mooring lines under tension

Snap-back zones mark the predicted recoil path of mooring lines if they part under tension, and crew must never stand in these areas during mooring operations.

Question 12: What does the abbreviation 'RPM' measure on a vessel's propulsion system?

Rated Power Margin of the engine
Radiated Power Measurement
Resistance Per Mile of the hull
Revolutions Per Minute of the shaft or engine (Correct answer)

Correct answer: Revolutions Per Minute of the shaft or engine

RPM (Revolutions Per Minute) measures how many complete rotations the engine crankshaft or propeller shaft makes per minute, indicating engine speed.

Question 13: What is the purpose of the MARPOL International Oil Pollution Prevention (IOPP) Certificate?

To document insurance coverage for oil spills
To certify that the vessel's oil pollution prevention equipment meets MARPOL requirements (Correct answer)
To certify the vessel's oil cargo capacity
To approve the vessel's Vessel Response Plan

Correct answer: To certify that the vessel's oil pollution prevention equipment meets MARPOL requirements

The IOPP Certificate, issued by the flag state, certifies that the vessel's equipment and procedures comply with MARPOL Annex I requirements for prevention of oil pollution.

Question 14: What is the 'dangerous semicircle' of a hurricane in the Northern Hemisphere?

The left side of the storm's path
The eye wall region
The right side of the storm's path (Correct answer)
The rear quadrant

Correct answer: The right side of the storm's path

The right semicircle of a Northern Hemisphere hurricane is considered dangerous because storm winds add to the forward speed of the storm, increasing wave heights and surge.

Question 15: A vessel overtaking another in a narrow channel must?

Sound two prolonged blasts and proceed
Keep out of the way of the vessel being overtaken (Correct answer)
Wait for the overtaken vessel to signal first
Proceed at reduced speed only

Correct answer: Keep out of the way of the vessel being overtaken

COLREGS Rule 13 states that any vessel overtaking another shall keep out of the way of the vessel being overtaken regardless of how the overtaking develops.

Question 16: What is the purpose of a 'deaerator' in a marine steam system?

To separate steam from condensate
To reduce steam pressure before the boiler
To measure steam quality and dryness
To remove dissolved oxygen and other gases from feedwater (Correct answer)

Correct answer: To remove dissolved oxygen and other gases from feedwater

A deaerator removes dissolved oxygen and carbon dioxide from boiler feedwater, preventing corrosion of the boiler and steam piping.

Question 17: Under the Navigation Rules, a 'give-way vessel' is required to?

Take early and substantial action to keep well clear (Correct answer)
Sound five short blasts
Increase speed to cross ahead
Maintain course and speed

Correct answer: Take early and substantial action to keep well clear

COLREGS Rule 16 requires the give-way vessel to take early and substantial action to keep well clear of the stand-on vessel.

Question 18: When is a vessel considered to be 'underway' for purposes of the Navigation Rules?

When the engines are running
When cleared from port
When not at anchor, made fast to shore, or aground (Correct answer)
When moving through the water

Correct answer: When not at anchor, made fast to shore, or aground

COLREGS Rule 3 defines underway as not at anchor, made fast to shore, or aground — the vessel need not be moving.

Question 19: Which VHF channel is designated exclusively for Digital Selective Calling (DSC) distress alerts?

Channel 70 (Correct answer)
Channel 16
Channel 6
Channel 22A

Correct answer: Channel 70

VHF Channel 70 is reserved exclusively for Digital Selective Calling (DSC) and must not be used for voice communications.

Question 20: What lights must a vessel restricted in her ability to maneuver display?

Two red lights in a vertical line
Two red lights over one white light
Red, white, red lights in a vertical line (Correct answer)
Three red lights in a vertical line

Correct answer: Red, white, red lights in a vertical line

COLREGS Rule 27 requires a vessel restricted in her ability to maneuver to show three all-round lights — red over white over red — in a vertical line.

Question 21: What is the primary purpose of a Traffic Separation Scheme (TSS)?

To designate anchorage areas
To mark submerged hazards
To organize vessel traffic flow and reduce collision risk (Correct answer)
To allocate fishing zones

Correct answer: To organize vessel traffic flow and reduce collision risk

Traffic Separation Schemes, established under COLREGS Rule 10, organize opposing traffic flow into separate lanes to reduce the risk of collision.

Question 22: What is the primary purpose of two-way VHF portable radios required in survival craft under GMDSS?

Broadcasting weather information to the crew
On-scene communications between survivors and rescue units (Correct answer)
Transmitting vessel position to satellites
Contacting commercial shipping for navigation updates

Correct answer: On-scene communications between survivors and rescue units

Two-way VHF portable radios in survival craft are used for on-scene communications between survivors and SAR rescue units during rescue operations.

Question 23: After removing someone from an electrical source who has been rendered unconscious by electric shock, you should _______.

Massage vigorously to restore circulation
Check for serious burn on the body
Administer ammonia smelling salts
Determine if he is breathing (Correct answer)

Correct answer: Determine if he is breathing

After safely removing someone from an electrical source who has been rendered unconscious by electric shock, the immediate priority is to determine if they are breathing. Electric shock can cause respiratory arrest or cardiac arrest, so checking for breathing and pulse is the first critical step in providing emergency medical care. If not breathing, CPR should be initiated.

Question 24: CO2 fire extinguishers are most effective in which environment?

Forest fires
Enclosed spaces where the CO2 concentration can build up (Correct answer)
Open deck fires
Fuel tank fires

Correct answer: Enclosed spaces where the CO2 concentration can build up

CO2 extinguishers work by displacing oxygen and are most effective in enclosed spaces where the gas concentration can reach levels sufficient to suppress the fire.

Question 25: Wind speed is measured using which instrument?

Barometer
Anemometer (Correct answer)
Psychrometer
Hygrometer

Correct answer: Anemometer

An anemometer measures wind speed; the readings are often combined with a wind vane to provide both speed and direction.

Question 26: What does one short blast on a whistle mean under the Inland Rules?

I am altering course to starboard (Correct answer)
I am altering course to port
I intend to leave you on my port side
I am operating astern propulsion

Correct answer: I am altering course to starboard

Under Inland Rule 34, one short blast means 'I intend to alter my course to starboard,' and the other vessel must respond with the same signal if in agreement.

Question 27: What is the first action a crew member should take upon discovering a fire aboard?

Attempt to extinguish it immediately
Muster at the lifeboat station
Sound the alarm to alert the crew and master (Correct answer)
Contact the Coast Guard on VHF Channel 16

Correct answer: Sound the alarm to alert the crew and master

The first action upon discovering a fire is to sound the alarm to alert the entire crew, enabling a coordinated response and ensuring safety of all persons aboard.

Question 28: Any individual maintaining a listening watch on a bridgeton-bridge radiotelephone must be able to _____.

Repair the unit
Speak English (Correct answer)
Speak a language the vessel's crew will understand
Send Morse Code

Correct answer: Speak English

Any individual maintaining a listening watch on a bridge-to-bridge radiotelephone must be able to speak English. This is a requirement under international maritime regulations (SOLAS) to ensure clear and effective communication between vessels, especially in critical situations. English is the internationally recognized language for maritime communication.

Question 29: What class of fire involves flammable liquids such as oil, gasoline, and paint?

Class A
Class C
Class D
Class B (Correct answer)

Correct answer: Class B

Class B fires involve flammable liquids and gases such as oil, gasoline, diesel fuel, and paints, which are common hazards aboard vessels.

Question 30: What is a 'gale warning' issued for?

Winds 64 knots and above
Winds 48–63 knots
Winds 34–47 knots (Correct answer)
Winds 20–33 knots

Correct answer: Winds 34–47 knots

The National Weather Service issues a gale warning when sustained winds of 34 to 47 knots are expected in marine areas.

Question 31: Small passenger ships must be built with or lined with ____ for paint and oil lockers.

sheetrock, asbestos, or other material that retards the spread of fire
steel or equivalent material (Correct answer)
fiberglass
marine plywood

Correct answer: steel or equivalent material

To enhance fire safety on small passenger ships, spaces containing highly flammable materials like paint and oil lockers must be constructed with fire-retardant materials. Steel or an equivalent fire-resistant material is mandated for bulkheads and linings in these areas. This prevents the rapid spread of fire and contains potential hazards, protecting passengers and crew.

Question 32: A center gage is used in machine shop practice to verify the angle of ____.

60 degree thread cutting tools (Correct answer)
drill points
screw threads
screw thread pitch

Correct answer: 60 degree thread cutting tools

A center gage, also known as a thread center gage or screw pitch gage, is a specialized tool used in machine shops. Its primary function is to accurately verify the angle of a 60-degree thread cutting tool before it is used to cut screw threads. This ensures that the cutting tool has the correct profile to produce threads with the standard 60-degree included angle, which is critical for proper thread engagement and strength.

USCG Merchant Mariner Credential (MMC) Exam

The USCG National Maritime Center (NMC) Merchant Mariner Credential exam tests deck officer competencies including navigation, cargo operations, vessel safety, fire prevention, marine environmental protection, and meteorology required for U.S. merchant mariner licensing.

Questions

35 min

Time Limit

70%

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