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

Question 1: What is the 'dangerous semicircle' of a hurricane in the Northern Hemisphere?

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

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 2: Which of the following best describes the 'buddy system' as applied to hazardous deck work?

Assigning a senior crew member to observe a junior one
Two crew members performing the same task to increase speed
Rotating crew members through high-risk jobs evenly
Working in pairs so each person can monitor the other and summon help if needed (Correct answer)

Correct answer: Working in pairs so each person can monitor the other and summon help if needed

The buddy system requires two people to work together so each can observe the other's safety and immediately summon help if one is injured or incapacitated.

Question 3: Which bearing type is most commonly used for a ship's main propulsion shaft?

Tapered roller bearing
Needle roller bearing
White metal (babbitt) journal bearing (Correct answer)
Deep groove ball bearing

Correct answer: White metal (babbitt) journal bearing

White metal (babbitt) journal bearings are used for main propulsion shafts because they can carry large radial loads and are self-lubricating with oil or water.

Question 4: What is the primary purpose of a diesel engine's intercooler?

To cool the engine block
To cool compressed intake air before it enters the cylinder (Correct answer)
To reduce exhaust gas temperature
To cool engine lubricating oil

Correct answer: To cool compressed intake air before it enters the cylinder

An intercooler cools compressed air from the turbocharger before it enters the cylinder, increasing air density and allowing more fuel to burn efficiently.

Question 5: What weather phenomenon is indicated by a halo around the sun or moon?

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

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 6: Enclosed space entry on a vessel requires which of the following before personnel enter?

Verbal clearance from the chief mate
Only a lookout posted outside
Hosing down the space with fresh water
Testing the atmosphere for oxygen, flammable gases, and toxic vapors (Correct answer)

Correct answer: Testing the atmosphere for oxygen, flammable gases, and toxic vapors

USCG regulations require atmospheric testing for oxygen levels, flammable gases, and toxic vapors before any enclosed space entry.

Question 7: What safety device prevents a boiler from operating with low water level?

Water hammer arrestor
Low-water fuel cutoff (low-level alarm and trip) (Correct answer)
Superheater safety valve
Pressure relief valve

Correct answer: Low-water fuel cutoff (low-level alarm and trip)

A low-water fuel cutoff senses dangerously low water level in the boiler and shuts off the fuel supply to prevent overheating and potential explosion.

Question 8: What lights must a vessel restricted in her ability to maneuver display?

Two red lights over one white light
Three red lights in a vertical line
Red, white, red lights in a vertical line (Correct answer)
Two 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 9: What light is shown by a vessel engaged in pilotage duty?

Yellow flashing light
White over red all-round lights (Correct answer)
All-round blue light
Red over white all-round lights

Correct answer: White over red all-round lights

COLREGS Rule 29 requires a pilot vessel on duty to show an all-round white light over an all-round red light at the masthead.

Question 10: Before activating a fixed CO2 system in the engine room, what must be done first?

Start emergency fire pumps
Ensure all personnel have evacuated the space and close all ventilation (Correct answer)
Notify the Coast Guard
Switch to manual steering

Correct answer: Ensure all personnel have evacuated the space and close all ventilation

All personnel must be evacuated from the CO2-protected space and all ventilation openings closed before activating the system, as CO2 in concentrations needed to suppress fires is fatal to humans.

Question 11: A vessel crew member notices a safety guard has been removed from a deck winch. What is the appropriate action?

Stop operations, tag the winch out-of-service, and report to the officer in charge (Correct answer)
Post a warning sign and allow other experienced crew to use it
Replace the guard after the current operation is complete
Continue operating the winch carefully

Correct answer: Stop operations, tag the winch out-of-service, and report to the officer in charge

Machinery with missing guards must be immediately taken out of service, tagged, and reported — using unguarded machinery is a USCG and OSHA violation.

Question 12: What class of fire involves flammable liquids such as oil, gasoline, and paint?

Class D
Class C
Class A
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 13: When shall a vessel in a narrow channel keep to the starboard side?

Only during restricted visibility
Only at night
At all times when safe and practicable (Correct answer)
Only when another vessel is approaching

Correct answer: At all times when safe and practicable

COLREGS Rule 9 requires every vessel proceeding along a narrow channel to keep as near to the outer limit on its starboard side as is safe and practicable.

Question 14: What does a single prolonged blast of a vessel's whistle indicate in restricted visibility?

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

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 15: Wind speed is measured using which instrument?

Psychrometer
Hygrometer
Anemometer (Correct answer)
Barometer

Correct answer: Anemometer

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

Question 16: What does one short blast on a whistle mean under the Inland Rules?

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

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 17: What is the recommended action when a vessel receives a severe thunderstorm warning?

Anchor in open water immediately
Seek shelter in a protected anchorage or harbor if possible (Correct answer)
Continue on course at reduced speed
Increase speed to outrun the storm

Correct answer: Seek shelter in a protected anchorage or harbor if possible

When a severe thunderstorm warning is issued, the safest action is to seek a protected anchorage or harbor to avoid lightning, waterspouts, and high seas.

Question 18: Which firefighting agent is most effective for a Class A (ordinary combustibles) fire?

Foam
Water (Correct answer)
Dry chemical
CO2

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

The vessel's call sign
The vessel's IMO number
The vessel's MMSI number (Correct answer)
The master's license 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 20: What does GMDSS stand for?

Global Marine Distress and Safety System
General Maritime Distress Safety Standards
General Maritime Defense Safety System
Global Maritime Distress and Safety System (Correct answer)

Correct answer: Global Maritime Distress and Safety System

GMDSS stands for Global Maritime Distress and Safety System, the international radio communications framework for maritime safety established under SOLAS.

Question 21: The _____ must contain a list of the kinds and strengths of steels utilized on a MODU.

builder's documentation
general plans
Construction portfolio (Correct answer)
Certificate of Inspection

Correct answer: Construction portfolio

The Construction Portfolio for a Mobile Offshore Drilling Unit (MODU) is a comprehensive document that details the unit's structural design and materials. It specifically includes a list of the kinds and strengths of steels used in the MODU's construction. This information is crucial for ensuring structural integrity, compliance with design specifications, and for future maintenance and repair operations.

Question 22: What information must be included in a MAYDAY distress call?

MAYDAY, vessel name, position, nature of distress, number of persons aboard, and any other relevant information (Correct answer)
MAYDAY, vessel name, home port, and cargo manifest
MAYDAY, vessel name, and owner contact information
MAYDAY, registration number, and destination port

Correct answer: MAYDAY, vessel name, position, nature of distress, number of persons aboard, and any other relevant information

A MAYDAY call must include the word MAYDAY spoken three times, vessel name, position, nature of distress, number of persons aboard, and any other information helpful to rescuers.

Question 23: What does GMDSS weather broadcast format NAVTEX provide to mariners?

Real-time radar imagery
Satellite cloud imagery
Printed text weather forecasts and navigational warnings (Correct answer)
Voice weather broadcasts

Correct answer: Printed text weather forecasts and navigational warnings

NAVTEX broadcasts meteorological warnings, navigational warnings, and search-and-rescue information as printed text via a dedicated 518 kHz frequency.

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

Forest fires
Fuel tank fires
Enclosed spaces where the CO2 concentration can build up (Correct answer)
Open deck 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: Which GMDSS Sea Area is defined as within VHF shore-based DSC coverage, typically within 20-30 miles of shore?

Sea Area A2
Sea Area A4
Sea Area A1 (Correct answer)
Sea Area A3

Correct answer: Sea Area A1

Sea Area A1 is defined as the area within range of VHF shore-based DSC stations, generally within 20-30 nautical miles of the coast.

Question 26: What is the primary purpose of a NAVTEX receiver aboard a vessel?

Communicating with other vessels on VHF
Transmitting vessel position to the Coast Guard
Receiving navigational warnings, weather forecasts, and urgent maritime safety information (Correct answer)
Automatically activating the vessel's EPIRB

Correct answer: Receiving navigational warnings, weather forecasts, and urgent maritime safety information

NAVTEX is an international automated direct-printing service that receives navigational warnings, meteorological forecasts, and urgent maritime safety information on MF frequencies.

Question 27: What is the purpose of the fire main system aboard a vessel?

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

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 28: What is the correct action if the 15 ppm bilge alarm activates while overboard discharge is underway?

Bypass the alarm and complete the discharge
Reduce pumping rate and continue discharge
Increase separator flow rate to dilute the oil concentration
Immediately stop the overboard discharge and divert to a holding tank (Correct answer)

Correct answer: Immediately stop the overboard discharge and divert to a holding tank

MARPOL requires immediate cessation of discharge when oil content exceeds 15 ppm; the oily water must be diverted to a slop or holding tank.

Question 29: What does a vessel display two cones apex-to-apex to indicate?

Vessel engaged in fishing (Correct answer)
Vessel not under command
Vessel at anchor
Vessel aground

Correct answer: Vessel engaged in fishing

COLREGS Rule 26 requires a vessel engaged in fishing to display two cones with apexes together (diamond shape) when not at anchor.

Question 30: The National Response Center (NRC) must be notified within what timeframe following an oil spill?

Within 72 hours
Within 48 hours
As soon as possible after discovery (Correct answer)
Within 24 hours

Correct answer: As soon as possible after discovery

OPA 90 and the Clean Water Act require the responsible party to notify the NRC (1-800-424-8802) as soon as possible — there is no grace period — upon discovery of a discharge.

Question 31: What is the purpose of a pyrotechnic distress signal (flare)?

To illuminate the vessel's deck at night
To test the vessel's electrical system
To mark a navigation hazard
To signal distress and attract the attention of rescuers visually (Correct answer)

Correct answer: To signal distress and attract the attention of rescuers visually

Pyrotechnic distress signals (parachute flares, handheld flares, and orange smoke) provide a highly visible visual distress signal to attract the attention of passing vessels and aircraft.

Question 32: What is an 'Aqueous Film-Forming Foam' (AFFF) used for aboard vessels?

Electrical equipment fires
Fighting fires in cook galley areas
Suppressing flammable liquid (Class B) fires, especially oil fires (Correct answer)
Suppressing Class A cargo 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 33: The Beaufort Scale is used to measure what?

Barometric pressure
Sea wave height
Visibility distance
Wind force and speed (Correct answer)

Correct answer: Wind force and speed

The Beaufort Scale is a numerical scale from 0 to 12 used to describe wind force and its effects on the sea surface.

Question 34: What is a 'small craft advisory' issued for?

Winds above 64 knots
Winds below 10 knots
Winds 15–33 knots or seas 5–7 feet (Correct answer)
Winds 34–47 knots or seas 8–12 feet

Correct answer: Winds 15–33 knots or seas 5–7 feet

The National Weather Service issues a small craft advisory when winds are forecast between 15 and 33 knots or seas are 5 to 7 feet, posing hazards to small vessels.

Question 35: What is indicated by a rising exhaust temperature on one cylinder of a diesel engine?

The fuel pump for that cylinder is delivering too little fuel
The cylinder is producing less power than normal
The cooling water flow to that cylinder is excessive
The cylinder may have a faulty injector or restriction in air flow (Correct answer)

Correct answer: The cylinder may have a faulty injector or restriction in air flow

A rising exhaust temperature on one cylinder typically indicates over-fueling due to a faulty injector or restricted air intake causing incomplete combustion.

Question 36: What action must be taken before entering a cargo hold classified as a confined space?

Test the atmosphere for oxygen level and toxic gases and obtain a confined space entry permit (Correct answer)
Obtain permission from the port authority
Notify the nearest Coast Guard station
Secure all cargo first

Correct answer: Test the atmosphere for oxygen level and toxic gases and obtain a confined space entry permit

Before entering a cargo hold or other confined space, the atmosphere must be tested for oxygen deficiency, enrichment, and toxic or flammable gases, and a confined space entry permit must be issued.

Question 37: What is the correct sequence for initiating a voice MAYDAY distress call?

MAYDAY once, all vessel information, then wait for acknowledgment
MAYDAY once, vessel name, position, nature of distress, persons aboard
MAYDAY twice, vessel name, position, type of assistance required
MAYDAY three times, vessel name three times, MAYDAY once, position, nature of distress, persons aboard, other relevant information (Correct answer)

Correct answer: MAYDAY three times, vessel name three times, MAYDAY once, position, nature of distress, persons aboard, other relevant information

The correct MAYDAY procedure begins with 'MAYDAY MAYDAY MAYDAY,' followed by the vessel's name three times, then 'MAYDAY' once more, then position, nature of distress, number of persons, and any other pertinent information.

Question 38: What does MARPOL Annex VI regulate?

Air pollution from ships including SOx, NOx, and ODS (Correct answer)
Sewage discharge
Garbage disposal
Oil pollution

Correct answer: Air pollution from ships including SOx, NOx, and ODS

MARPOL Annex VI addresses prevention of air pollution from ships, regulating sulfur oxide (SOx), nitrogen oxide (NOx), particulate matter, and ozone-depleting substance (ODS) emissions.

Question 39: What is the primary purpose of a Traffic Separation Scheme (TSS)?

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

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 40: What is the minimum freeboard for a vessel under load line regulations?

Determined only by the master
20% of the vessel's depth
The amount specified on the vessel's load line certificate for current conditions (Correct answer)
A fixed value of 12 inches

Correct answer: The amount specified on the vessel's load line certificate for current conditions

The minimum freeboard is the minimum distance from the waterline to the freeboard deck as specified on the vessel's load line certificate for the applicable zone and season.

Question 41: Which U.S. agency is the lead federal agency for oil spill response in coastal and inland waters?

NOAA
U.S. Navy
U.S. Coast Guard (Correct answer)
EPA

Correct answer: U.S. Coast Guard

The U.S. Coast Guard is the federal on-scene coordinator for oil spill response in coastal and offshore waters, responsible for directing cleanup and enforcement actions.

Question 42: What is a 'Vessel Response Plan' (VRP) required to address?

Crew training schedules
Procedures for responding to a worst-case oil spill scenario (Correct answer)
Only fuel transfer procedures
Equipment maintenance logs

Correct answer: Procedures for responding to a worst-case oil spill scenario

A Vessel Response Plan must include procedures for responding to a worst-case oil discharge scenario, identifying response resources, contacts, and cleanup procedures required by OPA 90.

Question 43: What is the purpose of a fire detection system aboard a vessel?

To provide early warning so the crew can respond before a fire spreads (Correct answer)
To shut down the engine room fans
To alert the Coast Guard automatically
To automatically extinguish fires

Correct answer: To provide early warning so the crew can respond before a fire spreads

Fire detection systems provide early warning through heat, smoke, or flame detectors, allowing the crew to respond quickly before a fire grows to an uncontrollable size.

Question 44: A wind rotating counterclockwise in the Northern Hemisphere is associated with which type of pressure system?

Low pressure (cyclone) (Correct answer)
High pressure (anticyclone)
A sea breeze
A stationary front

Correct answer: Low pressure (cyclone)

In the Northern Hemisphere, winds rotate counterclockwise around a low-pressure (cyclonic) system due to the Coriolis effect.

Question 45: Sea fog most commonly forms when?

Air and sea temperatures are nearly equal and humidity is high (Correct answer)
Barometric pressure is falling rapidly
Strong winds mix warm and cold air layers
Air temperature is much higher than sea surface temperature

Correct answer: Air and sea temperatures are nearly equal and humidity is high

Sea fog forms when warm, humid air is chilled to its dew point upon contact with a cooler sea surface, which most often occurs when air and sea temperatures are close.

Question 46: Fire drills aboard inspected vessels are required by USCG regulations at what interval?

Daily
Monthly
Quarterly
Weekly (Correct answer)

Correct answer: Weekly

USCG regulations (46 CFR 185.506) require fire and emergency drills to be conducted weekly on inspected passenger vessels to ensure crew readiness.

Question 47: What is the function of a sea chest in a ship's cooling water system?

To separate air from cooling water
To provide a protected intake for seawater used in cooling systems (Correct answer)
To filter fuel oil before combustion
To store emergency freshwater

Correct answer: To provide a protected intake for seawater used in cooling systems

A sea chest is a hull fitting with a strainer that provides a protected seawater intake point for the ship's cooling and other seawater systems.

Question 48: What is the first action a crew member should take upon discovering a fire aboard?

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

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 49: What does 'securing cargo' involve?

Covering cargo with tarps on deck
Completing customs documentation
Labeling cargo with shipping marks only
Using lashings, blocking, and bracing to prevent cargo movement during the voyage (Correct answer)

Correct answer: Using lashings, blocking, and bracing to prevent cargo movement during the voyage

Securing cargo involves the use of lashings, chains, wire, blocking, and bracing to prevent cargo from shifting, sliding, or falling during vessel motion at sea.

Question 50: Which VHF channel is designated exclusively for Digital Selective Calling (DSC) distress alerts?

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

Correct answer: Channel 70

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

Question 51: What is a 'fire party' on a vessel?

A designated team of trained crew members responsible for fighting fires (Correct answer)
A group from the Coast Guard called in to fight fires
Crew members celebrating after a fire drill
A method of fire suppression

Correct answer: A designated team of trained crew members responsible for fighting fires

A fire party is a designated group of trained crew members with assigned roles — hose team, boundary cooling, ventilation control — to respond to and combat fires aboard the vessel.

Question 52: What are the three elements of the fire triangle?

Oxygen, carbon dioxide, and nitrogen
Fuel, water, and heat
Fuel, heat, and oxygen (Correct answer)
Heat, smoke, and oxygen

Correct answer: Fuel, heat, and oxygen

The fire triangle consists of fuel (combustible material), heat (ignition source), and oxygen; removing any one element will extinguish the fire.

Question 53: What is the minimum sound signal equipment required for a vessel 12 to 20 meters in length?

A bell only
A whistle only
A whistle, bell, and gong
A whistle and a bell (Correct answer)

Correct answer: A whistle and a bell

COLREGS Rule 33 requires vessels 12 meters or more in length to carry a whistle and a bell.

Question 54: What VHF channel is designated as the primary maritime distress and calling channel?

Channel 22A
Channel 13
Channel 16 (Correct answer)
Channel 6

Correct answer: Channel 16

VHF Channel 16 (156.8 MHz) is the international maritime distress, safety, and calling channel monitored by all vessels and the Coast Guard at all times.

Question 55: In a four-stroke diesel engine, what occurs during the compression stroke?

The piston moves up with all valves closed, compressing the air charge (Correct answer)
Exhaust gases are expelled from the cylinder
Fuel is injected and burned
The piston moves down drawing in fresh air

Correct answer: The piston moves up with all valves closed, compressing the air charge

During the compression stroke, the piston moves upward with both valves closed, compressing the air charge to a high temperature sufficient to ignite injected fuel.

Question 56: When fighting a fire in an enclosed space, what is the primary personal safety concern?

Noise from the SCBA
Oxygen depletion and toxic smoke inhalation (Correct answer)
Damage to fire hoses
Running out of water

Correct answer: Oxygen depletion and toxic smoke inhalation

Enclosed spaces rapidly become oxygen-deficient and fill with toxic gases during a fire; firefighters must wear self-contained breathing apparatus (SCBA) to survive.

Question 57: A vessel overtaking another in a narrow channel must?

Sound two prolonged blasts and proceed
Wait for the overtaken vessel to signal first
Keep out of the way of the vessel being overtaken (Correct answer)
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 58: Which light is required on the stern of a power-driven vessel underway?

A red light
A yellow light
A white sternlight (Correct answer)
An all-round white light

Correct answer: A white sternlight

COLREGS Rule 23 requires a power-driven vessel underway to exhibit a white sternlight showing an arc of 135 degrees.

Question 59: When transferring fuel at sea or in port, what safety measure must be in place throughout the operation?

Only the chief engineer may be present on deck
All crew must wear flame-retardant suits
A continuous watch must be maintained at the transfer point with ready fire-fighting equipment (Correct answer)
The engine room must be sealed off

Correct answer: A continuous watch must be maintained at the transfer point with ready fire-fighting equipment

Fuel transfer operations require a continuous watch at the transfer point and readily available fire-fighting equipment to respond immediately to any spill or fire.

Question 60: What is the required content of a Garbage Management Plan under MARPOL Annex V?

Insurance coverage for spills
A record of all garbage weighed
A list of approved dumping sites only
Written procedures for minimizing, collecting, storing, and disposing of garbage aboard the vessel (Correct answer)

Correct answer: Written procedures for minimizing, collecting, storing, and disposing of garbage aboard the vessel

A Garbage Management Plan must describe procedures for minimizing, collecting, storing, processing, and disposing of garbage, and must assign responsibility for the plan's implementation.

Question 61: What does the acronym PASS stand for when using a portable fire extinguisher?

Prepare, Aim, Squeeze, Spray
Pull, Aim, Squeeze, Sweep (Correct answer)
Push, Aim, Shoot, Spray
Pull, Activate, Squeeze, Sweep

Correct answer: Pull, Aim, Squeeze, Sweep

PASS stands for Pull the pin, Aim at the base of the fire, Squeeze the handle, and Sweep side to side at the base of the flames.

Question 62: What is the dew point temperature?

The average daily temperature
The lowest temperature reached at night
The temperature of the sea surface
The temperature at which air becomes saturated and condensation forms (Correct answer)

Correct answer: The temperature at which air becomes saturated and condensation forms

The dew point is the temperature to which air must be cooled at constant pressure for water vapor to condense into dew or fog.

Question 63: Which immersion suit feature is most critical for survival in cold water?

Thermal insulation to prevent hypothermia (Correct answer)
Built-in radio beacon
Bright retroreflective tape
Bright color for visibility

Correct answer: Thermal insulation to prevent hypothermia

Thermal insulation is the most critical feature of an immersion suit because hypothermia kills within minutes to hours in cold water; the suit slows heat loss dramatically.

Question 64: What is the purpose of a 'stuffing box' (packing gland) on a centrifugal pump?

To prevent leakage along the pump shaft where it exits the casing (Correct answer)
To balance axial thrust on the pump shaft
To cool the pump bearing
To lubricate the pump impeller

Correct answer: To prevent leakage along the pump shaft where it exits the casing

A stuffing box contains packing material compressed around the pump shaft to minimize fluid leakage where the rotating shaft passes through the stationary pump casing.

Question 65: What is the function of a 'sounding tube' on a vessel?

To measure noise levels in the engine room
To allow measurement of liquid levels in tanks (Correct answer)
To test for gas accumulation in enclosed spaces
To check pressure in compressed air systems

Correct answer: To allow measurement of liquid levels in tanks

Sounding tubes are pipes that extend to the bottom of tanks, allowing crew members to lower a sounding rod or tape to measure the liquid level.

Question 66: A tropical cyclone in the Atlantic or eastern Pacific with sustained winds of 74 mph or greater is classified as?

A tropical storm
A typhoon
A hurricane (Correct answer)
A tropical depression

Correct answer: A hurricane

A tropical cyclone in the Atlantic or eastern Pacific is called a hurricane when sustained winds reach 74 mph (64 knots) or greater.

Question 67: When working aloft on a vessel, what is the primary safety requirement before beginning any task?

Check the weather forecast only
Wear a hard hat and gloves
Notify the bridge and secure a safety harness to a fixed point (Correct answer)
Obtain verbal permission from a crewmember

Correct answer: Notify the bridge and secure a safety harness to a fixed point

Working aloft requires notifying the bridge and wearing a properly secured safety harness attached to a fixed structural point to prevent falls.

Question 68: The Oil Pollution Act of 1990 (OPA 90) was primarily enacted in response to which disaster?

The Argo Merchant grounding
The Amoco Cadiz spill
The Exxon Valdez oil spill in Prince William Sound, Alaska (Correct answer)
The Deepwater Horizon spill

Correct answer: The Exxon Valdez oil spill in Prince William Sound, Alaska

OPA 90 was enacted following the 1989 Exxon Valdez oil spill, which released 11 million gallons of crude oil into Prince William Sound and caused massive environmental damage.

Question 69: Under the Navigation Rules, a 'give-way vessel' is required to?

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

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 70: What is the duty watch requirement for VHF Channel 16 on commercial vessels?

Monitor only when in a harbor
Maintain a continuous watch while underway (Correct answer)
Monitor only when other vessels are in the area
Monitor only during daylight hours

Correct answer: Maintain a continuous watch while underway

FCC and USCG regulations require commercial vessels subject to the Bridge-to-Bridge Communications Act to maintain a continuous watch on VHF Channel 16 at all times while underway.

Question 71: When a tank measuring 60 feet in length and 30 feet in width is equipped with a centerline bulkhead and partially filled with salt water, what is the decrease in metacentric height caused by free surface? (The displacement of the vessel is 10,000 tons.)

0.8 foot
1.2 feet
0.1 foot (Correct answer)
1.0 foot

Correct answer: 0.1 foot

The decrease in metacentric height (GM) caused by free surface effect is calculated using a specific formula that considers the tank's dimensions and the vessel's displacement. For a tank with a centerline bulkhead, the effective width for the calculation is halved, significantly reducing the free surface moment. This calculation yields a decrease of approximately 0.1 foot, indicating a reduction in the vessel's initial stability.

Question 72: What does the acronym RACE stand for in shipboard fire response?

Remove, Activate, Close, Extinguish
React, Alert, Call, Escape
Report, Aim, Contain, Evacuate
Rescue, Alarm, Contain, Extinguish or Evacuate (Correct answer)

Correct answer: Rescue, Alarm, Contain, Extinguish or Evacuate

RACE stands for Rescue anyone in immediate danger, Alarm to alert the crew, Contain the fire by closing doors and hatches, and Extinguish or Evacuate depending on the fire size.

Question 73: What is meant by 'boundary cooling' during a shipboard fire?

Applying water to bulkheads and decks surrounding the fire to prevent spread (Correct answer)
Removing fuel from around the fire
Using CO2 to cool the fire boundary
Cooling the fire directly with water fog

Correct answer: Applying water to bulkheads and decks surrounding the fire to prevent spread

Boundary cooling involves applying water to the metal structures surrounding a fire to prevent heat transfer that could ignite adjacent compartments or spaces.

Question 74: Under COLREGS, what action shall the stand-on vessel take when a collision cannot be avoided by the give-way vessel alone?

Take the best action to avoid collision (Correct answer)
Sound five short blasts and stop
Increase speed to pass clear
Maintain course and speed at all times

Correct answer: Take the best action to avoid collision

COLREGS Rule 17 allows the stand-on vessel, when collision cannot otherwise be avoided, to take whatever action will best aid in avoiding collision.

Question 75: What does the COSPAS-SARSAT system primarily do?

Controls VHF radio frequency assignments in ports
Monitors vessel traffic in coastal waters
Detects and locates 406 MHz emergency beacons including EPIRBs and PLBs (Correct answer)
Provides GPS navigation for commercial vessels

Correct answer: Detects and locates 406 MHz emergency beacons including EPIRBs and PLBs

COSPAS-SARSAT is an international satellite-based search and rescue system that detects and locates distress signals from 406 MHz emergency beacons.

Question 76: What is the primary goal of the National Contingency Plan (NCP) for oil spill response?

To provide a framework for coordinated response to oil spills and hazardous substance releases (Correct answer)
To set MARPOL compliance requirements
To establish shipping lane regulations
To manage port facility security

Correct answer: To provide a framework for coordinated response to oil spills and hazardous substance releases

The National Contingency Plan (NCP) establishes the framework for federal, state, and local agencies and private industry to coordinate response to oil spills and hazardous substance releases in U.S. waters.

Question 77: In a ship's electrical system, what is the purpose of a bus bar?

To supply power to the propulsion shaft
To isolate faulty circuits from the system
To step up voltage from generators
To serve as a common conductor connecting multiple circuits (Correct answer)

Correct answer: To serve as a common conductor connecting multiple circuits

A bus bar is a metallic conductor that acts as a common connection point distributing electrical power from generators to various shipboard circuits.

Question 78: The general by-products of oxidation caused by hydraulic il water contamination are ____.

harmless and have no effect on system components
gums, varnishes, and acids (Correct answer)
removed by cellulose type filters
always neutralized by oil additives

Correct answer: gums, varnishes, and acids

Water contamination in hydraulic oil, especially when combined with heat and oxygen, significantly accelerates the oil's oxidation process. This oxidation leads to the formation of harmful by-products such as gums, varnishes, and acids. Gums and varnishes can cause sticky residues and blockages, while acids corrode system components, leading to premature wear and system failure.

Question 79: A vessel observing a sudden shift in wind direction and a rapid pressure drop should?

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

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 80: Which type of fire extinguisher is most appropriate for a Class C (electrical) fire?

Water extinguisher
Dry chemical or CO2 extinguisher (Correct answer)
Halon extinguisher only
Foam extinguisher

Correct answer: Dry chemical or CO2 extinguisher

CO2 and dry chemical extinguishers are non-conductive and safe for Class C electrical fires; water and foam conduct electricity and can electrocute the operator.

Question 81: What type of fog forms when warm moist air moves over colder water?

Advection fog (Correct answer)
Steam fog
Radiation fog
Upslope fog

Correct answer: Advection fog

Advection fog forms when warm, moist air is transported over a cooler sea surface, cooling the air to its dew point and causing condensation.

Question 82: A center gage is used in machine shop practice to verify the angle of ____.

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

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.

Question 83: A crew member finds an oil spill on the main deck near the fuel manifold. What is the FIRST action to take?

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

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 84: What does a rapidly falling barometer (more than 0.06 inches per hour) typically indicate?

Improving weather conditions
High pressure system arrival
Fog formation
An approaching storm or severe weather (Correct answer)

Correct answer: An approaching storm or severe weather

A rapid barometric pressure drop indicates an approaching low-pressure system, which typically brings deteriorating weather and strong winds.

Question 85: When a vessel is in distress, it should transmit two alarm signals via radio telephone, promptly followed by the ______.

distress position
spoken words, "Mayday, Mayday, Mayday" (Correct answer)
ship's name
ship's call letters

Correct answer: spoken words, "Mayday, Mayday, Mayday"

According to international maritime radio communication procedures, after transmitting two alarm signals, a vessel in distress must immediately follow with the spoken words "Mayday, Mayday, Mayday." This clearly identifies the transmission as a distress call and alerts all listening stations to an immediate and grave danger. The "Mayday" call is the universally recognized voice distress signal, initiating emergency response protocols.

Question 86: Which type of breathing apparatus is required for fighting fires in enclosed spaces?

A self-contained breathing apparatus (SCBA) (Correct answer)
A simple dust mask
An emergency escape breathing device (EEBD)
A smoke hood

Correct answer: A self-contained breathing apparatus (SCBA)

Self-contained breathing apparatus (SCBA) provides firefighters with their own air supply, enabling them to work in smoke-filled and oxygen-deficient spaces for extended periods.

Question 87: What is the purpose of a fixed fire suppression system in the engine room?

To sound the fire alarm
To flood the engine room with seawater
To automatically deliver suppression agent to control or extinguish a fire without crew entry (Correct answer)
To ventilate the engine room during a fire

Correct answer: To automatically deliver suppression agent to control or extinguish a fire without crew entry

Fixed engine room fire suppression systems (CO2 or clean agent) automatically discharge suppression agent into the protected space, controlling fires without requiring crew entry into a dangerous environment.

Question 88: Under the Inland Rules, a white light visible all around the horizon is required for which vessel?

A sailing vessel underway
A vessel under oars
A vessel less than 7 meters at anchor (Correct answer)
A power-driven vessel underway

Correct answer: A vessel less than 7 meters at anchor

Under Inland Rule 30, a vessel less than 7 meters at anchor may show an all-round white light instead of anchor lights.

Question 89: What is the primary purpose of checking weather forecasts before departure?

To satisfy insurance requirements
To plan the voyage for safety and efficiency (Correct answer)
To meet USCG documentation requirements
To log the information in the deck log

Correct answer: To plan the voyage for safety and efficiency

Reviewing weather forecasts before departure allows mariners to plan routes that avoid hazardous conditions, ensuring the safety of the vessel and crew.

Question 90: What is the primary SAR coordination agency in the U.S.?

NOAA
The FAA
The U.S. Coast Guard (Correct answer)
The U.S. Navy

Correct answer: The U.S. Coast Guard

The U.S. Coast Guard is the lead federal agency responsible for maritime SAR coordination, operating Rescue Coordination Centers (RCCs) and Rescue Sub-Centers (RSCs) throughout the country.

Question 91: 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 92: A vessel is considered to be 'not under command' when she is?

Towing another vessel
Unable to maneuver as required by the rules due to exceptional circumstances (Correct answer)
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 93: Which vessel has the right of way when a sailing vessel and a power-driven vessel are crossing?

The vessel on the starboard side
The sailing vessel (Correct answer)
The power-driven vessel
The larger vessel

Correct answer: The sailing vessel

Under COLREGS Rule 18, a power-driven vessel underway shall keep out of the way of a sailing vessel, making sailing vessels the stand-on vessel in most crossing situations.

Question 94: What is the significance of a 'yellow' hard hat color convention on many commercial vessels?

Engineer or electrician role
Visitor or new crew member unfamiliar with vessel layout (Correct answer)
Medical officer or first aid team
Cargo officer or supercargo

Correct answer: Visitor or new crew member unfamiliar with vessel layout

Yellow hard hats are commonly used to identify visitors or newly-joined crew who may be unfamiliar with the vessel, so other crew know to provide additional guidance and supervision.

Question 95: Which of the following is a leading cause of fatalities during mooring operations?

Improper use of hand signals
Forgetting to wear a hard hat
Slipping on wet decks near cleats
Being struck by a snap-back from a parted mooring line (Correct answer)

Correct answer: Being struck by a snap-back from a parted mooring line

Snap-back from parted mooring lines under high tension is consistently identified as a leading cause of fatal injuries during mooring operations.

Question 96: When must a vessel's lifesaving appliances (life jackets, immersion suits) be inspected?

Once every five years per SOLAS requirements
Whenever the vessel changes ports
Regularly by the crew as required by the vessel's SMS and prior to each voyage (Correct answer)
Only during annual USCG inspection

Correct answer: Regularly by the crew as required by the vessel's SMS and prior to each voyage

The vessel's Safety Management System (SMS) and USCG regulations require regular crew inspection of lifesaving appliances and verify they are in place and serviceable before each voyage.

Question 97: What is the correct procedure when a relief valve on a high-pressure system lifts unexpectedly?

Bypass the relief valve and continue operation
Shut down the system and investigate the cause before restarting (Correct answer)
Immediately increase system pressure to reseat the valve
Replace the relief valve at the next port stop without investigating

Correct answer: Shut down the system and investigate the cause before restarting

An unexpected relief valve lift signals an overpressure condition; the system must be shut down and the root cause identified to prevent equipment damage or injury.

Question 98: Under FCC and SOLAS regulations, which vessels are required to carry GMDSS equipment?

Ships on international voyages and certain compulsory domestic routes meeting SOLAS thresholds (Correct answer)
All recreational vessels over 16 feet in length
Only naval vessels and Coast Guard cutters
All vessels carrying more than 6 passengers for hire

Correct answer: Ships on international voyages and certain compulsory domestic routes meeting SOLAS thresholds

GMDSS requirements under SOLAS and FCC rules apply to ships on international voyages and certain domestic compulsory routes, generally cargo ships of 300 GT or more and passenger ships; recreational vessels are exempt.

Question 99: When two power-driven vessels are meeting head-on, both vessels are required to do what?

Alter course to port
Sound five short blasts and stop
Alter course to starboard (Correct answer)
Maintain course and speed

Correct answer: Alter course to starboard

Under COLREGS Rule 14, when two power-driven vessels meet head-on, each shall alter course to starboard so they pass port-to-port.

Question 100: A power-driven vessel less than 50 meters may not show which light combination?

An all-round white light instead of masthead and sternlight
Sidelights and an all-round white light
A tricolor lantern at the masthead (Correct answer)
Masthead light, sidelights, and sternlight

Correct answer: A tricolor lantern at the masthead

A tricolor lantern combining sidelights and sternlight at the masthead is permitted only for sailing vessels under COLREGS Rule 25, not for power-driven vessels.

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.

100

Questions

120 min

Time Limit

70%

To Pass

Checking for saved progress...

Exam Rules

You can skip questions and return to them later
Flag questions for review before submitting
No feedback shown until you submit the entire exam
Unanswered questions count as wrong — answer everything
10 pretest questions are mixed in and don't affect your score
Timer auto-submits when time runs out
Your progress is auto-saved every 30 seconds