Wheelhouse Prep USCG Mariner Exam Prep

Master < 500-1600 GRT Rivers, Revision & Practice Exams

Master < 500-1600 GRT Rivers. Built from official USCG NMC sample examinations (public domain).
Content last updated 12 June 2026

Revision Mode

Revise with instant feedback: the moment you pick an answer you see whether it was right, with the explanation where available. Untimed — ideal before you sit a mock exam. Questions you miss keep coming back until you know them.

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Exam Mode

Exam-day conditions: no feedback until you submit, each module scored separately so you can see your weak areas, plus an overall score against the pass mark, with a full question-by-question review at the end.

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The real exam is passed module by module: Rules of the Road requires 90%, most other modules 70%. Chart-plotting modules are taken on paper and not included.

Modules & your progress

Unlock the full question bank

The free sample is 37 questions, spread across every module in the same proportions as the real exam. The full bank contains every question from the NMC's current published sample examinations for this credential, with written explanations on the popular small-vessel credentials, one-off $29, lifetime access on up to 3 devices, all credentials included.

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Score history

The real exam: key facts

Delivered byUS Coast Guard National Maritime Center; exams are sat at Coast Guard Regional Exam Centers (RECs)
Official examMerchant Mariner Credential (MMC) endorsement examinations
QuestionsSet per credential in your Approval to Test letter; the NMC does not publish module question counts
TimeEach module is sat in a 3½-hour examination period; modules are taken in consecutive periods
Passing scoreRules of the Road 90%; Deck General and Deck Safety 70% (NMC notice, January 2018)
Exam feeSet by 46 CFR 10.219: for an original officer endorsement, evaluation $100, examination $95 (lower level) or $110 (upper level), issuance $45
Pre-licensing or eligibilityApply to the Coast Guard first; you need the NMC's Approval to Test letter before you can book. The application stays valid for 12 months
Book your examdco.uscg.mil/nmc/Examinations

Checked 11 October 2026 from the official sources below. Rules and fees change, so confirm with US Coast Guard National Maritime Center; exams are sat at Coast Guard Regional Exam Centers (RECs) before you book.

Official sources

How Wheelhouse Prep compares

Wheelhouse is a $29 question bank built from the Coast Guard's own sample exams, not an approved course. Here is how it compares with the courses and tools mariners usually consider, including where they are the better choice. See the comparison with Mariners Learning System, Sea School, MPT and others.

Frequently asked questions

What score do I need to pass the Master < 500-1600 GRT Rivers exam?

You must pass each module separately. Most modules require 70% to pass.

What modules are on the Master < 500-1600 GRT Rivers exam?

The exam covers 3 modules: Deck General, Deck Safety, Navigation General – Rivers.

How many practice questions are available for Master < 500-1600 GRT Rivers?

This page includes free sample questions drawn from the official USCG sample examinations, with a full bank of around 146 questions across all modules available with lifetime access.

Are these real USCG exam questions?

Every question comes from the U.S. Coast Guard National Maritime Center's published sample examinations, which are U.S. government works in the public domain. Wheelhouse Prep is not affiliated with or endorsed by the U.S. Coast Guard.

Do I need to create an account?

No. The free practice tests work in your browser with no signup. Your score history is saved on your own device.

When were these Master < 500-1600 GRT Rivers questions last updated?

Last updated 12 June 2026. The bank is refreshed whenever the Coast Guard publishes revised sample examinations.

Sample Master < 500-1600 GRT Rivers practice questions

A selection of free questions from the official USCG sample examinations. Use the interactive modules above for timed, scored drills.

What is the purpose of the "reference hand" on an aneroid barometer?

  1. To adjust the barometer
  2. To indicate any change in the reading of the barometer ✓
  3. To provide a correction for height above sea level
  4. To provide a correction for temperature changes

Which is the proper way to correct a mistake in the logbook?

  1. Draw several lines through the entry, rewrite, and initial the correction
  2. Erase the entry and rewrite
  3. Completely black out the entry, rewrite, and initial the correction
  4. Draw a line through the entry, rewrite, and initial the correction ✓

Which is a disadvantage of using chain lashing on heavy vehicles aboard Ro-Ro vessels?

  1. The chain does not absorb shock ✓
  2. It can wrap around cargo
  3. The chain is affected by temperature
  4. It is easily damaged
Show all 37 sample questions with answers

The vessel shown in illustration D025DG has broken down and you are going to take her in tow. The wind is on her starboard beam. She is making more leeway than you. Where should you position your vessel when you start running lines?

  1. A
  2. B
  3. C
  4. D ✓

The scuppers had been plugged as required at the time a small oil spill occurs on deck from a leaking dresser coupler. After shutting down the transfer, the engine room should first be informed and then which action should be taken?

  1. Rig a fire hose to wash down the deck
  2. Spread an absorbent material, such as sawdust ✓
  3. Remove the plugs from the scuppers
  4. Sound the general alarm

Which defines the "flammable limits" of an atmosphere?

  1. The two temperatures between which an atmosphere will self-ignite
  2. The two temperatures between which an atmosphere will burn if an ignition source is present
  3. The upper and lower percentage of vapor concentrations in an atmosphere which will burn if an ignition source is present ✓
  4. The upper and lower pressures between which an atmosphere will not burn

What power source actuates a solenoid valve?

  1. Mechanical force
  2. Electric current ✓
  3. Hydraulic pressure
  4. Air pressure

A fire starts in a switchboard due to a short circuit. This is which class of fire?

  1. Class A
  2. Class B
  3. Class C ✓
  4. Class D

What is a common unit of measure for atmospheric pressure?

  1. Cubic Feet
  2. Inches ✓
  3. Degrees
  4. Tons

How should you warm up a diesel engine that has not been run for some time?

  1. Bring it up to top speed immediately and run until warmed up.
  2. Idle for a brief period of time and then warm up at half speed. ✓
  3. Inject ether into the air intake to shorten warm up time.
  4. Run it at minimum speed until warmed to operating temperature.

Which is a feature of a special daymark?

  1. A red-and-white octagon
  2. A green square
  3. A yellow diamond ✓
  4. A daymark with a yellow stripe on it

Who is responsible for establishing watches aboard a U.S. vessel?

  1. The company that operates the vessel
  2. The Master of the vessel ✓
  3. The company that charters the vessel
  4. The owner of the vessel

What will act to dissipate fog?

  1. Advection of warm air over a colder surface
  2. Downslope motion of an air mass along a coast ✓
  3. Rain that is warmer than air
  4. Upwelling cold water

Which term is given to magnetism which is present only when the material is under the influence of an external field?

  1. Terrestrial magnetism
  2. Permanent magnetism
  3. Induced magnetism ✓
  4. Residual magnetism

In the Northern Hemisphere, when the center of a high-pressure system is due east of your position, you can expect winds from which direction?

  1. South to west
  2. North to west
  3. North to east
  4. South to east ✓

You are sailing south on the Intracoastal Waterway (ICW) when you sight a red nun buoy with a yellow square painted on it. Which statement is TRUE?

  1. The waterway in that area has shoaled and the available depth of water is less than the project depth.
  2. You should leave the buoy to port. ✓
  3. ICW traffic should not proceed beyond the buoy unless the crossing waterway is clear of all traffic.
  4. The buoy is off station and should be ignored as a navigational mark.

Your vessel is proceeding through a narrow channel. What actions can you take to avoid any sudden sheers of the vessel?

  1. Reduce speed and stay to the outer limits of the channel
  2. Put your offshore anchor well in the water
  3. Reduce speed and stay in the deepest part of the channel ✓
  4. Increase speed and stay to the outer limits of the channel

The datum from which the predicted heights of tides are reckoned in the tide tables is __________.

  1. given in table three of the tide tables
  2. the highest possible level
  3. the same as that used for the charts of the locality ✓
  4. mean low water

Buoys are marked with reflective material to assist in their detection by searchlight. Which statement is TRUE?

  1. All reflective material is white because it is the most visible at night.
  2. A special-purpose mark will display either red or green reflective material to agree with its shape.
  3. A safe-water buoy will display red and white vertical stripes of reflective material.
  4. A preferred-channel buoy displays either red or green reflective material to agree with the top band of color. ✓

Which of the signals listed is required to be displayed during the day while bunkering?

  1. A yellow flag
  2. A red light
  3. A red and yellow flag
  4. A red flag ✓

As a rule, ships of most configurations, when drifting in calm water with negligible current, will lie in which orientation?

  1. The stern will be to the wind
  2. The bow will be to the wind
  3. With the wind on the quarter
  4. The beam will be to the wind ✓

Fires are grouped into what categories?

  1. Class A, B, C, and D ✓
  2. Type 1, 2, 3, and 4
  3. Combustible solids, liquids, and gases
  4. Flammable solids, liquids, and gases

What is the length of a nautical mile?

  1. 6,076 feet ✓
  2. 5,280 feet
  3. 1,800 meters
  4. 2,000 yards

What enables you to estimate the bearing of a storm's center?

  1. Buys Ballot's Law ✓
  2. The left-hand rule
  3. Pascal's Law
  4. An educated guess

On an Army Corps of Engineers navigation map, how is each mile A.H.P. on the Lower Mississippi River marked?

  1. A dashed red line
  2. A black dot ✓
  3. A navigation light
  4. A number showing mileage only

The primary function of which line(s) is to hold the vessel snuggly to the dock?

  1. The stern lines
  2. The bow cross spring lines
  3. The quarter cross spring lines
  4. The breast lines ✓

What is the minimum required protective clothing that must be worn while sampling hazardous cargo on a tankship?

  1. chemical resistant gloves
  2. boots
  3. a face mask or goggles ✓
  4. a hood or hard hat

The signal man assisting the crane operator has his forearm vertical, forefinger pointing up, and moves his hand in a small horizontal circle. This is the signal to __________.

  1. swing
  2. lower
  3. hoist ✓
  4. extend

An IOPP Certificate on an inspected vessel is valid for what period of time?

  1. 6 months
  2. 12 months
  3. 18 months
  4. 5 years ✓

Which international body is responsible for drafting the MARPOL convention prohibiting marine pollution?

  1. International Association of Shipping
  2. International Maritime Organization ✓
  3. Maritime Advisory Council
  4. Association of Seafaring Nations

How long shall the Oil Record Book be maintained on a vessel engaged in coastwise trade?

  1. 12 months
  2. 24 months
  3. 36 months ✓
  4. 48 months

You have abandoned ship in rough weather. After picking up other survivors in your liferaft, what should you do next?

  1. Prepare for the arrival of rescue units.
  2. Decide on food and water rations.
  3. Top up the buoyancy tubes.
  4. Deploy the sea anchor ✓

Which term is used to describe the projecting lugs of the rudderpost which furnish support to the rudder?

  1. Bases
  2. Gudgeons ✓
  3. Rudder lugs
  4. Pintles

Assuming an even transverse distribution of weight in a vessel, which condition could cause a list?

  1. Having KG smaller than KM
  2. Empty double bottoms and lower holds, and a heavy deck cargo ✓
  3. Having a small positive righting arm
  4. Flooding the forepeak to correct the vessel's trim

How do you determine the weight of the vessel that is supported by the ground when a vessel has run aground?

  1. Determine the point where aground and the draft at that point, then calculate it using the grounding formula.
  2. Use the inclining experiment formula and substitute the change of trim for the angle of list.
  3. This requires extensive calculation and is usually performed only by a naval architect not by a ship's officer.
  4. Use the hydrostatic tables and enter with the mean draft before grounding and the mean draft after grounding. ✓

On a passenger vessel, the vessel's name must appear on which item(s)?

  1. Lifeboats
  2. Lifeboat oars
  3. Ring life buoy
  4. All of the above ✓

Which is TRUE concerning a certified lifeboat operator assigned to command a lifeboat?

  1. Must have a list of the persons assigned to the lifeboat ✓
  2. Must drain the hydraulic pressure before lowering the craft
  3. They should be the first individual to board the craft
  4. Must be the brakeperson actually lowering the boat