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BD Deck Officer Class 3 (OOW) study materials
BD Deck Officer Class 3 (OOW) study resources

BD Deck Officer Class 3 (OOW) practice questions

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Question 1Navigation

On a Mercator chart, what does a rhumb line appear as?

  1. A straight line only on the equator
  2. A straight line crossing all meridians at the same angle Correct answer.
  3. A great circle concave to the equator
  4. A curved line spiralling toward the pole

Explanation

The Mercator projection is constructed so that every rhumb line plots as a straight line cutting each meridian at a constant angle. This property makes it ideal for marine navigation because a steady course can be drawn and steered without constant alteration. Great circles, by contrast, plot as curves except on the equator or a meridian.

Question 2Navigation

A vessel steams 090°T for 60 nautical miles. What is the change of longitude at latitude 60°N?

  1. 1°
  2. 30'
  3. 4°
  4. 2° Correct answer.

Explanation

Departure equals change of longitude multiplied by the cosine of the latitude, so change of longitude equals departure divided by cos latitude. Here departure is 60 miles and cos 60° is 0.5, giving 120 minutes of longitude, which is 2°. On an easterly or westerly course the distance run equals departure.

Question 3Navigation

What is the standard definition of a great circle?

  1. A circle on the Earth's surface whose plane passes through the Earth's centre Correct answer.
  2. Any circle drawn on a sphere parallel to the equator
  3. A circle whose plane is perpendicular to the polar axis
  4. The shortest curve joining two points on a chart

Explanation

A great circle is formed where a plane through the centre of the sphere cuts its surface, dividing the sphere into two equal halves. The equator and all meridians are great circles. The shortest distance between two surface points always lies along a great circle arc.

Question 4Navigation

What is the purpose of a gyrocompass repeater in a steering system?

  1. To provide a stable heading reference to the autopilot and steering stand Correct answer.
  2. To measure speed through the water
  3. To compare magnetic and true heading automatically
  4. To supply rate of turn information

Explanation

Repeaters receive heading signals from the master gyrocompass and display them at the steering position, bridge wings and other stations. They let the helmsman and autopilot steer a true heading without relying on the magnetic compass. A repeater is a display device and does not itself sense motion.

Question 5Navigation

The gyro error is 2° East. A bearing taken by gyrocompass reads 145°. What is the true bearing?

  1. 143°
  2. 147° Correct answer.
  3. 145°
  4. 149°

Explanation

When the compass is easterly, the compass reading is smaller than the true bearing, so easterly error is added to convert compass to true. Adding 2° to 145° gives a true bearing of 147°. The mnemonic is compass least, true best, for easterly error.

Question 6Navigation

What does the term variation describe?

  1. The annual change in the position of the magnetic pole
  2. The change in compass error as the ship alters course
  3. The deviation caused by the ship's own magnetism
  4. The angle between the magnetic and true meridians at a place Correct answer.

Explanation

Variation is the angular difference between true north and magnetic north at a given position, caused by the Earth's magnetic field. It is taken from the chart's compass rose and corrected for annual change. Deviation, in contrast, arises from the vessel's own magnetic field.

Question 7Navigation

On a chart, what does a magenta overprint generally indicate?

  1. Traffic separation scheme boundaries only
  2. Depths in fathoms
  3. Information relating to radio aids to navigation Correct answer.
  4. Areas of restricted anchoring

Explanation

Magenta is used on nautical charts for overprinted information such as radio reporting lines, limits of magnetic variation, and certain cautionary notes. It distinguishes this data from the black and blue used for charted features and depths. The colour convention follows international chart specifications.

Question 8Navigation

What is the meaning of a charted depth of 12.4 metres in a drying area?

  1. The depth is 12.4 m below the level of mean high water springs
  2. The depth is 12.4 m below the seabed
  3. The depth is 12.4 m below the keel of the vessel
  4. The depth is 12.4 m below chart datum at all times Correct answer.

Explanation

Depths on a nautical chart are measured from chart datum, which is normally the level of lowest astronomical tide. A charted depth of 12.4 m therefore means the least depth expected is 12.4 m below datum. Actual depth is obtained by adding the height of tide above datum.

Question 9Navigation

A tidal height of 2.0 m above chart datum is predicted, and the charted depth is 8.5 m. What is the total depth of water?

  1. 10.5 m Correct answer.
  2. 8.5 m
  3. 4.25 m
  4. 6.5 m

Explanation

The actual depth of water is the charted depth plus the height of tide above chart datum. Adding 8.5 m and 2.0 m gives 10.5 m. This total is then compared with the vessel's draught to determine under-keel clearance.

Question 10Navigation

What is the significance of a charted symbol showing a rock with a depth of 0.9 m in a general depth of 20 m?

  1. It is a drying rock that uncovers at low water
  2. It is a safe anchorage mark
  3. It is an isolated danger that must be avoided Correct answer.
  4. It is a sounding taken at low water springs

Explanation

A sounding much shallower than the surrounding depths indicates an isolated danger to navigation. It is usually marked with a danger symbol and may carry a note or a buoy. The prudent navigator treats it as an obstruction to be given a wide berth.

Question 11Navigation

In the IALA Maritime Buoyage System Region A, what does a port-hand mark look like when entering a harbour?

  1. Yellow spherical buoy
  2. Black and red horizontally striped buoy
  3. Red can-shaped buoy Correct answer.
  4. Green conical buoy

Explanation

In Region A, port-hand marks are red and can-shaped, and are kept to the port side when entering a harbour. Starboard-hand marks are green and conical. The shape and colour together allow identification by day or night.

Question 12Navigation

What is the purpose of a safe water mark?

  1. To mark a designated anchoring area
  2. To indicate navigable water all around the mark Correct answer.
  3. To warn of a newly discovered wreck
  4. To mark the edge of a dredged channel

Explanation

A safe water mark shows that there is navigable water all around it and is often used to mark the centre of a channel or the landfall position. It is painted with red and white vertical stripes and is spherical or has a red sphere topmark. It does not indicate a preferred side.

Question 13Navigation

Under the COLREGs, which vessel is the stand-on vessel in a crossing situation between two power-driven vessels?

  1. The vessel to the north of the other
  2. The vessel that has the other on her own starboard side Correct answer.
  3. The faster vessel
  4. The vessel with the wind on her port side

Explanation

In a crossing situation between two power-driven vessels, the vessel that has the other on her own starboard side must keep out of the way and is the give-way vessel. The other vessel is the stand-on vessel and must maintain course and speed. The stand-on vessel must still take action if a collision cannot be avoided by the give-way vessel alone.

Question 14Navigation

What does a vessel displaying two black cones point to point in a vertical line indicate?

  1. A vessel at anchor
  2. A vessel engaged in fishing
  3. A vessel not under command
  4. A vessel constrained by her draught Correct answer.

Explanation

Two cones point to point displayed vertically are the daytime signal for a vessel constrained by her draught. Such a vessel should be given plenty of room because her ability to manoeuvre is limited by the depth of water. At night the same vessel shows three all-round red lights in a vertical line.

Question 15Navigation

A power-driven vessel underway at night shows which lights?

  1. Two all-round red lights and a sternlight
  2. Three all-round red lights in a vertical line
  3. Sidelights and an all-round white light only
  4. Masthead light, sidelights and sternlight Correct answer.

Explanation

A power-driven vessel of less than 50 m shows one masthead light forward, sidelights and a sternlight. Larger vessels show a second masthead light abaft and higher. The sidelights indicate red to port and green to starboard, and the sternlight shows white over the required arc.

Question 16Navigation

What is the meaning of a relative bearing of 045° on the starboard bow?

  1. The object is directly ahead
  2. The object is 45° abaft the starboard beam
  3. The object bears 45° to the right of the vessel's heading Correct answer.
  4. The object bears 045° true from the vessel

Explanation

A relative bearing is measured clockwise from the vessel's heading line to the object, so 045° on the starboard bow means the object lies 45° to the right of the heading. To convert to a true bearing, add the relative bearing to the true heading, subtracting 360° if necessary. Relative bearings are useful for assessing risk of collision by eye.

Question 17Navigation

A vessel's true heading is 300° and an object bears 060° relative. What is the true bearing of the object?

  1. 360°
  2. 000° Correct answer.
  3. 240°
  4. 120°

Explanation

True bearing equals true heading plus relative bearing. Adding 300° and 060° gives 360°, which is written as 000°. When the sum exceeds 360°, subtract 360° to keep the result within the compass.

Question 18Navigation

What is the main advantage of a great circle route over a rhumb line route?

  1. It avoids all areas of ice
  2. It gives the shortest distance between two points on the globe Correct answer.
  3. It keeps a constant course for the whole passage
  4. It can be plotted as a straight line on a Mercator chart

Explanation

A great circle arc is the shortest path over the Earth's surface between two points, saving distance on long ocean passages. It requires continuous alteration of course, which is one reason it is often approximated by a series of rhumb line chords. Rhumb lines are easier to steer but longer.

Question 19Navigation

What is the primary purpose of the echo sounder in navigation?

  1. To determine the vessel's position by satellite
  2. To measure the depth of water beneath the keel Correct answer.
  3. To measure the vessel's speed through the water
  4. To detect other vessels in fog

Explanation

An echo sounder transmits an acoustic pulse downward and times its return from the seabed to compute depth. The result is displayed as depth below the transducer or keel, depending on the setting. It is a key aid for safe navigation in shallow water and for verifying charted depths.

Question 20Navigation

What is the function of the automatic identification system (AIS) in collision avoidance?

  1. It provides an independent position fix without external signals
  2. It exchanges vessel identity, position and course data between equipped vessels Correct answer.
  3. It automatically alters the vessel's course to avoid traffic
  4. It replaces radar for detecting small craft

Explanation

AIS broadcasts and receives dynamic and static data such as identity, position, course over ground and heading between suitably equipped stations. It supplements radar and visual lookout but does not replace them. The information depends on the accuracy of each vessel's own sensors.

Question 21Navigation

On a radar display, what does a target with a constant bearing and decreasing range indicate?

  1. The target is stationary
  2. A risk of collision exists Correct answer.
  3. The target is overtaking the vessel from astern
  4. The target is moving away

Explanation

If the bearing of an approaching target remains steady while the range decreases, the two vessels are on a collision course. This is the classic radar method of assessing risk of collision. The bearing should be monitored over a period to confirm the trend.

Question 22Navigation

What is the purpose of parallel indexing on radar?

  1. To identify rain clutter on the display
  2. To monitor the vessel's track relative to a fixed charted feature Correct answer.
  3. To calibrate the radar range scale
  4. To measure the target's true course and speed

Explanation

Parallel indexing uses a line drawn on the radar display parallel to a charted feature, such as a breakwater, to give continuous indication of the vessel's cross-track position. It allows the navigator to confirm that the vessel is holding the planned track. It is a position-monitoring technique rather than a target-tracking one.

Question 23Navigation

A vessel's position is fixed by bearings of two objects 30° apart. What is the main weakness of this fix?

  1. The position is poorly defined because the angle of cut is small Correct answer.
  2. The position is unreliable because the objects are too close together
  3. The fix is invalid unless three bearings are taken
  4. The fix cannot be plotted without a distance measurement

Explanation

The accuracy of a position fix depends on the angle at which the position lines intersect. A small angle of cut, such as 30°, produces a long, narrow cocked hat and a large positional uncertainty. Angles closer to 90° give the most reliable fix.

Question 24Navigation

What is the effect of current on a vessel's course made good compared with her course steered?

  1. The vessel's speed through the water increases
  2. The vessel is set in the direction of the current, so the track differs from the heading Correct answer.
  3. The vessel's heading automatically follows the current
  4. The vessel's compass error changes with the current

Explanation

A current sets the vessel in its direction while the vessel continues to move through the water along her heading. The resulting course made good is the vector sum of the vessel's own motion and the current. The navigator allows for this by applying a course to steer correction.

Question 25Navigation

What is the purpose of the vessel's deviation card?

  1. To record the deviation on various headings so it can be applied to compass readings Correct answer.
  2. To record the variation at the vessel's home port
  3. To list the vessel's draught and trim
  4. To show the gyrocompass error over time

Explanation

A deviation card is produced by swinging the ship and records the deviation found on each compass heading. It allows the watchkeeper to convert between compass and magnetic headings. Deviation changes with the ship's heading and with the vessel's magnetic condition.

Question 26Navigation

On a Mercator chart, what happens to the spacing between successive parallels of latitude as latitude increases?

  1. It remains constant at all latitudes
  2. It decreases progressively towards the poles
  3. It increases only between the tropics
  4. It increases progressively towards the poles Correct answer.

Explanation

The Mercator projection stretches the meridians apart by the same factor as the parallels, so the scale expands with latitude. To keep the rhumb line straight, the latitude graduations must be spaced progressively wider towards the poles. This is why a single latitude scale cannot be used across a long north-south passage.

Question 27Navigation

A vessel steams 090° true at 12 knots through water that has a current setting 180° at 3 knots. What is the vessel's speed made good?

  1. About 12.4 knots
  2. About 11.6 knots Correct answer.
  3. About 15.0 knots
  4. About 9.0 knots

Explanation

The current opposes the vessel's course, so the two vectors act along the same line in opposite directions. Speed made good is found by vector addition: 12 knots minus 3 knots gives 9 knots along the course, but the resulting ground track is not exactly 090° because the current is exactly astern, so the along-track component is 9 knots. Rechecking with the full vector triangle, the ground speed along 090° is 9 knots; where the current is not exactly astern the resultant is shorter than the arithmetic sum, giving about 11.6 knots only when the current is at right angles.

Question 28Navigation

What is the defining characteristic of a rhumb line on a Mercator chart?

  1. It plots as a curve concave to the equator
  2. It is always the shortest distance between two points
  3. It coincides with a great circle at all latitudes
  4. It plots as a straight line cutting all meridians at the same angle Correct answer.

Explanation

A rhumb line, or loxodrome, maintains a constant true course, so it crosses every meridian at the same angle. On a Mercator chart that constant angle plots as a straight line, which makes the projection convenient for plotting courses. The price is that the rhumb line is longer than the great circle except on the equator or a meridian.

Question 29Navigation

A vessel's compass heading is 045° and the deviation for that heading is 4° east. What is the magnetic heading?

  1. 041°
  2. 049° Correct answer.
  3. 045°
  4. 053°

Explanation

Deviation east means the compass needle is pulled east of magnetic north, so the compass reads less than the magnetic direction. To convert from compass to magnetic, apply easterly deviation by adding it: 045° plus 4° gives 049°. The mnemonic is compass to magnetic, add easterly.

Question 30Navigation

A vessel's log reads 12.0 nautical miles at 0800 and 46.0 nautical miles at 1600. What is the average speed through the water?

  1. 5.67 knots
  2. 4.25 knots Correct answer.
  3. 4.00 knots
  4. 6.80 knots

Explanation

Distance run is 46.0 minus 12.0, which is 34.0 nautical miles. The elapsed time is eight hours. Dividing 34.0 by 8 gives 4.25 knots, the average speed through the water over that period.

Question 31Navigation

An echo sounder is set with a speed of sound of 1500 m/s, but the actual speed of sound in the water is 1530 m/s. What is the effect on the displayed depth?

  1. The displayed depth is unaffected by sound speed
  2. The displayed depth is less than the true depth Correct answer.
  3. The displayed depth is greater than the true depth
  4. The displayed depth fluctuates randomly

Explanation

The sounder converts elapsed time to depth using its assumed speed, so it underestimates the distance travelled when the real speed is higher. The true depth is therefore greater than the displayed depth. The error is about two per cent, which matters in shallow water or critical pilotage.

Question 32Navigation

A vessel's true course is 000° and the wind is from 270° true. On which side is the vessel experiencing a following wind?

  1. Directly astern
  2. Starboard side
  3. Directly ahead
  4. Port side Correct answer.

Explanation

Wind direction is named by the direction it comes from, so a wind from 270° true blows towards 090° true. With the vessel steering 000°, that wind arrives over the port side and is a beam wind from port. It is not a following wind, which would come from ahead of the beam on the same side as the course.

Question 33Navigation

What does a charted tidal diamond indicate?

  1. The time of high water at a secondary port
  2. The height of tide above chart datum at a standard port
  3. The predicted tidal stream direction and rate for a specific position Correct answer.
  4. The location of a tidal stream measuring station only

Explanation

A tidal diamond is printed on the chart at a specific position and carries a table of the tidal stream set and rate for each hour of the tidal cycle. The rates are referenced to the tidal cycle at a designated standard port. It does not give tide heights, which come from tide tables and the charted tidal levels.

Question 34Navigation

A vessel is steering 090° true at 10 knots and a current sets 180° at 4 knots. What is the course and speed made good?

  1. About 068° at 10.8 knots Correct answer.
  2. About 090° at 14.0 knots
  3. About 112° at 10.8 knots
  4. About 090° at 6.0 knots

Explanation

The current acts at right angles to the course and pushes the vessel southwards while she makes easting. The resultant ground vector has components of 10 knots east and 4 knots south, giving a speed of about 10.8 knots and a track of about 068° true. The course made good is therefore set to the south of the course steered.

Question 35Navigation

What is the purpose of a transit bearing taken during a pilotage approach?

  1. To check the compass deviation only
  2. To measure the vessel's speed over the ground
  3. To determine the tidal stream rate
  4. To confirm the vessel is on the intended leading line Correct answer.

Explanation

A transit uses two charted objects that align along the intended track, such as leading marks into a harbour. When the two objects appear in line, the vessel is on the leading line. Any lateral displacement shows immediately as the objects opening out, allowing a prompt correction.

Question 36Navigation

Two position lines cross at a very acute angle. What is the effect on the resulting fix?

  1. The fix becomes a running fix automatically
  2. The fix is unaffected by the angle of intersection
  3. The fix becomes unreliable because the position lines are nearly parallel Correct answer.
  4. The fix becomes more accurate because the lines intersect

Explanation

The position is most reliable when the position lines cross at close to a right angle. At an acute angle the lines are nearly parallel, so a small error in either bearing shifts the intersection a long way. The fix should be treated with caution and, if possible, another object should be chosen to give a better cut.

Question 37Meteorology

In the Beaufort wind scale, which description corresponds to a fresh breeze (force 5)?

  1. Sea heaps up, white foam from breaking waves blown in streaks
  2. Small wavelets, crests of glassy appearance, no breaking waves
  3. Moderate waves of greater length, many whitecaps, some spray
  4. Large wavelets, crests begin to break, scattered whitecaps Correct answer.

Explanation

Force 5 on the Beaufort scale is defined by a wind speed of roughly 17 to 21 knots, producing large wavelets with crests beginning to break and scattered whitecaps appearing. This is the first stage at which visible whitecaps become frequent enough to be a reliable indicator. The description is used at sea to estimate wind strength when instruments are unavailable.

Question 38Meteorology

What is the standard sea-level pressure value used as the reference in meteorological pressure readings?

  1. 1025 hPa
  2. 1000 hPa
  3. 0980 hPa
  4. 1013.25 hPa Correct answer.

Explanation

Standard atmosphere sea-level pressure is defined as 1013.25 hectopascals, equivalent to 29.92 inches of mercury. This reference allows pressures measured at different elevations to be compared after reduction to sea level. Forecasters use it as the datum against which highs and lows are described.

Question 39Meteorology

In the Northern Hemisphere, air flowing outward from a high-pressure centre at the surface spirals in which direction?

  1. Anticlockwise and inward
  2. Anticlockwise and outward
  3. Clockwise and inward
  4. Clockwise and outward Correct answer.

Explanation

Surface friction causes air to cross the isobars toward lower pressure, so air diverges from a Northern Hemisphere anticyclone in a clockwise direction. The Coriolis force deflects the flow to the right of the pressure gradient. The combination of outward flow and rightward deflection produces the characteristic clockwise spiral.

Question 40Meteorology

A vessel reports a wind described as veering. What change has occurred?

  1. The wind has dropped to calm
  2. The wind has shifted anticlockwise in direction
  3. The wind speed has increased sharply
  4. The wind has shifted clockwise in direction Correct answer.

Explanation

Veering means the wind direction changes in a clockwise sense, for example from southwest to west to northwest. This is the typical pattern in the Northern Hemisphere after a cold front passes. Backing is the opposite, anticlockwise change.

Question 41Meteorology

A vessel is in the Northern Hemisphere and the wind is steady from the northeast. Where does the low-pressure centre lie relative to the vessel?

  1. To the north-west of the vessel
  2. To the north-east of the vessel
  3. To the south-east of the vessel Correct answer.
  4. To the south-west of the vessel

Explanation

Buys Ballot's law states that in the Northern Hemisphere, with your back to the wind, low pressure lies to your left and slightly ahead. Facing into a north-east wind, the left-hand side is the south-east. The centre of the depression therefore bears roughly south-east of the observer.

Question 42Meteorology

What is the main reason that advection fog forms over the sea?

  1. Air is forced to rise over a mountain range and expands and cools
  2. Cold air moves over a warmer sea surface and picks up additional moisture
  3. Strong daytime heating causes turbulent mixing of a deep surface layer
  4. Warm moist air moves over a colder sea surface and is cooled to its dew point Correct answer.

Explanation

Advection fog requires warm, humid air to be transported over a colder surface, which cools the air below its dew point and produces condensation. Over the sea this commonly happens when tropical air moves over cooler water at higher latitudes. The cooling is by contact with the cold surface, not by lifting or by heating.

Question 43Meteorology

In a tropical revolving storm in the Northern Hemisphere, which statement correctly describes the wind and sea state in the dangerous semicircle?

  1. Winds blow against the storm's track and are generally lighter than in the navigable semicircle
  2. Winds are light and variable because the storm's centre is close by
  3. Winds blow in the same direction as the storm's track and the sea is relatively moderate
  4. Winds are stronger and the sea is heavier because the wind opposes the storm's motion Correct answer.

Explanation

The dangerous semicircle lies to the right of the track in the Northern Hemisphere, where the circulating wind is reinforced by the forward motion of the storm. The result is stronger winds, higher seas and a greater risk of being drawn toward the centre. In the navigable semicircle the wind opposes the track and tends to carry a vessel away from the centre.

Question 44Meteorology

A marine barometer on a vessel shows a steady fall of about 1 hPa per hour over several hours. What does this most likely indicate?

  1. A rapid improvement with clearing skies
  2. An approaching depression with deteriorating weather Correct answer.
  3. No significant change in the weather pattern
  4. A settled period of fine weather ahead

Explanation

A steady, sustained fall in pressure indicates that a low-pressure system is approaching and that wind and sea conditions are likely to deteriorate. The rate of fall is often a useful guide to how quickly the system is closing in. A very rapid fall, often called a pressure bomb, warns of severe weather.

Question 45Meteorology

Which cloud type is most characteristic of a warm front approaching a vessel?

  1. Fair-weather cumulus with flat bases
  2. Cirrus thickening to altostratus and then nimbostratus Correct answer.
  3. Cumulonimbus with heavy showers
  4. Isolated stratocumulus with no precipitation

Explanation

A warm front has a gently sloping surface, so its approach is marked by a predictable sequence of cloud. High cirrus appears first and thickens through cirrostratus and altostratus to nimbostratus, bringing continuous steady rain. This gradual progression gives useful warning of the front's arrival.

Question 46Meteorology

Using the geostrophic wind relationship, if the pressure gradient force at a given latitude doubles while all else is unchanged, what happens to the geostrophic wind speed?

  1. It stays the same
  2. It increases by a factor of four
  3. It is halved
  4. It doubles Correct answer.

Explanation

In geostrophic balance the Coriolis force exactly opposes the pressure gradient force, so wind speed is directly proportional to the pressure gradient at a fixed latitude. Doubling the gradient therefore doubles the geostrophic wind speed. The relationship is linear, not squared.

Question 47Meteorology

A vessel at 20 degrees North is experiencing a wind of 20 knots. Using the surface wind relationship, what is the approximate geostrophic wind speed aloft over the same location?

  1. About 30 knots Correct answer.
  2. About 10 knots
  3. About 20 knots
  4. About 60 knots

Explanation

Over the open sea, surface friction reduces wind speed to roughly two-thirds of the geostrophic value and backs the direction by about 10 to 20 degrees. If the surface wind is 20 knots, the geostrophic wind is approximately 30 knots. This rule of thumb helps estimate the gradient wind from observed surface conditions.

Question 48Meteorology

A vessel is in the Southern Hemisphere with a low-pressure centre to the east. In which general direction should the strongest winds be expected?

  1. From the north
  2. From the south Correct answer.
  3. From the west
  4. From the east

Explanation

In the Southern Hemisphere, surface flow around a low is clockwise, so with the centre to the east the wind blows from the south. The dangerous semicircle lies to the left of the track, where the wind is reinforced by the storm's motion. The strongest winds therefore come from the southern quadrant in this configuration.

Question 49Ship Construction and Stability

Which term describes the upward force exerted by water on a floating vessel, equal to the weight of water displaced?

  1. Tonnage
  2. Deadweight
  3. Buoyancy Correct answer.
  4. Reserve displacement

Explanation

Buoyancy is the upward force produced by the displaced water, and for a floating body at rest it equals the weight of the water displaced, which in turn equals the weight of the vessel. This relationship is Archimedes' principle and underpins all flotation calculations.

Question 50Ship Construction and Stability

A vessel has a displacement of 8000 t and a lightweight of 3000 t. What is its deadweight?

  1. 5000 t Correct answer.
  2. 3000 t
  3. 8000 t
  4. 11000 t

Explanation

Deadweight is found by subtracting lightweight from displacement: 8000 minus 3000 equals 5000 t. Deadweight represents the total mass of cargo, bunkers, fresh water, ballast and stores that the ship can carry when loaded to her permitted draught.