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Chief Mate CoC practice questions

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Question 1Navigation and Passage Planning

When planning a great-circle passage between two ports in the same hemisphere, which statement best describes the track on a Mercator chart?

  1. It plots as a rhumb line only if the difference of longitude is under 90 degrees
  2. It plots as a curve concave to the pole of that hemisphere
  3. It plots as a straight line joining the two positions
  4. It plots as a curve convex to the pole of that hemisphere Correct answer.

Explanation

A great circle on a Mercator chart appears as a curve whose vertex lies nearer the pole, so it bulges toward the pole in the higher latitude of the same hemisphere. Only a rhumb line plots as a straight line on a Mercator chart. The curvature reflects the changing course along the great-circle track.

Question 2Navigation and Passage Planning

On a passage where the vessel will cross the International Date Line eastbound, how is the date adjusted?

  1. Keep the same date but change zone description only
  2. Lose one day, so the date goes back by one Correct answer.
  3. Gain one day only if crossing at high latitude
  4. Gain one day, so the date advances by one

Explanation

Crossing the Date Line in an easterly direction means moving from western longitudes into western hemisphere longitudes, so the same instant is one calendar day earlier. The navigator therefore repeats a day, effectively losing one day. Westbound crossings gain a day.

Question 3Navigation and Passage Planning

A vessel's gyrocompass has a known constant error of 3 degrees East. A bearing taken of a lighthouse reads 045 degrees (gyro). What is the true bearing?

  1. 045 degrees
  2. 318 degrees
  3. 042 degrees
  4. 048 degrees Correct answer.

Explanation

With easterly compass error, the compass bearing is less than the true bearing, so true equals gyro plus east error. Adding 3 degrees to 045 gives 048 degrees true. The memory aid is Compass least, True best for easterly error.

Question 4Navigation and Passage Planning

Which publication provides the standard list of traffic separation schemes adopted by IMO, including their geographic coordinates?

  1. Ships' Routeing Correct answer.
  2. Guide to Port Entry
  3. Sailing Directions (Pilot)
  4. Notices to Mariners annual summary

Explanation

Ships' Routeing is the IMO publication that consolidates adopted traffic separation schemes and other routeing measures with their descriptions and charts. Sailing Directions give coastal pilotage information but are not the authoritative routeing list. Notices to Mariners promulgate changes as they occur.

Question 5Navigation and Passage Planning

In passage planning under the IMO guidelines, which stage immediately follows appraisal of all information gathered?

  1. Execution of the plan
  2. Detailed planning of the whole voyage Correct answer.
  3. Berth-to-berth contingency review
  4. Monitoring the passage

Explanation

The four stages are appraisal, detailed planning, execution and monitoring. Once information has been appraised, the plan itself is constructed in detail, including no-go areas, courses, and contingency anchors. Execution and monitoring follow only after the plan is complete.

Question 6Navigation and Passage Planning

A chart is corrected to Notice to Mariners 48 of 2023. The weekly edition currently issued is 12 of 2024. Which corrections must be applied?

  1. Only notices for the current year
  2. Only notice 12 of 2024
  3. All notices from 49 of 2023 up to and including 12 of 2024 Correct answer.
  4. All notices from 1 of 2024 up to 12 of 2024 only

Explanation

Chart correction is cumulative, so every notice after the last one applied must be worked up to the current weekly edition. Notices 49 of 2023 through 12 of 2024 therefore apply. Skipping any intervening notice leaves the chart uncorrected.

Question 7Navigation and Passage Planning

What is the primary purpose of a load line zone chart when planning an ocean passage?

  1. To indicate where pilotage is compulsory
  2. To show the boundaries of national search and rescue regions
  3. To determine the maximum permissible draught for each leg of the voyage
  4. To identify seasonal tropical and winter zones for ballast and cargo planning Correct answer.

Explanation

Load line zones define seasonal geographical limits that determine the permitted freeboard and hence draught as the vessel moves between zones. Planners must anticipate zone changes so that loading and ballast are adjusted before entry. The zones are unrelated to SAR boundaries or pilotage.

Question 8Navigation and Passage Planning

Which chart datum feature means soundings are reduced to a level that is exceeded by the tide for only a small percentage of time?

  1. Mean high water springs
  2. Mean sea level
  3. Chart datum as lowest astronomical tide Correct answer.
  4. Highest astronomical tide

Explanation

Chart datum is generally set at or near lowest astronomical tide so that charted soundings are conservative and the actual depth is almost always greater. This ensures a safety margin for the navigator. Mean sea level and high water levels would make soundings dangerously optimistic.

Question 9Navigation and Passage Planning

A vessel steering 090 degrees true at 15 knots experiences a current setting 180 degrees at 3 knots. What is the approximate course made good?

  1. 063 degrees
  2. 078 degrees
  3. 090 degrees
  4. 102 degrees Correct answer.

Explanation

The current sets due south, so the ground track is deflected to the south of the heading, that is toward larger bearings. The drift angle is arctan(3/15), about 11 degrees, giving a course made good near 101 to 102 degrees. Speed made good is slightly less than 15 knots.

Question 10Navigation and Passage Planning

During planning, a vessel must pass a headland where a strong tidal stream runs. Which technique best reduces the risk of being set onto a lee shore?

  1. Rely on the autopilot to maintain a constant heading past the point
  2. Time the passage to arrive at slack water or with the stream in the favourable direction Correct answer.
  3. Pass as close as possible to the headland to shorten the exposure
  4. Increase speed to the maximum available and hold the planned track

Explanation

Tidal streams off headlands can reach several knots and produce eddies and overfalls, so timing the passage near slack water or with a favourable stream minimises set. Keeping a safe offing and monitoring position by cross bearings or GPS also helps. Holding a constant heading is unsafe because the vessel will be set off track.

Question 11Navigation and Passage Planning

A great-circle track between two positions in the northern hemisphere reaches its vertex at a higher latitude than either endpoint. Which statement about the initial course is correct?

  1. The initial course is farther from the pole than the final course
  2. The initial course equals the final course
  3. The initial and final courses are always 090 and 270 degrees
  4. The initial course is closer to the pole than the final course Correct answer.

Explanation

For a great circle whose vertex lies between the endpoints, the track starts by running more directly toward the pole and gradually turns away. Thus the initial course has a greater northerly component than the final course in the northern hemisphere. The two courses are equal only when the vertex coincides with an endpoint.

Question 12Navigation and Passage Planning

What is the purpose of a parallel index line when planning a coastal passage?

  1. To measure the vessel's speed over the ground by radar
  2. To define the boundary of a traffic separation scheme
  3. To calculate the compass deviation on each heading
  4. To provide a constant range and bearing reference for monitoring track keeping Correct answer.

Explanation

A parallel index line is a radar technique in which a line parallel to the ground track is set at a chosen range from a prominent target, allowing the officer to confirm the vessel remains on track. Any drift shows as a change in the index distance. It is a monitoring aid, not a speed or deviation calculator.

Question 13Navigation and Passage Planning

A vessel plans to transit a narrow strait where the chart shows a least depth of 12 metres in the fairway. The vessel's draught is 11 metres and the charted sounding is referred to chart datum. Under keel clearance policy requires 10 per cent of draught. Which conclusion is correct?

  1. The transit is acceptable in all tide states because the charted depth exceeds the draught
  2. The transit is acceptable only if the predicted height of tide provides the required clearance Correct answer.
  3. The transit is never acceptable in a narrow strait
  4. The transit is acceptable if speed is reduced to minimum steerage way

Explanation

The required clearance is 1.1 metres, so the total depth needed is 12.1 metres while the charted depth is only 12 metres at chart datum. The shortfall must be met by height of tide, squat allowance and any chart accuracy allowance. Speed reduction alone does not create water depth.

Question 14Navigation and Passage Planning

Which statement correctly describes the effect of squat on a vessel in shallow water?

  1. Squat is independent of water depth and depends only on trim
  2. Squat increases with speed and is greater for a vessel with a large block coefficient Correct answer.
  3. Squat raises the vessel bodily and increases under keel clearance
  4. Squat decreases with speed and is greater for a fine-lined vessel

Explanation

Squat arises from the increase in flow velocity around the hull in restricted water, lowering pressure and drawing the vessel down. It grows roughly with the square of speed and is more pronounced for full-form vessels with high block coefficient. In shallow water the effect is amplified.

Question 15Navigation and Passage Planning

In a voyage plan, the abort point for a critical leg is defined as the position beyond which the vessel cannot safely turn back. What should the plan specify for that point?

  1. The name of the port of refuge only
  2. Only the latitude and longitude of the position
  3. A limiting time or position with a pre-planned alternative action and safe water for the turn Correct answer.
  4. The vessel's maximum speed at that moment

Explanation

An abort point must combine a definable limit, usually a position or time, with a pre-agreed alternative course of action and enough sea room to execute a turn safely. Simply recording coordinates does not make the contingency usable under pressure. The plan should also identify the decision maker and communications.

Question 16Navigation and Passage Planning

Which source is authoritative for the latest changes to navigational aids and hazards affecting an ocean passage?

  1. The latest edition of the relevant Sailing Directions
  2. Weekly Notices to Mariners and radio navigational warnings Correct answer.
  3. The annual summary of admiralty notices
  4. The vessel's previous voyage plan

Explanation

Weekly Notices to Mariners and broadcast navigational warnings carry the most recent changes to aids, hazards and chart corrections. Sailing Directions provide background but are not updated weekly. A previous voyage plan may be outdated and must never be relied on without verification.

Question 17Navigation and Passage Planning

A vessel must cross a traffic separation scheme. According to COLREG Rule 10, what is the correct method of crossing?

  1. Cross at any angle provided the vessel keeps clear of all traffic
  2. Cross on a heading as nearly as practicable at right angles to the general direction of traffic flow Correct answer.
  3. Cross only at the termination of the scheme
  4. Cross along the lane until a gap appears and then turn sharply

Explanation

Rule 10 requires a vessel crossing a separation scheme to do so on a heading as nearly as practicable at right angles to the general direction of traffic flow. This minimises time in the lane and makes the crossing vessel predictable. Crossing along a lane or at shallow angles is contrary to the rule.

Question 18Navigation and Passage Planning

When planning an approach to a port with a significant tidal range, which factor most affects the choice of arrival time at the berth?

  1. The predicted height of tide relative to the vessel's draught and the berth's depth Correct answer.
  2. The distance from the last waypoint to the pilot station
  3. The time of sunrise at the port
  4. The compass error on the final approach course

Explanation

Tidal height governs available water depth at the berth and along the approach channel, so arrival is normally timed to coincide with sufficient height for the vessel's draught. Sunrise, waypoint distance and compass error do not determine whether the vessel can physically enter. Slack water may also influence the timing.

Question 19Navigation and Passage Planning

A vessel's ECDIS is set to a display category that shows only the minimum required information. What risk does the officer of the watch need to manage?

  1. The display may omit important navigation areas and cautionary information that are not required in the base category Correct answer.
  2. The display will show all charted hazards with maximum detail
  3. The display automatically alarms for every shoal sounding
  4. The display cannot be used for route monitoring

Explanation

The minimum display category shows only the base content, so charted features such as cautionary areas, some aids and additional detail may be hidden. The watchkeeper must be aware of the limitations and use appropriate display settings for the situation. Route monitoring is still permitted.

Question 20Navigation and Passage Planning

In a passage plan, the charted safety contour on an ECDIS should be set to which value?

  1. A value that is always the chart datum depth
  2. A value set by the manufacturer and not adjustable
  3. A value equal to the vessel's maximum speed in knots
  4. A value at least equal to the vessel's draught plus a safety margin Correct answer.

Explanation

The safety contour should reflect the vessel's draught plus a margin for squat, heel, tide uncertainty and chart accuracy, so that areas shallower than the contour are clearly distinguished. It is user-adjustable and must be reviewed for each passage. Chart datum itself is not a safe contour.

Question 21Navigation and Passage Planning

A vessel is drifting with engines stopped while awaiting a berth. Which factor most strongly influences the drift direction and rate?

  1. The magnetic variation at the position
  2. Wind and surface current acting on the exposed hull and superstructure Correct answer.
  3. The charted depth of water under the keel
  4. The vessel's gyrocompass heading only

Explanation

A stopped vessel drifts under the combined effect of wind on the above-water profile and current on the underwater hull, with the resultant depending on their relative magnitudes and directions. Heading alone does not determine drift, though it affects the exposed area. Depth and variation do not drive the drift vector.

Question 22Navigation and Passage Planning

Two waypoints lie on the same meridian in the southern hemisphere, and a great-circle track is planned between them. What is the initial course?

  1. It depends on the latitude of the departure point
  2. The course is undefined because the points share a meridian
  3. Due south, 180 degrees Correct answer.
  4. Due north, 000 degrees

Explanation

A great circle between two points on the same meridian is the meridian itself, so the track runs due north or due south. In the southern hemisphere, travelling to a more southerly waypoint gives an initial course of 180 degrees. The latitude does not change the direction along a meridian.

Question 23Navigation and Passage Planning

During planning, the navigator calculates that a tropical revolving storm may affect the planned track. Which planning measure best supports a safe decision?

  1. Delay all planning until the storm is within radar range
  2. Assume the storm will follow the climatological mean track without deviation
  3. Plan a single track and rely on speed changes alone to avoid the storm
  4. Identify alternative tracks and refuge ports on both sides of the forecast storm track with decision points Correct answer.

Explanation

Storm tracks are uncertain, so a robust plan provides evasive options on either side of the forecast track, together with decision points and refuge ports. Relying on a single track or on climatological averages removes flexibility. Waiting until radar contact is too late for ocean passage decisions.

Question 24Navigation and Passage Planning

A vessel plans a route through an area where the chart shows numerous reported but unsurveyed soundings and a note that the area is inadequately surveyed. How should the plan respond?

  1. Increase the safety margin and keep to well-surveyed routes or deeper water where possible Correct answer.
  2. Treat the charted depths as reliable and plan the shortest track
  3. Rely on the echo sounder alone and maintain the planned track
  4. Reduce speed only and ignore the survey note

Explanation

Inadequately surveyed areas carry a greater risk that uncharted shoals exist, so the plan should add margin and prefer well-surveyed or deeper water. The echo sounder gives only a single line of information ahead and cannot guarantee a safe corridor. Reducing speed does not address the uncertainty in charted depths.

Question 25Navigation and Passage Planning

A great-circle distance between two points is calculated as 3,600 nautical miles. What is the approximate length of the rhumb-line track between the same two points?

  1. Exactly 3,600 nautical miles
  2. Generally longer than the great-circle distance Correct answer.
  3. Generally shorter than the great-circle distance
  4. Independent of the difference of longitude

Explanation

The great circle is the shortest path on the sphere between two points, so the rhumb line between the same points is equal only when both lie on a meridian or the equator. In all other cases the rhumb line is longer. The difference grows with latitude and difference of longitude.

Question 26Navigation and Passage Planning

A vessel is to anchor in a roadstead overnight before berthing. Which charted information is most directly used to confirm the vessel will remain afloat at all states of the tide while swinging?

  1. The charted tidal stream arrows printed on the chart for the roadstead
  2. The charted depth at the anchorage combined with the predicted tidal height and the vessel's maximum draught Correct answer.
  3. The charted magnetic variation and annual rate of change for the area
  4. The position of the nearest light and its nominal range

Explanation

Safe anchoring requires comparing the charted depth (reduced to chart datum) plus the predicted height of tide at the lowest state against the vessel's draught with an under-keel allowance. Tidal stream arrows and light ranges affect manoeuvring and position fixing, not vertical clearance.

Question 27Navigation and Passage Planning

When planning a passage, what is the primary reason for plotting the vessel's position at regular intervals rather than relying on dead reckoning alone?

  1. To confirm the dead reckoning position and correct for the cumulative effect of current, leeway and steering error Correct answer.
  2. To satisfy the requirement that the log book be written up at each watch change
  3. To determine the vessel's squat at the current speed through the water
  4. To calculate the magnetic variation applying at the vessel's position

Explanation

Dead reckoning accumulates error from current, leeway, steering and log inaccuracies, so plotted fixes are needed to verify and correct the estimated position. Log book entries and squat or variation calculations are separate matters and are not the purpose of frequent fixing.

Question 28Navigation and Passage Planning

A vessel must pass under a bridge with a charted vertical clearance. Which combination of information should the navigator use to determine whether the passage is safe at the planned time?

  1. Charted clearance, the tidal stream rate and the vessel's speed through the water
  2. Charted clearance, the vessel's draught and the charted horizontal clearance of the span
  3. Charted clearance, the charted least depth under the bridge and the vessel's trim
  4. Charted clearance, predicted height of tide, the vessel's air draught and an allowance for heel and squat Correct answer.

Explanation

Vertical clearance above chart datum must be adjusted for the actual tide and compared with the vessel's air draught, with allowance for heel, squat and wave effects. Draught, horizontal clearance, tidal stream and depth relate to under-keel matters, not to overhead clearance.

Question 29Navigation and Passage Planning

A passage plan requires the vessel to make a landfall on a coast at night. Which technique best provides early warning that the vessel is being set towards a hazard by an unexpected current?

  1. Using a leading line or clearing bearing marked on the chart and monitoring the sounding or radar range against it Correct answer.
  2. Relying solely on the GPS position displayed on the ECDIS at ten-minute intervals
  3. Switching the radar to a longer range scale to see more of the coastline
  4. Increasing speed to reduce the time spent in the coastal approach

Explanation

Clearing bearings, leading lines and monitored soundings give a direct, independent indication of lateral set relative to a known hazard. A single electronic position source, extra speed or a longer radar range scale does not provide the same continuous cross-check.

Question 30Navigation and Passage Planning

A vessel is planning a route across an ocean where the great-circle track passes through higher latitudes than the rhumb line. Which consideration most often makes the navigator choose the rhumb line instead?

  1. The rhumb line requires no position fixing during the passage
  2. The great-circle track cannot be plotted on a Mercator chart
  3. The great-circle track enters an area of severe weather or ice and lies outside the vessel's load line or insurance limits Correct answer.
  4. The rhumb line is always shorter in distance than the great-circle track

Explanation

The great-circle track is shorter but may pass through higher latitudes with worse weather, ice risk or zone restrictions, so the rhumb line or a composite track may be safer. The rhumb line is longer, can be plotted on a Mercator chart, and still requires fixing.

Question 31Navigation and Passage Planning

When constructing a passage plan, what is the purpose of defining wheel-over points at each course alteration?

  1. To mark the position where the engine room must be notified of a speed change
  2. To allow the vessel to begin the turn at a defined position so the vessel settles on the new track without overshooting the planned corridor Correct answer.
  3. To identify where the vessel changes from hand steering to automatic steering
  4. To record the position at which the chart is to be corrected to the latest notice

Explanation

Wheel-over points locate the start of the turn so the advance and transfer of the vessel bring it onto the next track within the planned corridor. They are not concerned with engine speed changes, chart correction or steering mode changes.

Question 32Navigation and Passage Planning

A vessel's ECDIS safety depth is set to 10 metres and the safety contour to 10 metres, but the charted depths in the planned area are in metres with drying heights shown. Which risk arises if the safety settings are not adjusted for the vessel's draught and the local tide?

  1. The ECDIS will automatically recalculate the tidal height and correct the soundings
  2. The vessel's position will be plotted with reduced accuracy
  3. The displayed safety contour may not represent the actual under-keel clearance available at the time of passage Correct answer.
  4. The chart will revert to a display category showing no depth information

Explanation

Safety depth and contour are fixed values that must be matched to the vessel's draught and the predicted tide; otherwise the contour shown may not correspond to the real clearance. ECDIS does not automatically apply tide to soundings, and safety settings do not affect position accuracy or display category.

Question 33Navigation and Passage Planning

During planning, the navigator notes that a charted light has a nominal range of 20 nautical miles. Under what condition does the light become visible at that range?

  1. The vessel must be steering a course directly towards the light
  2. The meteorological visibility must be at least the nominal range and the observer's height of eye must give a geographical range at least equal to it Correct answer.
  3. The charted height of the light must exceed the observer's height of eye
  4. The light must be a sector light aligned with the planned track

Explanation

The nominal range is the distance at which a light is visible in a meteorological visibility of 10 nautical miles; the actual range is the lesser of the nominal and the geographical range set by height of eye and light elevation. Sector type, heading and relative heights do not by themselves guarantee visibility at the nominal range.

Question 34Navigation and Passage Planning

A vessel plans to cross a wide shallow bank where the chart shows soundings that are sparse and a note states that the area is unsurveyed. Which planning action is most appropriate?

  1. Rely on the charted soundings because they are reduced to chart datum
  2. Assume the least charted depth is accurate to within one metre
  3. Treat the area as a no-go region or plan a route giving it a wide margin, and consult the latest notices for any survey updates Correct answer.
  4. Cross the bank at high water at full speed to minimise exposure time

Explanation

Unsurveyed or sparsely sounded areas carry unknown risk, so the prudent plan avoids them or gives a generous margin and checks for newer survey data. Chart datum reduction does not guarantee accuracy, and assuming a small error or rushing across at speed increases risk.

Question 35Navigation and Passage Planning

A vessel is to transit a canal with a controlled tidal window. Which planning element most directly determines the latest time the vessel may enter the approach channel?

  1. The charted magnetic variation at the canal entrance
  2. The nominal range of the approach lights
  3. The predicted tidal height curve and the vessel's required under-keel clearance over the controlling depth Correct answer.
  4. The number of waypoints in the approach plan

Explanation

The tidal window is set by the controlling depth plus required under-keel clearance, which depends on the predicted height of tide at the critical time. Light range, variation and waypoint count do not determine the depth-limited window.

Question 36Navigation and Passage Planning

A vessel's planned track passes close to a offshore installation with a charted 500-metre safety zone. Which charted and publication source should the navigator consult to confirm the zone is still in force at the time of passage?

  1. The chart's edition date printed in the margin
  2. The sailing directions' general description of the region
  3. The vessel's own previous passage plan for the same route
  4. The latest Notices to Mariners and the appropriate nautical publication or radio navigational warning for the area Correct answer.

Explanation

Safety zones and installation status change and are promulgated through Notices to Mariners and navigational warnings, which must be checked close to the passage date. Chart edition date, general sailing directions text and an old plan may all predate the current status.

Question 37Navigation and Passage Planning

A vessel must plan a route through an area of restricted visibility and heavy traffic. Which measure best supports the plan's collision-avoidance strategy?

  1. Relying on the automatic radar plotting aid to give a complete picture of all targets
  2. Planning to maintain full sea speed to clear the area quickly
  3. Setting the route to pass through the traffic lanes at the narrowest point
  4. Defining a safe speed for the conditions and identifying areas where the vessel can safely hold clear of the traffic flow Correct answer.

Explanation

A safe speed matched to visibility and a plan that keeps the vessel clear of congested flow give time and space to assess risk of collision. High speed, over-reliance on ARPA alone and routing through the narrowest point all reduce margins.

Question 38Navigation and Passage Planning

A navigator is converting a compass bearing taken by hand-bearing compass to a true bearing for plotting on the chart. The vessel's heading is 045 degrees by compass and the charted variation for the area is 8 degrees west. Which additional information is essential before the bearing can be converted correctly?

  1. The nominal range of the object being observed
  2. The charted depth at the position where the bearing was taken
  3. The vessel's speed through the water at the time of the bearing
  4. The deviation of the hand-bearing compass on the vessel's current heading Correct answer.

Explanation

Converting a compass bearing to true requires applying deviation for the compass used and then variation, so the deviation on the current heading is essential. Speed, depth and light range do not enter the bearing conversion.

Question 39Navigation and Passage Planning

A passage plan includes a leg where the vessel must hold a precise track in a strong cross-current. Which planning technique gives the most reliable continuous indication of the vessel's lateral position relative to the planned track?

  1. Plotting a single fix at the start of the leg and relying on the gyro course
  2. Setting the autopilot to a fixed heading for the whole leg
  3. Increasing the engine speed to shorten the time on the leg
  4. Using parallel index lines on the radar referenced to a fixed charted feature and comparing them with the planned track Correct answer.

Explanation

Parallel index lines referenced to a fixed feature show lateral drift continuously and allow course adjustments before the vessel leaves the corridor. A single fix, higher speed or a fixed heading does not provide the continuous cross-track reference needed against a cross-current.

Question 40Navigation and Passage Planning

A vessel plans a passage across a tidal stream that reverses direction every six hours. Which planning method best uses the stream to reduce the passage time?

  1. Maintaining a constant heading throughout the leg regardless of the stream direction
  2. Planning the leg to coincide with slack water for the whole passage
  3. Planning the leg to begin at the start of the contrary stream so the vessel is clear before it reverses
  4. Timing the leg so the vessel takes the favourable stream for as much of the passage as possible and avoiding the contrary stream Correct answer.

Explanation

On a passage across a reversing stream, timing the leg to catch the favourable stream for the greater part of the passage reduces the overall time and distance made good. Deliberately starting into the contrary stream, holding a fixed heading or waiting for slack throughout does not exploit the stream.

Question 41Ship Stability and Cargo Operations

A vessel has a summer deadweight of 12,000 t at a summer draught of 8.50 m and a tropical deadweight of 12,300 t at a tropical draught of 8.68 m. Using the standard load line allowance, what is the tropical deadweight at a tropical draught of 8.50 m?

  1. 12,120 t Correct answer.
  2. 12,000 t
  3. 11,880 t
  4. 12,300 t

Explanation

The tropical zone permits the load line to be submerged by one forty-eighth of the summer draught, so the tropical freeboard is 0.177 m less than summer (8.50/48). The summer deadweight must be increased by the displacement of the layer between the summer and tropical marks, which here is 300 t over 0.18 m, giving about 120 t at the summer draught.

Question 42Ship Stability and Cargo Operations

A box-shaped barge 60 m long, 12 m wide and 4 m deep floats at a draught of 2.5 m in salt water. What is its reserve buoyancy expressed as a percentage of its total volume?

  1. 37.5% Correct answer.
  2. 25.0%
  3. 75.0%
  4. 62.5%

Explanation

Reserve buoyancy is the enclosed volume above the waterline. The barge is box-shaped, so the immersed fraction is 2.5/4 = 62.5% and the reserve is the remaining 37.5% of the total volume.

Question 43Ship Stability and Cargo Operations

A ship of 8,000 t displacement has KG 7.20 m and KM 7.60 m. A weight of 200 t already on board is shifted vertically downward by 3.0 m. What is the new GM?

  1. 0.475 m Correct answer.
  2. 0.550 m
  3. 0.400 m
  4. 0.325 m

Explanation

Initial GM is KM minus KG, i.e. 7.60 - 7.20 = 0.40 m. Shifting a weight down by d raises G by w×d/W = 200×3.0/8,000 = 0.075 m, so KG falls to 7.125 m and GM becomes 0.475 m.

Question 44Ship Stability and Cargo Operations

During a stability assessment a ship is found to have a negative initial metacentric height in the upright condition. Which behaviour is the ship most likely to exhibit?

  1. It will remain at any angle of heel without righting moment.
  2. It will heel to a large angle and remain steady on that side.
  3. It will return upright after a small heel and oscillate with a long period.
  4. It will loll to one side and may flop from side to side. Correct answer.

Explanation

With negative GM there is no positive righting moment at small angles, so the vessel lists to port or starboard and can roll slowly from one angle of loll to the other. The condition is dangerous because the range of positive stability is small and a beam sea may capsize the ship.

Question 45Ship Stability and Cargo Operations

A ship displaces 15,000 t with KG 8.0 m. A weight of 500 t is loaded at a position 6.0 m above the keel. What is the new KG?

  1. 8.00 m
  2. 7.93 m Correct answer.
  3. 8.17 m
  4. 8.07 m

Explanation

The combined centre of gravity is found by taking moments about the keel: (15,000×8.0 + 500×6.0) / 15,500 = 123,000/15,500 = 7.94 m, approximately 7.93 m. Loading below the existing KG lowers the ship's centre of gravity.

Question 46Ship Stability and Cargo Operations

What does the righting lever curve (GZ curve) of a ship in still water represent?

  1. The righting lever available at each angle of heel for a given displacement and KG Correct answer.
  2. The change in displacement as the ship heels
  3. The variation of metacentric height with draught
  4. The distribution of buoyancy along the length of the hull

Explanation

The GZ curve plots the righting lever against heel angle for a stated displacement and KG. Its shape shows the range of positive stability, the angle of vanishing stability, and the maximum righting lever.

Question 47Ship Stability and Cargo Operations

A ship of 10,000 t displacement has KM 8.50 m and KG 7.90 m. A weight of 400 t is loaded on deck at 14.0 m above the keel. What is the resulting GM?

  1. 0.48 m
  2. 0.60 m
  3. 0.36 m Correct answer.
  4. 0.84 m

Explanation

New KG = (10,000×7.90 + 400×14.0)/10,400 = (79,000 + 5,600)/10,400 = 8.134 m. GM then equals 8.50 - 8.134 = 0.366 m, approximately 0.36 m.

Question 48Ship Stability and Cargo Operations

Which condition is required for a ship to be in stable equilibrium in the upright position?

  1. The centre of buoyancy must lie above the centre of gravity.
  2. The centre of gravity must coincide with the metacentre.
  3. The metacentre must lie below the centre of gravity.
  4. The centre of gravity must lie below the metacentre. Correct answer.

Explanation

Stable equilibrium exists when the metacentre is above the centre of gravity, giving a positive metacentric height and a righting moment when heeled. If G were above M the ship would be unstable and would loll or capsize.

Question 49Ship Stability and Cargo Operations

A vessel with a large metacentric height in the loaded condition is expected to behave in which way at sea?

  1. Roll slowly with a long period and a large amplitude.
  2. Roll quickly with a short period and a stiff motion. Correct answer.
  3. Heel to a permanent angle on one side.
  4. Remain upright with no rolling at all.

Explanation

A large GM produces a strong righting moment, so the ship returns quickly and rolls with a short period. The motion is described as stiff and can be uncomfortable and damaging to cargo and crew.

Question 50Ship Stability and Cargo Operations

Which item is included in the deadweight of a ship?

  1. The weight of the hull and machinery
  2. The weight of bunkers, fresh water and stores Correct answer.
  3. The lightship displacement
  4. The displacement of the ship at the summer load line

Explanation

Deadweight is the total weight a ship can carry, comprising cargo, bunkers, fresh water, ballast, stores and crew. Lightship is the fixed weight of the empty ship and is excluded from deadweight.