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Egypt Maritime COC Deck practice questions

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Question 1Navigation and Passage Planning

Under COLREG Rule 14, when two power-driven vessels are meeting on reciprocal or nearly reciprocal courses and risk of collision exists, which action is required?

  1. The larger vessel maintains course while the smaller gives way
  2. Both vessels reduce speed and pass starboard to starboard
  3. The vessel with the other on her own starboard side keeps her course and speed
  4. Each vessel alters course to starboard so they pass port side to port side Correct answer.

Explanation

Rule 14 requires that when two power-driven vessels meet head-on or nearly so and risk of collision exists, each shall alter her course to starboard so that each passes on the port side of the other. This applies regardless of size or tonnage.

Question 2Navigation and Passage Planning

In an overtaking situation under COLREG Rule 13, which statement correctly describes the duty of the overtaking vessel?

  1. She becomes stand-on once her bow passes the other vessel's beam
  2. She must keep clear of the vessel being overtaken until finally past and clear Correct answer.
  3. She may hold course if the overtaken vessel is on her port side
  4. She need only keep clear while both vessels are in a narrow channel

Explanation

Rule 13 places the entire responsibility on the overtaking vessel, which must keep out of the way until she is finally past and clear. The overtaken vessel keeps her course and speed. The duty is not limited to narrow channels.

Question 3Navigation and Passage Planning

A vessel is proceeding along a narrow channel and wishes to overtake another vessel. Which sound signal indicates her intention under COLREG Rule 34?

  1. One prolonged blast followed by two short blasts
  2. Two prolonged blasts followed by one short blast Correct answer.
  3. Five short and rapid blasts
  4. Three short blasts

Explanation

In a narrow channel, a vessel intending to overtake on the other vessel's starboard side sounds two prolonged blasts followed by one short blast. The vessel to be overtaken answers with one prolonged, one short, one prolonged, one short blast if she agrees.

Question 4Navigation and Passage Planning

What is the required minimum vertical separation between the forward masthead light and the after masthead light on a power-driven vessel of 50 metres or more in length?

  1. 9 metres
  2. 6 metres Correct answer.
  3. 4 metres
  4. 12 metres

Explanation

Annex I to the COLREGS requires that on power-driven vessels of 50 metres or more in length the forward masthead light be placed at least 6 metres above the after masthead light. The horizontal separation must also be at least one quarter of the vessel's length.

Question 5Navigation and Passage Planning

A vessel at anchor in a busy roadstead during daylight is displaying the required shape. Which shape is correct for a vessel of 80 metres length overall?

  1. One black ball forward Correct answer.
  2. One black ball forward and a second black ball aft
  3. A black cone point downwards forward
  4. A black cylinder forward

Explanation

A vessel at anchor displays one black ball forward where it can best be seen. Only vessels of 100 metres or more are additionally required to display a second ball aft. A cylinder indicates a vessel constrained by her draught and a cone indicates a vessel under sail with a motor also in use.

Question 6Navigation and Passage Planning

When planning a passage through a traffic separation scheme adopted by IMO, which practice is correct for a vessel using a lane?

  1. Proceed in the general direction of traffic flow and keep clear of the separation line Correct answer.
  2. Cross the lane at as small an angle to the flow as is safe
  3. Anchor in the lane if waiting for a berth window
  4. Use the inshore traffic zone as a short cut in fine weather

Explanation

Rule 10 requires a vessel using a traffic lane to proceed in the general direction of the traffic flow and, so far as practicable, keep clear of the separation line or zone. Crossing should be on a heading as nearly as practicable at right angles to the flow, and the inshore zone is not a general through route.

Question 7Navigation and Passage Planning

A vessel is required to use a routeing measure but her safety is compromised by the presence of dense fishing gear. What does COLREGS Rule 10 permit?

  1. Passing on the wrong side of the scheme without any signal
  2. Deviation where she is obliged to do so to avoid immediate danger Correct answer.
  3. Use of the separation zone as a normal navigable channel
  4. Complete exemption from Rule 10 for the rest of the voyage

Explanation

Rule 10 does not relieve any vessel from her obligation to comply with other rules, and a vessel may deviate from the routeing measure where she is obliged to do so to avoid immediate danger. The deviation must be limited to what the danger requires.

Question 8Navigation and Passage Planning

On an ECDIS display set to true motion, how are static features such as coastline and buoys represented?

  1. They remain fixed while the vessel's symbol moves across the screen Correct answer.
  2. They are shown only as vectors from the vessel's position
  3. They are removed and replaced by a list of coordinates
  4. They move across the screen while the vessel's symbol stays fixed

Explanation

In true motion the vessel's own ship symbol moves across the chart while fixed geographic features remain stationary. Relative motion is the opposite, with own ship fixed and the chart moving. Both modes are standard ECDIS display options.

Question 9Navigation and Passage Planning

During passage planning on ECDIS, what is the primary purpose of setting a safety contour?

  1. To mark the boundary of the traffic separation scheme
  2. To indicate the vessel's maximum draught for stability calculations
  3. To define a depth below which the system gives an anti-grounding warning Correct answer.
  4. To set the range scale of the radar overlay

Explanation

The safety contour is the depth value at which the ECDIS highlights unsafe water and triggers anti-grounding alarms. It is normally set to a value slightly greater than the vessel's maximum draught plus an under-keel clearance allowance.

Question 10Navigation and Passage Planning

A vessel's ECDIS shows a safety depth different from the safety contour. What is the practical effect of the safety depth setting?

  1. It defines the radius of the look-ahead alarm zone
  2. It changes the colour of soundings equal to or shallower than the set value Correct answer.
  3. It replaces the safety contour for all anti-grounding alarms
  4. It sets the minimum chart compilation scale

Explanation

The safety depth controls the highlighting of individual soundings at or below the chosen value, drawing attention to shoal water within an otherwise safe area. The safety contour governs the main anti-grounding alarm, so the two settings have distinct roles.

Question 11Navigation and Passage Planning

When transferring a position fix from a paper chart to a GPS receiver, which datum consideration is essential?

  1. No datum check is needed if the chart is of a recent edition
  2. The chart must always be on WGS84 and the receiver on the local datum
  3. The receiver must be set to the chart's vertical datum
  4. Both chart and receiver must use the same horizontal datum, or a datum shift applied Correct answer.

Explanation

A position plotted from a receiver on one horizontal datum onto a chart compiled on another will be offset by the datum difference. Either set the receiver to the chart datum or apply the published shift. Vertical datum is a separate matter relating to charted heights and depths.

Question 12Navigation and Passage Planning

A chart is referred to a local horizontal datum rather than WGS84. What information is normally needed to convert a WGS84 GPS position for plotting?

  1. The datum shift values published in the chart's notes or a datum table Correct answer.
  2. The chart's vertical datum only
  3. The magnetic variation shown in the compass rose
  4. The tidal range for the area

Explanation

Where a chart uses a non-WGS84 datum, the chart notes or a datum conversion table give the shifts to apply to satellite-derived positions. Variation and tidal information do not correct horizontal datum offsets.

Question 13Navigation and Passage Planning

A vessel is making way in restricted visibility and hears a fog signal of one prolonged blast at intervals of not more than two minutes. What does this signal indicate?

  1. A vessel at anchor
  2. A vessel not under command
  3. A power-driven vessel making way through the water Correct answer.
  4. A vessel aground

Explanation

Under Rule 35, a power-driven vessel making way through the water sounds one prolonged blast at intervals of not more than two minutes. A vessel stopped but not at anchor sounds two prolonged blasts with a pause between them.

Question 14Navigation and Passage Planning

In restricted visibility, a radar plot shows a target whose bearing is steady and range is decreasing. What is the correct interpretation and action?

  1. Risk of collision exists; take avoiding action in ample time Correct answer.
  2. The target is passing clear; maintain course and speed
  3. The bearing will open once the target is abeam; wait for that to happen
  4. The target is stationary; no action is required

Explanation

A steady bearing with decreasing range indicates risk of collision. In restricted visibility, Rule 19 requires the vessel to take avoiding action in ample time, and if the action consists of a course alteration it should be substantial.

Question 15Navigation and Passage Planning

Which method of position fixing provides the strongest independent check on a GPS position in coastal passage planning?

  1. Dead reckoning from the last fix
  2. A single range from a charted light
  3. Radar range to a single headland
  4. Visual bearings of two or more charted objects with good angular separation Correct answer.

Explanation

Two or more visual bearings with good angular separation give an independent fix with a clear error ellipse. A single range or a single radar range gives a position along an arc only, and dead reckoning accumulates error.

Question 16Navigation and Passage Planning

A vessel plans a coastal passage and identifies a headland where tidal streams set strongly across the intended track. Which planning measure best reduces the risk?

  1. Keep the headland close abeam to shorten the passage
  2. Follow the charted leading line regardless of tide
  3. Increase speed through the area to reduce exposure time
  4. Plan the passage to pass the headland at slack water and lay off an appropriate allowance Correct answer.

Explanation

Timing the passage of a headland for slack water and applying a tidal allowance to the course reduces the risk of being set onto a lee shore. Simply increasing speed does not remove the cross-set, and charted leading lines may not be aligned with the vessel's intended route.

Question 17Navigation and Passage Planning

A vessel must cross a tidal stream that sets at 2 knots across a channel while the vessel makes 8 knots through the water. Which course adjustment is required to maintain a straight ground track?

  1. Alter course into the stream by an angle whose sine is the ratio of stream to boat speed Correct answer.
  2. Reduce speed to the stream rate
  3. Increase speed until the stream is negligible
  4. Alter course away from the stream by the same angle

Explanation

To make good a required ground track across a current, the vessel steers into the stream so that the vector triangle closes. The angle of crab is found from the ratio of the stream speed to the boat speed through the water, applied as a sine relationship.

Question 18Navigation and Passage Planning

What is the purpose of a parallel index line on a radar display during a coastal passage?

  1. To set the radar's heading marker alignment
  2. To measure the target's true course
  3. To determine the vessel's speed over the ground
  4. To monitor cross-track distance from a charted feature as the vessel proceeds Correct answer.

Explanation

A parallel index line is drawn parallel to the planned ground track at a chosen range from a conspicuous feature. Maintaining a constant index reading confirms the vessel is staying on track, giving early warning of a cross-track set.

Question 19Navigation and Passage Planning

When planning an ocean passage, what does the term 'great circle' track represent?

  1. A track of constant initial course
  2. A rhumb line crossing all meridians at the same angle
  3. The shortest surface distance between two points on the sphere Correct answer.
  4. A track followed only by aircraft

Explanation

A great circle is the shortest path over the Earth's surface between two points. Its course changes continuously along the track, unlike a rhumb line, which keeps a constant angle with all meridians.

Question 20Navigation and Passage Planning

A vessel is planning a passage near a compulsory pilotage area. Which document should be consulted to confirm the boundaries and reporting requirements?

  1. The engine room log book
  2. The relevant sailing directions and port authority notices Correct answer.
  3. The vessel's stability booklet
  4. The crew list

Explanation

Sailing directions and port authority notices set out compulsory pilotage boundaries, reporting points and local regulations. Stability, engine and crew records do not contain pilotage boundary information.

Question 21Navigation and Passage Planning

A vessel's ECDIS route is checked and found to pass over a charted wreck marked as dangerous to navigation. What is the correct planning response?

  1. Alter the route to keep a safe margin clear of the wreck and its charted safe clearance Correct answer.
  2. Note the wreck in the passage plan but leave the track unchanged
  3. Reduce speed only while crossing the wreck position
  4. Keep the route but rely on the look-ahead alarm to warn the watch

Explanation

A wreck marked as dangerous must be avoided by a margin consistent with the vessel's draught and the charted safe clearance. The route should be altered at the planning stage rather than relying on alarms during the passage.

Question 22Navigation and Passage Planning

What does a charted 'no anchoring' area associated with a submarine cable indicate to the navigator?

  1. The cable is decommissioned and no longer relevant
  2. The area is reserved for small craft only
  3. Anchoring is permitted if the anchor is recovered slowly
  4. Anchoring is prohibited to protect the cable, and the area should be avoided when selecting an anchorage Correct answer.

Explanation

No anchoring areas protect submarine cables and pipelines; anchoring there risks damage and possible liability. The navigator should select an anchorage clear of such areas and plan the approach accordingly.

Question 23Navigation and Passage Planning

A vessel is planning to enter a port with a strong ebb tide at the entrance. Which factor most affects the timing of the approach?

  1. The predicted tidal stream at the entrance and the vessel's ability to maintain steerage way Correct answer.
  2. The date of the chart edition
  3. The number of crew on deck
  4. The colour of the leading lights

Explanation

The tidal stream at an entrance strongly affects the vessel's ground track and ability to maintain steerage way, so the approach is timed to suit the predicted stream. Chart edition, light colour and crew numbers do not control the timing decision.

Question 24Navigation and Passage Planning

A vessel's passage plan requires a course change of 90 degrees at a waypoint close to a shoal. What planning principle should be applied?

  1. Rely on the helmsman to judge the turn without a planned wheel-over point
  2. Increase speed to reduce the turning circle
  3. Widen the turn by planning the wheel-over point before the waypoint and allowing for advance and transfer Correct answer.
  4. Place the waypoint exactly over the shoal to shorten the track

Explanation

A planned wheel-over point before the waypoint, with allowance for the vessel's advance and transfer, keeps the vessel clear of the shoal during the turn. Placing the waypoint over the shoal or leaving the turn to judgement increases risk.

Question 25Navigation and Passage Planning

When preparing a berth-to-berth passage plan, which element should be included for the pilotage leg?

  1. Courses, distances, wheel-over points and abort points for each leg Correct answer.
  2. Only the total distance from pilot station to berth
  3. The vessel's cargo manifest
  4. A single course from the fairway buoy to the berth

Explanation

The pilotage leg should be planned with the same detail as the ocean leg, including courses, distances, wheel-over points and abort or contingency points. A single course or total distance alone does not provide an executable plan.

Question 26Navigation and Passage Planning

Under SOLAS V/34 and the associated IMO guidelines, which element forms the first stage of the four-stage passage planning process from berth to berth?

  1. Appraisal, gathering all relevant information and assessing the intended voyage Correct answer.
  2. Execution, conning the vessel along the planned track
  3. Planning, drawing the tracks and marking no-go areas on the charts
  4. Monitoring, fixing the vessel's position against the plan

Explanation

The IMO guidance structures passage planning as appraisal, planning, execution and monitoring. Appraisal comes first because the navigator must collect and assess charts, publications, weather, traffic and vessel constraints before any track can be drawn. Only after that appraisal is complete does the detailed planning stage begin.

Question 27Navigation and Passage Planning

A master is preparing an ocean passage plan and wishes to comply with IMO guidance on the minimum content of a berth-to-berth plan. Which set of elements is required to be addressed?

  1. Only the areas where the company's SMS requires a written risk assessment
  2. Only the ocean leg, since coastal and pilotage waters are covered by the pilot
  3. All waters including pilotage, coastal and ocean legs, with no-go areas, abort points and contingency anchorages Correct answer.
  4. Only those waters where the vessel's own charts are on the largest scale

Explanation

IMO guidance requires the plan to cover the whole voyage from berth to berth, including pilotage waters and any waters where a pilot is embarked. It should identify no-go areas, safe abort points and contingency anchorages along the entire route. Delegating parts of the plan to a pilot does not remove the master's responsibility for the complete plan.

Question 28Navigation and Passage Planning

While appraising a route, the navigator finds that a charted depth in the intended channel is shown in a chart referred to a datum lower than chart datum. What is the correct interpretation of the sounding?

  1. The sounding already includes an allowance for squat and under-keel clearance
  2. The sounding represents the least depth available only at spring low water
  3. The sounding is referred to the stated chart datum, so actual depth is obtained by adding the height of tide above that datum Correct answer.
  4. The sounding is the actual depth expected at any state of tide

Explanation

Depths on a chart are reduced to the chart datum stated in the chart title, and the actual depth at any time is the charted sounding plus the predicted height of tide above that datum. The navigator must confirm which datum is used, since not all charts use the same one. Squat and under-keel clearance are never built into charted soundings.

Question 29Navigation and Passage Planning

A navigator is using an ECDIS route with a safety contour set to 10 m and a safety depth set to 15 m. How should depths between these two values be displayed and treated?

  1. Shown as safe water and ignored for route checking
  2. Suppressed entirely from the display
  3. Shown with a distinct shading or symbol indicating they are shallower than the safety depth but deeper than the safety contour Correct answer.
  4. Shown identically to depths greater than the safety depth

Explanation

The safety contour defines the boundary of safe navigable water, while the safety depth is the depth below which the navigator wants a visual warning. Depths between the two values are highlighted so the navigator can see water that is deeper than the contour but still of concern. This intermediate shading supports route checking and monitoring without hiding the information.

Question 30Navigation and Passage Planning

A vessel's planned track passes close to a headland where an eddy is charted inside the main tidal stream. When timing the passage, what is the practical effect of the eddy on the vessel's progress?

  1. The eddy sets in the opposite direction to the main stream, so progress close inshore may differ markedly from the offshore stream Correct answer.
  2. The eddy has no effect on a vessel making more than 10 knots
  3. The eddy only exists at neap tides and can be ignored at springs
  4. The eddy always sets in the same direction as the main stream and doubles its rate

Explanation

Eddies form where the main tidal stream is deflected by a headland and a counter-current develops close inshore. The resulting set close to the land can be opposite to the offshore stream, so the vessel may lose or gain ground depending on her chosen track. The navigator should use the tidal stream atlas or local sailing directions to assess the eddy and select the track that benefits from it.

Question 31Navigation and Passage Planning

A vessel is approaching a port where a compulsory pilotage area is established. Which source should the navigator consult to confirm the precise limits of the area and the pilot boarding position?

  1. The sailing directions and the port's pilotage regulations or notice to mariners Correct answer.
  2. The vessel's stability booklet
  3. The vessel's cargo manifest
  4. The engine room log book

Explanation

The limits of a compulsory pilotage area and the boarding position are published in sailing directions and in the port's pilotage regulations, and changes are promulgated by notice to mariners. These are the authoritative sources for the boundary and the boarding point. The navigator should also mark the limits on the chart and the ECDIS route.

Question 32Navigation and Passage Planning

A vessel is planning to enter a port where a strong ebb tide runs across the entrance. Which factor most directly determines the safest time to cross the entrance bar?

  1. The time of sunrise at the port
  2. The time of high water at the standard port
  3. The time of slack water at the bar combined with the tidal height over the bar Correct answer.
  4. The time of the next crew change

Explanation

Crossing a bar safely depends on having sufficient depth over the bar and avoiding the strongest cross-stream set. The navigator therefore times the crossing for slack water, when the stream is weakest, while confirming that the tide height still gives adequate depth. These two factors together determine the safest window.

Question 33Navigation and Passage Planning

A passage plan includes a waypoint where the vessel must alter course by 90 degrees close to a shoal. Which planning principle should be applied to this waypoint?

  1. Rely on the autopilot to make the turn without a planned waypoint
  2. Place the waypoint on the shoal so the turn is as short as possible
  3. Place the waypoint before the shoal so the vessel is steady on the new course before passing the danger Correct answer.
  4. Place the waypoint after the shoal so the turn is completed beyond the danger

Explanation

Course changes near a danger should be planned so the vessel is established on the new course before reaching the hazard. Placing the waypoint early gives the navigator time to check the turn and confirm the vessel is on track. This is a standard application of the principle of keeping a safe margin from dangers when planning waypoints.

Question 34Navigation and Passage Planning

A vessel is required to use a routeing measure, but her safety would be compromised by a concentration of fishing gear on the route. What is the correct action under the collision regulations?

  1. The vessel may deviate from the route to the extent necessary to avoid the hazard, and should do so safely Correct answer.
  2. The vessel must report the fishing gear and then continue on the route
  3. The vessel must follow the route regardless of the fishing gear
  4. The vessel must stop and wait until the fishing gear clears

Explanation

The collision regulations permit deviation from a routeing measure where the vessel's safety requires it, provided the deviation is made safely. The vessel should take early and substantial action to keep clear of the hazard and return to the route when practicable. This preserves the purpose of the routeing system while protecting the vessel.

Question 35Navigation and Passage Planning

A navigator is checking a paper chart for a coastal passage and finds a note stating that the chart is referred to a local horizontal datum. What must the navigator do before plotting GPS positions on that chart?

  1. Apply the datum shift stated in the chart note to convert WGS84 positions to the chart datum Correct answer.
  2. Plot the GPS positions directly, since all charts are on WGS84
  3. Ignore the note, since datum only affects depths
  4. Add the height of tide to the latitude and longitude

Explanation

GPS positions are referenced to WGS84, while a chart on a local datum will show positions offset by the datum shift. The chart note states the shift, and the navigator must apply it to convert positions before plotting. Failing to do so can put the plotted position hundreds of metres from the true position.

Question 36Navigation and Passage Planning

A vessel is using a parallel index line on the radar during a coastal passage. What is the primary purpose of this technique?

  1. To measure the vessel's speed through the water
  2. To determine the height of tide at the next port
  3. To calculate the vessel's fuel consumption
  4. To monitor the vessel's cross-track distance from a chosen feature as she passes it Correct answer.

Explanation

A parallel index line is set at a fixed range from a prominent feature, and the navigator monitors whether the echo stays on that line as the vessel passes. A steady index confirms the vessel is holding the planned track, while drift off the line gives early warning of a cross-track error. The technique provides a continuous check on track keeping without plotting fixes.

Question 37Navigation and Passage Planning

A vessel is navigating in restricted visibility and her radar shows a target whose bearing is steady and range is decreasing. What is the correct assessment and action?

  1. The target is passing clear and no action is needed
  2. There is a risk of collision, and the vessel should take early and substantial action in accordance with the regulations Correct answer.
  3. The target is stationary and the vessel may maintain course
  4. The target is a false echo and should be ignored

Explanation

A steady bearing with decreasing range is the classic indication of risk of collision. In restricted visibility the vessel must take early and substantial action to avoid the target, and must also sound the appropriate fog signal. The action should be large enough to be readily apparent to the other vessel.

Question 38Navigation and Passage Planning

When planning an ocean passage, what does a great circle track between two positions represent?

  1. The rhumb line followed by a vessel steering a constant compass course
  2. The shortest distance along the surface of the earth between the two positions Correct answer.
  3. The route that keeps the vessel on a single line of latitude
  4. The track of constant initial course between the two positions

Explanation

A great circle is the intersection of the earth's surface with a plane through the earth's centre, and the arc between two points is the shortest surface distance between them. On a Mercator chart it appears curved, which is why great circle tracks are plotted on gnomonic charts. It is not the same as a rhumb line, which crosses all meridians at a constant angle.

Question 39Navigation and Passage Planning

A vessel must cross a tidal stream that sets at 2 knots across a channel while the vessel makes 8 knots through the water. Which method should the navigator use to determine the course to steer to make good the intended ground track?

  1. Steer directly along the intended ground track and accept the drift
  2. Wait for slack water at every crossing regardless of schedule
  3. Increase speed to 12 knots so the stream has no effect
  4. Construct a vector triangle using the vessel's speed through the water and the tidal stream to find the course to steer Correct answer.

Explanation

The course to steer to make good a required ground track is found by constructing a vector triangle. The vessel's speed through the water is drawn in the required direction over the ground, and the tidal stream vector is applied to find the course to steer and the resulting speed made good. Steering the ground track directly would allow the stream to set the vessel off track.

Question 40Navigation and Passage Planning

A navigator is preparing a passage plan and must include contingency arrangements. Which element best describes a safe abort point on a coastal leg?

  1. A position where the vessel must switch off the ECDIS
  2. A position where the pilot must be disembarked
  3. A position where the vessel must increase speed to maintain schedule
  4. A position where the vessel can turn back or divert to a safe anchorage if the passage cannot continue Correct answer.

Explanation

An abort point is a planned position from which the vessel can safely turn back or divert to a contingency anchorage if conditions or circumstances prevent continuing. It gives the master a prepared decision point rather than an improvised one. Abort points are a required element of a complete berth-to-berth plan.

Question 41Celestial and Terrestrial Position Fixing

On a marine sextant, what does the term 'index error' describe?

  1. The angular difference between the direct and reflected views of the horizon when the sextant reads zero on the arc Correct answer.
  2. The height of the observer's eye above the sea surface used for dip correction
  3. The difference between apparent and true altitude caused by atmospheric refraction
  4. The angular radius of the sun used when correcting a limb observation

Explanation

Index error exists when the horizon and its reflected image do not coincide while the sextant reads exactly zero. It arises from misalignment of the index and horizon mirrors and must be measured and applied to every altitude. Refraction, dip and semi-diameter are separate corrections applied afterwards.

Question 42Celestial and Terrestrial Position Fixing

What is the purpose of the dip (or height of eye) correction when reducing a sextant altitude?

  1. To correct for the bending of light in the lower atmosphere
  2. To convert the observed altitude to the true altitude above the rational horizon Correct answer.
  3. To remove the effect of the index error from the reading
  4. To allow for the observer's personal error in reading the arc

Explanation

Dip converts an altitude measured from the visible sea horizon to one measured from the rational (celestial) horizon. It depends only on height of eye and increases as the observer's eye rises. It is applied before refraction and parallax corrections.

Question 43Celestial and Terrestrial Position Fixing

In the intercept method of sight reduction, what does the intercept (altitude difference) represent?

  1. The time interval between two successive observations of the same body
  2. The angular distance between the observer's dead-reckoning position and the position circle, measured along the azimuth Correct answer.
  3. The angle between the celestial body's true bearing and the ship's heading
  4. The angular radius of the equal-altitude circle on the Earth's surface

Explanation

The intercept is calculated altitude minus observed altitude (or its reverse depending on convention) and is laid off along the body's azimuth from the assumed position. It is a small angular quantity expressed in minutes of arc, equivalent to nautical miles. It locates one point on the position circle.

Question 44Celestial and Terrestrial Position Fixing

Which datum is used for the coordinates obtained from a GPS position fix plotted on a nautical chart?

  1. The chart's own local datum is irrelevant because all GPS positions are automatically true
  2. The datum of the nearest port's tide tables
  3. Whatever datum the receiver defaults to, since charts are datum-neutral
  4. The horizontal datum stated in the chart's title or legend, which must match the receiver setting Correct answer.

Explanation

GPS positions are referenced to WGS 84 by default, but charts may be drawn on a different horizontal datum. The chart legend states the datum, and the receiver must be set to match or a datum shift applied. Failure to do so can displace the plot by a significant distance.

Question 45Celestial and Terrestrial Position Fixing

What is the meaning of 'observed altitude' (Ho) in celestial navigation?

  1. The sextant altitude after index error, dip, refraction, parallax and semi-diameter corrections have been applied Correct answer.
  2. The altitude of the body at the moment of meridian passage only
  3. The altitude calculated from the assumed position using the nautical almanac
  4. The raw reading taken directly from the sextant arc without any correction

Explanation

Observed altitude is the fully corrected altitude referred to the centre of the body and the rational horizon. It is compared with the calculated altitude to find the intercept. The raw reading is the sextant altitude (Hs), which still contains all the errors.

Question 46Celestial and Terrestrial Position Fixing

On a Mercator chart used for ocean passage plotting, what is the characteristic of the rhumb line between two points?

  1. It coincides with a great circle at all latitudes
  2. It always passes through the poles of the Earth
  3. It crosses all meridians at the same angle and plots as a straight line on the chart Correct answer.
  4. It is the shortest distance on the Earth's surface and plots as a curve

Explanation

The Mercator projection is constructed so that a constant-bearing track plots as a straight line. This rhumb line is convenient for plotting but is not the shortest route. The great circle is shorter at high latitudes but plots as a curve.

Question 47Celestial and Terrestrial Position Fixing

A navigator measures a sextant altitude of 30°10.0' with an index error of 2.0' off the arc. What is the corrected sextant altitude?

  1. 30°08.0'
  2. 30°14.0'
  3. 30°10.0'
  4. 30°12.0' Correct answer.

Explanation

An error 'off the arc' means the reading is too small, so it is added to the sextant altitude. Adding 2.0' to 30°10.0' gives 30°12.0'. If the error were 'on the arc' the correction would be subtracted.

Question 48Celestial and Terrestrial Position Fixing

At a height of eye of 9 metres, the dip from tables is about 5.3'. A sextant altitude of 20°00.0' is observed. What is the apparent altitude after applying dip?

  1. 20°10.6'
  2. 20°05.3'
  3. 19°54.7' Correct answer.
  4. 19°59.9'

Explanation

Dip is always subtracted from the sextant altitude because the visible horizon lies below the rational horizon. Subtracting 5.3' from 20°00.0' gives 19°54.7', which is the apparent altitude. Refraction and other corrections are applied after this step.

Question 49Celestial and Terrestrial Position Fixing

An observer's dead-reckoning position is used as the assumed position for a sight reduction. The calculated altitude is 45°20.0' and the observed altitude is 45°26.0'. Along which direction and by how much is the intercept plotted?

  1. 6.0 nautical miles towards the body's azimuth (away from the assumed position)
  2. 0.6 nautical miles away from the body's azimuth
  3. 12.0 nautical miles towards the body's azimuth
  4. 6.0 nautical miles away from the body's azimuth (towards the body) Correct answer.

Explanation

Observed altitude greater than calculated altitude means the observer is closer to the body's geographical position than the assumed position. The intercept is 6.0' of arc, equal to 6 nautical miles, plotted from the assumed position towards the body along its azimuth. A position line is then drawn at right angles to that azimuth.

Question 50Celestial and Terrestrial Position Fixing

Two simultaneous position lines from the sun and a star intersect at 90°. What is the usual practice for the resulting fix?

  1. The position lines must be run up to a common time before plotting
  2. The fix is rejected because only bodies of equal altitude may be combined
  3. The fix is considered weak because the bodies are too far apart in azimuth
  4. The intersection is accepted as a reliable fix because the position lines cross at a large angle Correct answer.

Explanation

The angle of cut between position lines determines the strength of the fix; near 90° gives the most precise intersection. A small angle of cut magnifies any error in either line. Simultaneous observations already share a common time.