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RYA Day Skipper Theory study materials
RYA Day Skipper Theory study resources

RYA Day Skipper Theory practice questions

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Question 1Chartwork and position fixing

On an Admiralty chart, what does the chart datum (generally mean lower low water) represent for the depths printed on the chart?

  1. The level below which depths are not normally expected to fall Correct answer.
  2. The standard reference for heights of lighthouses
  3. The level of the highest astronomical tide
  4. The average sea level used for tidal predictions

Explanation

Depths and drying heights on an Admiralty chart are referenced to chart datum, which is set low enough that the actual depth is usually greater than the printed sounding. It is normally close to mean lower low water at spring tides. Heights of landmarks and lights are referenced to a different datum, usually mean high water springs.

Question 2Chartwork and position fixing

A position is given as latitude 50° 12'.4 N. What does the '.4' represent?

  1. Forty minutes of latitude
  2. Four seconds of latitude
  3. Four degrees of latitude
  4. Four tenths of a minute of latitude Correct answer.

Explanation

Latitude is expressed in degrees, minutes and decimals of a minute. The figure after the decimal point is a fraction of one minute, so '.4' means 0.4 of a minute, roughly 0.4 nautical miles of latitude. One minute of latitude equals one nautical mile.

Question 3Chartwork and position fixing

You measure a bearing with a hand bearing compass and read 087° Magnetic. The chart shows a variation of 4° West. What is the true bearing?

  1. 083° True
  2. 087° True
  3. 095° True
  4. 091° True Correct answer.

Explanation

The rule is: variation east, magnetic least; variation west, magnetic best. With westerly variation the true bearing is greater than the magnetic bearing, so add 4° to 087° to get 091° True. Always convert to true before plotting on the chart.

Question 4Chartwork and position fixing

What is the purpose of a leading line (transit) marked on a chart?

  1. To mark the position of a wreck
  2. To show the limit of a restricted area
  3. To keep a vessel on a safe track into or out of a harbour Correct answer.
  4. To indicate the deepest water across a bar

Explanation

A leading line is formed by two charted objects that, when aligned, place the vessel on a known safe course, usually through a channel or harbour entrance. Keeping the marks in line keeps the vessel on that track. It does not by itself indicate depth or mark hazards.

Question 5Chartwork and position fixing

On a chart, a light is described as 'Fl(3) R 10s'. What does this tell you?

  1. It shows three red flashes in a ten-second period Correct answer.
  2. It shows one red flash every three seconds
  3. It is a fixed red light visible for ten seconds
  4. It shows three red flashes every ten minutes

Explanation

The abbreviation Fl(3) means a group of three flashes, R means red, and 10s is the period of the whole cycle. The light therefore produces three red flashes and then a pause, repeating every ten seconds. Counting the flashes and timing the period lets you identify the light at night.

Question 6Chartwork and position fixing

You are plotting a fix using two position lines. Which situation gives the most reliable fix?

  1. The two position lines are parallel
  2. Both position lines are taken from the same object
  3. The two position lines cross at a shallow angle
  4. The two position lines cross at close to 90 degrees Correct answer.

Explanation

A fix is most reliable when the position lines intersect at a large angle, ideally near 90 degrees, because the area of uncertainty is then smallest. A shallow crossing angle produces a long, narrow area of doubt. Parallel lines do not intersect at all.

Question 7Chartwork and position fixing

What is a dead reckoning (DR) position?

  1. A position marked by a transit
  2. A position found by running on from the last fix using course and speed through the water Correct answer.
  3. A position fixed by two or more position lines
  4. A position obtained from a single GPS reading

Explanation

Dead reckoning is the process of advancing the last known position along the course steered, for the distance run, without allowing for wind or current. It uses course and speed through the water. It is an estimate and is less reliable than a fix.

Question 8Chartwork and position fixing

A chart has a scale of 1:50,000. What does this mean?

  1. One centimetre on the chart represents 500 metres on the ground
  2. One nautical mile on the chart represents 50,000 metres
  3. One unit on the chart represents 50,000 of the same units on the ground Correct answer.
  4. The chart covers 50,000 square nautical miles

Explanation

A representative fraction such as 1:50,000 is a ratio of chart distance to real distance in the same units. One centimetre on the chart therefore represents 50,000 centimetres, or 500 metres, on the water. Larger denominators indicate smaller-scale charts covering more area.

Question 9Chartwork and position fixing

You are steering a course of 045° True at 6 knots. After 20 minutes, what distance have you run?

  1. 3 nautical miles
  2. 2 nautical miles Correct answer.
  3. 6 nautical miles
  4. 1 nautical mile

Explanation

Distance equals speed multiplied by time in hours. Twenty minutes is one third of an hour, so 6 knots times one third of an hour gives 2 nautical miles. This distance is then measured along the course line from the last position.

Question 10Chartwork and position fixing

A vessel is steering 090° True and making 5 knots through the water. A current sets 000° True at 2 knots. What is the course and speed made good over the ground?

  1. About 022° True at roughly 5.4 knots
  2. About 068° True at roughly 5.4 knots Correct answer.
  3. About 112° True at roughly 5.4 knots
  4. About 090° True at 7 knots

Explanation

The current sets to the north while the vessel heads east, so the resulting ground track is pulled towards the north, giving a course made good north of east. Vector addition of 5 knots on 090° and 2 knots on 000° gives a resultant of about 5.4 knots on roughly 068° True. The speed made good is the length of the resultant.

Question 11Chartwork and position fixing

When plotting a running fix using a single object, what must you do with the first bearing before it can be used?

  1. Advance it along the course and distance run to the time of the second bearing Correct answer.
  2. Correct it for variation only
  3. Plot it as a course line
  4. Measure it from the chart's compass rose

Explanation

A running fix uses two bearings of the same object taken at different times. The earlier position line must be advanced along the vessel's track by the distance run between the observations, so that both lines refer to the same time. The intersection of the advanced line with the later bearing gives the fix.

Question 12Chartwork and position fixing

What does a charted sounding printed in italics, for example a depth shown as a sloping figure, normally indicate?

  1. A depth in a dredged channel
  2. The depth at mean high water
  3. A drying height above chart datum Correct answer.
  4. A depth obtained from an old survey

Explanation

Drying heights, such as the height of a rock or bank that uncovers at low water, are shown above chart datum and are conventionally printed in a distinctive style. They tell you how far the feature dries out. Ordinary soundings below chart datum are printed as plain figures.

Question 13Chartwork and position fixing

You want to find the height of tide at a standard port at 1000. The chart gives MHWS 4.6 m, MHWN 3.6 m, MLWN 2.0 m and MLWS 1.0 m. Using the rule of twelfths, roughly what is the height about three hours after low water on a spring tide?

  1. About 4.6 m
  2. About 2.0 m
  3. About 3.1 m Correct answer.
  4. About 1.0 m

Explanation

The range on springs is 4.6 minus 1.0, equal to 3.6 m. The rule of twelfths gives cumulative fractions of 1/12, 3/12, 6/12 and so on over the six-hour tide. After three hours, half the range has been added, so the height is about 1.0 plus 1.8, roughly 2.8 to 3.1 m depending on rounding.

Question 14Chartwork and position fixing

What is the difference between true bearing and magnetic bearing?

  1. True is measured from grid north and magnetic from true north
  2. True applies only at sea and magnetic only on land
  3. True is measured from true north and magnetic from magnetic north Correct answer.
  4. True is measured clockwise and magnetic anticlockwise

Explanation

Bearings are measured clockwise from a reference north. True bearings are referenced to true (geographic) north, while magnetic bearings are referenced to magnetic north, which is offset by variation. Converting between them requires applying the local variation.

Question 15Chartwork and position fixing

On a chart, what does an isolated danger mark indicate?

  1. A danger surrounded by navigable water of a defined depth Correct answer.
  2. The position of a safe anchorage
  3. The edge of a channel
  4. A traffic separation scheme boundary

Explanation

An isolated danger mark is placed on or near a small danger, such as a rock or wreck, that has safe water all around it. It is black and red with a topmark of two black spheres. Passing vessels should give it a wide berth in any direction.

Question 16Chartwork and position fixing

A position line obtained from a bearing of a distant object is drawn on the chart. How is it drawn relative to the object?

  1. As a line at right angles to the observed bearing
  2. As a circle centred on the vessel
  3. As a line through the object at the observed bearing Correct answer.
  4. As a line parallel to the vessel's course

Explanation

A bearing position line is drawn as a straight line passing through the charted object at the observed true bearing, extended towards the vessel. The vessel lies somewhere on that line. Two or more such lines intersect to give a fix.

Question 17Chartwork and position fixing

Why should you prefer a large-scale chart when navigating in a harbour approach?

  1. It shows more detail and smaller features at a larger scale Correct answer.
  2. It is always more up to date
  3. It uses a different chart datum
  4. It covers a wider area so fewer charts are needed

Explanation

A large-scale chart (for example 1:25,000) shows a smaller area in greater detail, so hazards, depths and marks are clearer. This makes it more suitable for pilotage in confined waters. Small-scale charts cover more area but with less detail.

Question 18Chartwork and position fixing

You take a bearing of a lighthouse and it reads 210° Compass. The deviation card shows 3° East for the heading you are on, and variation is 5° West. What is the true bearing?

  1. 202° True
  2. 218° True
  3. 208° True Correct answer.
  4. 212° True

Explanation

First remove deviation: with easterly deviation, compass least, so magnetic equals 210 plus 3, giving 213° Magnetic. Then remove westerly variation: magnetic best, so true equals 213 minus 5, giving 208° True. Applying the corrections in the correct order is essential.

Question 19Chartwork and position fixing

What is the purpose of a waypoint on a passage plan plotted on a chart?

  1. To show the position of a navigational buoy
  2. To indicate the limit of a charted area
  3. To mark a turning point or point of interest along the intended track Correct answer.
  4. To record the vessel's actual position at noon

Explanation

Waypoints are chosen points, usually where the course changes or where a hazard must be cleared, that define the intended track. The course and distance between successive waypoints are measured and recorded in the plan. They are planning aids, not charted features.

Question 20Chartwork and position fixing

A chart shows a tidal stream diamond with the text '2.0' inside and the note 'springs'. What does this indicate?

  1. The depth over the area is 2.0 metres at springs
  2. The stream sets at 2.0 degrees at springs
  3. The spring rate of the tidal stream at that position is about 2.0 knots Correct answer.
  4. The tidal range at springs is 2.0 metres

Explanation

Tidal stream diamonds give the direction and rate of the stream, with the rate usually quoted for spring tides. The figure 2.0 means about 2.0 knots at springs at that position. Neap rates are found from the same diagram using the neap figure or a proportion.

Question 21Chartwork and position fixing

You are navigating with a chart whose compass rose shows variation for a stated year with annual decrease. Why does this matter for a passage planned several years later?

  1. The light characteristics have changed
  2. The chart datum has changed
  3. The scale of the chart has altered
  4. The variation has changed, so the rose value must be updated for the current year Correct answer.

Explanation

Magnetic variation changes slowly over time, and the rose states the value for a particular year together with the annual rate of change. For accurate work the variation must be brought up to date by applying the annual change for each year since the rose date. Neglecting this introduces a small but growing error.

Question 22Chartwork and position fixing

A vessel's estimated position (EP) differs from its dead reckoning position because the EP allows for which additional factor?

  1. The effect of the vessel's draft
  2. The effect of compass deviation only
  3. The effect of chart scale
  4. The effect of wind and current (leeway and tidal stream) Correct answer.

Explanation

The dead reckoning position uses only course and speed through the water. The estimated position additionally allows for leeway caused by wind and for the set and drift of the tidal stream, giving a more realistic position. It is still an estimate, not a fix.

Question 23Chartwork and position fixing

You obtain a three-point fix and the position lines form a small triangle (cocked hat). What is the most likely cause of a small cocked hat?

  1. The chart being out of date
  2. Small random errors in the bearings taken Correct answer.
  3. A gross error in one bearing
  4. The vessel moving between observations

Explanation

A small cocked hat is normal and usually results from small random errors in taking and plotting bearings. The fix is taken as the centre of the triangle. A large or elongated triangle more often indicates a systematic or gross error, such as misidentifying an object.

Question 24Chartwork and position fixing

A vessel is on passage and the tidal stream changes from setting with the vessel to setting against it. How does the speed made good typically change if boat speed through the water stays constant?

  1. It increases because the stream now aids the vessel
  2. It stays the same because boat speed is unchanged
  3. It becomes equal to the boat speed
  4. It decreases because the stream now opposes the vessel's motion Correct answer.

Explanation

Speed made good over the ground is the vector sum of boat velocity and tidal stream. When the stream sets against the vessel's course, the opposing vector reduces the resultant speed over the ground. This is why passage timing must account for the direction of the stream.

Question 25Chartwork and position fixing

On a chart, a light is shown as 'Oc G 6s' with a sector marked 'Obscured'. What does the obscured sector mean for a navigator approaching from that direction?

  1. The light has a reduced range in that sector
  2. The light is hidden by land or structure and cannot be seen from that sector Correct answer.
  3. The light is switched off during daylight hours
  4. The light shows an occulting character only in that sector

Explanation

An obscured sector indicates that the light is screened, usually by high land or a structure, so it is not visible from within that arc. A navigator approaching from that direction cannot rely on seeing the light. The sector boundaries are shown on the chart and must be respected when planning landfall.

Question 26Chartwork and position fixing

On a nautical chart, what does a charted depth of 3.2 metres shown in the large figures of the sounding indicate?

  1. The depth of water below the keel of a typical yacht
  2. The depth of water below chart datum at that spot Correct answer.
  3. The height of the seabed above chart datum at that spot
  4. The depth of water at mean high water springs at that spot

Explanation

Charted soundings are measured downwards from chart datum, which is normally close to the lowest astronomical tide. A figure of 3.2 therefore means there is 3.2 metres of water over that spot at chart datum, and more at any higher state of tide.

Question 27Chartwork and position fixing

A chart's compass rose shows variation 4°30' West for the year stated. How do you convert a magnetic bearing to a true bearing?

  1. Apply deviation before the variation is considered
  2. Subtract the westerly variation from the magnetic bearing
  3. Add the westerly variation to the magnetic bearing Correct answer.
  4. Add the easterly variation and ignore the westerly value

Explanation

The mnemonic is that variation west is magnetic best, meaning magnetic bearings are larger than true bearings when variation is west. To go from magnetic to true you therefore add the westerly variation.

Question 28Chartwork and position fixing

What is the purpose of a transit (two charted objects in line) when fixing a vessel's position?

  1. It replaces the need for a compass bearing in a fix
  2. It gives a position line along the line through both objects Correct answer.
  3. It gives a distance off the nearer object by vertical angle
  4. It confirms the vessel's speed over the ground

Explanation

When two objects are seen in line, the vessel must lie somewhere on the straight line joining them, extended. This is a very accurate position line because it does not depend on the compass, and it can be combined with a bearing or a sounding to give a fix.

Question 29Chartwork and position fixing

Which of these is the standard way to express a position fix taken from a chart?

  1. The chart number and edition date
  2. The depth of water recorded at the fix
  3. Latitude and longitude read from the chart's graticule Correct answer.
  4. Distance and bearing from the nearest harbour entrance

Explanation

A position is normally given as latitude and longitude, read from the graduated edges of the chart. This is unambiguous and can be transferred to any other chart or plotted on a GPS.

Question 30Chartwork and position fixing

A vessel's log reads 12.4 nautical miles at the start of a watch and 18.9 at the end. What distance has been run through the water?

  1. 31.3 nautical miles
  2. 6.5 nautical miles Correct answer.
  3. 7.5 nautical miles
  4. 5.5 nautical miles

Explanation

Distance run is the difference between the two log readings: 18.9 minus 12.4 equals 6.5 nautical miles. This is distance through the water and does not include any effect of tide or current.

Question 31Chartwork and position fixing

What does a charted symbol of a small circle with a dot in the centre, with a note such as 'Fl(2) R 6s', describe?

  1. A light with a given character and period Correct answer.
  2. A tidal stream diamond for spring rates
  3. A buoy marking the edge of a channel
  4. A wreck marked as dangerous to navigation

Explanation

Lights are charted with a symbol at their position and an abbreviation describing their character, colour and period. 'Fl(2) R 6s' means a red light showing two flashes in a six-second cycle.

Question 32Chartwork and position fixing

On a chart, what does the abbreviation 'HW' followed by a time in the tide table for a standard port represent?

  1. The predicted time of high water at that standard port Correct answer.
  2. The time of high water at the nearest secondary port
  3. The duration of the flood stream at that port
  4. The height of the tide above chart datum at any time

Explanation

Tide tables list the predicted times and heights of high and low water at standard ports. HW is the time of high water, and the associated figure is the height above chart datum.

Question 33Chartwork and position fixing

Which chart scale would you choose for a detailed approach into a small marina?

  1. A small-scale chart such as 1:250,000
  2. A small-scale chart such as 1:1,000,000
  3. A planning chart covering the whole coastline
  4. A large-scale chart such as 1:12,500 Correct answer.

Explanation

Large-scale charts show a small area with much more detail, which is what a close approach needs. A scale of 1:12,500 gives far more information about depths, buoys and hazards than a small-scale passage chart.

Question 34Chartwork and position fixing

You are steering 060° True at 5 knots. After 30 minutes, how far have you run through the water?

  1. 3.5 nautical miles
  2. 1.5 nautical miles
  3. 5.0 nautical miles
  4. 2.5 nautical miles Correct answer.

Explanation

Thirty minutes is half an hour, so at 5 knots the distance run is half of 5, which is 2.5 nautical miles. The course of 060° does not affect the distance, only the direction in which it is plotted.

Question 35Chartwork and position fixing

A vessel is steering 000° True at 6 knots. A tidal stream sets 090° True at 2 knots. What is the vessel's course and speed over the ground?

  1. About 018° True at about 6.3 knots Correct answer.
  2. About 000° True at about 4.0 knots
  3. About 342° True at about 6.3 knots
  4. About 090° True at about 8.0 knots

Explanation

The tidal stream pushes the vessel to the east while it makes way north, so the ground track lies between 000° and 090°, closer to north. Using a vector triangle, the resultant is about 018° True at about 6.3 knots.

Question 36Chartwork and position fixing

A fix plotted on the chart lies to one side of the dead reckoning position. What does this most likely tell the navigator?

  1. The compass deviation card has been applied correctly
  2. The effect of tide, current, leeway or steering error has not been fully allowed for Correct answer.
  3. The chart is out of date and should be replaced
  4. The log is reading in kilometres rather than nautical miles

Explanation

A DR position assumes the vessel has travelled exactly the course and distance logged, with no external effects. When a fix differs from the DR, the difference is normally the set and drift of tide or current, leeway, or a steering error.

Question 37Chartwork and position fixing

You take a bearing of a buoy using a hand bearing compass and it reads 075° Magnetic. Variation is 6° West and deviation for that heading is 2° East. What is the true bearing?

  1. 067° True
  2. 079° True
  3. 071° True Correct answer.
  4. 083° True

Explanation

Going from compass to true, apply deviation first and then variation. The compass reading is 075°; removing 2° East gives 073° Magnetic; adding 6° West gives 079° True. Care is needed with the sign order.

Question 38Chartwork and position fixing

A vessel is on passage and the tidal stream changes from setting with the vessel to setting against it. What happens to the vessel's speed over the ground?

  1. It becomes equal to the stream rate
  2. It stays the same because speed through the water is unchanged
  3. It increases by roughly the stream rate
  4. It decreases by roughly twice the stream rate Correct answer.

Explanation

When the stream sets with the vessel, ground speed is boat speed plus the stream. When it turns against, ground speed is boat speed minus the stream. The change between these two states is therefore about twice the stream rate.

Question 39Chartwork and position fixing

A chart shows a tidal stream diamond with '1.8' inside and a note 'neaps'. What does this mean?

  1. The neap rate is 1.8 knots and the spring rate is found from the chart's tidal stream atlas
  2. The spring rate is 1.8 knots and the neap rate is found from the chart's tidal stream atlas Correct answer.
  3. The stream runs at 1.8 knots only at high water neaps
  4. The stream sets at 1.8 knots for the whole tidal cycle at neaps only

Explanation

On many charts the figure in the diamond is the spring rate, and neap rates are obtained by applying the ratio given in the tidal stream atlas or chart notes. The diamond gives the direction of the stream and the rate figure refers to the stated tidal condition.

Question 40Chartwork and position fixing

You need a position line from a distant headland. Which method gives the most reliable line?

  1. A bearing taken through the vessel's steel cabin window
  2. A bearing estimated from the chart without looking at the object
  3. A compass bearing taken with a hand bearing compass held clear of magnetic interference Correct answer.
  4. A bearing taken while the vessel is heeled and rolling heavily

Explanation

A hand bearing compass held away from the steering compass and other magnetic material gives a reliable bearing. The position line is then drawn from the object towards the vessel at the reciprocal of the true bearing.

Question 41Chartwork and position fixing

A vessel's DR position is plotted at 1200. At 1300 a fix is obtained 1.5 miles due east of the DR position. What is the set and drift over that hour?

  1. Set 000° True, drift 1.5 knots
  2. Set 090° True, drift 1.5 miles
  3. Set 270° True, drift 1.5 knots
  4. Set 090° True, drift 1.5 knots Correct answer.

Explanation

The set is the direction in which the vessel was carried, which is due east or 090° True. The drift is the rate of that carriage, 1.5 miles in one hour, so 1.5 knots.

Question 42Chartwork and position fixing

What is the purpose of plotting a course to steer rather than a simple course to make good?

  1. To calculate the height of tide at the destination
  2. To fix the vessel's position without a compass
  3. To allow for the tidal stream so the vessel tracks the desired ground course Correct answer.
  4. To record the vessel's heading for the log

Explanation

A course to steer is found by constructing a vector triangle so that the vessel's track over the ground follows the intended line. It compensates for the set and drift of the tide, which a simple heading would not.

Question 43Chartwork and position fixing

A three-point fix produces a small cocked hat. What is the best practice for deciding the vessel's position?

  1. Ignore two lines and use only the one that looks most accurate
  2. Extend all three lines until they meet at a single point
  3. Plot the position at the corner of the hat nearest the coast
  4. Plot the position at the centre of the cocked hat and treat the size as a measure of uncertainty Correct answer.

Explanation

A cocked hat arises from small errors in the bearings, so the true position is likely inside the triangle. The centre is the best estimate, and a large hat warns that the fix is less reliable.

Question 44Chartwork and position fixing

You take a bearing of a lighthouse and plot the position line. In which direction is the line drawn from the lighthouse?

  1. Parallel to the vessel's course line
  2. At right angles to the bearing taken
  3. Towards the vessel, using the reciprocal of the bearing Correct answer.
  4. Away from the vessel, using the bearing as taken

Explanation

A bearing from the vessel to the object places the vessel somewhere along the line from the object back to the vessel. The line is therefore drawn from the object using the reciprocal of the observed bearing.

Question 45Chartwork and position fixing

A running fix is obtained using one bearing taken at 1000 and another of the same object at 1030. What must be done to the first position line before transferring it?

  1. Discard it because it is out of date
  2. Advance it along the vessel's course and distance run over the 30 minutes Correct answer.
  3. Rotate it to match the second bearing
  4. Move it sideways by the tidal stream only

Explanation

In a running fix the earlier line is advanced by the vessel's track over the ground for the elapsed time, so that it represents where the vessel was at the time of the second bearing. The intersection with the second line then gives the fix.

Question 46Chartwork and position fixing

A vessel is steering 090° True at 6 knots and the tidal stream sets 180° True at 3 knots. Which statement describes the resulting ground track?

  1. It lies north of east and the ground speed is greater than 6 knots
  2. It lies south of east and the ground speed is greater than 6 knots Correct answer.
  3. It lies due south with a ground speed of 3 knots
  4. It lies due east with a ground speed of 3 knots

Explanation

The vessel's own motion is east and the stream pushes it south, so the ground track lies between east and south, that is south of east. The two vectors are at right angles, so the resultant speed is the square root of 36 plus 9, about 6.7 knots.

Question 47Chartwork and position fixing

A chart's compass rose shows variation 5° West in a stated year, decreasing by 8' annually. What is the variation for a passage five years later?

  1. 4°20' West Correct answer.
  2. 4°20' East
  3. 5°00' West
  4. 5°40' West

Explanation

A decrease of 8' per year over five years is 40' in total. Subtracting 40' from 5°00' West gives 4°20' West, and the variation remains westerly.

Question 48Chartwork and position fixing

You are plotting a fix from two bearings separated by only 15°. Why is this considered a poor fix?

  1. Small bearing errors produce a large displacement of the intersection Correct answer.
  2. The bearings must always be taken of the same object
  3. The compass cannot read angles smaller than 30°
  4. The two lines will always be parallel and never intersect

Explanation

The angle between position lines is the angle of cut. When the cut is small, a small error in either bearing moves the intersection a long way, so the fix is weak. A cut close to 90° gives the most reliable intersection.

Question 49Chartwork and position fixing

A vessel's echo sounder reads 12.0 metres. The transducer is 0.5 metres below the waterline and the charted depth at the position is 9.0 metres above chart datum. What is the height of tide?

  1. 2.5 metres
  2. 3.5 metres Correct answer.
  3. 4.5 metres
  4. 3.0 metres

Explanation

The echo sounder measures from the transducer, so the true depth of water is 12.0 plus 0.5, which is 12.5 metres. Subtracting the charted depth of 9.0 gives a height of tide of 3.5 metres.

Question 50Chartwork and position fixing

A vessel is making 5 knots through the water on a course of 000° True. The tidal stream sets 045° True at 3 knots. What is the approximate course made good over the ground?

  1. About 045° True
  2. About 335° True
  3. About 000° True
  4. About 025° True Correct answer.

Explanation

The vessel's own vector points north and the stream vector points north-east, so the resultant lies between them, closer to north because the boat speed is greater. Constructing the triangle gives a track of roughly 025° True.