Use Chart AUS 819, the Gladstone Boating Safety Chart 2004, and Official Qld. Tide Tables 2006.
For exercises in this quiz only, assume variation = 10 deg.E and deviation = 3 deg.W.
Play fair and attempt the questions before checking answers.
Tides.
The Compass
Chart Work
Lights
- Q.31. What name is given to the type of mark indicating the entrance channel to a port. What colours are the marks and how are they numbered. [ Answer 31. ]
- Q.32. What are the day and night characteristics of a 'special' mark. What can a special mark indicate. [ Answer 32. ]
- Q.33. When entering via the North Entrance Channel, on which side is mark N1 passed, and why. [ Answer 33. ]
- Q.34. At night, you are steering a course of 100 deg. and encounter a buoy with a continuous quick flashing light. What would be your course of action and why. [ Answer 34. ]
- Q.35. How are lateral buoys marked on large scale coastal charts. [ Answer 35. ]
- Q.36. You are navigating across an open waterway and encounter a beacon with two black spheres disposed vertically. What does this indicate, and what precautions should be taken. [ Answer 36. ]
- Q.37. What are the characteristics and abreviations of an Occulting light, an Isophase light, and a Flashing light.[ Answer 37. ]
- Q.38. You are approaching an entrance channel at night. What colour lead lights would you be seeking, and what would be typical light characteristics. [ Answer 38. ]
- Q.39. You are navigating in a busy harbour at night with rain squalls, and are disorientated by background lighting. What precautions should be taken. [ Answer 39. ]
- Q.40. A coastal light has the following description on a chart - Fl(2) 10s 102m 21M. What type of characteristic is this. What does this description indicate to the mariner. [ Answer 40. ]
- Q.41. You are undertaking a night passage, and encounter a steady green light and a steady red light with a central white light, dead ahead. What would this indicate, and what action should you take. [ Answer 41. ]
Answer 1. Spring tides occur when the Sun and Moon are in conjunction, i.e. new moon, and in opposition, i.e. full moon, relative to the Earth. Spring tides are also described as the highest of high waters, and the lowest of low waters in a lunar cycle. See | Phases of the moon |
Answer 2.. Neap tides are those with a smaller range than spring tides, and occur midway between the spring tidal times, ( 7.25 days), when the moon and sun are in quadrature. i.e. displaced at 90 deg. relative to the Earth. Neap tides are also described as the lowest of high waters, and the highest of low waters in a lunar cycle. See | Phases of the moon |
Answer 3. Tidal range is the difference in height above datum between any consecutive high and low tide. Tidal rise is the height of high water above port datum. Tidal flow is strongest during the third and fourth hour of the tidal ebb or flood.
Answer 4. MHWS = Mean High Water Springs. MLWS = Mean Low Water Springs. MSL = Mean Sea Level. ( mean meaning the annual average). MHWS in particular, is significant as the datum for the heights of land based objects such as coastal lights. MLWS and other similar ' mean' tidal data is of value to designers of shoreline infrastructure and port facilities.
Answer 5. Tidal or Chart Datum is the lowest astronomical tide recorded over a solar cycle of 18.6 years, and is noted in the Tide Book as LAT. The complimentry high tide is HAT. Refer to p. 202 - 209 of the 2007 tide book.
Drying height is the height to which a charted object dries above the Chart Datum.
Charted Depth as noted on a chart, is the depth of water below the Chart Datum.and represents the least depth which may be encountered for any tidal predictions.
Answer 6. Primary ports are those which have published tidal data. Secondary ports are those associated with a primary port, and whose tidal data can be calculated. Refer to the official Tide Book.
Answer 7. (a) By determining the depth of water at a particular state of the tide by use of the Standard Tidal Curve Tables or by application of the Rule of Twelfths. (b) The solution is to determine a safe depth of water over the bank, say 1.7 m., allowing for chop and swell, and then calculate at what states of the tide this will occur. The Gladstone Boating Safety chart indicates a drying height on Middle Bank of 0.9 m above datum. Therefore the tide will have to flood by 2.6 m. above datum to allow passage. The low tide at 0311 hrs. is 0.66m. above datum, so will have to flood an additional 1.94 m. to give a depth of 1.7 m. Say approx. 4 hours after low tide.
The following high tide at 0909 hrs., 3.28 m, indicates a depth of 2.38 m. over the bank, so there should be sufficient depth until the tide ebbs by 0.68 m. ( 2.38 - 1.7 ) or approx. 2 hours after the high tide. Note the importance of using the tidal datum. Remember, these methods are approximations, and any such crossing would be done at reduced speed and monitoring the depth sounder.
Answer 8. By reference to the Official Qld. 2007 Tide Tables, Semidiurnal Tidal Planes. - Gatcombe Hd. = High tide at 0903 hrs. 3.15 m. above datum.
- Pancake Ck. = High tide at 0844 hrs. 2.71 m. above datum.
On this morning a spring tide will be experienced ( new moon).
Answer 9. From the 2007 tide tables, the estimated depth of water will be 1.75 metre. You could risk touching bottom, so it would be prudent to plan the passage for an earlier tide.
See Narrows Tides.
Answer 10. (a) Tide refers only to the vertical movement of sea level, or depth of water. The terms tidal flow, tidal run, tidal set, tidal stream, refer only to the currents created by the horizontal movement of water. Refering to the Gladstone Boating Safety chart, note the strong tidal flow indicated across the Golding and Boyne Channels.
(b) You were keeping the next mark in alignment, but were not watching your compass course. Wind and current set you off course out of the channel. When in a channel, keep marks aft and fwd. in alignment, and watch the compass and depth sounder.
Answer 11. A magnetic compass card is basicly a bar magnet, and will align itself with the Earths magnetic field, which is oriented variably in a south to north direction. As the south pole of the Earth's field is in the north, the compass north pole will always seek a northerly direction, and the compass is graduated accordingly.
Answer 12. Compass error is the combination of error caused by magnetic variation, and error caused by magnetic deviation. Variation is an effect of the Earth's magnetic field at a particular location, which causes a compass needle to deflect relative to true north, or to an angle to the meridian. Deviation is the magnetic influence on a compass caused by the construction materials of a vessel and installed equipment, and varies with the vessel heading.
Answer 13. True bearing,. Magnetic bearing,. Compass course.
1. Lay off the intended track on the chart to obtain the True bearing. This is the shortest distance to travel. 2. Convert the true bearing to Magnetic bearing by applying correction for variation. This correction is essential to compensate for the effect of the Earth's magnetic field at our particular location. 3. Convert the magnetic bearing to Compass bearing by applying correction for deviation. This correction is neccessary to compensate for any inbuilt magnetic effects of the vessel and its heading.
Answer 14. Compass directions are expressed in three figure notation in a clockwise direction from North. e.g. 043° 147 deg. 326°
True North is indicated by the position of the north geographic pole, which is on the Earth's axis of rotation. As all meridians of longitude converge at the geographic poles, True North is also indicated by the northerly direction of any meridian. Mariners originally designated true north as the direction indicated by the pole star Polaris.
Answer 15. - Take the sights clear of any magnetic influences.
- Take sights on three fixed objects over the widest arc and over a short period, preferably taking the sight which is abeam, last.
- Convert each compass bearing to a true bearing by applying compass error correction, observing the correct mathematical rules, and the rule for deviation.
- On the chart, set the parallel rule on the compass rose for each true bearing, step each to pass through its observed point, and lay off lines at the estimated vessel position. Alternatively, lay off each line using the square protractor centered on the observed point.
- The vessel position will be within the small triangle formed by the intersecting lines.
Answer 16. In Eastern Australia, the Earth's magnetic field deflects a compass needle to the East, relative to true north, regardless of the heading, creating a compass error called variation, which has to be corrected by applying a reduction to the true bearing, as read off the chart, to give a magnetic bearing. If variation deflected the compass to the West of true north, the correction would be made by applying an addition to the true bearing.
Answer 17. 245 deg. True. 238° C - 3° deviation + 10° variation = 245° T.
Answer 18. By keeping on board magnetic influences as far from the desired position of the compass as possible. The magnetic deviation is dependent on the direction in which the vessel is heading.
Answer 19. There are four Cardinal points on the compass face or compass rose, at 90° increments.
North 0° East 090° South 180° West 270°.
There are four Intercardinal points, each at 45° to the Cardinal points.
NE 45° SE 135° SW 225° NW 315°.
Answer 20. The sequence is true bearing ---> magnetic bearing ---> compass course.
- Compass course = True bearing +/- Variation +/- Deviation.
- True bearing = Compass course +/- Deviation +/- Variation.
- In either case, the magnetic bearing must be the first obtained.
Answer 21. Position is defined as the intersection of a parallel and a meridian, or the Latitude and Longitude coordinates. e.g. Lat. - 23 ° 40.40' S. Long. - 151 ° 50.60' E. It can also be defined as the vessel's location on a position line.
Answer 22. Minutes of angle represent nautical miles on the Mercator chart latitude scale ( vertical), and all distance measurements must be taken off this scale. The chart horizontal scale ( longitude) must not be used to measure distance because of distortion of meridians on the Mercator projection.
Answer 23. The Mercator Projection, where the spheroid shape of the Earth is represented on a flat surface. Meridians do not converge, and parallels are progressively further apart from the equator. Consequently, areas in the high latitudes are distorted, and importantly, the longitude scale does not accurately represent distance.
Answer 24. In degrees and minutes of angular measurement N or S and E or W. e.g. 23° 34.3' S.
152 ° 44.72' E. One decimal place gives accuracy of 185.2 metres and two decimal places gives an accuracy of 18.52 metres. ( 1 n.m. = 1852 m.).
Answer 25. The unit of speed is the knot, which is one nautical mile per hour. Speed of a vessel through the water is termed Sw, and for calculation purposes, is assumed to be a constant figure. Speed of a vessel over the bottom, or SOG, is termed Sb, and is subject to set and wind influence.
Answer 26. Check if the chart is metric or imperial units. The former could mean either 25.4 metres, or 25 fathoms 4 feet. The latter could mean a drying height of either 0.5 metres, or 5 feet.
Answer 27. Draw the compass course line from the origin to the dead reckoned or estimated position of the first fix, marking it with a single arrowhead and the compass course, and mark the first dead reckoned or estimated position with a small triangle. Repeat this procedure for all subsequent compass courses.
Answer 28. Speed ( knots) = Distance / Time. Distance ( n. miles) = Speed x Time.
Time ( hours) = Distance / Speed.
Answer 29. Set is the direction in which tidal or ocean currents move, causing offset to a vessel's intended track and Sb. Correction for set is applied to the true bearing.
Leeway is the angle a vessel is offset from its intended track due to wind and wave action, and a correction is applied to the true bearing.
Drift is the distance a vessel is offset from the intended track due to the combined effect of set and leeway.
Rate is the speed of the drift in knots.
Answer 30. 1 hour 20 min. 29 n.m. 45 deg. C. ( 52 - 10 + 3 ). Reference to the Gladstone Boating Safety chart will detail the harbour passage and enable that leg of the distance to be determined.
Answer 31. Lateral marks. When entering port, the designation is red to port and green to starboard. Red are numbered even and green numbered odd.
Answer 32. By day - may be any conventional shape, but always yellow with a St. Andrews Cross top mark. By night - always flashing yellow. May denote a change in direction of a channel, or a channel junction, or some operation such as dredging, pile driving, as noted on the chart or in a Notice to Mariners.
Answer 33. Although shown on the chart as a special mark indicating the junction with the channel to South End, N1 is also a Stbd. mark (odd number), and so is passed leaving it to stbd. when entering port.
Answer 34. The buoy is a North Cardinal mark, indicating safe water on its northern side. Pass the buoy leaving it to stbd., reducing speed, and watching the depth sounder.
Answer 35. On large scale charts such as the Gladstone Boating Safety Chart or AUS 245 and 246, lateral lights are marked with a coloured flash oriented towards the navigable channel.
Answer 36. The buoy is an Isolated Danger mark, possibly marking a submerged hazard. Consult the chart for additional details. Proceed with caution and monitor the depth sounder.
Answer 37. Occulting Oc - A light with total eclipse at regular intervals. The period of darkness is less than that of light.
Isophase Iso - where periods of light and darkness are equal.
Flashing Fl - A single brilliant flash at regular intervals e.g. Fl 5s means one flash every 5 secs. Duration of the light is always less than the period of darkness.
It is important to be able to recognise the differences between these types of lights.
Answer 38. The lead light characteristics would be detailed on the chart, but would normally be white or blue flashing, occulting, or isophase.
Answer 39. Reduce speed and confirm your position. Consult the chart and determine a magnetic bearing to the next mark. This will greatly assist in looking in the right direction to identify the mark. Monitor the depth sounder. Proceed with caution. Consider consulting Harbour Control or VMR for advice.
Answer 40. This is a Group Flashing light, flashing twice in succession every ten seconds. Height 102 metres above MHWS tide, and visible from 21 n.m. under standard conditions. From the observed characteristic, the mariner is able to identify any light by the chart description.
Answer 41. The lights would indicate another vessel dead ahead and probably on collision course. He would be seeing the same thing. Alter course immediately, being mindful of evasive action the other vessel might take. Generally, the idea is to present the same color light that the nearing vessel displays. If you see a green light, i.e. its starboard or right side, show that vessel your
own green light. You are now poised to pass starboard to starboard. If you see a red
light, show a red light, and pass port to port.
Note also the need to recognise the vessel steaming light, indicating if it is under sail or motor power.
Remember, when encountering a large vessel, might is right, as it may be difficult for it to take quick evasive action. Also, in a channel, pass red to red. If time permits, make radio contact to clarify your intentions.
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