CHARTWORK: POSITION FIXING


PART A - THE COMPASS AND FIXES. Use RYA Chart 4, Plan F


1. a) What is the magnetic variation south of Rozelle Cove in 2005? b) What will the variation be in 2020, in the same area?


2. a) Convert 090°(T) from the chart to a magnetic bearing for the steering compass. Variation 6°W. b) If the variation was 10°E would 090°(T) convert to: (i) 100°(M)? (ii) 080°(M)?


3. a) Convert 270°(M) from the steering compass to a true bearing to plot on the chart. Variation 6°W. b) Convert 270°(M) to a true bearing. Variation 10°E.


4. Steering compasses can also be affected by deviation. How does deviation differ from variation? What are some of the possible causes of deviation?


5. At 1120 DST west of Strong Holm Island the navigator sees the radio tower on Plover Hill and the Skerries west cardinal buoy west of Creech Bluff come into transit.


a) Plot this transit on the chart. b) What magnetic bearing would you see on a hand held compass for this transit? Variation 4°E. c) One position line does not give a fix. How can the position be established?


6. At 1524 DST the following bearings were taken to the south west of Rozelle Cove: Safe water mark, south of Rozelle Cove Skerries west cardinal buoy Radio tower, Plover Hill


088°(M) 306°(M) 019°(M)


At the time the bearings were taken and written in the logbook the depth was 19.7m and the log reading was 21.2M. a) Using variation of 6°W plot the 1524 fix. b) Is a depth of 19.7m a cause for concern about the accuracy of the fix?


7. A skipper navigating to Rozelle Cove has placed a GNSS waypoint just to the south of the safe water mark at the entrance to the cove.


a) At 1550 DST the GNSS gives the bearing and distance to the waypoint as 029º(T) 1.2 miles. Plot this fix. b) How can this be verified?


8. At 1929 DST the GNSS position is 46°15’.38N a) Plot the fix.


005°52’.45W. It is noted in the logbook and plotted on the chart.


b) Besides the latitude and longitude what other information should be recorded? c) How can this position be confirmed?


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