USING GLOBAL NAVIGATION SATELLITE SYSTEMS


1. The skipper of a 7m RIB plans to do a coastal passage using a hand held GNSS and a paper chart inside a waterproof cover. His estimated cruising speed is 15kts.


a) A GNSS is generally very reliable and accurate. Give two possible causes of inaccurate positions. b) Suggest two simple precautions to take in case of GNSS failure.


2. GNSS receivers usually have functions to allow you to view the number of satellites in use and to view the value of Horizontal Dilution of Precision (HDOP). Why is it useful to be able to see these?


3. A waypoint is a reference point used in navigation, often as part of a route. Their latitude and longitude can be measured from the chart or found in almanacs and other books.


a) The GNSS will display the direction and distance to the waypoint, but does a basic GNSS make an allowance for the tidal stream when giving the direction? b) Explain the abbreviation XTE.


c) If a waypoint is chosen in an unsafe area or if the route crosses a hazard will a basic GNSS give a warning or navigate round the danger? d) If the latitude and longitude position from the GNSS has been plotted on the chart can that position be confirmed by plotting the direction and distance to the next waypoint?


Use RYA Chart 4, plan F.


4. You are a skipper on passage from Endal Bay to Rozelle Cove. Below is an extract from the log. Variation is 6°W. Time Position


1000 DST


1025 DST


Endal Bay Entrance


46°16’.05N


005°50’.20W (by GNSS)


a) Plot the boat’s GNSS position at 1025 DST. b) Does the depth at the plotted position match that shown in the log? Why might that be?


You use the rolling road function on a GNSS to monitor progress towards the next waypoint (WPT 2), which is on the 20m contour south of Range Head South Cardinal Mark (south of Holm Island). The rolling road display at 1025 DST is shown below. Use this information to plot the vessel’s position.


c) What is the latitude and longitude of this new position?


Course Log 330°(M) 10.5


285°(M) 12.5


Baro 1002


1002


Wind S3


S3


Depth 22m


35m Comments


On transit and 20m contour, A/c 285M


d) Does the depth at this new position match the depth shown in the logbook at 1025 DST? e) Which position is most likely to be true and why? f) What else could you do to verify your position?


14


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24