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GPS - Global Positioning System    

Satellite derived position, course and speed
Accurate to 5 - 10 metres.

  • Waypoint entry – a position or destination where you enter the Lat and Long. The GPS gives you bearing and distance from your present position to the Waypoint
  • Routes – a series of several Waypoints
  • Man Overboard or Mark – fix at time of MOB
  • Position: - Latitude, Longitude and Time
  • Speed Over Ground - SOG (compare with log to get tide effect)
  • Course over Ground – COG (True or Magnetic)
  • Bearing (T or M) to Waypoint
  • Distance to Waypoint
  • Time to Waypoint
  • Cross Track Error (XTE) in Miles – how far off the selected track route you are
  • Charts

In Use:

  • Plot Lat and Long on chart – maintain log book every hour. 
  • Back up with another source if possible
  • Draw a GPS web on the chart for fast boats 
  • Find Waypoints from chart, almanac etc. Don’t enter the exact position. Check entry for bearing and distance on chart. 
  • Use a compass rose as a waypoint for plotting position
  • Find Course to Steer – GPS cannot do this, you may sail on a curve.

Possible Errors:

  • Aerial Position - should be low, around the stern rail, not up the mast.
  • Aerial failure. 
  • Battery failure.
  • Datum entry – WGS84 is usual
  • User input on waypoint
  • Mobile phones signals.


Click for handout

It has immense benefits  but there are drawbacks - see here

BU 353  GPS Dongle for laptops

28th March 2011

GPS, yacht, XTE, waypoint, wgs84, GPS web, SOG, COG, cross track error, bearing to waypoint, go to, MOB, nav,