Session III GPS DEPTH-FINDER UNITS

1. Session III GPS DEPTH-FINDER UNITS

2. GPS positions are not error free User and/or Satellite clock bias. Satellite signal can be blocked. Atmospheric interference is possible. Poor satellite geometry is possible. You can monitor these errors with your GPS receiver.

3. Signal Quality and Accuracy • The height of the bars in display shows signal strength from each satellite • The “clock face”shows the positions of satellites currently in view to your GPS.

4. Horizontal Dilution of Precision • Horizontal Dilution of Precision (HDOP) is a measure of satellite fix geometry quality • Figure at far left has lower (better) HDOP • GPS receivers measure and display HDOP Good Geometry Poor Geometry

5. Many GPS units display EPE instead of HDOP It’s an expression of the diameter of a circle in which your position target exists EPE is expressed in feet or meters – user choice Estimated Position Error“EPE”

6. Accuracy GPS with SA on - 100 meters GPS with SA off - 10 meters(33 ft) 95% of time DGPS – approx 10 feet, 95% of time WAAS – approx 8 feet, 99.85% of time Specifications

8. GPS Setup Parameters • True or Magnetic Direction • Nautical/Statue Miles • Clock –24hrs • Speed in Knots • Variation – 013°West • Altitude • Horizontal Datum – WGS84 • Lat & Lon – Degrees°/Minutes'/Seconds"

9. Course and Bearings • Select a heading format: • TRUE • MAGNETIC

10. GPS is not a Compass • GPS reports movement over ground - often different than the vessels heading. • GPS errors affect accuracy. • Always steer off your compass, not the GPS.

11. Distance When you are using your GPS on a boat, set the Distance Unit of Measure to Nautical Miles.

12. Time Format • Select a time format: • 12 or 24 hour clock format • UTC or Local time

13. Speed When you are using GPS on a boat, set the speed unit of measure to KNOTS – Nautical Miles Per Hour.

14. Variation Some GPS receivers are Automatic, some have to be done manually. Variation is found on the inside of the compass rose.

15. Horizontal Datum WGS84 • WGS-84 is the US standard, NAD-27 is common.

16. LAT. & LON. Set GPS Unit to • Degrees-Minutes-Seconds 074 – 23 - 39.0 Most units are set Degrees-Minutes- Tenths of Minute 074 – 23 .650

17. CONVERSIONS • Tenths of Minutes to Seconds • .650 X 60 = 39.0 • Seconds to Tenths of Minutes • 39.0 ÷ 60 = .650

18. DEPTH-FINDER

19. Depth Measurement Set your depth sounder to correspond to the vertical datum referenced on the nautical chart that you are using. Depth-Finder should be set for chart datumi.e. Feet, Meters or Fathoms

20. Soundings in Fathoms

21. REMEMBER Your depth-finder shows the depth of water below you now, not where your going!!!

22. TRANSDUCER • It is very important to know where the transducer is mounted • You need to know the distance from your waterline to the transducer • You also need to know the distance from the transducer to the lowest point of your boat.

23. END OF Session III