Session III GPS DEPTH-FINDER UNITS

F 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.

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

Estimated Position Error “EPE” F 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

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

Course and Bearings F Select a heading format: –TRUE –MAGNETIC

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

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

F Select a time format: 12 or 24 hour clock format –UTC or Local time Time Format

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

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

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

LAT. & LON. LAT. & LON. Set GPS Unit to F Degrees-Minutes-Seconds 074 – Most units are set Degrees-Minutes- Tenths of Minute 074 –

F CONVERSIONS F Decimal portion of Minutes to Seconds F.650 X 60 = 39.0 F Seconds to Decimal portion of Minutes F 39.0 ÷ 60 =.650

DEPTH-FINDER

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

Soundings in Fathoms

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

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. TRANSDUCER TRANSDUCER

END OF Session III