Session IIIGPS DEPTH-FINDERUNITS

GPS positions are not error freeGPS 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

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.

Estimated Position Error“EPE”

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

Always validate satellite reception &

accuracy before using your GPS set

for navigation.

GPS Setup ParametersGPS Setup Parameters– True or Magnetic DirectionTrue or Magnetic Direction

– Nautical/Statue MilesNautical/Statue Miles

– Clock –Clock –24hrs24hrs

– Speed in KnotsSpeed in Knots

– Variation – Variation – 013013°West°West

– Horizontal Datum – Horizontal Datum – WGS84WGS84

– Lat & Lon – Lat & Lon – Degrees/Minutes/SecondsDegrees/Minutes/Seconds

Course and BearingsCourse and Bearings

Select a heading format:

–TRUE

–MAGNETIC

GPS reports movement over GPS reports movement over ground - often different than the ground - often different than the vessels heading.vessels heading.

GPS errors affect accuracy.GPS errors affect accuracy.

Always steer off your compass, Always steer off your compass, not the GPS.not the GPS.

GPS is not a CompassGPS is not a Compass

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

Distance

Select a time format:

12 or 24 hour clock format

–UTC or Local time

Time FormatTime Format

When you are using GPS on a boat, set the speed unit of measure to KNOTS

– Nautical Miles Per Hour.

SpeedSpeed

Some GPS receivers are Automatic, some have to be done manually.

Variation is found on the inside of the compass rose.

VariationVariation

WGS84WGS84

Horizontal Datum

WGS-84 is the US standard, NAD-27 is common.

LAT. & LON.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

CONVERSIONS

Decimal portion of Minutes to Seconds

.650 X 60 = 39.0

Seconds to Decimal portion of Minutes

39.0 ÷ 60 = .650

DEPTH-FINDERDEPTH-FINDER

Set your depth sounder to correspond to the vertical datum referenced on the nautical chart that you are using.

Depth MeasurementDepth Measurement

Depth-Finder should be set for chart datumi.e. Feet, Meters or Fathoms

Soundings in Fathoms

REMEMBERREMEMBER

Your depth-finder shows Your depth-finder shows the depth of the depth of

water below you now, not water below you now, not where your going!!!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.

TRANSDUCERTRANSDUCER

END OFSession III