HDOP

[telsyork]

Hi Ladies and Gents
During a recent cruise I noticed an error in our GPS position of approx 20 meters.
I used a buoy as a reference.
I also noticed the autopilot behaving strangely, turning way beyond say a ten degree increase or decrease in heading.
I have recently replaced the GPS mushroom as the old raymarine unit died.
Checking the satellite page it showed an HDOP of 1.2 but with plenty of locked sat signals
The above behaviour was noticed at very low speed (approx 5 knots)
When on our berth the position seems almost spot on
Also ais positions seem to be displaced but I have no accurate reference for this.
Btw this is on a C 120 plotter
Any tips greatly appreciated

 

[iapetus]

How fore the AIS unit receive GPS positions? It should theoretically have its own GPS mushroom

 

[telsyork]

Yes the AIS does have its own ariel, which makes it a little more confusing!

 

[n.herring]

If your berthing position is correct you do not have a problem, you can not use a bouy as a reference point they will move with the tide and can easily be 20mts out, neil