[TG] [TG11] Speed sensor problems at low speed with i70s and DST800

[Tom - Raymarine - Moderator]

Hello brownr377,

This isn't a setup or calibration issue, and there's no setting that will resolve this. I've seen erratic and false high speed readings on both STW and wind-speed in the past be caused by noise signals being picked up on the transducer cabling. In one memorable instance a wind speed issue was being caused by noise from the invertor being used to charge a laptop when racing. The paddlewheel outputs 0..5V square-wave pulses at 5.5Hz per knot - if something else is putting a voltage onto the cable, the ITC5 can end up counting the wrong number of pulses and show the wrong speed.

This isn't a particularly easy one to test. The clearest diagnosis would be for a technical dealer to put an oscilloscope onto the signal wires when the problem is apparent and see what's there (it should be a completely stable 0V or 5V if the boat isn't moving, toggling slowly between the two if there is a little tide and the paddlewheel is spinning slowly). Alternatively, someone could check with a different ITC or transducer., perhaps it's a fault with one of these. The transducer cable run is also well worth checking, in case there's a break in the shielding or something like that.

Regards,
Tom