Sonic speed not working when motoring

Willem J. Kroes

Sonic speed gives a lot of surprises on my Amel Santorin. Every time the boat was launched readings are different. So I had to adjust the spacing knob in instument black box.
But now I experienced a very strange 'behaviour'of the instrument. When motoring there is no reliable reading (light is out). When engine is stopped, fine accurate readings and of course the light comes on.

When starting the engine (not in gear) the light stays on, but goes out when putting the gear on.

Is there anybody who can give me a clue were to look?

Willem J. Kroes

Amel Santorin # 69 "Kavanga"

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