[LW] [LW11] Tacktick speed problem

[larsgrubbe]

I have a Tacktick system consisting of Airmar B44 Through hull transmitter, Tacktick T121 and mn100 display. It has been running smoothly for many years but suddenly the speed went down to zero. I reckoned it was weed or similar so I hoped it would disappear by itself, and after some more sailing the display started to pick up speed again. The figures were fluctuating for a while but were climbing up to the assumed correct speed, so I reckoned the weeds were gone. Then it was stable and OK for another 100nm when it suddenly went down to 0knots again, but after a while it went through the same pattern with fluctuations until stable. Then a period of correct speed until it was down to 0kn again. This time I was suspicious and inspected the paddlewheel, and the paddlewheel was moving freely. Fortunately I had a spare transducer insert onboard but that did not make any difference. I inspected cabling, etc and found nothing irregular. The display showed 0kn for the next 150nm, when suddenly the display started fluctuating again until correct speed. Anyone having an idea of what is going on?