Thanks for the replies.

When removed and spun by hand I can get a reading of up to 3 or 4 knots. The
paddle spins freely and is clean and in the correct way round.

I will try a new paddle wheel.

It could be that when in the water the wheel spins a little further from the
sensor due to water flow and if the magnet is weak then a loss or
sensitivity has occurred. Is the sensor a coil or a reed relay?
The problem came on intermittently and over two or three months

Alec


"Matt Colie" wrote in message
...
Alec,

Does the paddle wheel always stop with the same blade down?

When it sort of works does it read about half what you expect?

If yes, buy a paddle wheel and replace it before you do anything else.

To date, I have replaced the paddles wheels on no less than four
Raytheon/Autohelm/Raymarine units. All had magnets gone. the corrode as
soon as there is any breach of the plastic they are molded into.

Matt Colie
www.yachtek.com


Alec wrote:
I have a Autohelm Tri Data log and depthsounder.
It has always been no trouble until this year when the log has been
playing up.
It started by being intermittent and now does not indicate at all in
normal use.
If I remove the sensor unit from the hull and spin the wheel it seems to
work. I have given it a good clean. However it still does not work in
normal use.
I suppose there could be something on the hull but as the hull is very
clean and the boat performs normally I suspect the hull is clean.

Is there a known problem with these units? Does the magnet ever wear out?
The unit is probably 15 or so years old. can a new paddle wheel help?

Alec