paddle wheel type speed log

[gjgm]

do these ever go wrong, and/or is the angle of the paddle wheel into the water very critical. Not sure when why it stopped working, but I m trying all sorts of angles, and 99pct of the time it doesnt read anything on the speedometer. Very occasionally, i get a reading for 1 or 2 seconds.
What to do?

 

[reeac]

Do you get a reading if you spin the paddlewheel with your finger? If so then the problem is either paddlewheel friction due to fouling or maybe insufficient exposure outside the hull. If no reading when you flick the wheel then try substituting another transducer.

 

[savageseadog]

There can be problems with the magnets on paddlewheels.

 

[john_morris_uk]

Could be a break in the wire. Connects occasionally when you wiggle the thing around?

 

[Guest]

Have you had the underhull pressure-washed ? It is a game that some play - putting the spray onto the wheel to see what speed they can get it up to .... it can cause the small magnet embedded into a small notch in one paddle to dislodge or even fly out.

If you have "intermittent" reading - it could be due to dislodged magnet facing askew or poor cable ... possibly break that connects when wiggled. Difficult to diagnose - best way is to substitute with another transducer......... but also you need to spin up the paddle to get pulses.

 

[gjgm]

thanks all. No, I tried spinning by hand, but nothing. But I wasnt sure how fast it needs to spin! Trying to find a faulty connection sounds a nightmare, but even if I get a new one, I ll need to find the routing anyway. Is there something that magnifies the electric reading, or is the speedometer really that sensitive, and do i need to go back to the manufacturer to get the same one, or will all versions work with all speedos?

 

[Twister_Ken]

Most transducers are made by Airmar (no matter what the brand name on the box). Airmar has a very useful website telling you what works with what.

 

[john_morris_uk]

The electronics don't 'magnify the readings', but they do count the pulses from the paddle wheel and do the calculations to produce the log reading.

Spinning the wheel by hand (just flick it with your finger) should produce a reading of anything up to a few knots. If its very free and you can blow it to spin it you might get up to 10 or 15 knots showing for a few seconds. I always spin the log when I've cleaned it and ask if the log has started reading before putting it back into the through-hull fitting.

 

[Danny]

Have a close look at the paddle wheel and see if the little magnet that should be imbedded in the end of one of the paddles has fallen out. This happened to mine (a Stowe) and, having found that a replacement wheel was apparently made of platinum (judging from the price), I found someone who could supply very small bar magnets. Got one of approximately the right size and stuck it in with epoxy. Works fine now.

They work by something called 'Hall effect' and may be polarity sensitive, so make sure the magnet is the right way round before glueing! If you need a small bar magnet PM me - I got a few extra just in case.

 

[gjgm]

ok, I ve found more or less the unit on their web page, and it says neither the paddle wheel or the housing project below the hull. Maybe I ve got it protruding too much, as I assumed it should do so. But I think I ll look at the wheel and see if I can spot a tiny magnet.

 

[Guest]

The paddle should project below the hull line .... if fitted in correct thru-hull tibe as supplied with the transducer - it should be correct. The transducer is matched to tube and "bottom paddle" should be proud and clear of tube end and turbulence.

How else is it going to work ?

 

[Danny]

If the magnet's still there it may be difficult to see. Just a little bit of filler at the end of one of the paddles probably. If the magnet's missing it should be fairly obvious - a hole in the end of the paddle!