Our boat speed paddlewheel mystery

alexincornwall

alexincornwall

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Evening all,

Wondered if anybody could shed any light on our mysterious lack of paddlewheel boat speed on our newish Airmar integrated sounder/speed log. Worked fine last year and spinning freely on relaunch... but now nothing.

I've pulled it up, cleaned it off and it's spinning perfectly out of the water, no signs of damage or growth, and I can see the boat speed reported back to our instruments no problem. Yet when it goes back into the thru-hull it refuses to display even 0.1kn.

So frustrating was this that I donned the snorkel this afternoon (still pretty chilly in Cornwall!), assuming that something was going on under there. Everything looks right below the surface - the sounder is perfectly flush with the thru-hill so I know the unit it is correctly inserted, and I can spin it no problem by hand under the water. It just simply doesn't want to do what it's supposed to when the boat is moving. I've tried mm adjustments underway but to no avail.

Any ideas please?
 
I had a similar problem last year with my paddlewheel not reading correctly it was about 10 years old and other than needing cleaning every now and then ad never had any issues. Like yours it rotated freely when removed and registered on the instrument when spun. I could see no problem at all other than it didn't work! I bought a replacement wheel kit and when removing it noticed a little wear on the stainless steel shaft. In order to understand the problem and only change one thing at a time I tried the old paddlewheel with the new pin. It worked fine. I then changed the paddle wheel as well so that all was new. My only conclusion is that wear on the pin caused some sort of drag on the paddlewheel and this stopped it turning in the water. Over 800 miles later everything is still working fine. Might not be your problem at all but worth checking the pin. Raymarine ST60
 
mickbond said:
I had a similar problem last year with my paddlewheel not reading correctly it was about 10 years old and other than needing cleaning every now and then ad never had any issues. Like yours it rotated freely when removed and registered on the instrument when spun. I could see no problem at all other than it didn't work! I bought a replacement wheel kit and when removing it noticed a little wear on the stainless steel shaft. In order to understand the problem and only change one thing at a time I tried the old paddlewheel with the new pin. It worked fine. I then changed the paddle wheel as well so that all was new. My only conclusion is that wear on the pin caused some sort of drag on the paddlewheel and this stopped it turning in the water. Over 800 miles later everything is still working fine. Might not be your problem at all but worth checking the pin. Raymarine ST60
Click to expand...

I guess it’s possible but the log is showing a mear 900 miles since install. Surely they can’t fail that quickly?
 
alexincornwall said:
Wondered if anybody could shed any light on our mysterious lack of paddlewheel boat speed on our newish Airmar integrated sounder/speed log. Worked fine last year and spinning freely on relaunch... but now nothing.
Click to expand...

Has the magnet fallen out, or lost its effect?
I am not familiar with your model but usually there is a magnet in the paddle that operates a reed switch embedded in the body to provide pulses to the display. If magnet OK it may be a wiring fault either in the body or cable.
 
When you get a result let me know please I have the exact same problem.. Reads when you flick it and some times for abit once cleaned but not for more than a day or two.. ?
 
Suffered from similar problem once. Turned out to be a splash of antifouling on the inside edge of the paddlewheel hull fitting. Turning by hand moved the paddlewheel slightly, either sideways or on the worn bearing. A quick rub with scraper and wet or dry fixed it. I carry a spare paddlewheel, so I can swap them if I get weed on it - saves two lots of water getting in! Problem only occurred with one of them as they had slightly different dimensions.
 
Have I not read in these hallowed pages that very slight misalignment can cause this? As in within the wiggle room when fitted? Puts the paddle wheel at a slight angle to the water stream, which stops it dead?
 
When you spun the paddle wheel under water, was there anyone in the cockpit monitoring the speed display and if so, did the speed register? If so, maybe the wheel isn’t rotating underway in which case, KevinV may be onto something in #10.

is it possible to loosen the fitting away from its ‘locked’ fore and aft position and rotate it slightly whilst underway and with someone monitoring the speed display? There may not be enough wheel exposed to the water flow but it might be worth a try…. Good luck!
 
Goldie said:
When you spun the paddle wheel under water, was there anyone in the cockpit monitoring the speed display and if so, did the speed register? If so, maybe the wheel isn’t rotating underway in which case, KevinV may be onto something in #10.

is it possible to loosen the fitting away from its ‘locked’ fore and aft position and rotate it slightly whilst underway and with someone monitoring the speed display? There may not be enough wheel exposed to the water flow but it might be worth a try…. Good luck!
Click to expand...

Unfortunately I wasn't able to test the display with the log submerged as, whilst the paddlewheel spins freely, it's tricky to get any inertia going with the boat at a standstill. Not helped by my limited lung capacity in the seemingly freezing water!

On the other note, yes I've tried moving the log with an observer at the instruments. There is no locked fore and aft position so the log could theoretically be turned a full 360 degrees. I've tested from my perceived forward position to around 20 degrees either side. I've even tried turning it 180 degrees to see if it might work backwards - it didn't! This is proving to be a real head scratcher.
 
I second SteveG's answer above. That has happened to my log, too, several times You can still turn the paddlewheel with a finger, but water flow won't do it. I know now to check inside the rim of the hull fitting before re-launch. Sometimes a tiny barnacle gets in there, though, and then you have to dry out to fix it.
 
Last year my 15 years old Airmar paddlewheel feeding a Raymarine Tridata started to get intermittently non-reading, even after cleaning. It worked mostly, but occasionally did not. When non-working you could spin the wheel by hand and you would not get a speed reading. During one non-working Tried a different Tridata head, no different. Checked cables continuity, nothing wrong.

Eventually gave in and bought a new paddlewheel, running 30+ feet of cable from near bow to pod at helm a horrible job, but since than it has always worked as long as the paddlewheel is clean. Personally I often don't bother to put the paddlewheel in, but others seem to like to see STW displayed, and have the true wind option on the othr dials.
 
Interesting that you can freely rotate the log unit and that there is no locating position when it is inserted. My Raymarine log sensor (old ST60) will go in and rotate but the final few mm need it to be perfectly aligned. If yours is like this, then the paddle wheel will not be 100% inserted?
 
DipperToo said:
Interesting that you can freely rotate the log unit and that there is no locating position when it is inserted. My Raymarine log sensor (old ST60) will go in and rotate but the final few mm need it to be perfectly aligned. If yours is like this, then the paddle wheel will not be 100% inserted?
Click to expand...
Yes: my Airmar log feeding a ST60 definitely " locates" the last bit of the way fore and aft in it's housing. Once fully in you can't rotate it more than a degree or two.
 
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