Knot meter help

[kmart]

Sooo I have a Pearson 10m. (33'). The electronics are autohelm st50 vintage
The knot meter is the removable though hull paddle wheel type. It's located to the forward port side of my keel
Worked fine for the last several seasons. This season the gauge always reads 0.00kts
I did the obvious and pulled up the paddlewheel. All was clean and spun free. Put it back. Still reads 000
So now I think it's either a bad connection or the st50 control head gone bad and not the transducer. But I test again
I pulled the paddlewheel up again but this time I manually spin the paddle and watch the gauge. It worked perfectly. Read up to 6 kts. Put the paddle back in. Took the boat sailing. Nothing. Gauge still reads 0
Repeated pulling the paddle and manual spinning. Again it worked when spun by hand . But not when I put it back.
That kinda rules out the wire, bad connection and control head

If the issue was poor location of paddle wheel. Then It should not have worked in the past
No changes have been made under the boat that would impact water flow past the paddle
Yes the paddle is put in in the correct orientation. Not aligned backwards or sideways. There is a notch to ensure proper alignment. Anyone have any ideas....I'm stumped

Note this is not critical as I can get speed from the gps. But it really bothers me when things aren't functional on the boat and I can't figure it out.
Tks
K

 

[Jackdaw]

Try spinning it wheel down, in a bucket of water.

There might be a short or a crack in the housing somewhere.

 

[capta]

Is it possible there is something in proximity to the paddle wheel, on the hull interfering with it, like a barnacle or a bit of weed, preventing the wheel from turning in the water?? You can push the pin out and clean around the wheel in case there's something you can't see that won't let the water turn it, or the hole in the wheel is no longer true and in the water it jams.
Otherwise, perhaps an offering to the boat gremlins might be in order.

 

[jviss]

Take a dive under the boat and have a look - may be a barnacle in the way.

 

[FourPoints]

I had a very similar situation 2 weeks ago over labor day weekend, turned out there was a small barnacle growing inside the cavity of the paddle wheel. When upside down in my hand it moved out of the way of the wheel, but when facing down like when installed, it would jam the wheel. took a little coaxing with a pocket knife but it cleaned out and had no problems with spinning for nearly 200nm we traveled.

 

[Ted]

Most speed transducers supplied for Raytheon/Raymarine instruments were made by Airmar. The paddlewheel spins on a small axel that can easily be removed by pressing it out of the plastic transducer housing with a slightly smaller diameter pin or nail. Remove the axel and paddle wheel and make sure there isn't any slime or other growth on the axel. Reassemble with the paddlewheel oriented in the correct direction. While the paddlewheel is out, do a careful cleaning of the area above the paddlewheel.

 

[kmart]

Ok. Got a few ideas to try now
I'll try them and report back what I find
Thanks all. This forum is great!

K