knot meter paddle wheel mystery

[hertfordnc]

I have Raymarine ST4000 autopilot. with ST50 instruments. ALl works great except the speed indicator. I assumed the paddle wheel was fouled. I looked at removing it from the inside and I don't think it comes out that way.

Yesterday the water was finally warm enough to swim so I went under to have a look. There is no paddle. The place on the outside of the hull where the sensor wires end is capped off. sealed, flat, no access.

So what's going on?

Is there a solid state type that senses the water passing with no moving parts in the water?

Or was it capped off for some hull work and never uncapped?

[pfatyol]

Sounds like the dummy plug is in and not the sensor, are there wires going to the thru hull? if not then it is the filler plug.

[TrueBlue]

Either what you saw was as Patrick noted, a dummy plug - removable from the inside of the hull, or, you're confusing the knotmeter with the depth sounder.

[hertfordnc]

Knot meter and depth sounder are next to each other just outboard of the keel about one third forward of the stern. There is a molded factory-made flat spot in the hull for the two sensors.


I followed two wires from the instruments. I am not sure which is which but I figured when I got under the boat it would be obvious.

From the inside the wires lead to plastic threaded ends, one is about 2" and the other is less than an inch. The wires are bedded in a silicone product. A threaded collar is easily movable from both devices but when removed it does not appear that the sensor comes out from the inside. The threaded collar seems to be pulling it snug to the hull, suggesting it is only removed from the outside.

I've researched what a typical installation is supposed to look like and this is apparently not typical.

Now back to my questions;


Are there other ways this thing might have been put together?

Or, is it likely that a factory made cap was put on the outside for hull work?

Or, is there such a thing as a solid state water flow meter that works with Raymarine ST50 ?

thanks

[bettyswollocks]

If it looks like my one from the inside you will have a metal pin going across with a small circlip in the middle. Remove them both then undo the large plastic ring counterclockwise. Put the pin back in to give you leverage and twist back and forth while pulling. It will gradually (depending on how fouled up it is) come out. Be prepared for a real flood.....have a bung ready as you would not believe just how much pressure it has behind it, especially when you are trying to get the bung in.
I have to do my one after only 2 weeks of no use. It doesn't take a lot to stop it spinning. If it hasn't been used for a while you are much better off taking it out as above as you just wont be able to do as good a job while it is under the boat.

[hertfordnc]

no metal pin, no clip, no evidence that it comes out from the inside. I'll try to add photos.

[erps]

We've had three boats with knot meters on them now. All of them had some sort of paddle wheel on them. All of them also had a dummy plug that we used to put in during the off season so the paddle wheel wouldn't foul so bad. The dummy plug didn't have wires going to it though, so I don't know how they could be confused. Pulling out the paddle wheel and sticking in the dummy plug while the boat is in the water has been discussed here before. It certainly got my heart rate up each time I did it.

I think it's going to take pictures so the guys can better understand your situation.

[BarryL]

Originally Posted by hertfordnc

From the inside the wires lead to plastic threaded ends, one is about 2" and the other is less than an inch. The wires are bedded in a silicone product. A threaded collar is easily movable from both devices but when removed it does not appear that the sensor comes out from the inside. The threaded collar seems to be pulling it snug to the hull, suggesting it is only removed from the outside.

Your description matches what a depth finder transducer looks like. Perhaps you have two depth transducers, an old one that is not in service and a newer one for your current instrument.

Usually, the depth and speed transducers are placed on opposite sides of the boat. At least that's the way it is on most boats I have seen. I would look around for another transducer.

Good luck,
Barry

[sailingdog]

Airmar does make a solid state speed transducer, but it is very rare and the piece is bronze and looks like this:



If yours doesn't look like this, it is either a depth transducer or a dummy plug.

[hertfordnc]

Thanks Dog. There was a second depth finder on the boat. Vinatage with a spinning orange light flickering the depth. Now that I think about it, it appeared to read correctly at the pier but I never checked it out underway. It may have been connected. That would explain the two sensors I found.

I'll keep looking.