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Catalina 25 Specific Forum

removing knot meter

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jerlim
Master Marine Consultant

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USA
1484 Posts

Initially Posted - 05/15/2009 : 04:31:22

It's time to replace the original knot meter - am uncertain w/ what at the moment - but I'm having a tough time getting the cockpit side off. The interior guts and housing are easy enough to disassemble and remove, but the external ring is pretty snug and I don't want to damage the surface.

Any suggestions?

Many thanks!

Jerry

Edited by - on

fpill
1st Mate

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USA
51 Posts

Response Posted - 05/15/2009 : 08:40:11

I have been thinking about a similar idea, but instead of replacing the knot meter I was going to put a mount for my GPS. Is there any reason to have both the paddle wheel knot meter and GPS knot meter?

Jerry: Have you found your replacement knot meter already? Are you sure you need to remove/replace the external ring?

Edited by - fpill on 05/15/2009 08:41:56

Voyager
Master Marine Consultant

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USA
5353 Posts

Response Posted - 05/15/2009 : 20:09:41

I like having both a GPS and the knotmeter on Passage, because I can compare my VMG from the GPS and the velocity through the water (currents) and determine what the current strength is. With Passage on the Housatonic River, I have been motoring at 5.1 kts against a 4.5 kt current, moving at about 0.6 kt VMG. The scenery goes by painfully slowly at that rate, but at least I know why.

For those who do not have to deal with river or tidal currents, I don't think there's any reason to have a knotmeter, as the GPS will give you a much more accurate reading of CMG and VMG.

I do have a problem with the knotmeter readout: if I read it with the naked eye, there's nothing to see. It's just grey on grey - no numbers. But, when I put on my polarized sunglasses, VIOLA!, I can see the data clearly. I think I should be able to buy some kind of polarized mylar film to put it over the indicator, but have not run across it so far.

Lastly, I did not remove the knot meter, but I did pull out my depth gauge display from the starboard cockpit bulkhead (they are a pair).

I removed the screw attachments in the rear but found the front section was really stuck on hard. I took a very thin blade knife and wedged it in between the gauge and the bulkhead, tapped the back of the housing with a rubber mallet and I finally dislodged it.

Afterward I removed all the old electronics and replaced it with a smaller unit. The new unit fit inside the same housing and is a lot easier to read.

Edited by - on

skipperof ballanato
Deckhand

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13 Posts

Response Posted - 05/16/2009 : 04:35:33

I would love to have your paddlewheel if it is from a Navman 3100. My paddle wheel got sanded off during my blister fixin/bottom painting ordeal this spring, and I cant find a replacement anywhere as Navman is no more.

Jim Crane
Ballenato
C25 #5034
TR-FK
Rome, Ga

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fpill
1st Mate

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USA
51 Posts

Response Posted - 05/16/2009 : 06:26:23

On Great South Bay, the currents are minimal,(except near the inlet to the Atlantic) but the bay is very shallow.
<i>http://sailvector.com/696/South-Oyster-Bay-to-Great-South-Bay-Long-Island-Ny</i>
I can appreciate the use of both the paddle wheel and GPS to find currents however.

Is there a way to troubleshoot the knot meter to find if the problem is the paddle wheel or the electronics?
I checked the paddle wheel before splashing the boat last weekend, and it spun fine. Once in the water I only had readings of 0.0. I'm not sure if I have the original knot meter, and have no manuals for it.

Edited by - on

Deric
Captain

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USA
408 Posts

Response Posted - 05/16/2009 : 12:31:53

I removed my broken know meter as well. Because the housing was set hard (glue) in the cockpit bulkhead, I had to use a heat gun to loosen the glue while working a stiff flat-edge to get the housing out. The heat gun was the tool that helped.

Be careful with the heat gun should you decide to use it... go slow, start with the least amount of heat required to get the glue to loosen.

Good luck,
Deric

Edited by - on

Voyager
Master Marine Consultant

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USA
5353 Posts

Response Posted - 05/16/2009 : 20:05:20

Frank -
I'm not 100% sure about this, but I believe the paddlewheel has a small magnet in it and when it passes a "Hall-Effect" or reed switch in the hull fixture, a semiconductor or electromechanical switch senses the closure of the switch.

If the circuit in the speed guage "head" knows the distance through which the paddle wheel turns one revolution, it can calculate distance divided by time which, of course, is speed.

Hall effect switches are extremely reliable (unless they get hit with a high current such as lightning or static discharge). Reed switches will eventually fatigue and fail.

If you have a Digital Multimeter or an Ohm-meter, you can see whether the switch is working.

If it's working, then the fault may lie in the cable. It always pays to look for corrosion.

If the cable looks clean and you get continuity with the ohm-meter, then the head has failed.

At that point, check e-Bay or Craig's list.

Edited by - on

jerlim
Master Marine Consultant

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USA
1484 Posts

Response Posted - 05/17/2009 : 18:20:52

Deric - thanks for the advice, I got it out, and fortunately didn't need the heat gun

Edited by - on

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