I think what Joe is saying is that you have most likely been mislead into thinking that you have any "tubes" that may clog. I would agree with that assessment. From the pictures, it appears that you have a relatively normal paddle wheel style marine knot meter. The way I believe these typically work is with a hall-effect switch. It's kinda like a solid state (digital) reed switch. There is a small magnet in the paddle wheel and each turn trips the switch. A square wave pulse is generated and sent to the brain box. The brain converts the frequency of the pulses into a speed through the water.
https://youtu.be/wpAA3qeOYiI You can pretty well confirm this by following the output cable to the terminal board in the brain box. Depending on the design you will have 3 or 4 terminations. I would expect 3. One will be some level of positive voltage (VCC). One will be a reference ground (GND). And the final one will be your signal. If you can use a volt meter to find VCC and GND then that leaves the last one to be the output signal (SIG). With an oscilloscope you can test the output signal in reference to the ground and then spin the paddle wheel to see a square wave on the scope screen. Typically I would expect the pulse to be 0 to +5v but who knows. At the very least I would expect it to be 0v to +VCC. Move through those identification steps and see if you can confirm my suspicions about the design. You might simply find that there is a continuity problem - Loose terminal, broken solder joint, corrosion. With the wires removed from the terminal board you should probably read at least 5v between VCC and GND. Maybe less but still probably not less than 1v. If power is bad then you are not likely to be able to fix the control head (brain box) but should at least shift your attention there. If the power is good then start looking for a signal. Again probably not going to be able to fix the paddle wheel portion but at least shift your attention to the wiring. The point where it exits the paddle wheel unit tends to get a hard flex which can break the conductors inside the insulating jacket. While looking for a signal, move and flex the wire in that area. You may get an inconsistent connection which would momentarily show as speed on the display or as a square wave on the oscilloscope. Let us know what you find. Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Mon, Apr 13, 2020, 08:58 Della Barba, Joe via CnC-List < [email protected]> wrote: > Pitot tube knotmeters are found on fast powerboats and airplanes. They > don’t really work much below 10 knots and in both cases the tubes can get > plugged with bugs or seaweed. > > It took me literally years to find spares for my ancient S-H knotmeter > that has been out of production since the 1980s. The paddle wheel gets > clogged so easily I never leave it in anymore if not using it. > > > > *Joe Della Barba Coquina C&C 35 MK I* > > *www.dellabarba.com <http://www.dellabarba.com>* > > > > > > > > *From:* CnC-List [mailto:[email protected]] *On Behalf Of *John > and Maryann Read via CnC-List > *Sent:* Monday, April 13, 2020 7:49 AM > *To:* [email protected] > *Cc:* John and Maryann Read <[email protected]> > *Subject:* [EXTERNAL] Re: Stus-List speedometer - C&C 35 Mk2 > > > > Have had similar issues with my prior unit – Standard Horizon model 150 > which went out of production some 15 years ago and parts are hard to come > by and only on flea bay. > > What brand and model is your speedometer? > > No – no tubes per se. Yours is all electric. The paddle wheel has a > small magnet in one of the blades. As it rotates, the electric pulse is > picked up by the transducer creating an electrical pulse which is > transmitted via the wire to your bulkhead gauge. The faster the wheel > turns the pulse increases and your gauge registers greater speed. > > > > Vast majority of issues are caused by growth around the blades, the blade > shaft or water facing of the transducer. Ensure this is absolutely clean > and blades turn freely. Normally requires cleaning several times each > season. If this is good, then your transducer may be worn out / faulty. > Virtually all are made by Airmar and their web site has an excellent cross > reference of your unit to their current part number. This will require re > running the wire to your gauge which is often PITA and involves boat yoga. > In my case this fixed the problem. > > > > When I had problem with other units of my instruments and parts were > nowhere to be found, Santa was very nice and provided a new suite with all > the latest whiz bang features > > > > Best of luck > > > > John and Maryann > > Legacy III > > 1982 C&C 34 > > Noank, CT > > > > > > > > > > *From:* CnC-List [mailto:[email protected] > <[email protected]>] *On Behalf Of *General Gao via CnC-List > *Sent:* Sunday, April 12, 2020 9:18 PM > *To:* [email protected] > *Cc:* General Gao > *Subject:* Stus-List speedometer - C&C 35 Mk2 > > > > My speedometer was not behaving well last season. I am planning to fix it > myself. Googled the keyword, it came up a few documents suggesting blowing > the tube to clear clog. I looked at my gauge and where there sensor is, I > don't seem to find a tube there. Please see the pictures attached in the > link. Could someone help me with the diagnostics? Thank you in advance. > > > > https://drive.google.com/open?id=1nYSpxnzb1BImby5jz3ASLnSD3OYxKT3P > <https://protect2.fireeye.com/v1/url?k=837e7d76-dfe835d6-837e5401-0cc47adca788-b178bd7dca34f18d&q=1&e=756d065d-3ce3-4c05-a863-e82db01be882&u=https%3A%2F%2Fdrive.google.com%2Fopen%3Fid%3D1nYSpxnzb1BImby5jz3ASLnSD3OYxKT3P> > > > > https://drive.google.com/open?id=1bBgw-Ln_wr2Qae-GUCk3L_I_dAQO-ekY > <https://protect2.fireeye.com/v1/url?k=8f8e2f51-d31867f1-8f8e0626-0cc47adca788-77686a1316f3f8b1&q=1&e=756d065d-3ce3-4c05-a863-e82db01be882&u=https%3A%2F%2Fdrive.google.com%2Fopen%3Fid%3D1bBgw-Ln_wr2Qae-GUCk3L_I_dAQO-ekY> > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each > and every one is greatly appreciated. If you want to support the list - > use PayPal to send contribution -- https://www.paypal.me/stumurray > >
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