Knotmeter, impeller, and transducer paint

[obsailor]

After carefully painting my depthsounder transducer with special paint this spring, I also applied it to my knotmeter (old standard horizon) impeller to keep out the pesky barnacles. Launched the boat yesterday and sailed to my summer harbor - no knotmeter reading, nothing, nada (reading of 0.0 so there is power)! All other instruments working fine.

I will pull the impeller in a few days (it spun easily this spring) but wondered if the transducer paint on the impeller interfered with getting a reading? Just for once it would be nice to have everything on the boat working at the same time.

Any ideas? Thanks

 

[higgs]

Re: knotmeter impeller & transducer paint

Everything working at the same time....hahahahahahahahaha....it's a boat.

 

[higgs]

Re: knotmeter impeller & transducer paint

Sorry - I know I didn't help with that last post. I have never painted my knot meter with anything and it usually works fine. Perhaps the paint is interfereing with the impeller. Pull it out and spin it and you may be fine. That would be my first step.

 

[navigator97]

Re: knotmeter impeller & transducer paint

MDR Makes a Transducer Paint to brush on the paddle wheel blades. I have used it for years. You do have to be sure that the paint does not get on to the little pin "axel".

The other caution is that it doesn't take much time sitting in the water for those very small pesky critters to take up residence around the paddle wheel and keep it from turning. they are shaped like shrimp and smaller than mesquitos. If it sat in the water for several days before the boat was moving thru the water, that would do it. You have to quickly pull the transducer and put in the dummy plug, to allow you to clean the transducer paddle wheel. WE have one person hold a basin upside down over the transducer while the other pulls it and inserts the dummy. We then sponge up the water in that bilge section after the completed process. I put a cork in the limber hole temporarly while doing all this to contain the water to that bilge section.

 

[Joe]

Re: knotmeter impeller & transducer paint

After you scrape the bottom paint off the transducer, you might try smearing a little Desitin (diaper rash ointment) on the paddles. It is greasy so it won't dribble down into the pins and dry. The ointment is basically zinc oxide but it is toxic to marine growth... it's a small investment and it won't clog up the impeller.

 

[Ron20324]

I take out the paddlewheel then paint the rest of the transducer then replace pin and paddlewheel. Last weekend I got no speed reading, so I had to clean the paddlewheel while underway (less water comes in) and got a number of mud shrimp out. They were swimming around the puddle on the floor! Yesterday, after just one week, the they were back and the wheel didn't turn. I thought sailing would clear them out, but didn't. I think we slammed down off a wave, and that blew them out of the wheel.

It's that warm time of year, so I'll have to start pulling the wheel after sailing, then put it back in for the next one. I have the GPS/chart plotter for the speed reading, but the paddlewheel keeps the boats mileage log updated.

 

[jimg]

Knotmeter

Also, remember that the paddlewheel is just a small magnet that spins past a sensor in the body of the transducer, from which the knotmeter counts revolutions, etc. etc. (Essentially the same technology as a $12 bicycle speedometer). Anything, such as antifouling paint, that blocks the reading of that spinning magnet will give a big zero on the knotmeter. If the boat sits for a long time, it may be better to take it out when you're not there (with the dummy plug in of course).

 

[firehoser75]

Second for Diaper Rash Ointment

Like Joe, I use a diaper rash ointment (Penaten), but I mix it with a little white lithium grease to improve the "sticking power". Just put it on the wheel (don't go too thick) and on the sides. For me, it works quite well.
Tom

 

[Warren Milberg]

I think most makers of knotmeters advise against painting the impeller with anything. Depth sounder transducers can usually be painted with one thin coat of bottom paint. I use ordinary zinc oxide cream on my knotmeter impeller (cheaper than Desitin, et al) and it typically lasts 1-2 months before requiring recoating. I sometimes can free up my impeller when crud has gathered on it by going at speed in reverse for a short distance.