Knots?

[BROGERS]

For some unknown reason my knot meter on my 1994 29.5 Hunter has quit working this season. It appeared to be functioning while I was painting the keel this spring but did not check it out until later when I did my spring launch. It now reads (0) no matter the speed I'm going. Depth reading is still working fine.

I recently installed a Garmin GPS chartplotter and did not find anything in the pilot area which would indicate that it is disconnected.

Where do I start to troubleshoot this problem and has anyone else experienced this?

L. W. Rogers
Air Mobile

 

[Warren Milberg]

Assume you tried the obvious: pull out the knot meter impeller (don't forget to put a dummy plug in.....) and spin it by hand while someonr checks the readout in the cockpit? While its out(1) see if it's fouled or (2) see if the impeller axle has somehow bent. On a previous boat with a mid-80s Datamarine Knot Meter, the impeller axle bent slightly (probably due to hitting something underwater). I replaced it with a SS bolt of the right diameter and cut its head off. Your good news is that the readout unit seems to be working. Work back from there to the impeller checking for corrosion in the sending unit line.

 

[Ron Roman]

If all of the above doesn't work for you, it most likely is your transducer. Mine quit working last summer. When I replaced the transducer everything was back to normal.

 

[Laurinurse]

Same thing happened to ours- come to find out it got one of the paddles knocked off during lau Ching after bottom job

 

[GreggL]

I recently had the same issue. After pulling the impeller there was all sorts of debris lodged in there. Once it was cleaned out, the speed meter worked perfectly fine again.

 

[BROGERS]

Assume you tried the obvious: pull out the knot meter impeller (don't forget to put a dummy plug in.....) and spin it by hand while someonr checks the readout in the cockpit? While its out(1) see if it's fouled or (2) see if the impeller axle has somehow bent. On a previous boat with a mid-80s Datamarine Knot Meter, the impeller axle bent slightly (probably due to hitting something underwater). I replaced it with a SS bolt of the right diameter and cut its head off. Your good news is that the readout unit seems to be working. Work back from there to the impeller checking for corrosion in the sending unit line.

How do I access the transducer?

 

[Warren Milberg]

I'm not familiar with the interior of the 29.5, but on my H28.5 access to the knot meter transducer (and depth sounder) is located a few feet forward and to port of the keel in a tiny compartment under the V-berth. If you've had your boat out of the water, you should have been able to see the location of impeller. In any event, look for access to the transducer in all of the lowest points of your boat's interior hull unusually forward and to one side or the other of the keel. Make sure you have dummy plug to install if your boat is in the water.

 

[syoun10]

I find that just cleaning it out is not always a complete solution. I soak the paddle end of the probe in vinegar for 24 hrs, then clean out any debris remaining. This takes out any barnacle-like stuff which is the main problem.

 

[onecoolair]

I use the KISS principle..... I pulled mine out one day to clean it. Put the dummy plug in. Cleaned up the mess and dried out the surrounding bilge area. Then forgot about it just started using the COG off the gps. That was about 6 years ago. Never looked back.

 

[syoun10]

I use the KISS principle..... I pulled mine out one day to clean it. Put the dummy plug in. Cleaned up the mess and dried out the surrounding bilge area. Then forgot about it just started using the COG off the gps. That was about 6 years ago. Never looked back.

This is a fine solution if you are not interested in the DIFFERENCE between the GPS speed and the through-the-water speed. I (or rather my electronics) uses this difference to calculate real wind vs apparent wind, and a host of other relevant factors, specifically related to current.

 

[catsailor]

I use the KISS principle..... I pulled mine out one day to clean it. Put the dummy plug in. Cleaned up the mess and dried out the surrounding bilge area. Then forgot about it just started using the COG off the gps. That was about 6 years ago. Never looked back.

Two thumbs up. Me too.

Yeah, I know the difference between SOG and STW, but I can either guess the difference or don't care, depending on the day. Anyone who can't figure the true wind speed and direction in their head has forgotten their physics anyway, and cruisers don't worry over speed polars and target velocities. We understand, we just don't worry.

 

[onecoolair]

Catsailor...Some seem to have forgotten, we are suposed to be relaxing. I did not even have a knot meter back in my younger days racing j boats. Did not need one in one design racing. Now I just do not care!

 

[tlowum]

How do I access the transducer?

Pull the cushions out of your vee berth and there is an access panel covering a storage compartment (just forward of the table). Look inside the storage compartment and I believe there is another access panel at the bottom. It's near the potable water pump, if you know where that is. You have to crawl down into the compartment to reach it. If you remove this panel, you should see the knotmeter transducer and the depth transducer both sticking through the bottom of the hull. Hopefully, there is a plug there as well. At least on my 29.5, the knotmeter transducer is the starboard one. Remove it by unscrewing the locking ring and quickly stick in the plug because you will have a gushing geyser of water coming through the hole! The water that comes in will drain down to the bilge pump so not to worry. Reverse the process to reinstall.

 

[BROGERS]

Thanks for the directions. I'll try it out and let you know the results.