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Old 13-09-2012, 02:20   #1
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Depth readout problem with bronze thru-hull

I installed a bronze skin fitting to house my Nexus depth triducer in my timber yacht last year, replacing the 3 year old plastic fitting. All worked fine for months but recently the depth readout suddenly stopped, giving only 3 horizontal lines. Speed, temperature and all other function continue to work fine. A Nexus tech came to the boat, installed a new WSI box, triducer and cable, which work fine when the triducer is dropped in the water over the side. But when screwed into the skin fitting the depth readout doesn't work but all other functions do work. The skin fitting is not grounded or looped. This has both the Nexus people and me mystified, any suggestions?
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Old 13-09-2012, 04:15   #2
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Re: Depth readout problem with bronze thru-hull

Greetings and welcome aboard the CF, powerpak.

It's seems you've brought us a real puzzle.
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Old 13-09-2012, 06:32   #3
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Re: Depth readout problem with bronze thru-hull

Since it now works when tested dropping the transducer over the side and into the water, my guess is that just maybe when you install it back into the boat and the cable is run a different path then look carefully at that path. Could it be that some sort of electronic interference is causing a portion of that info to be distorted as it runs from the transducer to the display??
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Old 13-09-2012, 06:43   #4
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Re: Depth readout problem with bronze thru-hull

Welcome to the forum Powerpack.

That is a strange one.
Three thoughts
1. A lot of the transducers have a little plastic flap in the housing that reduces the water coming in. Is this broken and jamming under the transducer face?

2. You have not mounted the transducer internally? This only works with solid fiberglass not wood.

3. Is there a break in the cable. Some of these can be intermittent and show up when the cable is bent a certain way.
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Old 13-09-2012, 15:40   #5
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Re: Depth readout problem with bronze thru-hull

Thanks guys.
Noelex, the housing doesn't have a flap and the transducer is installed thru the hull, not internally. Also the cable is new and clear so not broken.
Lancelot, the cable route is the same as when it worked before, I've turned off all systems so the only current nearby should be the input from the solar panel, I'll try rerunning it away from that on the weekend.
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Old 13-09-2012, 15:51   #6
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Re: Depth readout problem with bronze thru-hull

There could be weed growing across the window where the depth beam comes out. Even growth NEAR to the thru-hull could stop the beam hitting bottom, especially if the triducer is mounted at an angle. When was the bottom last cleaned?

Had the reverse issue, where depth worked but speed didn't, was bottom growth.

The transducer and the blank plug often get neglected when it comes to anti-fouling paint! I get a beautiful mass of weed on the end of the blanking plug whenever I leave it for a few weeks...
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Old 13-09-2012, 15:54   #7
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Re: Depth readout problem with bronze thru-hull

It must be a Nexus thing. Just last week I posted about my paddle wheel log not working for no apparant reason, yet when moved to the other through hull (I have the 2 x 42 mm system) it now works perfectly
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Old 13-09-2012, 16:49   #8
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Re: Depth readout problem with bronze thru-hull

The boat was last antifouled a year ago, my first reaction to the problem was to dive on the transducer and clean it and around it with a broom, the growth was only light so I dont think weed is the problem. Hopefully its not a Nexus thing, the system worked well for the last 5 years, the problem only arose recently.
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Old 13-09-2012, 18:48   #9
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Quote:
Originally Posted by powerpak
The boat was last antifouled a year ago, my first reaction to the problem was to dive on the transducer and clean it and around it with a broom, the growth was only light so I dont think weed is the problem. Hopefully its not a Nexus thing, the system worked well for the last 5 years, the problem only arose recently.
OK Ive now rerun the cable away from all potential interfernce, same result. I also rechecked by hanging the triducer ove the side again, works fine there. Only other thing I can think to try is to ground the skin fitting to the engine block, does that create a potential problem with lightning strike blowing out the skin fitting?
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Old 13-09-2012, 20:42   #10
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Re: Depth readout problem with bronze thru-hull

Tried grounding the skin fitting to the engine, no difference. Nexus are suggesting maybe stray current at the marina blew my old transducer and is now preventing the new one from working, so I'll go for a sail and also dive and clean the bottom again around the transducer while in cleaner water. Will keep you posted, but please let me know if you have any other thoughts.
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Old 14-09-2012, 00:58   #11
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Re: Depth readout problem with bronze thru-hull

If its a timber yacht I don't see how "grounding" is any different installed in the boat, or with the transducer over the side.
The timber is non conducting, so the only electrical conection are via the wires, or the seawater acting as an electrolyte. This would be the same installed, or over the side.
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Old 14-09-2012, 01:06   #12
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Re: Depth readout problem with bronze thru-hull

Does it have the metal tangs for holding it in the skin fitting? If so try shorting them together with a bit of wire and seeing if it still reads when dangled over the sides. I'm thinking there may be a circuit in the tangs causing a problem when shorted. Highly unlikely, I know, but stranger things have happened!
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Old 14-09-2012, 01:09   #13
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Re: Depth readout problem with bronze thru-hull

And on a similar note the problem could be caused by some kind of capacitive or inductive effect between the metal through hull and internal circuitry of the transducer.
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Old 14-09-2012, 01:19   #14
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Re: Depth readout problem with bronze thru-hull

No metal tangs, just a plastic housing with O rings and a plastic screw-down to hold it in place. The capacitive or inductive effect could possibly be an explanation, I'll run that by the Nexus guys.
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Old 15-09-2012, 19:10   #15
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Re: Depth readout problem with bronze thru-hull

EUREKA! Took the boat out of the harbour today, intending to dive and give the bottom an extra scrub around the transducer. As soon as we were about 10m from the dock the depth sounder started working perfectly. Took a good long run down the river and back, worked perfectly all the way, then once back at the dock it immediately started to play up again, jumping between an accurate reading, 0.3metres and nil readout. My conclusion is that there is some stray current around the dock, possibly from a large steel yacht adjoining, that is interfering with the tranducer electronics, as suggested by Reefmagnet. Many thanks everybody for your suggestions, my only query now is should I be concerned about galvanic action with the steel boat next door?
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