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Old 05-12-2014, 06:23   #1
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Help: Underwater sanding of depth sounder transducer

During the bottom-paint process, I applied copper paint, barrier coat and ablative to the face of my depth sounder transducer. DMI (the instrument is an old Data Marine depth sounder which worked on the sea trial but not since the launch a few days ago) informs me I need to remove the paint from the face of the transducer. The boat is now in the water. Is it possible to sand the transducer underwater? And if so, what material should I use? What are possible problems?


DMI tells me that the transducer thru-hull cannot be removed. Sanding must be done with it attached to boat.

Very much appreciate your reply. Thank you.
Susan
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Old 05-12-2014, 07:32   #2
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Re: Help:Underwater sanding of depth sounder transducer

You can certainly sand underwater. Various options from waterproof sandpaper, bronze wool, scrubbing pads or any other sanding type product that won't melt in the water. Did DMI recommend sanding or for or against any specific technique for removing the paint? When I installed my new transducer the instructions strongly cautioned against use of certain solvents or caulks containing solvents. If sanding I would be very careful to not remove anything deeper than the paint.

I don't understand that this unit is not removable??? The through hull is probably well glued in and not removeable but typically the actual transducer is mounted into the through hull fitting and the transducer itself will come out. I had an old Datamarine on my boat that was dead that I removed and installed a new Raymarine transducer in the same through hull. This could be done in the water if you pull the transducer quickly and have a plug to pop into the hole. In fact, mine has a special plug that was made for this and screws tightly into the through hull.
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Old 05-12-2014, 08:29   #3
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Re: Help:Underwater sanding of depth sounder transducer

When I remove my depth transducer for cleaning, I pull the transducer w/ one hand and cover the opening w/ the other hand, then insert the plug, to minimize water intrusion.

The speed transducer has a flap to make the removal / replacement easy.

Here is an image of the DMI transducer and blanking plug.

It may be difficult to remove if the gap was painted over, "bonding" the parts together.

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Old 05-12-2014, 16:20   #4
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Re: Help:Underwater sanding of depth sounder transducer

Sue,

Use the softest sort of pad you can find, to avoid scratching the plastic on the transducer. You can always escalate the abrasiveness, but the gentlest one that'll do the job is what I'd suggest.

Ann
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Old 05-12-2014, 16:32   #5
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Re: Help:Underwater sanding of depth sounder transducer

My Morgan had a DMI depth finder on it when I got it. It went out after about 5 years. I had a friend buy me a new one in Florida and bring it to Guatemala when he came down.
It was a different type of transducer, so I pulled the one out of the bottom of the boat while in the water, it had a keeper ring that held it in and was sealed with two O rings. I drilled the insides of the plastic plug out entirely and placed the new transducer in it and filled it with epoxy. Then slid it back in. It is kind of scary when you pull it and a stream of water that big comes sailing up about 2 ft high. It makes you realize how fast your boat would get wet inside if a through hull rotted off. The operation was a success, and the depth finder worked flawlessly for the rest of its time with me. Mac
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Old 05-12-2014, 17:16   #6
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Re: Help:Underwater sanding of depth sounder transducer

Quote:
Originally Posted by wingless View Post
When I remove my depth transducer for cleaning, I pull the transducer w/ one hand and cover the opening w/ the other hand, then insert the plug, to minimize water intrusion.

The speed transducer has a flap to make the removal / replacement easy.

Here is an image of the DMI transducer and blanking plug.

It may be difficult to remove if the gap was painted over, "bonding" the parts together.

That's how I do it with my knotmeter also. A cup or two of water at most. A towel catches that.
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Old 05-12-2014, 19:40   #7
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Re: Help: Underwater sanding of depth sounder transducer

Before you start the surgery, are you really sure that the problem lies in the paint? I've painted over my depth sounder transducers for years with out any problems. Remember that many folks glue the transducer to the inside of FRP hulls with good results. In those cases, it not only must shoot through the hull, but all the accumulated paint as well.

Is it not possible that there is some other problem ? One way to tell is to borrow a transducer from someone and just drop it over the side (with it connected to the head unit, of course!). If that works ok, it could still be in the cabling between transducer and head unit, a faulty transducer, or finally the paint... but I doubt the latter.

Good luck,

Jim
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Old 05-12-2014, 23:05   #8
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Re: Help: Underwater sanding of depth sounder transducer

I'm surprised paint would stop your transducer. Look at the transducer itself I'll bet it's an electrical fault.

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Old 06-12-2014, 09:31   #9
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Re: Help: Underwater sanding of depth sounder transducer

I have a transducer in a wet box on my boat, and it works fine. Through the hull and antifouling paint.
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Old 06-12-2014, 13:29   #10
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Re: Help: Underwater sanding of depth sounder transducer

30 yrs in mar.electronics. Never paint the face of a t-ducer-it reduces sensitivity drastically & this instruction is printed in most manuals.
Many t-ducers come with a yellow & black sticker to emphasize not painting.

Operate your sounder regularly-this flexes the surface of the ducer & "beats" the growth off it-best antifouling there is for it.

If growth has built up,use a sharp paint scraper under water.
Out of water-dip face in full strength bleach to kill growth,wait a bit,& scrape it.
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Old 06-12-2014, 15:20   #11
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Re: Help: Underwater sanding of depth sounder transducer

Quote:
Originally Posted by deblen View Post
30 yrs in mar.electronics. Never paint the face of a t-ducer-it reduces sensitivity drastically & this instruction is printed in most manuals.
Many t-ducers come with a yellow & black sticker to emphasize not painting.

Operate your sounder regularly-this flexes the surface of the ducer & "beats" the growth off it-best antifouling there is for it.

If growth has built up,use a sharp paint scraper under water.
Out of water-dip face in full strength bleach to kill growth,wait a bit,& scrape it.
Well, this

Quote:
it reduces sensitivity drastically
just does not agree with my experience, nor does it explain how internal mounting of the transducer can possibly work.

I suspect that the admonition to not paint is more to do with worries about the solvents in the paint attacking the plastic surface of the transducer than reduction of sensitivity.

And while you have 30 years in marine electronics, I have well more than 30 years practical experience with painted depthsounders that worked quite well...

So, I still don't believe that the paint has caused a total malfunction of the OP's sounder.

Jim
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Old 06-12-2014, 15:29   #12
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Re: Help: Underwater sanding of depth sounder transducer

The problem with bottom paint is the metal in it often wont pass the pulses. I would just scrape it off with your bottom scraper. Had to do that with barnacles many times.
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Old 06-12-2014, 15:40   #13
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Re: Help: Underwater sanding of depth sounder transducer

I think shoot thru the hull xducers are different than ones that don't.
I know it's RF and not sound, but aircraft antennas aren't supposed to be painted either.
Mine has bottom paint on it, if it didn't wouldn't it foul rather quickly?
Last boat I had I put it a shoot thru the hull xducer, and it worked great, makes me wonder why they aren't all that way?
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Old 06-12-2014, 16:14   #14
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Re: Help: Underwater sanding of depth sounder transducer

Airmar makes the majority of recreational transducers.
You can use Water Base a/f paint on them-my apologies-I come from the olden days.Airmar FAQ - powered by phpMyFAQ 2.6.6
Airmar FAQ will answer about any t-ducer question you have.
Cheers / Len
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Old 06-12-2014, 16:41   #15
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Re: Help: Underwater sanding of depth sounder transducer

Most of my boats had two depth units. one was always a shoot thru the hull. if the unit is strong enough it'll do it. I have no idea what "strong enough " means! It seem the fish finders shoot deeper and work well for thru hull work. One of my boats was about 1.25 thick solid glass and the fish finder read to about 600 feet shooting through!
I've not found "shoot thru" units to be specified any different than others.... I just installed them that way or didn't....
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