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Old 17-11-2020, 08:33   #1
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Transducer sealed to inside of hull

The PO of my 89 C27 sealed a depth transducer to the inside of the hull on the starboard side just aft of the keel where the angle is as flat as could be. White epoxy guessing maybe 4200. So his point was obviously to "sound" through the fiberglass hull. The wire is cut and has been out of service for a long time. This boat does not have a thru hull for a transducer. I know a transducer will "sound" through a hull if it is surrounded by water or sealed in with no air bubbles between the face and the bottom but I don't like the feel of doing it that way. I have tested this on an aluminum boat. My questions are:

Does anyone know about this setup and what if any latency issues could cause a bad depth to be returned possibly reporting a depth deeper than actual? And also might affect depth range? Might be negligible. Draft is 4 ft and I don't like getting anywhere near that depth so if the true depth is 12 ft and my sonar says its 12.4ft It might not be an issue and i can always adjust the draft setting to compensate.

I like not putting another hole in the bottom of the boat but is it a workable option to get the boat yard to make a thru hull in a better place like forward of the fin keel where it will be looking down with very little or no slant range? Making a proper setup that would be deep enough to avoid most aeriation.

I currently have my transducer mounted on a small pole jury rigged off the stern with no holes or screws in the boat and as normal my temporary setup has become permanent and I want to get this setup more in line with a proper setup.

Lastly, if this is 4200 or some tougher epoxy/sealant, what would be the best way to clean this off of my hull? I am very OCD about all spaces being clean and free of un-needed or abandoned stuff.

I can use my jury rig for now as I have a haul out for bottom work early next year and want to have a plan for all work when that happens.
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Old 17-11-2020, 09:01   #2
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Re: Transducer sealed to inside of hull

Quote:
Originally Posted by Mer Sauvage View Post
Does anyone know about this setup and what if any latency issues could cause a bad depth to be returned possibly reporting a depth deeper than actual? And also might affect depth range?

As long as the fiberglass is solid (no foam core) it works fine although there will be some attenuation. The attenuation reduces the maximum depth at which the sounder will work. For fishfinder-type sounders it increases the minimum size object that can be detected in the water column. Generally, it does not affect shallow water performance.



Quote:
I like not putting another hole in the bottom of the boat but is it a workable option to get the boat yard to make a thru hull in a better place like forward of the fin keel where it will be looking down with very little or no slant range? Making a proper setup that would be deep enough to avoid most aeriation.


Only a matter of money. Ideally you would schedule it while the boat is already hauled out.



Quote:

Lastly, if this is 4200 or some tougher epoxy/sealant, what would be the best way to clean this off of my hull? I am very OCD about all spaces being clean and free of un-needed or abandoned stuff.

4200/5200 are polyurethane and are soft enough that you can saw through them with a wound guitar string or maybe a sharp, flexible knife if you use some oil on the blade. Then clean up with a die grinder and abrasive disc.


If it's epoxy, that won't work, you would probably have to cut through the transducer with a cutoff wheel or hacksaw, then again use a die grinder and abrasive disc to clean up whatever's left. Or it may be possible to break the bond with a sideways hit on the transducer with a sledge (doubtful). Any method can damage the hull if executed carelessly.
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Old 17-11-2020, 09:13   #3
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Re: Transducer sealed to inside of hull

Most of mine have been inside the hull, even on thick hulls and worked great. I have used epoxy or silicone.
You tested on an aluminum boat? I thought they wouldn't work shooting through metal?
4200 isn't epoxy, it's sealant. They are not the same.
4200 should come off fairly readily with a scraper and sanding. Heat gun if necessary. But the key thing when putting a transducer inside is a flat surface with no debris or bubbles /pits. For that reason I would sand well anyway.
One a 1-1.25" thick hull my fish finder would read to over 400 feet of depth.
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Old 17-11-2020, 09:22   #4
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Re: Transducer sealed to inside of hull

I've had 2 boats with transducers glued to the inside of the hull. Both worked perfectly. As far as epoxy goes .. I just gave it a whack and the transducer came right off.
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Old 17-11-2020, 10:14   #5
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Re: Transducer sealed to inside of hull

Splice a cable to the existing transducer and see if it works. It probably is 200 KHz. If it is a shield and 1 or 2 wires then it is a simple depth transducer. If there are more wires then it could be depth and temperature. Most depth transduces come with 30' cables. Some Garmin and Raymarine depth sounders test for a temperature thermistor. i.e. Airmar DT800. The sounders will work if you substitute a 10K resistor across the 2 wires where the sounders look for the thermister..
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Old 17-11-2020, 10:17   #6
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Re: Transducer sealed to inside of hull

Airmar (major transducer maker) makes complete transducers with collard that are glued to the inside of the hull and filled with antifreeze. The collar has a beveled bottom so an angle marked on the collar can be set for the angle of the boat bottom where you mount it.



The actual ducer snaps into the collar.


Easy install and works great on solid glass boats...others as indicated in instructions.
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Old 17-11-2020, 10:33   #7
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Re: Transducer sealed to inside of hull

There is no problem with a transducer "shooting" through the solid fiberglass save for a bit of range attenuation. My unit looses contact with the bottom at something greater than 250 ft.

4200 is quite tough stuff but it should be possible cut through it with flexible knife, serrated if possible, pressed flat against the hull.

A better idea I used was to mount the transducer in a mineral oil filled cylinder made of 4" PVC pipe beveled to match the hull and bonded to the hull with 4200. The transducer is fitted into a end cap fitting over the pipe suspending the transducer in the oil. That way the transducer is easily removed if it ever needs inspection or replacement and the oil guarantees an non-compressible media between the transducer and the hull. Been working great for almost three years.
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Old 17-11-2020, 11:00   #8
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Re: Transducer sealed to inside of hull

they come ready made doing the same thing....
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Old 17-11-2020, 11:10   #9
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Re: Transducer sealed to inside of hull

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they come ready made doing the same thing....

But I had so much more fun doing it all myself!
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Old 17-11-2020, 11:38   #10
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Re: Transducer sealed to inside of hull

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But I had so much more fun doing it all myself!
Looks good C-A!

Is the cap sealed to the beveled pipe that is glued to the hull with 4200? Do you check the oil every so often? Which oil? Thanks!
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Old 17-11-2020, 12:00   #11
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Re: Transducer sealed to inside of hull

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Looks good C-A!

Is the cap sealed to the beveled pipe that is glued to the hull with 4200? Do you check the oil every so often? Which oil? Thanks!
The end cap is seal is unmodified. It just presses down until it makes a snug fit. I used "mineral oil" from the drug store. I probably should check it but I admit I have not.
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Old 17-11-2020, 12:18   #12
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Re: Transducer sealed to inside of hull

Have this set-up on my RIB with a Garmin MFD, it works flawlessly.
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Old 17-11-2020, 12:21   #13
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Re: Transducer sealed to inside of hull

I've had / have three different boats with the transducer sealed to the inside of the hull with absolutely no problem.

The first was a foam core. The core was ground down to the outer glass layer and epoxied into position.

The second is a solid glass hull and I simply used an old soft drink bottle to form a bath which was filled with silicone.

I used the silicone bath technique in a chamber on my polypropylene tender too and it works well also.

The most important thing about a "bath", whether it be resin or silicone based, is not to get any air trapped under the transducer. My technique is to fill the bath with the silicone then , lower the transducer in at an angle before rotating it into its correct position.

Based on my experiences I will never make a hole in the hull for a transducer again.

Regards,

Brian
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Old 17-11-2020, 12:23   #14
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Re: Transducer sealed to inside of hull

Quote:
Originally Posted by Mer Sauvage View Post
The PO of my 89 C27 sealed a depth transducer to the inside of the hull on the starboard side just aft of the keel where the angle is as flat as could be. White epoxy guessing maybe 4200. So his point was obviously to "sound" through the fiberglass hull. The wire is cut and has been out of service for a long time. This boat does not have a thru hull for a transducer. I know a transducer will "sound" through a hull if it is surrounded by water or sealed in with no air bubbles between the face and the bottom but I don't like the feel of doing it that way. I have tested this on an aluminum boat. My questions are:

Does anyone know about this setup and what if any latency issues could cause a bad depth to be returned possibly reporting a depth deeper than actual? And also might affect depth range? Might be negligible. Draft is 4 ft and I don't like getting anywhere near that depth so if the true depth is 12 ft and my sonar says its 12.4ft It might not be an issue and i can always adjust the draft setting to compensate.

I like not putting another hole in the bottom of the boat but is it a workable option to get the boat yard to make a thru hull in a better place like forward of the fin keel where it will be looking down with very little or no slant range? Making a proper setup that would be deep enough to avoid most aeriation.

I currently have my transducer mounted on a small pole jury rigged off the stern with no holes or screws in the boat and as normal my temporary setup has become permanent and I want to get this setup more in line with a proper setup.

Lastly, if this is 4200 or some tougher epoxy/sealant, what would be the best way to clean this off of my hull? I am very OCD about all spaces being clean and free of un-needed or abandoned stuff.

I can use my jury rig for now as I have a haul out for bottom work early next year and want to have a plan for all work when that happens.
I can't answer most of your questions but RTV worked will on a SR31 which is ply and glassed over. It read fine and was not an expensive depth finder.
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Old 17-11-2020, 12:53   #15
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Re: Transducer sealed to inside of hull

Like some others above, I had very reliable depth sounder transducers epoxy fit to the hull and in mineral oil wells. It's easy to select the function of a plausible location to mount the transducer by placing the transducer on a plastic bag of water. A "zip-lock" style sandwich bag partially filled with water and without air bubbles works well.
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