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Old 11-04-2015, 17:58   #1
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Bonding Sonar Transducer to inside of hull

Hello All
Im curious about bonding a transducer to the inside of my boat, Has anyone done this and can you comment on the signal degradation or lack thereof?
My boat came with a stand alone depth sounder and an unused sounder function in my chartplotter . Id like to have the plotters resolution of the bottom for fishing but would rather not drill another hole....
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Old 11-04-2015, 18:42   #2
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Re: Bonding Sonar Transducer to inside of hull

If you don't already have the transducer, the one that sits in an antifreeze filled cup is the best choice.

Airmar p79, See if they have one for your plotter.

P79 In-Hull - Airmar Marine Transducers

I installed one in my boat and it works fine. It's adjustable for angled hulls.
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Old 11-04-2015, 19:27   #3
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Re: Bonding Sonar Transducer to inside of hull

Quote:
Originally Posted by rwidman View Post
If you don't already have the transducer, the one that sits in an antifreeze filled cup is the best choice.

Airmar p79, See if they have one for your plotter.

P79 In-Hull - Airmar Marine Transducers

I installed one in my boat and it works fine. It's adjustable for angled hulls.
Do you use it for fishing? I just bought this transducer thinking it was a through-hull. I am fine with not drilling a hole as long as we will see fish!
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Old 12-04-2015, 08:18   #4
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Re: Bonding Sonar Transducer to inside of hull

Silicon works just fine, but the transducer needs to be mounted reasonably level (manufacturer usually gives specs on permitted mounting angles) and in an area where the transducer is submerged in water (just by a few inches is fine). You can create a sump just for this purpose and fill with water (some use mineral oil).

Clean the mounting surface and face of the transducer. Squirt a liberal dollop of silicone on the mounting surface and press transducer into place taking care to eliminate gaps (pressing firmly should do this). Let cure and the fill area with liquid of choice. This is the recommended method of some manufactures (like Vexilar).

I did this as a temporary solution many years ago for a failed transducer using the intergral sump in the port head. The hull forms the bottom of this sump and a small amount of water is always in the bottom. Has worked so well for many years that its now the permanent solution.

You will lose a small amount of performance, but typically not enough to be relavant to sailing using (so what if your max depth range goes from 250' to 225').
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Old 12-04-2015, 08:47   #5
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Re: Bonding Sonar Transducer to inside of hull

<rant> NEVER use silicone seal on anything you ever plan to touch again - it leaves a nasty film that you have to *sand* off. Use 4200 instead, 5200 if you *really* know it will be permanent</rant>

I've installed sonar/depth finders on 2 of my sailboat. Both the same way.

Get a (short) piece of PVC pipe big enough for the transducer to fit in easily.

Get some plumbers putty and use it to seal the pvc to the hull where you think you will get good results (for a sailboat, *not* over your centerboard, deep keel, etc).

Fill the PVC with water. Drop your transducer in there and test the performance. Repeat till satisfied.

Remove the PVC pipe and plumbers putty. Carefully clean the mounting location with <your favorite awful smelling, cancer causing cleaner>

Mount the PVC pipe (or a new one if you don't want to waste time cleaning a $2 part) using 4200 [or 5200 if you think it's permanent]. Wait till the mounting is good and dry, test for watertight.

Fill the PVC pipe with your choice of water or <cooking/light> oil. Water is less messy, easy to replace, but evaporates over time.

Drop in the transducer, re-test. Enjoy
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Old 12-04-2015, 08:56   #6
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Re: Bonding Sonar Transducer to inside of hull

This is an easy install by bonding directly to the inside of the hull using epoxy resin. I've done this on 4 boats so far and had perfect success every time.
Here is the process I use.
1. Find the best location - fill a ziplock bag with water, make sure no air bubbles, wire up the transducer. Place the bag on your preferred location in the hull and put the transducer on top in it's correct orientation. the display should read if it's a good spot. Alternatively i've just laid the transducer against the hull in my last install and gotten a good read.
2. Prepare the location.- once you have the spot use sandpaper or a stiff wire brush to remove any paint or loose debris.
3. make a dam - I use modeling clay to create a dam that i will fill with epoxy for the bonding step.
4. Pattern bond - Wrap the transducer in cellophane, Mix up enough epoxy so that when you add it to the form made by the dam that it will allow the wrapped transducer to settle in but not cover it. Here you are just trying to create the pattern of the bottom of the transducer. (Don't over mix the epoxy and atempt to have no air bubbles. The air bubbles will degrade the signal.) The reason for this step is that the epoxy shrinks as it cures and if you did this all in one there might be an air space between the transducer and the epoxy bed.
5. Final bond- here we go deep breath as this is where we commit. Remover the wrapped transducer from the dried epoxy bed. Remover the cellophane. you may want to lightly scuff the transducer wit sandpaper to get a better bond. Mix up a small amount of epoxy (again no air bubbles), full the pool created by the removed transducer. press the transducer into the wet epoxy and make sure it is secure while the epoxy cures. Don't panic if the transducer doesn't read at this point. The uncured epoxy doesn't transmit a good signal. Once the epoxy cures all will be fine and your transduce should read correctly.
6. final adjustments - set your offsets and go sailing.
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Old 12-04-2015, 09:06   #7
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Re: Bonding Sonar Transducer to inside of hull

I'm replacing all my electronics with Garmin. The installer plans to use an inside the hull transponder bonded directly to the hull, no water bath.

This will be fine for sailing but pretty useless for fishing. For detailed fish finding I guess that they are using CHIRP sonar that displays either on my multifunction display or a dedicated display. Not cheap but the little I've read it seams pretty impressive.

Rich


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Old 12-04-2015, 10:13   #8
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Re: Bonding Sonar Transducer to inside of hull

I'm going to mention one thing not covered here.
If you have a foam cored hull (like my Dragonfly), you need to remove the foam core to make this work.
It can be done in the water, but be really careful !
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Old 12-04-2015, 12:00   #9
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Re: Bonding Sonar Transducer to inside of hull

Quote:
Originally Posted by nekkidsailin View Post
<rant> NEVER use silicone seal on anything you ever plan to touch again - it leaves a nasty film that you have to *sand* off. Use 4200 instead, 5200 if you *really* know it will be permanent</rant>
...
And 5200 cleans up easy, right?

A uique position, with which I disagree. You don't need an aggressive adhesive for this application (which is why the manufactures don't recommend it). Never encountered a formulation of silicone which was not easy to clean up with alcohol or slightly more aggressive solvent.
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Old 12-04-2015, 12:02   #10
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Re: Bonding Sonar Transducer to inside of hull

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Originally Posted by senormechanico View Post
I'm going to mention one thing not covered here.
If you have a foam cored hull (like my Dragonfly), you need to remove the foam core to make this work.
It can be done in the water, but be really careful !
Good point.

Most cored hulls are not cored below the water line (like mine)...should not be a problem in that case.
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Old 12-04-2015, 12:59   #11
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Re: Bonding Sonar Transducer to inside of hull

The easy way to test mounting locations: put a big blob of KY Jelly on the bottom of the puck, being careful to not get air bubbles in it, and press it down against the hull. It works a charm. I built up flat mounting pads (of polyester resin) so there was very little jelly in the gap but it should work equally well with a rougher fit. Mine lasted for years with just KY so I decided to not bother gluing down with epoxy - a good choice as I am changing all of my instruments now. The suction of the dried jelly was still hard to overcome when I removed the puck.

My boat has a very thick hull and I was still able to read depths greater than 500 feet shooting through the hull. No need for another hole.

Greg
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Old 12-04-2015, 13:11   #12
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Re: Bonding Sonar Transducer to inside of hull

The biggest problem with bonding transducer directly to the hull is finding a suitable location with little deadrise (i.e., hull skin is nearly horizontal), the beam will not be obstructed by the keel, and it's in a area with little turbulence (i.e., away from the propeller.) If you can find such a spot, I think a sillicon or polyurethane (3M 4200) adhesive would work fine.

I use the The Airmar P79 in-hull transducer. It comes in a plastic housing, adjustable to compensate for the hull deadrise angle (up to 22 deg, but a few degrees more will still work). Airmar advises filling it with propylene glycol nontoxic antifreeze. I'm pretty happy with it, but I don't fish. You can find the installation instructions here: http://www.airmartechnology.com/uplo.../17-217-01.pdf
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Old 12-04-2015, 14:45   #13
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Re: Bonding Sonar Transducer to inside of hull

My Garmin chartplotter has sonar and a fishfinder and the puck epoxied to the hull works just fine. Stay away from silicone or the 3M adhesives as they are not rigid.
As I understand it the more ridid the bond (epoxy) the better the transducer works as it resonates thru the hull.
Again I have done 4 instals in my own boats and at 2 others in friends boats bonding directly to the inside of the hull with epoxy and they all work just fine.
The boats I have used this method in are a Niagara 26, Hinterhoeller Shark 24, C&C 34, Morgan 383, C&C 25 and C&C 27.

Cheers
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Old 12-04-2015, 16:30   #14
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Re: Bonding Sonar Transducer to inside of hull

To nitpick a bit, there is no need for a rigid bond: water itself is not rigid. But water is not compressible which I believe is the issue. Sealants usually remain compressible and so absorb the sound energy (think foam sound deadening). As I noted earlier KY Jelly works just fine - because it is mostly water. What is surprising is that my sounder still worked well years after the jelly had dried out, which I think is down to the extremely close fit between puck and mounting. I made the mounting area by damming a spot on the hull and filling with catalyzed resin; once hard I sanded flat (at an angle of about 11 for a 22 transducer).

I recently bought a P79 transducer but will use KY on the pad first and skip the glycol for now.

Greg
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Old 12-04-2015, 17:19   #15
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Re: Bonding Sonar Transducer to inside of hull

Carina PDX
You make a good point. The issue is that there is a secure transmission bond to the hull and your solution meets that need. i'm just somewhat adverse to using Silicone and other flexible adhesives. i think we're on the same page with our solutions and considering the same variables. Just using some different techniques to address the same scenario.
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