Transducer sealed to inside of hull

[Mer Sauvage]

Originally Posted by Calaban-Alleria

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.

Did you glue the cap on or just friction to keep the oil from leaking out over time and rough seas?

[Mer Sauvage]

Thanks everyone for the replies. I have a Garmin GPSmap 741xs with 8pin and 12pin sonar connectors on it. the Stock transom mount transducer that I am currently using is the 8pin. Will check with Garmin on other transducers more suitable for surface mounting are available, i am guessing a model that would be used as a thru hull but can angle to fit plumb. I am not needing water speed or anything like that on this little boat. Thanks again.

[sinnerman]

I just picked up Catalina that has the same kind of transducer. Mine is made by Airmar pn 80170 and is used by many different manufacturers with their depth gauges. It is a Raymarine unit they call a P79..

The bottom "cup" of the transducer is glued to the hull with adhesive-sealant, and the transducer is set inside. The top cap is adjustable to allow you to change the transducer angle to compensate for the hull rise angle to have the transducer pointing straight downward. You put a level on top of it to verify this.

When you are all adjusted, you put about two ounces of ANTIFREEZE in the bottom cup and lock the transducer in place. The transducer will ping through the liquid. They probably suggest antifreeze so it doens't freeze as water would work also...

My boat had a Raymarine transducer installed but no display unit. I bought a cheap FARIA depth gauge with the same type Airmar transducer. I was able to drop it right into the already existing bonded-in Raymarine base cup assembly. Worked like a charm..

[wingssail]

I installed my first "through the hull" depthsounder tranducer in a dome filled with mineral oil.

On my next boat I tested the depth attentuation by dropping the tranducer over the side dangling by the cable and (in 600ft of water) reducing the sensitivity (power) until it stopped reading the bottom. Then I rested the transducer in a puddle of water in the bilge and repeated the sensitivity test.

I observed about a 10% loss.

Deeming that acceptable rather than having a hole in the boat and a transducer projecting into the flow, I glued the tranducer inside, in the bilge, with a puddle of epoxy. It worked fine.

On my current boat I repeated the test because I was unsure whether or not the "C-Flex" hull construction would allow the sound to go through. It did. I now have three depth sounder transducers pinging away simultaneously (196Hz 200hz and 50hz), all glued to the inside of the hull, they don't interfere with each other, and as far as I can tell they all work fine, though with some loss of range I guess.

[CATJAVA]

I’ve got two transducers mounted inside the hulls on my cat. Original one up forward port hull has been there since 1991, works good. Added a Humminbird fishfinder mounted in small square open-top box alongside of my original speedo (paddle wheel) which is mounted near stern of stbd hull. Just fill box w/ fresh water now and then to keep fishfinder “underwater”. Never have a problem; if it’s not working I just top up the water! But I am on a cat, so no water spills out because no healing. As you can tell I am a KISS advocate. Nice to have redundancy! And YES, they read the same on flat seabed. Evan on JAVA

[CarinaPDX]

There is nothing wrong with shooting through the hull - I have done it for decades. In my case, Carina is narrow with a full keel so there is no place to glue it that is within 15 or 20 degrees of flat, so I made a mold with some plywood and putty and slowly filled it with catalyzed polyester resin (slow as over many hours because the heat can cause cracking). Then I ground a flat on top at about 10 degrees (the transducer had a 22 degree cone IIRC) so as to minimize any reflections from the hull/keel. I have read down to 800 feet through this, which is at least 2 inches thick including the hull - usually thermoclines or other phenomena are the limitation on reading. I initially tested it with K-Y jelly under the transducer; sloth being what it is it was still there and working 30 years later, though dried at that point. Since the surfaces were so smooth and flat the vacuum held them together and it took a chisel and mallet to separate them. (In the initial testing the puck was held down with tape, as otherwise it would slide off.) The point is that almost any sealant without air will work fine - epoxy is not necessary. Also, I prefer to not have an oil bath aboard, and certainly not silicone oil (it is almost impossible to remove silicone, and it prevents all other adhesives from attaching).

If I were doing it again today I would probably buy a bit of G-10/FR4, fair the bottom to approximately mate to the hull, then attach that to the hull with 4200 or similar. That would leave a perfectly flat surface for the transducer to mate to.

I assume the OP does not know anything about the existing transducer; otherwise it might be compatible with the current display. So remove the current one and mount new (outboard) one in place with K-Y jelly and check the result. If good then install permanently.

Greg

[Nico Domino]

Originally Posted by CarinaPDX

There is nothing wrong with shooting through the hull - I have done it for decades. In my case, Carina is narrow with a full keel so there is no place to glue it that is within 15 or 20 degrees of flat, so I made a mold with some plywood and putty and slowly filled it with catalyzed polyester resin (slow as over many hours because the heat can cause cracking). Then I ground a flat on top at about 10 degrees (the transducer had a 22 degree cone IIRC) so as to minimize any reflections from the hull/keel. I have read down to 800 feet through this, which is at least 2 inches thick including the hull - usually thermoclines or other phenomena are the limitation on reading. I initially tested it with K-Y jelly under the transducer; sloth being what it is it was still there and working 30 years later, though dried at that point. Since the surfaces were so smooth and flat the vacuum held them together and it took a chisel and mallet to separate them. (In the initial testing the puck was held down with tape, as otherwise it would slide off.) The point is that almost any sealant without air will work fine - epoxy is not necessary. Also, I prefer to not have an oil bath aboard, and certainly not silicone oil (it is almost impossible to remove silicone, and it prevents all other adhesives from attaching).

If I were doing it again today I would probably buy a bit of G-10/FR4, fair the bottom to approximately mate to the hull, then attach that to the hull with 4200 or similar. That would leave a perfectly flat surface for the transducer to mate to.

I assume the OP does not know anything about the existing transducer; otherwise it might be compatible with the current display. So remove the current one and mount new (outboard) one in place with K-Y jelly and check the result. If good then install permanently.

Greg

Hi, I have transducer siliconed in in current boat and had in most previous boats, never had any issues. Created a large blob of silicone and pressed the transducer into it , left overnight and then cleaned up with sharp knife, leaving a 10mm soround .

[sailasia]

https://support.norcrossmarine.com/h...-Illustrations

[CarinaPDX]

Originally Posted by Nico Domino

Hi, I have transducer siliconed in in current boat and had in most previous boats, never had any issues. Created a large blob of silicone and pressed the transducer into it , left overnight and then cleaned up with sharp knife, leaving a 10mm soround .

My concern was with using silicone oil instead of mineral oil. Silicone sealant works fine, but you will not want to use anything else in the future as traces of silicone will remain and prevent full adhesion.

Greg

[CarinaPDX]

Originally Posted by sailasia

https://support.norcrossmarine.com/h...-Illustrations

That is a nice article. I do disagree with the use of petroleum jelly (Vaseline) for testing as it is hard to completely remove. K-Y Jelly is water based and cleans off easily. Also, epoxy is a bit too permanent for me - a sealant will do fine, especially if the surface is flat.

Greg

[Mer Sauvage]

Does anyone know if the hull of a 1989 Catalina27 is solid or cored down low but not near the keel?

[SVTatia]

Originally Posted by psneeld

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

There are two kinds of ready-made ones and the second is shown below.
I am also installing an in-hull transducer, and the issue with the ready made ones is the max deadrise. My sailboat has a fine entry and the deadrise is close to 32 degrees, so I had to do my own.

[SVTatia]

Originally Posted by CarinaPDX

My concern was with using silicone oil instead of mineral oil. Silicone sealant works fine, but you will not want to use anything else in the future as traces of silicone will remain and prevent full adhesion.

Greg

Not sure if I understand, but can the transducer be attached to a solid (resin, cured silicone, etc.) rather than liquid (oil, anti-freeze, etc)?

[CarinaPDX]

Originally Posted by SVTatia

Not sure if I understand, but can the transducer be attached to a solid (resin, cured silicone, etc.) rather than liquid (oil, anti-freeze, etc)?

That is what I explained at some length. Suspending the transducer in mineral oil is just one solution, and it seems to me a higher maintenance and messier one. Transducers shoot through solid material just fine (even with oil it is still passing through the hull). The issue is always that any air gap or bubbles will block the signal, whether in solid or liquid. It seems likely that solids attenuate the signal more than liquids but in practice shooting through the hull works fine to the depths normally measured with a depth sounder. A more interesting question is if the different rate of propagation between all water (thru-hull install) versus through a relatively short path of solid (hull plus mounting) before the water would affect accuracy to any noticeable degree; I don't think so - I certainly never noticed any consistent error - but a thought for further study.

Greg

[SVTatia]

Originally Posted by CarinaPDX

That is what I explained at some length. Suspending the transducer in mineral oil is just one solution, and it seems to me a higher maintenance and messier one. Transducers shoot through solid material just fine (even with oil it is still passing through the hull). The issue is always that any air gap or bubbles will block the signal, whether in solid or liquid. It seems likely that solids attenuate the signal more than liquids but in practice shooting through the hull works fine to the depths normally measured with a depth sounder. A more interesting question is if the different rate of propagation between all water (thru-hull install) versus through a relatively short path of solid (hull plus mounting) before the water would affect accuracy to any noticeable degree; I don't think so - I certainly never noticed any consistent error - but a thought for further study.

Greg

Cool, thanks Greg.
I think I'll will use neutral silicone, the lesser of two evils and the one that is not acidic and without the vinegar smell.
I do have a depth sounder installed thru the hull but it is right beside the keel in the beamest part of the boat. My intention is to remove it, cover the hole and place the new one (Airmar M78713) in a PVC pipe inside and forward of the keel. Since I won't have time to remove and plug the hole until after next season, I'll have both and will be able to measure the differences.