Transom mounted transducer on A25, Location?

[tribologist]

I made a fool out of myself yesterday drilling in a transducer in the transom.... I had some short screws that would penetrate just about 3/16 into the transom, I figured it would be much thicker than that down near the bottom of the hull so I taped up a drill and drilled at where I thought it would be good, about half way from the rudder on the right side. and just as I finished to the tape I could feel it go through, next hole I drilled slightly shallower but after installing the screw and backing it out I could notice a through hole when checking with mechanics wire. O'well I thought, I would just mix up some west epoxy with filler and build up on the back..... But when going inside the boat looking for the tips of the screws I realized I drilled right into the DUCT!!! I'm not going to leave it like this. the problem is if I hit something and tears out the screws I will have a leak into the duct. I will clean them out and fill with thickened epoxy after the Life caulk is fully hard so it can be removed.

I'm considering what to do next. One option would be to make a plate and bond that in the lame location so I get something to screw into, correcting for the curvature at the same time so that the transducer is in-line with the boat... Maybe just 5200 it in place? Another option is to move it further toward the center so I can properly fill the back side where the screws penetrates the transom. Issue now is that I am getting near the rudder.

Does anyone of you have transom mounted transducers? Location? At a low speed boat like this does it really matter if you are getting close to the rudder? , I don't care if I loose sonar when turning but the auto ranging tends to get messed up and is not resetting itself when sending bubbles over the transducer in the boat it was installed before.

Ulf

[kerrye]

I bought a fish finder with a transom transducer but just put it on the hull in the front bilge. It works fine there. I’d plug the holes in the transom with sel tapping screws set in 4200

[tribologist]

I was considering through hull but was worried about performance. Do you use it for fishing or mainly for knowing the depth?

Ulf

[dkirsop]

Clean out the screw holes and use an epoxy product like MarineTex. It will completely seal them and there won't be any leakage. Use 400 followed by 600 wet sand paper to finish the job and you won't even know there had been a hole.

You can use the transom mount transducer as an in-hull transducer as Kerrye has suggested. In a previous boat I had one set in a small puddle of epoxy against the bottom of the hull and it worked like a charm. Try to avoid getting air bubbles in the epoxy between the transducer and the hull.

[WillieC]

Through-hull or shoot through hull. These terms used to confuse me. I removed the unused through-hull transducer with attached 500 foot of wire and plugged the hole. The boat shaped hunk of rotting wood on the outside of the hull barely missed the bunks on the trailer. Every time. A PO installed a transom mount style transducer behind the engine cooling water pickup in a bed of fiberglass or epoxy resin. I cleverly deduced the transom mount nomenclature by watching my neighbor boat buddy install that exact device on his transom, with its attendant 1000' of wire. Mine is a shoot-through installation. It took me a long time to figure out what that slobbered wad of resin had to do with that black hunk of plastic. Works great. It is an older 6 wire transducer that I was able to use on my new Garmin 741 plotter but I had to add a 6 wire to 8 wire converter to do that. A bit of head scratching because the color coding of the old xducer wiring did not match the schematics I was able to hunt down. The old electrician joke was: 2 wire hook it up, 3 wire blow it up, 4 wire, drag up (move to another job). Six wires almost let all the smoke out of my head!

[kerrye]

I installed it as a depth finder but it also finds fish. It shoots thru the hull. You can test yours by putting the transducer in a zip lock bag with some liquid, laying it in the bilge and putting another zip lock with some sand in it on top of it to hold it in place. I used mine that way for a year before turning to a more permanent installation

[kerrye]

My final installation was to attach a pvc pipe fitting with a threaded plug to the floor of the bilge with some epoxy putty then drilling a hole thru the threaded plug for the transducer wire and putting the transducer inside with some rv antifreeze and installing the plug. I had a very slight leak around the epoxy putty so I finally ended up putting the transducer with the antifreeze inside a ziplock bag inside the pvc fitting and screwing in the plug. Works fine.

[tribologist]

Thats to funny!! I might give that bag trick a try to see how it performs. I will beg for some ultrasound gel from my chiropractor buddy to put between bag and hull.

Re 100’ cables.. i had to buy a $59 extension to get to the transom..

[DesertAlbin736]

The usual recommended transducer location for trawler type displacement hulls like ours is about 1/3rd of the way back from the front waterline length. Thru hull 'ducer is somewhat better than in hull, but either way don't forget to account for deadrise angle & avoid sources of turbulence and/or electrical signal interference as much as possible.

Thru-Hull-9.jpg

Here's where our Airmar thru hull transducer is located, under the starboard bench seat storage locker, which is also where our batteries are now located after installing the larger sewage holding tank. I would think this would be a good location for yours. The smaller of the two hoses passing through the space is the electric bilge pump discharge line, and the larger diameter hose is the discharge from the manual Whale bilge pump, both of which are located in the aft most accessible section of the bilge. The rectangular bit with cables attached above (outboard) of the transducer is a bronze bonding plate.

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New battery bank location. Transducer is directly under. Floor panel is appropriately reinforced. Also mainly why I switched from conventional FLA (flooded lead-acid) to sealed AGM batteries.

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Transducer & bonding plate location. Further aft than ideal, more like 2/3rds back, but for various reasons of accessibility & deadrise I guess about as good as PO's could do.

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Here's a Boating Magazine article on the subject

https://www.boatingmag.com/how-to/insta ... nce#page-4