Re-Bedding a replacement through haul transducer

[John Marrone]

Old Transducer has failed after 34-years' service. The opening remains the same so there is no new drilling required.
What procedure do I take with re-bedding before wrenching down the new transducer? I assume I'll need to sand the opening and re-bed with 3-M 4200, then seal the above with either Butyl or more 4200 around the transducer penetration before wrenching down?.......Does the large had toggled plastic nut need to be more than hand tight? How long does the boat need to remain out of the water before relaunching?

Sorry, lots of questions or I'll need someone else to take the responsibility to do all this and be left with a comfort level that the boat will not sink.

 

[AaronD]

My $.02 worth:

My understanding is that you're right about using 4200 - butyl isn't the right product under the waterline, and unlike 5200, you can do it again if needed (hopefully in another 34 years).

I'm going from memory here on what I did 8 years ago (because I see I didn't record any details in my maintenance log):
--Sanded / wiped / cleaned off bottom paint for an inch or so around the opening. Wipe with acetone.
--Put a good bead of 4200 on the transducer, and maybe a little more on the bottom of the tightener nut (technical term ?).
--Tightened it down - solidly hand-tight; maybe a big pair of channel-locks on the nut, but you can't torque it too much while holding the transducer threads by hand.

No leaks thus far. When I got around to it, I put a little water-based anti-fouling paint on the transducer, to try to keep critters from growing there. But I think we sailed for a couple years before that without any problems.

 

[John Marrone]

Is it difficult to get this device out of its position? I'd imagine having to rammer the old unit out assuming these 4200 products would require that process initially.
When you say 4200 around the transducer, I am assuming you also coat all the threads before inserting back up into the cavity. Do you not also coat the hull surround opening to prevent water infiltrating the hull fiberglass?
How long do you leave the installation to cure before getting back into the water?

 

[AaronD]

Is it difficult to get this device out of its position? I'd imagine having to rammer the old unit out assuming these 4200 products would require that process initially.
When you say 4200 around the transducer, I am assuming you also coat all the threads before inserting back up into the cavity. Do you not also coat the hull surround opening to prevent water infiltrating the hull fiberglass?
How long do you leave the installation to cure before getting back into the water?

Some of those details are lost in my flaky memory. Hopefully you can find someone who did it more recently.

I don't recall having a difficult time getting the old one off. I think I might have used a putty knife and/or a chisel from underneath to cut the old sealant. And at that point, you don't care about mangling the threads with a pipe wrench if you need to torque the old transducer a little.

I don't recall exactly where I slathered the 4200, but I'm sure I used enough that it would squeeze up the threads just a hair. I don't think I put any on the interior (because I wanted the backing nut to tighten down smoothly without sticking on 4200).

As for time, I did mine on a trailer in the offseason, so it sat for a long time. 4200 might take a couple days to cure at room temperature? See a little discussion at 3m 4200 cure & temperature.

 

[LakeShark]

This article may help with the bedding procedure.

Installing a Thru-Hull Transducer | West Marine

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If the old one is not leaking you could always abandon it in place and shoot through the hull with the new one mounted in a hunk of plumbers putty or toilet bowl wax. It actually works really well for transducers since it will eventually fail again. For re-bedding the through hull it is generally 24-48 hours after install before most sealants want to be fully submerged below the waterline. I had to redo a speed paddle a few years back that I have since abandoned but the process was pretty easy. Break loose the sealant with a knife etch on the trailer. Remove the old fitting, clean it all up as previously discussed, coat in sealant and reinstall. The trouble is generally getting the old one out and cleaned up for the new one to seal well.

 

[Ward H]

Assuming you are talking about a transducer with mushroom head on the outside here is how I did mine.
I cut the old nut off with multi-tool vibrating saw.
With a sharp knife I cut into the sealant that remained around the old tube. I then wriggled the old tube by hand until it loosened enough I could knock it through to the outside with a rubber mallet.
I cleaned off all the old calk inside and out and sanded off any bottom paint that would be under the new mushroom head.
To make cleanup easier, on the outside I put wide masking tape over the hole, wider than the mushroom head. I then used a sharp knife to cut out the tape over the hole. I put the transducer into the hole and used the sharp knife to cut the outline of the mushroom head into the tape. Remove the transducer, remove the ring of tape. After you are all done and before the sealant is completely set you can remove the masking tape and any squeeze out of sealant.
Use your sealant of choice, as @AaronD said Butyl Tape is the wrong product for this use. 3M 4200 would be a good choice.
Put sealant under the mushroom head and on the threads for about the thickness of the hull. Push it in hard and let excess sealant squeeze out onto the masking tape.
Then go into the inside, put sealant around the area the nut will sit, up to the threads.
Screw the nut down very snug. I used a large spanner wrench like the type used when installing a new sink. The transducer tubes I've seen have a flat on the threads so you can put a wrench on it without damaging the threads so you can keep it from spinning while tightening the nut.
Clean up and you're done.

 

[John Marrone]

Perfect blow by blow.............Appreciate the heads up on the tape at the mushroom, makes for a clean install.
I was also told that 3M 5200 is a better below water line sealant. I know it is difficult to remove, but not planning on seeing this transducer for at least as long as I'll own the boat.
Again, thanks for the help. Greatly appreciated

 

[AaronD]

Glad you got a detailed answer from someone who remembers and understands this process better than I do.

 

[pclarksurf]

Satan's Glue ? = 5200. You would be fine with 4200-- you can literally delaminate fiberglass pulling well cured 5200. Be kind to the next owner

 

[Gene Neill]

Satan's Glue ? = 5200. You would be fine with 4200-- you can literally delaminate fiberglass pulling well cured 5200. Be kind to the next owner

The only thing 5200 is good for is attaching the deck to the hull. Any other use will be regretted eventually.

 

[Grotto]

D

Satan's Glue ? = 5200. You would be fine with 4200-- you can literally delaminate fiberglass pulling well cured 5200. Be kind to the next owner

I ended up buying blanks for the sr mariner thru hulls on my boat because of 5200. I would end up damaging more trying to cut them out.