Replacing shoot through hull depth finder

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Hey guys,
My depth finder failed, it is an old Lawrence that looks like it is threaded into a piece of wood that is glued down to the hull at a flat angle. I am a bit afraid to start trying to turn it, is there any chance there is a water seal in there, or is it just sitting on top of some water tight surface?
Anyone replace one that shoots through the hull and works well? Brand recommendation?
 
Most thru-hull transducers will have the wood or "fairing" as the technical name on the inside to make the nut level against the inside of the hull. Unscrew the nut on the inside and pray that a few sharp smacks with a dead blow hammer will loosen it. Most installers use 3M 5200 or 4200 on the wet side to seal the mounting flange against the hull. You can try and pry it loose from the outside as well. If unsuccessful, you will need a de-bonding agent-I forget the product name-injected between the flange and hull or down along the threads from the inside to break the bond from the hull. Can be quick and easy...or long and tedious. Good luck!!!
 
How does a thru-hull answer help with a shoot-thru question?????????
 
So if I understand correctly the hull is undisturbed in the process you are describing?
This can be done in the water with no worries?
 
IMHO, If there is any chance you will damage the hull by removing the old transducer, cut the cable and leave in place. Install the new one close to the old one using the method the mfgr. recommends.
 
I think it need clarification if there is a hole in the hull or not. A wood backing plate and a threaded nut makes me believe it's a thru hull setup -- there is a hole in the hull. You would want to pull the boat to replace.

If there is no hole, it's shoot thru, and you can do in the water by trying to pry, gently, the old unit off the hull.
 
Here's the deal. Unless you are 100% sure that there is no hole in the boat. Do not do anything with the existing transducer unless it is out of the water. If you are sure, as what was said above, lightly tap to see if you can break loose. If not, I also agree with the above and just install a new one as close as possible to the existing if in fact it worked well where it was.
 
I can't be the only one who's changed a through hull with the boat in the water? Have help on hand and appropriately sized plugs nearby. Have everything prepared in advance of pulling the old one and work fast. After pulling the old through hull, stick a plug in the hole to give you some time to clean up the area so the new thru hull can seal cleanly.
 
quote:
Originally posted by Brian N

I can't be the only one who's changed a through hull with the boat in the water?

Click to expand...


Not on purpose. :)

I suppose if the water is warm and you can get under the boat it's doable. Not sure how you would get a good seal on the outside though.
 
I would rather guess at the depth then attempt to do that. I'm not sure what would be worse. Having my boat pulled from the bottom of the river or explaining why I tried such a thing. :)
 
If it's truly a shoot thru the hull, do what sugilbert said. Leave the old one there and put the new one nearby.

Roy
 
quote:
Originally posted by Brian N

I can't be the only one who's changed a through hull with the boat in the water? Have help on hand and appropriately sized plugs nearby. Have everything prepared in advance of pulling the old one and work fast. After pulling the old through hull, stick a plug in the hole to give you some time to clean up the area so the new thru hull can seal cleanly.

Click to expand...


You're not alone. I've done it on a boat on a deep water mooring on a windy day. But it takes good coordinated planning and teamwork and available "Plan B " and maybe "C".

I made the switch underwater with 2 people inside the boat. I had scuba. The few U/Wtools had secured lanyards and a bucket with new T/D and cable was hanging next to me with plug end hanging over the lip for a quick grab
.
The old t/d and cable had to be hit from inside with a maul to free it after I had used a putty knife and hammer U/W to slice as much of the sealant as I could.
I had a soft foam rubber ball to seal the hole momentarily while I grabbed the new plug to insert.
The new one had the plug tightly sealed in bag which I pushed into the hole to be hauled up inside with water coming in around a plastic-bagged towel pressed against the hole.

The upper surface of the T/D already had new sealant and the stem was led into the hole and nut placed over the plug, cable and threaded stem to secure it as I held it in proper orientation which was also marked on the stem. All pretty much one smooth motion from inside and out.

It went surprisingly smoothly and only took < a few minutes start to finish of the actual switch, but I wouldn't have tried it in the water with a T/D in a fairing block.

I don't recommend doing this in the water,... but it's not rocket science.
 
If I misunderstood the OP's statement about the transducer being "threaded into" a piece of wood when it was actually a shoot-thru-the-hull type transducer, then shame on me. In my limited 40+ years of boating, I have not been exposed to a threaded transducer that was not installed through an actual hole through the hull. I suppose there are boats out there that mount a through the hull transducer as a shoot through the hull transducer but I will be the first to admit I have led a sheltered life. I just attempt to provide a simple answer to a simple question and support this forum as best I can.
 
X2.
I've seen thru-hull and T/M models epoxied down as shoot-thru but not threaded into wood too.
 
had to read the original post a couple times - but looks like you have a through hull on there now, it's failed, and you are trying to decide if instead of replacing this one, you can simply put in a shoot thru in a nearby location to use instead?

I tired that once, it worked ok, didn't give temp reading like the through hulls do, cant use it to look for anything beyond a depth reading - but it worked ok. Is your hull cored, or solid glass? I believe the shoot thru's work better shooting through solid glass. There's a few different brands, but they are probably all identical. I followed the directions when installing, and it worked fine - certainly less work than installing a thru hull.

The shoot thru I used was inserted into a cylinder that was glued to the hull - the cylinder was filled with something, I can't recall what, perhaps mineral spirits, or mineral oil?
 
I added a Garmin unit a couple of years ago.
Used a mount for inflatables, just stuck it down with silicone in the bilge.
Installed the transducer inside the mount with a thin layer of wax from a toilet wax ring.
Works great and easy to repair replace if needed
 
I was asking two question really. I don't really know if this is a shoot thru or true through hull. Was hoping someone replaced one on a similar boat. It does seem most likely that is a thru hull. There is something sticking down out of the hull there that I remember seeing when painting.
 
It's a very safe bet that you you have a thru hull transducer- meaning there is a hole in your hull and the transducer is in the water. Unless it look like this. https://www.starmarinedepot.com/low...mngVZX43ydxswEBNKFcq9WrU6ds3SnqRoCdoUQAvD_BwE

While the shoot thru, or 'in hull', or whatever you call it also need to be leveled, I can't imagine it ever being done with wood fairing. Because you need the cup of oil between the xducer and the hull.

You didn't by any chance paint over the "something sticking down out of the hull", did you? They make a special bottom paint for the transducer. If you painted over it with regular bottom paint, that may be your problem ( probably not though, they should work thru a coat or two of paint)

What do you mean when you say it's not working ? It is not giving an accurate reading, not giving any reading, not powering up? As far as I know, there really aren't any moving parts, or other parts, in a thru hull depth transducer to fail ( except the speed sensing wheels) - so as long as you didn't paint over it, or break it by smashing it on the ground - not sure how you can be sure the problem is the transducer and not the wiring, or the depth finder itself?

I would not try to change this one in the water. If you put it in yourself, and know what sealant was used, perhaps. I once tried to remove one on land ( because it was 35 years old and the unit it was attached to was being replaced - the xducer still was fine). The previous owner had used a 5 gallon drum of 5200 it seemed. There was NO way this one was coming off without taking a few feet of fiberglass with it. I just let it be, and put the new one somewhere else. Transom mounts work very well on some boats, 100x better than the shoot thru, in my opinion. Just be sure you mount it correctly. Yes, it takes a LOT longer to do it right - but if you don't you will most likely destroy your transom. Correctly doesn't mean a little sealant on the screws. Thru bolt, seal the core, the whole enchilada.
 
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