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SV Raven
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Discussion Starter · #1 · (Edited)
I have 2" holes in my hull for the transducers. The B150M that goes to my plotter decided to quit. I can easily just swap in another next haul out, but I have been mulling the Garmin GT23M or similar scanning type transducer. Most of the water I plod is on the shallow side. The beam angle of the B150M is pretty narrow in shallow water, and while yes, I ultimately just need the depth info of what is immediately below my keel, having a larger picture for situational awareness to compare against charts could come in handy. Some of the shoaling around here can be a surprise. If I go this route, I'm faced with a 1" threaded stem on the GT23M for a 2" hole. Aside from glassing over the hole and redrilling it the proper size, is there a proven way to sleeve or collar the 1" stem? I have some ideas in my head such as a large backplate epoxied to the inside of the hull with a 1" hole and copious sealant. The backface of the GT23M transducer is wide and itself could be sealed against the outside of the hull since I think my deadrise is within tolerances to not need the fairing block.

This is just my initial thinking out loud. I may just end up swapping in a new B150M since that's worked for as long as I've had the boat and is the easiest and least expensive solution. But I am curious about what one does, aside from reglassing and drilling a new hole, when putting an undersized stem into a hole in one's hull...
 

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Discussion Starter · #15 ·
Den, well familiar with helicoils on the smaller fastener scale. That's a fantastic idea for this application (and an excuse to someday get a 3D printer for my own additive manufacturing bright ideas). In this case it wouldn't need to be threaded on the inside since it just needs a properly sized inner diameter for the threaded shaft of the transduced to pass through, which is subsequently mechanically "clamped" by the nut. But this could be a very clever method to make a larger hole a smaller hole below the waterline on this scale, especially since in this case, inside the hull also has a 3/4" thick ply backing plate for added strength as a part of the transducer mounting location.

Stated conversationally, not trying to be a smarty pants, but wouldn't putting a zinc nut on the inside of the boat be utterly useless as an anode? It won't be in the water...
 

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Discussion Starter · #22 ·
Den. brain fart on my part: I misread and wasn't thinking of dissimilar metals in contact... fully understand your intent and and aware.

IF I had a 3D printer or easy access to one, in this specific application I agree this would work given this "bushing" would not just fill the thickness of the solid fiberglass hull (I don't recall how thick my Pearson's hull is but it is pretty thick), but also the thickness of the existing backing plate. We are talking a 2" OD, 1" ID "externally threaded bushing" essentially. Epoxied to the hull and backing plate (the threading is a bonus for bonding surface area). Seems pretty straight forward. If made of a non-metal material (which in this case would be the course of action) I don't need to mess with galvanic issues given compatible metals of the transducer's mounting shaft and nut. Add to it that the transducer's back face is larger than the surface area of the original hole. The true mechanical clamping is from the transducer's nut. All this "helicoil" would be doing is filling a ~1/2 void, and in this case the inside would not be threaded. I see internal threading as unnecessary (screwing the transducer into the "helicoil"). Consider how hard it is to remove a transducer that is just slid into a hole with copious amounts of 4200 (or 5200 for the sadists). Have it subsequently bonded to the threads from sealant... no thanks.

Cole, I likewise agree just glassing it over is easy, aside from the added mess. This is such a small area being dealt with, though the work area would be much larger if glassing given the scarf.

I could just as easily glass it over and redrill, but then I'd still have a void in the backing plate. But the counter to that is this isn't under any dynamic load. Just the clamping force of the nut. So I could fill that void with 4200 and would just need to make sure the nut is large enough to have adequate surface contact to the backing plate, but that seems sloppy... So I'd prefer as close tolerances as possible. I'd either have to chisel off the factory installed (assumed epoxied to the the inside of the hull) ply backing plate and install a new one, or still fashion a small bushing/collar to reduce the size of the hole in the backing plate (could just get a piece of epoxy compatible material and make a "ring" and epoxy it into the backing plate's hole...

In the mean time, I ended up just swapping in another B150M because the stars aligned to get the job done when the travel lift was available coincident with my spare time. And just getting the dead B150 out was a chore... But next haul out in a year or two I will pursue this one way or another.
 

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Discussion Starter · #24 ·
Den, so every hole in your hull is threaded to receive the threads of every through hull (transducers, seacocks, discharge, etc)? Thats an impressive set of taps to do that! Or did I misunderstand you?
 
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