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Making holes for transducers

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Gday all,


This is my first post here, hoping you can provide some good advice.


My chart plotter died some time ago and the old transducer that was connected to it will not work anymore. I want to install a couple of standard Airmar transducers for depth and speed. They are about 51mm in diameter. Can anyone tell me the best and easiest and neatest way to make the holes required? I have tried using a diamond holes when I had to make a hole in the deck for the windlass cables, it would cost the concrete fine but struggled through the steel and had a big tendency to wander. Masonry bits go straight through no worries but are deflected by the steel. Drilling a ring of small holes around the perimeter would work but is not neat.


I am thinking they will need to be somewhere between 55 and 60 mm diameter and be sealed with thickened epoxy to protect the steel in the boat. I am wondering if I should fill the hole with epoxy then rebore them to the size needed for the transducers or whether I should try and find something the right diameter to plug the hole and get the epoxy around that. Standard sikaflex tubes are an almost perfect size for that. Another option would be to bore slightly oversize then just epoxy the outside part of the transducer into the hole, thereby sealing the hole and protecting the steel in one go.


All opinions and advice gratefully accepted.





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A difficult material to get through tis FC. You have covered the ways pretty much and the issues that come with each way. The totally perfect way is a fixed drilling machine with plenty of water on the diamond hole saw  and a real good hole saw. the good expensive ones will cut through steel. That makes the neatest hole. The other way is as you said, to cut small holes and break the concrete out with a punch or cold chisel. Yes go over size and fair, but use Epoxy Mortar, not thickened epoxy. Epoxy mortar bonds well, goes very hard and most importantly, expands and contracts at the same rate the FC does. Once you have the mortar in place, you can smooth and shape it with wet fingers. I would make the hole just a tad bigger than the transducer housing and then seal it in place with a sealant. Then do the backing nut up on it.
For the transducer, you can actually make a fairing block so as the transducer points straight down and a sort of boat shape leading and trailing end on that to reduce turbulence.

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Drilling through the wetted hull is a tricky business indeed.


What I recommend is to rent a corer with an appropriate diamond bit.  This will cut both the cement as well as the armature/steel reinforcement.  It will cut it accurately.  You will have to figure out how to rest the drill against the hull if you use a plunger type.  A hand corer is okay if you can ensure it doesn't change angle as you drill.


I picked up a handheld corer for $400 pesos, about $25USD at the time, with a 2inch bit on it.  Bits are $200 and up, and the drills, used, are $1500.  I will be testing it before I even consider drilling for through-hulls.  I may still rent a plunger style, as they make me feel more comfortable, and spending hard-earned money making sure I don't destroy a priceless hull seems like a wise decision.  However, my ship is laminated ferro-cement, which presents interesting challenges for through-hulls (the hull is two layers with a hollow armature between) and does not represent the same challenges as your hull.


Still...rent the plunger type and figure out how to set it up properly.  That's my recommendation.



Whatever you do, DO NOT CHISEL OR HAMMER the wetted hull.  That's an incredibly bad idea.  If you struck armature you could easily take out a large chunk of hull and would be in a world of hurt.


And also always remember that hammer drills should NEVER be used for holes all the way through material.  The hammer will take out large chunks on the exit side.  I speak from experience.


Do not cut your hull except with a proper corer.

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