The transom of my Lund is aluminum, single layer. I figured that corroding
hardware would develop gaps which could contribute to leakage, so I used
stainless steel hardware. (This should be obvious anyway). I made the holes
slightly larger than the bolts and filled them with silicone caulk before
inserting the hardware. A day later, I added a thin bead inside & out around
the bolt head on one side and the nut on the other. In 4 years, no leakage.

By the way, choose hardware with smooth edges, like acorn nuts on one side
instead of an exposed bolt shaft. Easier to clean around them, and less
chance of slicing hands & feet on rough edges.

Finally: If your mounting bracket has slotted mounting holes so you can
slide the thing up & down a little to adjust height, fine. If not, you may
want to begin by mounting a small piece of wood to the boat in roughly the
right place, so you can drill a series of holes in the wood as you
experiment with the right height for the transducer. The guidelines in the
manufacturer's manual are just that: guidelines. It took me a few trips on
the water to get the position just right.

"Paul" wrote in message
...
I have an aluminum boat. I want to purchase a fish/depth finder for it. I
am
cautious about drilling holes in my perfect aluminum hull. Is there
another
way to mount it? Epoxy perhaps? Silicone? What have others done?


Paul