Only Boat shaped ones that I have seen are one piece thru hull
Goes thru the hull, with a big nut on the inside of the hull.
There is no downside to a shoot thru the hull xducer that I can see.
I have two depth
sounders, the Raymarine
one, and a shoot thru that I installed for my Zeus touch, the Raymarine thru hull
only works to a few hundred feet, the shoot thru the hull works to about 1,500 or so and is good enough for the bottom machine, and of course itís not another hole in the boat.
Since your on the hard
, think about removing yours and fill the hole and install a shoot thru the hull xducer, assuming your hull is not cored. Although they can be installed in a cored hull too.