[throwback]

airslot

Have put a few thruhulls in. I assume that your putting it in the V20. The trick is to get it to shoot straight down.
Look at hull make sure that your location does not line up with a stringer. Put it back as far as possible it needs to be in the water when boat is on plane.

On a deep v hull you need to fabricate a wedged shaped fairing blockl that matches the deadrise of the hull. As a pattern I have always used a piece of cellulose form. Its easy to shape and work with. Cut it to
fit the hull deadrise- trial and error. Once you get the angle right drill a hole thru it size of transducer. Use this to mark spot on hull to drill hole. Drill hole. You can make the permainent block out of hardwood but the last one I made used a couple of pieces of nylon that I glued togather. Used the cellulose template as a model
A bandsaw makes the whole process easy. Stick fearing block to hull with silicon underwater sticky stuff 3 m 5200
I think. You will also need to fabracate a piece to fit under the ring on the tranducer for inside of the hull. Plywood works about 4 inches sq with hole for tranducer
glue it into place so it lines up with bottom fairing block.
Lots of sealent or it will leak.
Slide transducer thru so it lines up with bottom of fairing
block. Adj with locking nut.

Again its a bit tricky with a deep v hull because you need to get the beam to shoot
as straight down as possible.