Making a Hole

I would like to have a depth sounder on my boat, but where I could put one? Transom mount would be easiest but I expect the transoms would be out of the water some of the time especially at rest, a through hull would get squashed and be draggy, so I decided that in in-hull transducer would be best. However ultrasonic signals can't punch through wood, so what to do?... Drill a big hole!

It felt a bit wrong drilling a massive hole in the bottom of the boat but this small piece of the hull will be solid GRP so that the transducer signals can get through. This is another advantage of the flat bottom of the hull which makes this process quite easy.

Here is the first stage where I have wet out glass cloth on a piece of plastic film and pressed it against the inside.

Once cured I filled the hole with thickened epoxy.

Here is the finished result looking from inside the hull.

As you can see, light gets through. Hopefully the signals should get through also.