Edgar wrote:
The earlier comment about the depth sounder is interesting because ISTR that
I read somewhere that a transducer working through the hull does leave a
clear spot.

Well, I'm like Bruce, I have a depth sounder with the transducer in a
well epoxied to the inside of the hull; I have never seen a "clear" spot
on the outside of the hull where the transducer is mounted.

Cheers
Martin