I tried to use this hole rather than glue the transducer inside the kayak.
I filled the quoting of the sonde with SikaFlex plyuethane mastic.
Rather badly than definitely, because it is inaccessible and unless being contortionist or having power to shrink, they work blindly. A shapeless patty is in order.
Result is deplorable. Under the sonde picture is almost correct, but on the quoting nada. After looking to the hull, this is normal : the hull shape both side is down one inch than the hole, so the waves go thru the air of them!
So I tried after a system of tubes allowing to go down and up the sonde.
Then I went on a post to river with 5m of water:
First picture transducer raised, second was lowered:
( note that the transducer is not held perfectly right in water)
I had the right intuition, the hole plate blurs waves because pictures are net while during the first try with the Hobie hole plate were blurred.
We see very well on the first picture the border of waves 8 in 9m (I made an average of both quoting to take into account the incline of the sonde).
On the second picture waves are free (the black border to the right is the bank)
Roughly we will have in lateral sweeping the double of the depth. In 20m for instance, we will have both quoting 40m.
What very informative and that supports my hypotheses, it is that Down (fit to 'narrow ') does not vary.
What proves that with this fiiting, alone the central party of the waves of the side cone is taken back..