perhaps I should also have explained that I don't use the expensive yacht type sounders with only a depth
readout as they tend to be excessively expensive and I found them to be electrically delicate and experienced a burnout from voltage spikes in the electrical system
Years ago I changed over to using fish
finders as depth
sounders. They are very inexpensive and I find that the nice picture of the bottom profile on the screen
which shows the depth trend which is much handier than just a depth readout which requires a is-that-deeper-or shallower calculation.
Unfortunately, whilst they may be a more practicable device, fish
finders usually come with a transom mount transducer and you have to purchase
the thru hull
as an optional extra. (It's also interesting to see the fish underneath you.)
The housing I installed inside the hull, in addition to relieving my concern regarding retention of watertight integrity, also allow me to use the transom mount transducer as a thru hull type and I don't have to purchase
the optional one.