I installed a Uniden depth sounder in my 25.5 recently. I wanted to avoid another hole if possible, so I filled a plastic bag with water, hooked up the depth sounder temporarily, put the transducer inside the bag, and started to see if I could locate a place below the waterline where the transducer would work if mounted to the hull instead ot drilling through the hull. I found that the area below the floorboards at the center of the boat, directly abeam the hanging locker right behind the V-berth and ahead of the end of the keel allowed the signals to pass with apparent accuracy of the depth reading. I had a transducer that was designed to be mounted through the hull, so it was actually too tall for this location. I cut off enough of the inboard part of the transducer to fit in the space and decided to try the "Wax Ring" mounting technique. Went to the hardware store and bought a toilet wax ring, cut off a piece and carefully stuck it to the hull (cleaned) so as to avoid as much manipulation of the wax as possible and to avoid capturing any air bubbles, and carefully pushed the transducer into the wax (avoiding air) until it was within an eighth of an inch or so of making contact with the hull. Everything worked as expected, so I ran the wiring and mounted the instrument. It has worked without problems for over a year and, since there is no additional hole in my hull, will be relatively easy to upgrade or replace when I want to do it. The soundings displayed agree with the depths indicated on the chart of the lake she sails on.
