For a number of years, I have been making my own Starboard blocks for transom mount transducers : 3/4" thick--using black Starboard recently, with black bottom paint. Initially I was using a small Dremel tool Dovetail bit to grove the back so the epoxy had a good bite. More recently, after some experimenting, I have gone to using a Fein (or other oscillating saw, with a 3/4" wide blade, and making cuts at 45* outward from a single "trench" in a series of grooves along the Back. Prepare the transom by sanding down to bare gel coat--use masking tape to define the area. Use G Flex Glue, do a rapid flame harden on the gluing surface of the Starboard. I usually use one of the old screw holes, pot it with epoxy, and put a screw to hold the Starboard in place while the G Flex dries. This is basically what these various kits do.
I am currently running two very large down/side scan transducers on the 8" x 4" block on the transom of the 25. You can move the transducers around to your hearts content, and no chance of damage to the transom core with multiple holes.
I am currently running two very large down/side scan transducers on the 8" x 4" block on the transom of the 25. You can move the transducers around to your hearts content, and no chance of damage to the transom core with multiple holes.