Transducer block (before wire properly routed or secured). This is a 3/4" Starboard™ block. I over-drilled and removed a very generous amount of transom core, then painted with neat epoxy and then filled holes with thickened epoxy. After that cured, I drilled and tapped (into the thickened epoxy areas) for the bronze machine screws that secure the block to the transom. The bedding is an experiment with butyl (later I removed it and it was holding very tenaciously, but I have not tested it long-term yet).

After mounting the block, I tapped the Starboard for the transducer fasteners.