Some folks trust epoxy glues to hold a piece of mounting board of some sort to attach the transducer to. Some drull just two holes to bolt on a mounting board then make all the holes needed in the mounting board. Have saw some make a bracket that attaches above the water line with clamps or bolts that hold their transducers. Personally, I mount a piece of plastic lumber, with two bolt holes well sealed, big enough to mount everything to then I can make all the mounts and adjustments without drilling more thru holes.. With the quality of sealants today, thru holes are not a problem as long as you don't create swiss cheese with to many !