Re: transducer instalation................
BHM, In a cored hull is is advisible to drill a hole larger than the object to be installed, fill the hole with fiberglass, and then drill the new fiberglass to install the unit. This precludes any water from getting to the core material. In your case, you should be able to fill the hole(Marine Tex or other epoxy putty product), and then redrill for the smaller transducer.