The first step is to determine what material the transducer should be composed of.
Plastic housings are recommended for fiberglass or metal hulls.
Stainless Steel housings are recommended for steel or aluminium hulls.
Bronze housings are recommended for fiberglass or wood hulls.
Bronze is preferable to plastic for wooden hulls because the expansion of wood could damage a plastic transducer and cause a leak. Installation of a stainless steel housing in a metal hull requires an insulating fairing, available from your Raymarine dealer.
A metal housing should NOT be installed in a vessel with a positive ground system.