Re: mounting in hull fishfinder... what epoxy
THere is nothing specila about a P79 transducer. It's the same transducer design as the one you mount on the transom. The difference is that the transducer is suspended inside a tank of antifreeze or mineral oil. that is "glued" to the inside of the hull. The silicon is used for no other prupose than to seal the oil tank to the bottom of the hull. It has nothing to do with the installation of the transducer itself.
Using a sound deadening material like silicon to attach a transducer to the hull is like stuffing a pillow in your loud speaker.
When mounting a puck type thru hull to the bottom of the boat use a 30 or 60 mintue 2 part epoxy.
The only reason I highlighted "liquid filled" was to differentiate the base of this particular model/system from some puck style transducers that may be epoxied directly to the inside of the hull. I believe (from the install illustrations) the P79 base is essentially a hollow tube, installed to the inside of the hull, then filled w/ non-toxic antifreeze, then the actual transducer is mounted to the base. I have read elsewhere some use mineral oil, as you mention above, as a base liquid and this may interact with epoxy...and loosen it...again I do not have first hand experience so don't know this to be true.
If the base is indeed a hollow tube as it appears, and the base rim was secured w/ silicone the transducer would not need to shoot through the silicone. I do know the mfg installation instructions linked to above recommend GE Silicone II.
CAUTION: The base must be liquid-tight.
Do Not use an epoxy adhesive because it is too brittle.
Again, I only posted this b/c I was reading up on various fishfinders/depth finders and came across this, I'm no expert. It most likely only applies to this particular system and I would hope most mfgs have specific instructions included with their units. The vast majority of what I've read on forums mentions using epoxy, so this stood out to me...it may be an exception to the rule.
