Backing plate

[weephee]

Can someone provide me with some information on how to build a fiberglass backing plate for a thru hull transducer. My idea would be to sand the inside of the hull where the plate is to be built to remove old paint etc and then start building the area up with epoxy and fiberglass to get a large enough flat surface to support the washer and nut that tightens down the transducer. The hull is approx 3/8 inches thick in this area. Do I need to use any other material, ie. plywood to build this backing plate or is my suggested way good enough. Thanks

[weephee]

Hello. I'm still looking for some information on this subject. Is the backing plate built as an independant piece that can be removed or is it an intergral part of the hull and formed as I have possibly suggested. Sure would appreciate some help in this. Thanks

[ambianceack]

Yes, your idea sounds fine but I suggest using marine grade plywood since the glue adhering the laminates is superior to common CDX etc. I would also coat/cover the plywood with epoxy and glass to prevent moisture from breaking down the plywood. Attached is a link to a pdf that the manufacturer of my boat a 34' Sabre recommends for thru hull installation. Granted the document is dated but so is my boat, regardless current methods do not vary much. http://www.sabreyachts.com/pdf/Knotmeter.pdf

[scottyt]

simply the best way is solid fiber glass, second best is ply or wood.

glass is easy, as you say clean the area. then out side the boat make up a "stack" of wetted out fiber glass squares or circles. make sure to not over saturate the glass then run the stack into the boat and apply while still wet. then let cure over night. then drill

but if this is for a depth ducer you dont need to drill it into the hull if your hull is solid. you can do several other things that work just as well

[weephee]

Thanks for the advice. I have already drilled the 2 3/8 inch diameter hole as there was a smaller hole there before for an older stye depth transducer. I also thought about building a solid fiberglass back plate say 5 inches in diameter x 1/4 to 1/2 inch thick and then pre drilling it and then epoxy tthe back plate o the inside of the hull. There would be less mess that way. Would that also work.