No wood behind transom, only foam. Trying to mount a transducer

Bart-Man

Recruit
Joined
Oct 2, 2015
Messages
1
I drilled three holes to mount the transducer. It appears it just went through the fiberglass into some foam. I don't know if the fiberglass is strong enough to hold the screws? I am very worried it will leak if the mount gets loose or the screws get loose. I have been researching this issue.....one guy says to oversize the drill holes, and fill with epoxy and then drill the pilot holes through the epoxy? Would any kind of epoxy work? How big should the oversize holes be. My boat is a 1997 Dynasty Elan 180......I am trying to mount it on the drivers side just below the exposed u bolt for securing the boat to the trailer.........
 

robert graham

Admiral
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Apr 16, 2009
Messages
6,908
That 3M 5200 is a good product for marine applications....3 stainless steel screws and the 5200 would be a good combination to use. Maybe fill the holes already drilled with 5200, sand it smooth, then drill 3 small holes for screws and mount with more 5200....
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
Welcome aboard.

Can you post a picture? Mounting the transducer "just below the exposed u bolt for securing the boat to the trailer" doesn't sound right. Either the eye is very low or the transducer is very high.
 

pckeen

Commander
Joined
Jun 20, 2012
Messages
2,067
Ditto the location sounds incorrect- the transducer should sit just below the bottom of the hull. Just google 'mounting transducer', and you'll come up with some instructions.

If you can access the back of the transom - you can add a backer plate there - a piece of ordinary (not treated) plywood, for the screws to bite into.

If you have drilled holes in the wrong place - fill them with 5200.
 
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JimS123

Fleet Admiral
Joined
Jul 27, 2007
Messages
7,952
Use teflon or UHMW for a backer plate. It'll outlast the boat and need no maintenance.
 

gm280

Supreme Mariner
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Jun 26, 2011
Messages
14,585
Not knowing your particular boat, are you certain you are drilling into foam? I like the drill holes, fill with epoxy and then redrill the holes to mount the transducer idea and do that my self. If you are using size 8 or 10 screws, drill your initial holes about 1/4" to 3/8" in size. Then fill them with epoxy and let it cure. Then drill the holes for the size screw you will use. That way there will never be any issue with water intrusion with those holes. And the mount will be extremely strong as well. And even if you removed those screws later on. No water will penetrate the holes either, even if you leave them open... JMHO!
 
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Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Mount it inside the hull and be done with it. Pick a spot immediately in front of the transom preferably near the centerline for minimum disturbance with wave action. Clean off the spot and epoxy the transducer to the hull with a good, preferably the bubble free type 2 part epoxy, or if you can't find that, stir regular epoxy carefully to minimize bubbles. Then you are done with it and it's out of the way from your trailer, kids playing with water sports, logs and docks and all that stuff you encounter while boating........Now how do you suppose I know this?

Your hull needs to be solid alum, or fiberglass where you mount it. If you have a foam filler in the hull then it will attenuate the signal. You are transmitting and receiving sound waves and they travel best through hard surfaces so bubbles in your epoxy and especially balsa/foam sandwiched hulls, at the mounting point, are a no no.
 
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