Mounting transducer on fibreglass hull?

[ninepointer]

Should I mount my transducer on the outside of the fibreglass hull (on nylon or teak mounting board) or should I epoxy it inside the hull?

[sabmgb]

When I had my 19ft sea ray I went through hull, best thing I ever did. Worked great and never got caught on any weeds or anything else. I just used silicon, big gob of it and pressed transducer into it, wiggling it around to make sure no air bubbles.

[Marker]

As above, 'shoot through hull' method by epoxying the transducer to the lowest part of the floor on the inside of the boat (no drilling). It must be glued directly on to the fibreglass which is solid enough for the sound waves to pass through.

https://www.youtube.com/watch?v=0s21HKdyXS4

[ninepointer]

Thanks guys.
Another question: If I mount it in-hull, the V-shape of the hull will prevent the transducer from being positioned perfectly level to the water, thus throwing the beam cone slightly to one side rather than vertical. What, if any, performance/accuracy issues might this cause?

[Marker]

Build up an epoxy base to create a flat surface, use a slow cure hardener so the bubbles have time to escape, it will be solid enough for the sound to travel through. It can be done in two stages, first build up a flat surface, after it has cured you can sand flat if required, then epoxy the transducer to it.

Here is a guide from West Systems, I have had good luck with their marine grade epoxy:

http://www.westsystem.com/instruction-2/

[ninepointer]

Awesome, thanks Marker!

[skypilot]

Mount inside as mentioned. Centerline inside is good as far as your vertical scanning concerns.

Outside hull mounting can cause motor/prop/cavitation issues if not located correctly away from the front area of the prop / hull alignment.

[MarkB]

Yeah, mout inside. Less interference from water turbulance, plus I hear that the sound vibrates through and makes your entire hull a sending and receiving surface. Compared to my outside mounted transducer, my mate's through hull always showed clearer images.