John I have a HDS7 & 10. I originally had my transducer mounted with silastic in the bilge area. Work faultlessly and worked excellent at speed. No worries about it getting hit and broken.
Now my transducer is out on the transom. Not ideal, but due to mounting the structure scan transducer under the hull in the centre line at the transom, I had to relocate the normal transducer.
So for peace of mind and great sounder readings at speed (only if the hull structure is sound and no air gaps in the layers) in hull is the way to go for me.
Cheers
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