They make shoot-thru-the-hull transducers for this. Not to be confused with
"thru-hull" transducers
that actually get mounted through a hole in the hull. The
shoot-thru-the-hull types need:

- To be stuck down to the inside of the hull with the supplied sealent.
- Or be emersed in an oil.
- Both of the above are so there are no air bubbles between transducer &
hull
- The hull must be fiberglass as the transducer won't work through materials
with voids
- The location under the hull (outside) still must be one where water is
always covering
that area when the boat is moving. And where no air-bubbles will
collect.



"Randy" wrote in message
.. .
I'm putting a fish finder in my boat and would rather silicone the
transducer to the inside of the bottom of the hull. Do I need a special
transducer or will any one work?