My experience with Humminbird equipment is strictly on bass boats - they
worked well enough here on the Nanticoke River.
On two of my previous sailboats though, I used Apelco 360 Fishfinders with
speed/temp as well. Now, since Apelco is now Raytheon, the equivalent model
is called the L365. (It should run roughly around what my old 360 was; about
$200 or so.) My transducer was mounted on the transom. It caused no problems
in day to day operation on my P15.
To check it out, you can visit the Raytheon site at http://www.raymarine.com
or you can see them directly at
http://www.raymarine.com/products/index/fishfinders/index.html
-- "Sea" ya!--Lars S. Mulford, President East Coast Potter Association (ECPA) Come visit us at http://members.tripod.com/~SpeedSailor "Forgive, and live. Life is worth the challenge of living." --LSSM