The link below is a video that explains how to place and install the transducer...its not an entertaining watch but informative.
https://youtu.be/22SzRXa21hgIt's for a particular brand but install is same for them all...hard to say best spot on your boat as you need to test beforehand.
Mine works well...just an depth reading but it's been accurate as far as I can tell... but honestly I'm not worried about absolute accuracy over 20'...I am for less than 20 and mine has been spot on.. I rely on it to prevent bottom strikes and keeping safe depth for water sports.
For my use I set alarm to sound at 10 feet or less.