i use 2 sounders--one forward, set inside boat, is a grmin, with a liquid so it can read thru the hull. is correct.
i also have an apelco which has begun to malfunction-- i will be replacing both as soon as i can find a garmin
with a good lens--mine went black. functioning well, screen
blac, so i am getting a replacement
my apelco has begun to misread--when garmin
says 9 ft, the apelco says 69 ft...lol...i will be replacing my apelco with, i hope, a comp[atible apelco that actually works. is good to have spares. i dont have em yet, but they are necessary. stuff happens.
also, make sure depth is under keel not water line, and not from transducer to bottom.. makes a difference.