Re: Chartplotter and transducers
I believe the 521s has a transducer and costs about 50 bucks more for the depth option. The "s" is for "sounder". I have the 421s and the difference in price was less than 50 bucks when I bought it. A nice thing about getting the sounder option is you have another redundant depth gauge. The installation is a breeze and is best done with silicone in case you decide to move or remove the transducer. You should have no problem shooting through a thick fiberglass hull as long as it isn't cored.