Dual beam is great for shallow water fishing in my opinion. Its will allow you to open up the beam shooting down a little bit...not much but every little bit helps in shallow water. You going to hear Humminbird here alot. I was a lowrance man for a long time but Humminbird is smoking the field with the side image at this point. I have had both lowrance and humminbird gps and both had external antennas.....no problems. Just make sure its out in the open when you mount it.  Never had a Internal myself. Welcome to mastercatters and Jim will be along shortly to help you out....be ready for humminbird though.

For most waters less than 30 ft you'll find the wide scanning transducers like hummingbird matrix 37 (thats being an option on all the newer and better birds) the cats meow for crappie, instead of being stuck looking at 20 degree and 60 degree cones, that will give you 90 degrees of coverage ---think looking straight down then with a 45 degree circumfrence around that,,,with 60 you loose that other 3rd of coverage and with 20 you might as well be looking down a toilet paper roll.  Now with the wide scanning your using a higher freq --- 455 I think which doesnt penetrate deeper water as well as 200khz at 60degrees or 50khz at 20 degrees.....but your freshwater fishing and probably are seldom looking deeper than 30 ft.  I have a 797SiC2 and love it, but I'm stuck at 60 degrees and do miss the 90 degrees on my b&W matrix 37,,,so I run both now    The birds are taking over,,,might as well join the crowd