Replying late as I just found this question

I think that the 997 unit will go to 100 ft and 240 ft in each direction using the 445 kHz side scanning frequency. If you use the 800 kHz frequency it won't go at far to the side.

Lower sound wave frequency will penetrate much farther into the water. But the lower frequency won't show detail as well as the higher frequency sound wave. The Humminbird 997 unit can be switched to either of these two frequencies for side scanning operations. Plus it's dual or quadrabeam downward looking sonar can be used from the same transducer. So you can look down like a regular 2 D sonar unit at the same time with the same transducer as you are side scanning the bottom.

The dual-beam sonar will look straight down and out to the side using two different frequencies. 200 KHz and one other that I can't recall right now. The 200 KHz is the one that looks straight down in a 20 deg cone angle while the other looks more to the sides. It doubles the amount of bottom coverage that the regular 200 KHz transducer can see.

And the Quadrabeam Sonar unit (Optional purchase item) will look even farther out to the side in 2D mode. Again you can use the 2D and side scanning modes at the same time form the same transducer by simply using split screen views on the control head or display unit.

Quote Originally Posted by Wormin View Post
How deep will these thing read in side scan mode, I can see it in shallow water but what about 30' or 50'. Seems that it would shut over top of it.