LP, I have down imaging on my hummingbird so I know how useful DI can be. I hope this is not a dumb question but what added benefits are you getting from side scans besides side view of your DI? Are there things that you see can sometimes on SI but not on DI?
There are no dumb questions. The answer is yes, you see a lot of stuff on sidescan that doesn't show up on downscan. Also, I use Lowrance stuff so my explanations are based on that brand but I'm sure HB is about the same.
Downscan is throwing a cone from the transducer to the bottom just like a 2D transducer, but it's showing you a 3D image of what's underneath you.
Sidescan is showing you what's out to the side, and further outside of the range of the downscan "cone".
Sidescan took me awhile to figure out just what it was showing me, I know there were times when I was just twisting my head around trying to make sense of it then one day it finally "clicked" and I since then I always have a unit on sidescan on while "searching" and have found numerous pieces of structure that I would have missed with downscan only.
Look at the shot below. The black cross on the left (downscan) shot is the exact location of the black cross in the sidescan image on the right side of the screen, and is showing top of a laydown tree that is slightly off to my right side but still pretty much directly under the boat.
Now look down to the lower part of the sidescreen image at the laydown off the the left side. Other than a couple little twigs, that laydown did not show up on downscan because it was outside of the range of the downscan "cone" and I probably would have missed it seeing the "whole" picture with downscan only.
In sidescan, your tranducer (boat) is located at the very top center of the screen, everything from top to bottom is stuff you've already passed over. The line down the center of the shot is center line of your transducer and it shows the water column on each side of centerline. In this instance I had the sidescan range at 50' meaning I'm projecting images 50' each way, minus the water depth.
The cool thing about Lowrance, and HB may be the same but again I'm not familiar with them, is that I can scroll backwards and look at something, take a screen shot of it, or most importantly make a waypoint of something I passed over quite a ways behind me. I've done that before, scroll back, mark a waypoint, then go back over the waypoint and thoroughly graph the area, it's a helpful tool IMO.
Clear as mud??