This may be a long post because of pictures but here goes anyway. I am not a proponent of any particular brand or style of fish finder, but because of the questions about the low resolution B & W unit I thought it might be instructional to show features of a more modern unit in contrast. I am not very well versed in this technology and am learning every time I fish. Some people say a unit with down scan or side scan is not really well suited for tubes because of the slow speed of travel. I agree that to get nice pictures of structure it is better to be moving a bit. Now, the problem with cruising around in a boat and watching down and side scan is that the fish seen on sonar are often overlooked dots on down and side scan. There is a reason for that and it is simply that down and side imaging uses a wide side to side beam but narrow front to back beam. A fish is in and out of the beam in no time and therefore you will not see traditional arches. Sonar, on the other hand, is a circular beam and the fish is in the beam much longer. As the fish progresses from one end of the beam (a further distance) through something closer to the center (closer distance) and then out the other edge (further again) you see the arch formed. An arch with a bright colored center is located more closely to the direct center of the cone and has a strong return.
OK, so for tubing we have to understand the effects of slow or no speed. Instead of arches you may see long streaks as fish swim around below, entering and leaving the cone. For down and side scan this is a good thing if looking for fish signals. The longer time the fish is in the very narrow coverage the more it actually resembles a fish instead of a dot.
On my last trip on my Colorado XTS on Deep Pond in Mendon Park here in Western NY I recorded the trip to submit my log file to Insight Genesis to process into depth contours and bottom hardness/vegetation maps which I can then import into my machine and overlay the pond chart. For this recording I needed to use 200 kHz sonar as opposed to the wider angle 83 kHz. I took screen shots of actual fish as I played back the recording yesterday. This pond is fairly featureless and devoid of structure so don't expect to see sunken vessels or old train tracks! For much of the pond the depth drops quickly from the weeds and lily pads along the shoreline and maximum depth is around 30 ft. in one section. Most of these pictures are taken in about 15 ft of water just off the weed line and just drifting around with the wind.
In this shot you can see actual fish arches on sonar but also see the fish on down scan and side scan about 12 ft on each side of me.
[You must be registered and logged in to see this link.]This shot shows something similar. Fish to both left and right. Being more or less stationary at a 0.3 MPH drift, the side scan image of the bottom (light areas from around 15 ft on each side) is real granular and hard to spot fish in it.
[You must be registered and logged in to see this link.]This image shows something interesting. the school of fish is off to the side of the sonar and only a few fish are in the cone. The wide and narrow beam of the down scan shows more fish and the side scan shows how far and to which side they are. Some fish are moving slowly and become more elongated.
[You must be registered and logged in to see this link.]Below two charts are nothing special except to illustrate how slow moving fish or perhaps fish swimming in the same direction as my drift can look long and wormy. These are not big fish and are must likely bluegills.
[You must be registered and logged in to see this link.]Here is a three shot sequence where at first I am coming from shallower weedy water where you see the weeds and bottom slope in the sonar and down scan and see a few fish, which are very hard to find in the sonar image, on down scan and side scan. The next two images are in succession after the first.
[You must be registered and logged in to see this link.]This image seems to show a larger fish on the sonar but the smaller fish must be outside of the beam cone. They are clearer in the other views.
[You must be registered and logged in to see this link.]Finally some more weeds for all three views. You see at least one fish on sonar, about 4 ft below the transducer. The down scan image shows the same fish, a clearer shot of the weeds and a few more fish toward the right side. The side scan clearly shows the abundance of weeds to the left with bright returns and some weeds also on the right, with a few fish mixed in.
[You must be registered and logged in to see this link.]I am including one more final picture because you can see fish in the central down scan area of the side scan panel but you can also see additional bright fish returns on the left where the side beam starts picking up the bottom.
[You must be registered and logged in to see this link.]I did say this would be a long post but I find the charts kind of fascinating and wanted to illustrate the differences between older technology and newer with modern features. I hope this helps someone in some way.