My side imaging - Helix 7 - has never looked good to me even scouting at 2-3-4 mph- yesterday while running the trolling motor the side imaging it looked great so then I fired up the big motor and cruising slow and it looked grainy and rough again -put it in neutral and let the boat float but the motor running and it looks good ........so I have to try to reposition the transducer somewhere but on a riveted aluminum boat don't get too many choices- it is right at 15 inches from the motor on the driver side - I don't know if I need to go further from the motor and prop or put it to closer to the center of the boat. I was scouting in timber and there was a major difference in picture

It's not electrical interference as it is on its own battery and motor running but in neutral it looks good.
I do need to raise it as it rooster tails at speed...........

You may find the sweet spot for the transducer. From what I have seen especially on aluminum boats, between the vibration of the boat and the turbulence of the motor it's hard to get a great pic.

Have you tried trimming motor up? Are you matching screen speed with boat speed? One thing you can test is to raise the transducer you will not get 2d at speed but if the SI improves then you can add a separate 2d transducer to get high speed reading with a y splitter cable

I have bout the same boat as yours with hds 8 on it and the si transducer is on the left bout the same as yours but closer to the motor and it works ok just have to raise the motor for good image on both sides. I do have a HB on it also and it will not get a good picture if it is on

I always match chart speed n boat speed. I was seeing on intronet many have done that Diesel 44.

My Mariner is rough at low speeds too.......shakes.........my prop is beat up too........

When you use 2 transducers and a Y cable do you have to tell it which to read.? Switch it or it'll pick up whatever signal depending on what screen mode you are in.?

So far I'm not benefiting from Si and I miss my 859 - it was faster on mapping and even better 2D images.....

No, the way the plug is pinned out you will constantly be reading si/di/2d. Be just like using one transducer. I have 2 on the back of a tracker. The hdsi and a 2d transducer and it works great

Can you post pic of ducer locations.?

I had a clear picture on my aluminum boat and had my transducer mounts at least 6" above the bottom of my transom. It also helps to protect the expensive transducer.

If I go to 2 ducers what 2D ducer do I get.?

http://www.humminbird.com/Products/XNT-9-20/

I have a splitter cable you can have

Cool.