Just my opinion, and what I talked my father-in-law into.... I would consider the Helix 10 DI for the bow unit. Don't open the transducer packet that comes with the unit, call Humminbird and swap it for the trolling motor version this is supposed to be more shielded to "help" prevent interference. The 9 and the 10 are exactly the same size, only the actual screen is smaller, so the 9 does not save space. It is cheaper.... however, the screen is clearer on the 10 because the pixel count is higher. My father-in-law already had a Helix 10 SI at his console, so he is used to that screen/clarity already. The DI version of the transducer is supposed to produce a better image than the SI transducer that "blends" the two sides together in the middle to give you a down image.

I would put the 10 SI at the dash. It comes with the upgraded transducer already and as I said before, the screen clarity is better than the 9. If you choose the 9 for the dash, I would still opt to upgrade to the better transducer. If you haven't thought about it, I would also consider adding a AS GPS HS (heading sensor/gps) antenna to your rig. It works so much better if you fish off shore structure like brush piles. It will always show the correct position of your boat on your map, and show the direction your boat is pointing. This will keep the map from spinning around when you are sitting still or the wind is slowly drifting you. I wish this antenna could be shared the heading sensor with both units like you can do with Lowrance, but you can not with these units and you would need one for each graph if you wanted it. I would recommend it at both units though. You could also go with the heading sensor antenna on the bow unit since a lot of your slower idling time will be there and put a regular antenna on the back of the boat as close to being above your transom transducer as you reasonably can. Your waypoints marked at the console will be more accurate than if using the internal gps of the console unit. ALL this stuff is expensive and confusing sometimes, but get the biggest screen you can to start with.

Joe