You could put the SI transducer on the bow mount trolling motor. I only have SI on the transom so I have no experience with it. SI does require some dedication to learn and benefit from. I probably use SI more for hunting then use 2D/DI while fishing. Using SI in the bow would come down to:
- How much time you spend in the bow with the trolling motor down.
- SI doesn't work that well if you are constantly turning (which bow mounts tend to do). Every time you turn it's repositioning the transducer and can "smear" the sonar returns. You get better images if you are driving in straight lines.
Is the 997c something you already have and are just looking to utilize? I personally wouldn't buy that old of a model unless it was really cheap (under $200 for sure). No software updates available for those legacy units anymore. If you already have it are just looking to use it I would be tempted to put it at the console next to the Helix 9. Dedicate the 997c to SI and use the Helix 9 for mapping and 2D sonar. I would then find another basic unit for the bow. I bought a Helix 7 G2 (non-networking and no DI or SI) for $350 last year. Does what I need it to do for bow fishing (2D sonar and a map).
For learning Humminbird check out YouTube. Jason Halfen has a good page:
https://www.youtube.com/user/jasonhalfenoutdoors