Hi. I just bought a Helix 9 si. And I had a 778c humminbird given to me. If I run a either net cable between them, do I have to mount the transducer for the 778c?

I'm no expert, but as I understand it, you can select the transducer in the settings of the "other" (778c) unit if it has the ability to run off multiple transducers.  But both units have to have the same capabilities.  For example, if the 778c does not have side imaging capability, the you will not have side imaging on that unit even though it's set to the transducer of the Helix.

 

I expect you will get more expert responses than I can provide.  I provide questions better than I provide answers.

Thank you

That is correct. The two units will share 83/200 kHz 2D sonar only. PLUS GPS data.

 

It takes at least a XX9 model to cross-share sonar technologies with the Helix.