What cabling do I need to add another Raymarine i70s on port side?

[Cool Hand Luke]

I replaced an old Raymarine ST70 earlier this year with a new Raymarine i70s unit in early 2019. Both the autopilot unit and the new i70s are on the starboard side. I'd like to add another i70s on the port side. See attached photos. I was thinking of the Raymarine i50 TRIDATA but the prices are so high that they exceed the i70s. Is that normal???

In any case... What cabling do I need? Do I need to run just a normal STng cable or do I need a backbone cable? Do I need a splitter of some sort?

I installed the first i70s by myself, but I'm still an amateur with marine cabling and marine networks.

Any help will be greatly appreciated!

[smac999]

It depends what you currently have in place. A drop cable is max 6m. If the run is over 6m from new gauge to existing backbone. You’re have to extend the backbone.

If you want any future stuff on that side. Then extend the backbone over.

[HeinSdL]

Extend the backbone to the port side, terminate it there with a T-piece and the backbone terminator and run a spur cable to the new unit.

Don't know about the i50 TRIDATA prices...