The bilge pump is a 15HP 3phase 480v pump. EMI has never really been a big issue with the existing ethernet, CAN, and low voltage signals and the controllers won't be near any EMI sources.
Basically my thought is to use one Arduino as an input device and the other as an output device. I'm trying to figure out the best way to get the input device to communicate with the output device when necessary. Should I just do the routing through the software I'll be writing (python)?