I use an ATEN "CAT-5 KVM Extender" on our boat and it's really great!
The computer stays nice and dry in the pilothouse and has two
keyboards, two mice, and two monitors connected to it. I only had to
run one thin CAT-5 (network) cable to the upper helm since power was
already there. The really great thing is that I don't have to flip any
switches when I change stations. The only problem is that waterproof
sunlight visible monitors are really expensive...

I'm writing an article about my setup and you can preview it at:
http://coastalexplorer.net/Boats/Urania/default.htm

I considered and/or tried lots of other options, including two
computers on a network, wireless keyboards and mice, and even a
wireless monitor (a "Smart Display"). None of these other options
works anywhere near as well as the simple KVM Extender.

Good luck with whatever you end up doing!

Brad Christian
Rose Point Navigation Systems, LLC
http://rosepointnav.com/