Re: Chartplotter repeater
Regarding needing any waypoints twice, that should not be necessary. Depending on the model there are several options for transferring waypoints and routes from one Garmin unit to another. For older units Garmin has a Maosource program that will upload or download waypoints, lutes, etc to and from chart plotters or data cards and computers. You can do the same with newer units using their Homeport program. They also have iPhone iPad app which will wirelessly transfer waypoints and routes to comparable units.
Rather than get a repeater screen get a separate portable charter that will serve as a backup and just transfer the waypoints between units. It's much easier to creat waypoints on the computer and transfer to units that creating them on the units although it might be easier with the newer touch screen units.