Waypoints are written directly into the internal memory of the unit that created the waypoint ...
Ethernet allows each unit to "read" waypoints in each other's memory ...and display those waypoints in a different color (green) ...
Waypoints reside in the unit memory until you manually command them to Export (to a SD Card) from the waypoint management menu under the Nav tab ...
You can Export the waypoints to a SD Card and manually import them into the other unit if you want to see all your waypoints on one unit while the other unit is powered off ...
The "Cleanest" may be to keep waypoints on the unit that created them, Export occasionally to a SD Card, and run them thru HBPC to create a hard copy backup ...
You just need to have both units powered on so that each unit can "read" each other's waypoints during fishing ...
Rickie