I have a 899 on the bow, built in gps antenna and a 898 on the console, no gps antenna. I do exactly that, I hit the power button and turn off the sonar on which ever unit I'm not looking at at the moment. I leave both units on due to the fact that I share gps antenna and waypoints on the network works well, I do plan on getting a puck and mounting it above the transom ducer soon, but for now I can get within 10' of the target. Then I pinpoint with the TM / Bow ducer. One pointer before you power down either unit for the day turn the sonar back on and then power down, turning it back on after the menu window is gone takes a little more menu searching when you have to turn it back on after a power cycle.