What do you recommend as a good combo chart plotter/depthfinder unit? I currently have a depthfinder and use a handheld gps to track my trolling speed. I would like to get one of those split screen units so I can see where I am on a map. Also what transducer to pick? I have a 17.5 ft boat with a 115 hp motor. I usually dont go more than 8 miles offshore.