The Garmin Lake Vu HD provides very detailed bottom contours based on the sonar mapping that they did 3 years ago.
http://www.winnipesaukee.com/forums/...ht=garmin+boat
Also clearly shows docks along the shore. My only complaint is that flashing lights are shown in white rather than the color of the red or black companion marker. Red and black markers not next to a FL are shown correctly.
I have a 541xs and really like the user interface.
http://gpstracklog.com/2013/06/hands...map-547xs.html
I also use Garmin Home Port on the PC to view the Lake Vu HD chart of Winni and generate waypoints & routes to download to the GPS unit.
I had the most basic sonar transponder installed as I don't fish, just want depth info.