You might do what I did, get the better fish finder and a good portable gps. Although the screen is small and I sometimes have to come off plane to check my position and progress, the Lowrance globalmap 100 is dead nuts on every time. I used to get to my ledges in the fog by compass and nautical miles, then shut down in shorter and shorter intervals until I heard the surf on the rocks. Both work, but the gps is quicker and it's nice to just reach down and log in a quick waypoint for later. The only problem with later is, if you wait too long until you name it, you end up with a bunch of numbers waypoints, which you no longer remember which is which

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I'll tell you another place I've found it to be great is up in Maine on rocky lakes during my 4-5 day camping/fishing trips. Save the plot trails and once you have a clear rock free course laid in, you can put the throttle down and go after a while, just follow the plot trail. I wouldn't do it to navigate through a real bony spot, but it works great for avoiding that rocky point or bar.