I have used the 15 for 5 years and the 17 has even better resolution.In my opinion it is the best monochrome out there and it will do every thing you want.I would get the fishing hotspot map for your area and run that so you can actually GPS yourself on the structure.It is a great unit and I have navigated around Santee and the local rivers without looking.Of course my son continues to watch just to make sure but that GPS is very accurate and many a night have come back to the dock just using my previous trail.Go to Lowrances web site and download the Emulator and play with it all you want.