I have the factory concentric in 7.75 khz , 9 inch and also the 6 in DD in 18.75 khz. I like the double d detection pattern but not for sure if I would be better off with a medium frequency or a high frequency coil. Has anyone else tried the beach with a xterra 50 with different coils and how was the results. I am trying to get set up for next spring. I would be hunting dry sand down to the water line.