I'm in the northeast and the 18khz might handle the hot rocks we have here along with the salt. I use my Multi Kruzer and often run it at 19khz that fairs better than the lower frequencies around them.

Recently snagged another Gold Racer 56khz and had used one previouslty at the beach in the wet sand and it ran very smooth. I did have to manually ground balance it same as the Multi Kruzer.

The Vista X if it handles the salt might be a better machine as it is much faster and more finite to use a potentiometer to gb vs digital controls.