If you take this shot with AF, it will most likely fail because it will pick up overexposed glare off the water. On this shot, I'd recommend setting manual focus to the very lowest center point, choose "center weighted average" metering mode, and open the lens up to around f11 at least, or go f5.6, and raise the shutter speed up. Take a few shots and make sure the water/sky isnt too overly exposed, if the beach is a bit too dark, you can always lighten it up in photo editing tools, but you gotta make sure the sun/water is okay because you can't change that as much as the land.
Another easier way would be setting up auto exposure bracketing to 5 shots (or 3) and combining 5 different exposures in one shot.
This glare off the water is one of the main reasons people use circular polarizing filters. It takes care of that.