Hovering Boats are Usually Not Mirages, they are beyond False Horizons
Perfect images of boats hovering in the sky are not mirages. Mirages distort and invert images. Even non-mirage refraction effects like looming will not create this effect (as they raise up the water as well as the boat).
It's a false horizon. The surface of the water is just taking on the color of the sky because of a combination of lighting, clouds, the calmness of the water surface, and a little haze.
In this video, I show how to use my refraction simulator to see what's going on with mirages, and why this is not a mirage.