If certain air conditions can make a boat fly, then maybe different ones can make a boat sink. 
What conditions do you think will cause the boat to appear to sink?
I don't know.
How about you explain to me why you are happy to believe certain air conditions can make a boat rise, but you do not believe certain air conditions can make a boat appear to sink.
From this thread, I already linked to
my thread where this was demonstrated.
Refraction occurs when a subject, such as light, goes from one type of medium into a lighter or denser medium. If it goes from a lighter medium to a denser medium, the light refracts toward the normal (in the atmosphere's case this would be downward), which in turn makes the object we are viewing appear to be higher. On the other hand, if it goes from a denser medium to a lighter medium, the light refract refracts away from the normal (in this atmosphere's case this would be upward), which in turn makes the object we are viewing appear to be lower.
Nevermind the fact that a sinking ship will happen every single time but the earths atmosphere is always denser the lower you go. There are times, on the earths surface, where there can be subrefraction over land because land can heat up and cool down very quickly but this is NOT the case with water. Over water there is ALWAYS a dense duct directly over the waters surface which causes trapping and typically above that exists a super refractive layer of air.
I have empirical proof of this. I launch weather balloons all the time. The air gets less dense the higher you go. I graph these findings and determine just how much refraction occurs and how that refraction will affect the propagation of a radar. In the Navy, surface search radars absolutely depend on utilizing the fact that radars will always perform better there than above the surface. We can see a target that is further away because the target is actually appearing to be higher than it really is, every single time.
The funny thing is, that in all these sinking ship pictures, the ship we are viewing is most likely behind the water obstruction and should not be viewable whatsoever, but because of the properties of water and how water affects the air directly above it, we can see some of the object we intend to view. Thanks to refraction, which again, does work both ways and sometimes can work the opposite way that I've explained here over land, but over water? NEVER.