How does the Cornwall "floating ship" illusion work? Article


BBC meteorologist David Braine said the "superior mirage" occurred because of "special atmospheric conditions that bend light".
He said the illusion is common in the Arctic, but can appear "very rarely" in the UK during winter.
Mr Braine said: "Superior mirages occur because of the weather condition known as a temperature inversion, where cold air lies close to the sea with warmer air above it.

What is happening here?
Why is the surface of the water, where it touches the boat, not "bent" equally with the boat itself?
Why is this common in the arctic?
 A: This effect is also called Fata Morgana, or mirage.

Fata Morgana, mirage that appeared periodically in the Strait of Messina between Italy and Sicily, named in Italian after the legendary enchantress of Arthurian romance, Morgan le Fay [Source]

What is happening here?

The optical phenomenon occurs because rays of light are bent when they
pass through air layers of different temperatures in a steep thermal
inversion where an atmospheric duct has formed. (A thermal inversion
is an atmospheric condition where warmer air exists in a well-defined
layer above a layer of significantly cooler air. This temperature
inversion is the opposite of what is normally the case; air is usually
warmer close to the surface, and cooler higher up.)
In calm weather, a layer of significantly warmer air may rest over
colder dense air, forming an atmospheric duct that acts like a
refracting lens, producing a series of both inverted and erect images.
A Fata Morgana requires a duct to be present; thermal inversion alone
is not enough to produce this kind of mirage. While a thermal
inversion often takes place without there being an atmospheric duct,
an atmospheric duct cannot exist without there first being a thermal
inversion. [Source]

Here are two visual aids:

*

*In this one one may see that there are various mirages possible of happening


(Source)

*

*This one focuses on Superior mirages, the one that appears to be present in the case you mention


(Source)
Why is the surface of the water, where it touches the boat, not "bent" equally with the boat itself?
As @Farcher pointed out

The water is elevated but the it blends into the sky.

Here you'll be able to find additional diagrams that may help.
Why is this common in the arctic?

A Fata Morgana is most commonly seen in polar regions, especially over
large sheets of ice that have a uniform low temperature. It may,
however, be observed in almost any area. In polar regions the Fata
Morgana phenomenon is observed on relatively cold days. In deserts,
over oceans, and over lakes, however, a Fata Morgana may be observed
on hot days.
To generate the Fata Morgana phenomenon, the thermal inversion has to
be strong enough that the curvature of the light rays within the
inversion layer is stronger than the curvature of the Earth. Under
these conditions, the rays bend and create arcs. An observer needs to
be within or below an atmospheric duct in order to be able to see a
Fata Morgana. [Source]

A: tl;dr: The popular explanation of this image is likely wrong. It could be, rather, an inferior mirage.
Many news articles claim this is a superior mirage, that is, one that's due to a temperature inversion.  Here's an image borrowed from hyperphysics that shows the idea: warm air lies above cold, and the rays bend toward the slower medium (the colder air) causing objects near the horizon to appear higher. 
I am QUITE CONFIDENT that this in not the correct explanation for the image in question.  The photo was apparently taken over the southern English Channel in February 2021.  The water temperature, and therefore the temperature of the air very close to the sea surface, was around 10 C. The air a bit higher up was likely colder (weather records show that it was never far above 10 C in that month, and often considerably below). Rather than a superior mirage, it could be an inferior mirage (assuming it's not a fake)--the same kind as causes the appearance of water on a hot road. The rays near the surface bend upward, causing them to cross those that originate at a slightly higher angle. The actual mirage is not the ship, but the sky below it. Here is a sketch:

The result is that the ship does not appear distorted--the rays from it don't deflect--and the distortion that would be apparent in the rays that do deflect doesn't appear because there are no features in the sky to distort.
This actually happens routinely on chilly days where I live--albeit to less dramatic effect. A thin strip of sky appears below distant land.  It is definitely an inferior mirage as it happens exclusively on days when the air is colder than the water (usually below freezing).  I took this photo with my phone after seeing the reporting on the Cornwall mirage:

If I'd had a telephoto lens rather than a cell phone, the depth of the apparent layer of sky would appear similar to that in the Cornwall image (though the level of detail likely would not measure up).
