The first (but late) warm spring day, when the sea is still cold: the air near surface is 8-10 °C, and higher maybe 15 °C.

https://en.wikipedia.org/wiki/Inversion_(meteorology): As the temperature of air increases, the index of refraction of air decreases, a side effect of hotter air being less dense. Normally this results in distant objects being shortened vertically, an effect that is easy to see at sunset when the sun is visible as an oval. In an inversion, the normal pattern is reversed, and distant objects are instead stretched out or appear to be above the horizon, leading to the phenomenon known as a Fata Morgana or mirage.

In this case, it appears that the upper part of the ship is reflected from the warmer air is seen twice: direc and reflection?