The reason is that the ship has its own position-on the water, in the rivers and lakes. Without rivers, lakes and seas, it would be a useless thing. I asked him: doesn't it mean "smooth sailing" He said: Besides sailing, is it meaningful to have smooth sailing?
Finally, he explained: if the painting is a ship sailing on the vast sea, the sky is clear and calm, which is an acceptable goodwill blessing; If the ship sails in the storm, it is likely to be rejected. As for the physical ship model, it is difficult to predict.
I think his statement is a little different, but it is not unreasonable. Write it here for reference only.