I think its important to have the horizon level in a landscape painting. I will always draw this important line first before the sketch is started. On bigger paintings I will measure the distance to be absolutely sure its correct.
Its not so noticeable on standard landscape because of distant hills or mountains but when the flat line of the sea is included in a painting its critical its completely level. Its all about the illusion of reality I continuously try and achieve.
I have a steel ruler I use to help me in this endeavour. By lying it flat on the surface of the painting and using it like a stencil to brush flat the lowest sky colours I get a final paint layer completely straight and level. Its amazing how crooked this line can be when painted by hand alone. Only when the ruler is employed can you see how wobbly this horizon line can be. If the ruler causes a few smudges on the lower part, usually the sea, that’s OK as these are going to be overpainted later on.
Here is the video of the painting. See you soon.