I only have a slight understanding of the concept of underpainting. It's the first layer of color or colors that serve as the basic definition of the painting in progress. It "blocks in" the composition and serves as a blueprint for subsequent layers of color as details are added or refined. This first layer, according to some of the sources I looked at, should lay down the darkest color for the sky, water, and foreground and then the overpainting will add highlights, brightness, and variations in color.
I read about it, but I wasn't really conscious of "underpainting" as I began the canvas. Start with the sky and work forward was the basic principle my father had taught me. So that's what I thought I would do here. But acrylic is different from chalk or pastel or watercolor. So I wasn't going to be able to do what I thought I was going to do. I saw very quickly I was going to have to go back to the sky multiple times.
The horizon was an accident, albeit a happy one. I got too much dark blue on my brush as I was painting the lower portion of the sky. But I saw immediately that it worked for the deeper water of the background. So I actually ended up doing what was in my ead two steps at once. From there it was a simple step to block in the lighter water of the foreground. And since the sky was pretty much dry, I decided to try to lighten it up.
I was satisfied with that day's work, and I felt like I'd learned something.
To be continued...