I set myself a challenge of 100 paintings of waves a little over a month ago, and as I completed it, I set myself a final exam. I did these four little paintings from memory, to test all my skills. Most of the old seascape masters I've read say you must be able to paint the sea from memory to do it well. They used sketches and studies made on the spot but all of them spent many many hours just watching and studying the water and weather.William Trost Richards son said his father spent so much time standing in a trance on the beach watching water that people thought him insane. Then in the studio( many painted before the camera was so easy) they would rely on their memory and maybe a few small sketches. We artists today do not have or use our memories so much, and even in school kids don't have to memorize poems or the Gettysburg address like they used to. For seascape painter memory is a must, you can't just stop the water and light. A camera is not much use either if you want to paint like the eye sees, it is a blind mechanical thing, the human eye is attached to the heart and mind of a person with feelings, something no camera has.
So this is my exam, 4 little works about 4.5 x5 inches each...this is a great exercise to try, it tells you what you know and what you don't. This took about an hour total