The horizon is slightly skewed. The vastness of the ocean and the insignificance of your subject shows good porportion. Also, the two different shades of blue really stand out nicely.
I like the colours, a lot but what about the proportion, 3:1?
(all the pictures I've taken of my husband look like this: a hat, shades and beard, no face - not the photographer's fault though!)
I kind of like this as a candid portrait but I don't see how it meets the challenge. I like the extreme of placing the subject to the very edge of the frame with the expanse of water and sky filling the rest. I guess in a way the composition demonstrates proportion. I think your title has thrown me off. Fill-flash would reveal more detail in the subject's face, although you might have lost that intriguing blur of his hand at the edge. Overall, I think it's an effective image.