When I draw the rule of third grids on your photo, the intersecting lines fall into the water, and thus lack interest. I do like your composition, but for me, it doesn't meet the challenge as well as other entries.
Some more contrast would've helped me with this shot as it feels somewhat flat such as a scanned photo. The darkness of the photo blends in alot of the neat details that could stand out.
The man standing on the right should be the main point of the photo but now he swamps to the scenery. A bigger aperture would have taken him off the background. A cloudy weather is not the best one to these kinds of pics, too. But the composition is succesful and fits well the rules of this competition.
I like the single figure against the sea setting. Maybe up the contrast a smidge. The composition works but is a tad boring. Hmmmm - maybe more contrast would help although that might not be available with the mid tones in this shot.