The blacks seem somehow...foreced black - as in the people in the boat, but I very well could be wrong. I love the clouds though and it does fall into the rule of thirds.
The clouds are awesome, slightly more contrast and some leveling would benefit the picture. And one small thing the horizon is titled slightly counter clockwise.
I think this photo should have been taken one hour earlier. The main point of the pic is a boat but it is in deep shadow. The horizontal line is sloping, too. However, the composition fits the rules of this competition well.
If you straighten your horizon and crop some of the top your composition would be stronger. Also a little noise reduction would clean up the graininess. Some people like the grain, I personally prefer a more smooth look.