I’ve looked at this image for a while, and it does convey the tranquillity of your title. My eye starts at the center of the image, at the very dark boat hull, and travels up along the mast, then downward to the almost invisible reflection of the mast in the water. It then circles the perimeter, and returns to the boat.
Part of what makes the image striking is the brightness of the water relative to the relative darkness of the sky. The vignette seen at the upper corners seems a bit heavy. The horizontal cloudstreaks echo the horizontal striations in the water, and lend a reinforcement tying the two parts of the image togther.
The positioning of the horizon and the boat at dead center works for me in that it supports the symmetry of the composition. The missing element for me is that the mast reflection in the water is very muted, and would have created a stronger image if it was more prominent. But you can’t always arrange the the scene to suit the camera.
The rather large expanse of water in the lower half of the image works for me, in that it reinforces the quietness of the scene. However, as my eye travels up the mast, it almost immediately runs into the upper edge, and that feels somewhat uncomfortable. On the other hand, the boat serves as a visual anchor that allows the eye to wander off in each direction (into the emptiness), and then dart back onto the boat before venturing out again. This makes the “empty”space the center of attention.
