I agree with marky that the first shot feels slightly odd. I think the problem is the proportions. By the law of thirds, the initial focus of attention falls on the 2/3 portion of the picture, e.g. if the horizon divides the scene 1/3 sky, 2/3 ground you start by looking at the ground, whereas with 2/3 sky, 1/3 ground you look at the sky. Here the boats etc take just under half of the vertical space, and the pebbles and water just over half, this draws your eye somewhat vaguely to the lower portion, however it doesn't hold your gaze and finally you settle on the boats etc after a bit of vacillating. In a better composition the pebbles and waves would be more dominant, and would also lead your eye up to the boats. If it was redone as a vertical composition with about 50% more foreground so the pebbles and water took up 2/3 of the image, they would sweep in much closer to the viewer and become a point of interest, and the stonger perspective and vertical layout would then lead the eye upwards to the boats. Alternatively, leaving it as a horizontal picture, you would want to crop off most of the bottom so that the boats and horizon dominate the picture from the outset, which is essentially why the second shot works better.
The final shot suffers the same problem, here the boat is slap bang in the middle of the picture, the above-centre horizon brings your eye downwards towards the pebbles but not enough is made of them to hold your attention which settles on the boats again. Although it's something of a cliche, the law of thirds really does work, and if you put the horizon either on the 1/3 or 2/3 line the picture would be greatly improved, with the patterns of pebbles being either emphasised or marginalised depending on whether you swung your camera up or down.