Honestly, I would try and find more simple and isolated subject matter. These photos are very busy. As landscape shots they don't hold up (#1 is framed too low, #2 too high, #3 too low and #4 too tight). If you want to have a photo of a boat as the subject, it should, ideally, stand out against its surroundings. The easiest way to achieve that would be to find a boat in the open water and focus on that, use the rule of thirds for your composition and voila.. usually a nice photo.
I'm not sure what you meant by your title 'achieving depth of field' though. All of these shots have a very deep depth of field, meaning most of the photo is in focus.