Cheese - A lot of your photos look great too! Simply, try to get the horizon straight, and have as little as possible under the ferry (water, land, etc.) Many of my ferry photos from my first year of phototaking look very similar to yours. Scott is my model, and it's always my goal to make my photos look as good as his! ;D
I have to say that I don't even follow those rules. I like going for the art in the shot. If the ferry looks better on the top of the frame, or in the center, then frame it that way. Uniqueness in the situation is the way to go. Find a spot that nobody else has been. An angle unseen by other eyes. It's what I live for.