Yeah, the thing about sunsets is that by the time they reach the point of maximum drama, everything that isn't sky gets reduced to a silhouette. That silhouette needs to be really interesting and 'descriptive'--downright iconic, even. The shots posted in this thread by Doylem and RobLS are great examples of iconic silhouettes. Doylem's shot is "about" the lighthouse, and the viewer can read into it all of the metaphors associated with such a structure. RobLS's shot is "about" the sailboat, giving the viewer plenty to contemplate about the experience of sailing or about the metaphors associated with that activity.
The problem of the missing "subject" is common in a lot of landscape shots, not just those that show sunsets. People very often enjoy the experience of being in a place and have trouble packaging that experience in a successful photo. But with sunset shots, the problem gets compounded because of the reductive nature of the lighting.
In the OP's first photo, we see a magnificent sky, but quickly lose interest because there is nothing else in the frame to give the photo some extra meaning; it's all setting and no subject. In the second photo, there is a boat, but it has very little visual weight in the frame. The boat is relatively minuscule, is surrounded by relatively dark tones, and is very close to the line of the shore; so it's not very well isolated and doesn't work well as a subject.
If you can't find anything to serve as a good subject for your sunset shot, consider including a figure, either as a portrait with some fill flash or else as an interesting silhouette. If you're using a tripod, you can even be that figure yourself. Alternatively, see if there are any small objects in your possession or somewhere nearby that you can position somewhere and foreground in your frame. Look around, be creative, and try to get beyond the "wow, what a cool sky" point.
Hope that helps.
