So here is the story. A couple of days ago, Cagil and I went to the beach and after the sun was gone, I tried to do something like that. Because of the lanterns on the near boardwalk, it was not totally dark and I only needed to do exposures of around 15 minutes with ISO 100.
This is what it looks like.
The white blurry areas are the waves obviously. The little light in the back blinked from time to time, which came out quite bright.
Also interesting: besides a lot of grain, you can see how the stars "move" on the sky because of earth rotation.
And what I found most surprising: Because of the light from the near boardwalk, you can actually see a very ghosty shadow of my tripod on top of the blurry waves. This is on the right side of the image.