I decided to go with three different thread colors: a medium gray, a slightly darker medium gray, and the steel blue.
The top couple of inches is the lighter gray. The next inch or so is the slightly darker gray. Right about this time is when the following happened...
My thread tension was messed up. I spent the next hour or so ripping out thread. Unfortunately, I didn't notice the problem soon enough. One of the hazards of working at an art show, there is so much ambient noise that it is hard to hear when something isn't quite right. Much of what is in that previous image had to be ripped out.
Once the thread tension problem was solved I was able to continue. Here's the two gray threads. I'm only about halfway done with the slightly darker gray at this point.
Here's all the ocean all stitched with the three colors of thread.
I don't usually show this, but here is what a portion of the back looks like. Notice that the top part has very straight stitching while the bottom has a lot of curves. I do the random curved stitching to give more wavelike movement to the water. Below is a brief video showing how I get that curved stitching.
Next I start work on the ship!