Thank you, Hannes. That's a nice one, too.
I took Ulco's advice for placing the texture from the other thread – copy the boat's position into a transform input shader connected to the image map. I suppose you could do the same thing with an orthogonal camera, and use that to position the image map. Once the position matches the boat it's just a matter of offsetting it the right amount.
It would be nice if you could link translation (and rotation and scale) values programmatically, either through an input port or an expression. That would eliminate having to update them manually.