The ship and sky are black and white while the ocean has a blue overlay. Or the photo was originally color and the ship and sky were layered black and white. It is a striking effect, though I might have upped the contrast on the ship.
This was inspired by my father's blue moon shot. For those that are wondering, this is a mixture of two separate photos and Photoshop. The moon is taken from my previous full moon shot from Sept. The city was taken with my old Nikon