The photo shows a tank-test model of the new Viking 82 Convertible. Some changes were made from the model to the finished boat, but the prop tunnels stayed much the same. The sides of the tunnels are parallel to the centerline of the boat, and parallel to each other as well for their entire length. The sides do not converge either forward or aft. Looking closely at the black lines drawn athwartship, you can see that at the forward end of the tunnel, the shape of the tunnel roof begins very flat, and then transforms into a progressively tighter radius as we move aft toward the transom. At the point of the propeller location, very near the end of the keel on this example, the tunnel reaches its smallest radius. Aft of this point, from prop to transom, the shape can be maintained as in this Viking, or might converge just a bit to create a slight "nozzle" effect on some boats.