big boats and little wake

On this morning's ferry to work, we passed a tanker leaving the harbor. In the photo below (not the greatest, I apologize), you can see the tanker and the pilot boat. Despite the immense size of the tanker relative to the pilot boat and the fact that both the boats were traveling at the same speed, the wake you can see in the picture is all from the pilot boat. The tanker had a bulge of water on it's bow, but no visible wake. This is neat because a boat moving through water (or any generally incompressible fluid) displaces the water in it's path. Logically, since a larger vessel needs to displace more water, one would expect a larger wake. Perhaps the equations which describe wake formation involve velocity/length, which would explain why a large and small boat traveling at the same velocity would have such markedly different wakes, OR someone did some pretty sweet hydrodynamic work and built the hull of the tanker to pass through the water with greater efficiency (than the hull of the pilot boat, for example), thus reducing the wake.