I wonder if he really was an unusually large whale or if the sailors had to exaggerate in order to make themselves feel better over the loss of the ship. Again, my understanding from some TV show or another was that the Essex was in rather poor shape, suffering from dry rot and was therefore more vulnerable to the whale's attack.
In any event, the whale gets full points for cussedness. He hit the ship twice, and may even have knocked himself out. It is really no different than a rhino charging a Land Rover I suppose, but it still makes for a compelling story.