To explain the fragment we should pay attention to the name of the character: Ahab. It means uncle in Hebrew and is well known because A. Melville used in his novel 'Moby D-i.c.k' (1851).
In the fragment, we read a detailed description of the emotion of the character. This emotion envolved Ahab at a precise moment in which he apparently faces death. He feels a mad force, some power only comparable to the resistance of an entire army troop.
The narrative construction uses a third-person narrator, which reveals the feelings that Ahab experienced. It is a moment of great narrative tension, possibly the passage that begins the end of the story.