"beelzebub himself might climb up the side and step down into the cabin to chat with the captain and it would not create any unsubduable excitement un the forecastle" why is this statement ironic

The irony is that even this early in the story, the sailors already feel that they are in a kind of hell, one that obviously centers on Ahab and his "focus" on only finding Moby Dick. Yet, the further irony is that even in this hell, they do not feel particularly upset by anything that happens. The most interesting thing about this is that they would associate Ahab with Beelzebub and not be upset about it. Obviously something is out of line in the entire story.