Can exceptional behavior be considered ordinary?

The answer is Yes, according to Justice Wilmer in the 1955 case of Velox vs. Viking Monarch, wherein one anchored vessel dragged anchor and collided with another when both were sheltering from a severe storm, when there were maneuvers and procedures that might have avoided it if taken.

The nicely put conclusion was:

"I have been reminded, and quite properly reminded, that no seaman can be called upon to exercise more than ordinary care (we add, see Rule 2a); but I think it is necessary to observe that when a seaman is called upon to face wholly exceptional conditions, ordinary care of itself necessarily demands that exceptional precautions may have to be taken."

In other words, it is the ordinary practice of seaman to take exceptional precautions in exceptional conditions, just as it is to take normal precautions in normal conditions.