What obstacle do the men NOT encounter in "The Open Boat"?
One could answer this question in a variety of ways. This almost sounds like a multiple choice question given it lacks if the ask-er is looking for a concrete or abstract answer.
Given that Crane typically wrote from a Naturalistic perspective, the men in the boat did not encounter any choice of free will. Lack of free will is a common and important characteristic seen in Naturalistic literature. In this genre, authors wrote from a scientific perspective and looked at their texts as an experiment. Nature is always in control of the lives of the characters and, no matter how hard they try, they will always fall.
Therefore, abstractly, the men in "The Open Boat" fail to encounter anything that would allow them to pull out of the challenge that they are facing given that nature is more powerful than man and man will always fall to the power of nature. Free will has no hold or power over the outcome of a character- they are simply carried along only as long as nature wishes to deal with them.