The irony which plays into Stephen Crane's short story "The Open Boat" could exemplify the fact that the men, when regarding the shipwrecks as apropos (meaning "fitting"), fully expect to find a similar fate for their dingy.
Not only does the irony exist as a sign of their past fate (their ship is gone and is most likely wrecked), the irony compounds as one regards the situation the men are in.
Crane was (given he passed in 1990) a Naturalistic writer. According to the characteristics which these authors upheld, nature was far more powerful than man. Essentially, if nature desired (personified given the power nature was allotted) to take the life of a man, nature would take the life. The irony, therefore, lies in the fact that nature is toying with the men while showing "her" power over them by displaying the shipwrecks in front of them.