Incredibly, Frankenstein's small skiff has drifted a distance of several hundred miles, from the Orkneys to the northern coast of Ireland, while he slept. By a coincidence which is never explained he lands at the same remote coastal village where Henry Clerval has been murdered by the creature. Victor's timely jaunt does provide him with an alibi for Clerval's murder, committed while he was still in the Orkneys, but the incident's usefulness as a plot device is surely outweighed by its sheer improbability.
This sense of unreality can be seen as the passage's goal, coming at a point when Frankenstein himself starts to question the coherence of his narrative: "my life appeared to me as a dream; I sometimes doubted if indeed it were all true, for it never presented itself to my mind with the force of reality" (p.149).
From the Orkneys (top right)... to Ireland (bottom left):