The correct answer is D) Expanding square. When the vessel in distress is not sighted at the reported position, an expanding square search pattern is the recommended technique. This type of search involves starting at the last known position and systematically searching in increasingly larger squares or rectangles until the vessel is located or the search is called off. The expanding square search ensures a thorough coverage of the area and increases the likelihood of locating the distressed vessel, even if it has drifted from the initial reported position. The other options are not as suitable in this scenario. A sector search is used when the probable location of the vessel is known, but the expanding square is more appropriate when the vessel's location is uncertain. Parallel track and track crawl searches are better suited for situations where the vessel's approximate location is known, but the expanding square provides a more comprehensive search when the position is unknown.