A sailing ship was, of course, dependent on the wind for maneuverability. The wind’s strength determined the speed at which the ship might travel, while its direction limited those in which the ship might go. When the wind was kept abaft the beam—blowing from somewhere behind the ship—she could sail along with little effort in a range of directions. But when a ship wanted to go toward the wind’s source, she had to sail a zigzag course, gradually working her way into the wind much as a skier works his way down a slope. From this it is clear that a ship in an upwind position has an advantage in deciding whether a downwind ship will be allowed to get closer.
The Dutch word for changing a ship’s direction toward the wind was “loufing,” a word that came into English as “luffing.” By extension, to the Dutch a ship that was “a-louf” was one that could keep her distance from a downwind ship as she chose. It was a small step ashore for “aloof’ to come to mean “keeping apart” or “to keep one’s distance” from others.