Abstract: Reefing apparatus for a sail of a sailing boat makes use of a hollow boom for the sail. The boom has a lengthwise slit in the top extending over the length of the sail footrope and contains a tubular shaft which can rotate within the boom and to which the footrope is attached. A second shaft is located within the tubular shaft and is coupled to the tubular shaft by a spring, which is stressed on rotation of the tubular shaft relative to the second shaft.The sail is rolled up on the tubular shaft and within the boom. When the sail is raised, it is unrolled from the tubular shaft and drawn through the slit, the spring being progressively stressed. When the sail is to be reefed, the halyard is appropriately slackened, when the sail is drawn into the boom by the action of the spring and rolled on the tubular shaft, until the required reduced sail area is obtained.