"Winglets" were tried years ago on A class cats. The principle is sound and the reduction in drag due to the reduction in "tip vortex" is very measurable, the problem with a rotating mast is that to have the winglet as part of the mast, when it is rotated in relation to the sail the "plate" that forms the winglet has to be very large to still offer its effects to the sail on both tacks, the head of the sail has to be "squared" off and attached to the winglet plate by something similar to a "radial traveller" so that sail and the winglet form as near as possible a "one piece" tip. An offshoot of this unsuccessful "experiment" with winglets on masts that is being adopted more and more today was the early application of the square head sail. The same problems are not an issue on aircraft wings as both components are a “fixed” one part. The "Americas Cup" "J" class boats used the same principle at the bottom of the sail when they reduced (to advantage) the "vortex" or "equalisation of pressure" around the foot of their mainsail by using the "Park avenue" boom.