I'm not sure if the savings in drag from the winglets will be all that advantageous when considering all of the other things on the boat that cause drag. You have all of the standing rigging, the trap wires, some of the running rigging, spin poles and socks (on some boats), the crew, and harware placed on the mast that will interrupt the airfoil shape... Basically and non-streamlined object on the boat.

Unless the "mastlets" give you a substantial increase in lift they really are not worth the expense. I believe the winglets on the airlines do not increase lift, but just reduce drag (and save about 10% in fuel consumption each flight) by reducing the draga for vortex generation as mentioned earlier.

I may be wrong, but I also don't remember seeing winglets on non-swept wing aircraft. This could be due to the fact that most swept wing aircraft are high speed, heavy aircraft who would benefit from the drag reduction.