Unusual Types Of Sail Rigs
Biplane Rig
You aren't seeing double -- there are 2 complete sail rigs on one hull. This is Dave Gray of Polysail.com and he is using 2 leg-o-mutton sails. The theory is that the sails won't spoil each other's wind and a larger amount of sail area can be flown with a lower center of effort. When sailing down wind, the sails are let out on opposit sides. This sail rig is also known as a side by side rig.
Wing Sail
Wing sails have been around for a long time, and are just coming into common use with the America's Cup boats. The way they work is the sail is shaped like an airplane wing and has internal parts that allow the crew to adjust the airfoil shape. The wing sail is proven on the race course and can beat a conventional sail of larger size.
The wing sail in this picture was made by Jason Nabors and he was going for something a little different. Instead of adjusting the wing shape when sailing, it flops the entire rig over when tacking. Kind of like a Gibbons does. That way the proper airfoil shape is presented on each tack.
Gibbons Rig
The sail is suspended in the middle along the luff, and sort of looks like a batwing. Most often used on proas, when the hull shunts, the sail can swing to the other side to start pulling in the other direction.
The Bolger, or AYRS Sail
(Amateur Yacht Research Society) Also commonly used on proas, the Bolger (not to be confused with the "Bolger 59") uses battons to shape the sail, and the theory is that it has a better shape control, and the upper portion of the sail can be kept from twisting. Also the clear luff is supposed to give it higher performance because the air isn't spoiled by a mast.
Ljungstrom RigWhen sailing to windward, it looks like a single jib. When sailing down wind, it is opened so it looks like 2 jibs that both are opened to catch the wind.
Often used on long down wind runs by blue water sailboats who usually carry multiple backup sails, they simply attach 2 jibs to the forestay. The sheets can be led back to the tiller to automatically steer down wind.
The "SoDoIt" class used this as their only sail. The guy who sailed a Montgomery 15 from California to Hawaii used one of these rigs most of the time.
Balestron Rig
It looks like a sloop, only that the mast rotates with a large horizontal spar that the jib and main are flown from. The theory is that the sail can be shaped properly from the large spar, and keeps it's shape because the spar is always pointed into the wind.
Segmental sail
It is a sail with a bunch of vertical slats, looks rather like gills of a fish
Windmill
A large fan is used to catch the wind and turn a shaft, which turns a propeller. The catamaran from waterworld had one. The theory is that a boat can sail dead to windward, which is a 2:1 advantage over a boat that can only go 45 degrees into the wind.
Rotor sail
Large spinning cylinders that stand vertical on a boat.