Crab claw sail

The crab claw sail ( also Delta sail ) comes from Polynesia. It has a triangular shape and is used to Proas or outrigger canoes. The lift is not generated as in the conventional sail types by an airfoil profile to be flowing around as laminar as possible. The crab claw sail is flown at the top of the triangle to the legs in each case forms a wingtip vortex, in which the flow is so fast that on this side, a negative pressure ( delta wing ). In this way, reached 1.7 times more boost with the same sail area.

The cancer scissor-like sail shape has the same efficiency as one of the outer edges measured rectangular area - has been recognized as in wind tunnel tests. Presumably, with the indented shape of the sail under lateral wind prevents excessive pressure rise ( " stall " ) and thus the net effect strengthened. The one side of the sail attached " Ziergehänge " is used for turbulence control.

There are attempts to rotate the sail overhead to turn as conventional boats.

Crab claw sail of a proa

Crab claw sail