Crab claw sail

The crab claw sail or, as it is sometimes known, Oceanic lateen or Oceanic sprit, is a triangular sail with spars along upper and lower edges. The crab claw sail is used in many traditional Pacific Ocean cultures, as can be seen by the traditional proa and tepukei.

Construction

The crab claw sail consists of a sail, approximately an isosceles triangle in shape. The equal length sides are longer than the third side, with spars along the long sides. The forward intersection of the spars is placed towards the bow. The sail is supported by a short mast attached near the middle of the upper spar, and the forward corner is attached to the hull. The lower spar, or boom, is attached at the forward intersection, but is not attached to the mast. The crab claw is a shunting sail. It is used on a boat which has a permanent windward and leeward side, and exchanges one end for the other when coming about, such as a proa.

To tack, or switch directions across the wind, the forward corner of the sail is loosened and then transferred to the opposite end of the boat. While remaining attached to the top of the mast, the upper spar tilts to vertical and beyond as the forward corner moves past the mast and onward to the other end of the boat. Meanwhile, the mainsheet is detached and used to rotate the rearward end of the boom through a horizontal half circle. The forward corner is then re-attached at the new "forward" end of the boat and the mainsheet is re-tightened at the new "rearward" end.