Aka (sailing)
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The aka of a multihull sailboat is a member of the framework that connects the hull to the ama(s) (outrigger). The term aka originated with the proa, but is also applied to modern trimarans.
The design of the akas depends on the forces it will encounter when sailing. For example, there are two modern variations of the proa, the traditional or Pacific proa, with the ama to the windward side, and the modern Atlantic proa, with the ama to the leeward. The windward ama provides stability by placing the center of gravity far to the windward of the sail, so it is generally heavy. Ropes leading from the mast to the ama provide the force to lift the ama, so the akas must contend mainly with compressive forces, and the weight of the crew, who generally ride on a platform running between the akas.
An Atlantic proa or a trimaran rely on an ama to leeward to provide stability. The ama provides stability by moving the center of buoyancy to the leeward side, and well designed leeward amas will also provide dynamic lift to increase the stability further. The aka for a leeward ama must be designed to handle significant amounts of torque from the lift produced by the ama. Often trimarans will have a platform between the akas, so the crew can ride out on the windward side. While this is not truly necessary from a stability point of view (the ama generally provides a tremendous amount of lift) it does reduce the drag generated by the leeward ama.
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