The Vortex Sail, Variable Geometry Proa

by Malcolm Smith

VP5 Concept Design

The sketches below show a conceptual design for a Vortex Proa which utilises cant angle control to maintain neutral heeling moment. This design is for a radio controlled test model based on utilising the main hull of the existing model 3.

In this arrangement, the ama is placed to leeward of the main hull. The single aka (cross beam connecting the ama to the main hull) is attached to the main cross beam with a hinge. This allows the main hull/sail assembly to roll with respect to the ama. The ama is thus used as a roll sensing device. Wires attach the aka to the sail, via a bellcrank arrangement, to control the sail cant angle (see detail sketch below).

The sail shown is a wire luffed flat plate type sail attached to a Y spar arrangement. The swinging cross beam is intended to be self aligning. The sail attachment wires will be tuned so that tilting the sail forward on each shunt will cause the sail to pull the cross beam around until the sail is optimally aligned with the apparent wind for best lift/drag ratio.

The nacelle to windward provides accommodation space (in this case for the RC gear) and acts as both a counterweight for the sail to leeward, and reserve buoyancy in case of inadvertent heel to windward.

The twin linked rudders under the main hull are of the "vector fin" type to prevent the boat from lifting completely out of the water.


Perpective View from Forward Quarter

Perspective View from Aft Quarter

Detail of Aka Hinge and Bellcrank Arrangement

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