Alternative Rigs Page 4
Hoyt Offset Rig
Garry Hoyt recently added the Offset Rig to his quiver of innovative ideas. The carbon-fiber rig features a gaff that runs parallel to the boom, with both spars permanently offset from the mast on short horizontal struts. This allows the sail to have a clean leading edge free of windage interference from the mast; also, the spars can extend forward of the mast, creating a semibalanced rig. About 25 percent of the rigs sail area projects forward of the mast, acting as a brake as the boom swings through the wind during a gybe.
The low-aspect quadrilateral sail is hoisted on two halyards, one at each end of the boom and gaff. The boom and gaff are connected by two stays. The forestay supports the sails luff hanks during hoisting, lowering, and reefing, while the backstay ensures that the boom and gaff remain parallel to each other, avoiding the twist-off that affects conventional gaff rigs. The sail is controlled with an end-boom mainsheet, a cunningham (situated at the deck-level offset arm), and a boomvang tackle. With single-line reefing, the sail is easy to manage for a solo sailor.
To further increase aerodynamic efficiency, the large-diameter freestanding mast is enclosed in a lightweight wing sleeve that reportedly reduces mast windage by 75 percent. Hoyt claims that the square-headed sail is much more efficient than a triangular sail. He says there is no aerodynamic penalty resulting from the sail being offset. The wind does not recognize a centerline, he says.
An interesting variant on the gaff is the Wharram Wingsail, which catamaran designer James Wharram chose for his own boat, Spirit of Gaia .
Wharram Wingsails have a higher aspect ratio than most traditional gaff rigs. More important, the Wingsails luff wraps around the mast and the sail is soft (without battens), eliminating turbulence from both rigging and sails. When the sail is lowered, its short gaff is easy to handle. Some of these sails are set on booms, but often they are completely loose-footed. The sails are trimmed with a pair of powerful sheet purchases. These are necessary to get enough tension to flatten the sail when required, and the windward one can be used to haul the clew inboard for close-hauled sailing.
A masthead forestay and a pair of shrouds keep the rig upright; the wide shroud base on a catamaran makes both spreaders and running backstays superfluous. All components can be replaced cheaply and easily almost anywhere on the planet, making this a good globe-girdling option.
The Cogito (COntrle de GITe Optimis) rig features a canting mast linked to twin canting keels that limit the heeling of the hull. The system is integral to a boats design and construction and depends on a partially exposed stainless-steel ring that encircles the hull in a dedicated groove. Stainless-steel thrust blocks, port and starboard, limit the rings range of motion (35 degrees is the farthest to leeward that the rig will cant); adjustable, constant-force gas springs control the rings rotation (one spring end is attached to the hull, the other to a block, with a steel cable attached to the ring).
The mast is stepped on the ring atop the rounded cabintop, and the shrouds attach to the ring port and starboard; opposite are the twin keels, which are bolted to the ring and are splayed outward. Stainless-steel ball bearings carry the load on the ring and help it rotate. A fractional forestay and a backstay are attached to the hull fore and aft and support the rig as it cants. Once under way, pressure on the sail cants the rig to leeward; the keels meanwhile rotate to windward, generating a righting moment that opposes the rigs heeling moment. As with a normal boat, the sails spill air as they heel (or cant) and the center of effort is lowered. The designers say the boat will heel no more than 10 degrees. Unlike standard canting-keel designs, the Cogito requires no hull apertures. The system is being used on a production boat, the Fan Class 32.