Sailing against the wind

How do you design a boat which can sail directly into the wind? And, how can you do it in a practical, simple and inexpensive way, while ensuring that the craft is simple to operate. That was the problem that was faced by the Amateur Yacht Research Society.

To sail directly against the wind it was felt that a rotating sail which converts the wind power into mechanical motion driving an underwater propeller would be needed.

Tests showed it would be most efficient to use a horizontal axis wind-turbine (similar to a wind mill) which could align itself automatically to the prevailing wind direction.

With the experience gained in tests with models, two man-carrying prototypes were tested using 7ft 6in diameter six-bladed rotors with a quite small total blade area of 12ft2. Tests with these prototypes confirmed that the design objectives had been met and that the craft was able to sail directly into the eye of the wind. Speed was reckoned to be about 2 to 3knot into a 10knot wind.

The basic design philosophy was to use large area blades that rotated slowly, rather than small area blades which rotated at high speed.

The advantage of using slow rotating speeds is that the craft is much safer to operate. The blades never travel faster than the windspeed, and the pitch angle, from the fully feathered parked position to a maximum operating angle of about 45 , can be adjusted by the helmsman.

To keep the drive axis horizontal at all times, a belt drive is used between the air-rotor and the water-propeller. By arranging the rotor to be positioned well behind the mast about which it rotates automatic wind-seeking can be achieved. If a vertical drive shaft had been used, drive-torque would have made this impossible.

To demonstrate the concept, a12ft ‘Seaskater’ catamaran named ‘Jensa’ was converted to use wind power derived from a 7ft 6in diameter wind-turbine.

The turbine is a patented concept that consists of six ‘sails’ of 2ft2 area/sail. Because of the method of mounting, the rotor head automatically aligns itself with the wind direction. A fortunate safety effect of this is that the rotating sails do not pass anywhere near the operator.

The drive to the underwater propeller is by two belts, upper and lower, the lower one being toothed. The propeller is mounted on a ‘skeg’ which folds up into a horizontal position to avoid damaging the propeller when the boat approaches the shore.

The rotor assembly aligns itself with the wind direction automatically by weathercock action about the vertical axis pivot. It can swing 90 each way. For downwind sailing, the Windblades are feathered and the craft driven by drag alone.

The prop shaft can swing sideways 90 for landing and sailing downwind, enabled by the universal joint.

Tests on the design have been successful and the general layout of the craft has been finalised and patented.

Amateur Yacht Research Society Tel: 0181 397 4427