General

Due to the weathervane nature of the wing-sails, the aerodynamics are partially decoupled from the hydrodynamics. For example, the wing-sail lift is fairly independent of the pitching of the main hull.

An aero-elasticity problem normally associated with forward swept wings, i.e. increased bending gives increased incidence at the tip, is not applicable since our wing-sail planks freely rotate. However, coupled fluid-structure-interaction analysis is being carried out to tune the wing-sails to be free from flutter and oscillations within their performance envelope.

Roll trim

As with all conventional sailing craft, there is a heeling moment induced from the vertical wing-sail side force. With the v-44, this is largely balanced by the lift force from the horizontal wing-sail.  An aerodynamic moment to further oppose the heeling moment is induced through twisting each wing-sail as shown in the opposite figure. This twist lowers the centre of lift from the vertical wing-sail, and extends outboard the centre of lift from the horizontal wing-sail. A further opposing moment is induced through deflecting trailing edge flaps on the fixed horizontal wing which supports the aft outriggers.

A moving mass-balance weight is located within the fixed horizontal wing to provide a more favourable boat centre of gravity position.

Longitudinal trim

As with all conventional sailing craft, there is a nose down pitching moment from the high thrust line and low drag line. With the v-44, this is conventionally balanced by the longitudinal stability gained from an elongated hull in the water.  However, as the hulls rise free from the surface of the water, this buoyancy stability diminishes to nothing.

When the hulls are flying, the v-44 achieves longitudinal trim from a nose up pitching moment gained by a relatively forward centre of lift from the horizontal wing-sail and a relatively aft centre of gravity. Finally, the small hydrofoil at the base of the rudder maintains longitudinal stability.

Control system

The skipper has directional control of the boat by operating rudder pedals with his feet. He also has a control stick to provide lift/speed and roll control.

Pulling the control stick backwards increases the upwards deflection of each trailing edge flap and therefore increases the lift generated by each of the planks.  Moving the stick fore to aft gives the skipper control of the speed of the boat when the hulls remain in the water. When the hulls lift free from the water, moving the stick fore to aft controls the height of the boat above the surface and therefore controls the speed by setting the amount of keel in the water.

Moving the stick left to right gives the skipper roll control of the boat. This is achieved by moving all four trailing edge flaps, each in the opposite sense to its neighbouring flap, to effectively shift the spanwise lift distribution of each wing-sail, without transferring overall lift from one wing-sail to the other. This will minimise any lift/roll cross coupling effects.  

Tacking

Before tacking, the skipper has a short checklist: move mass balance to centreline of boat; retract centre hull fairing (to allow wing-sails and keels to rotate).

During the tacking maneuver itself, the skipper rolls the wing-sails as the boat turns through the wind.

Post tack checklist: move mass balance fully to windward; close fairing; reverse position of fixed wing trailing edge flaps.

Once established on a new tack, the principal controls are the control stick and rudder pedals.

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