Yacht self steering Windvanes considering 2 Types:

Neptune Servo pendulum windvane.

Vessel is steered by a servo rudder linked to the main rudder; therefore rudder volume is increased as both rudders work together.

The servo rudder is controlled by a light airfoil / vane(horizontal axis type). The force required for controlling the servo is approximately 1/3 of the force required by an auxiliary rudder.

Auxiliary Rudder wind vane.

Vessel is steered by the auxiliary rudder only. A large auxiliary rudder is required, as the main rudder is locked; reducing the control rudder area. The auxiliary rudder is controlled by a large airfoil /vane (horizontal axis type)

PLEASE NOTE: Yacht designers calculate the minimum rudder size to steer the vessel, so the assumption that a smaller auxiliary rudder will suffice is questionable.


  • Low Friction, for sensitivity in light winds.
  • Light weight, for quick response to wind shifts
  • Low drag, to avoid impairing yachts windward performance
CRITERIA Auxiliary Rudder
38 tons    54 Ft. Length Maximum Vessel size: 12 tons     42 ft. length.For larger vessels, increasing the dimensions of the auxiliary rudder should be considered.
18 KG Weight 38 KG
Main rudder does most of the steering so a substantial mount is not required. The correct servo to helm gearing and routing of the control lines requires careful design.
Mounting: Requires heavy mounts and struts, as all the steering loading relies on the Auxiliary rudder.
Yes Mounting Off centre: Yes
lock the powerarm on cleats  |   Fair Emergency Rudder use: Excellent
Slacken airfoil clamp, Lower vane in slot &/or tilt back away from wind direction. Alternately fit heavy weather vane. |  Good Unsettled Sea Wind strength Beaufort 5 Increasing Recommended use autopilot Or main helm.  |  Poor
Good Vessel with weather helm Poor,try reducing and/ or adjusting sail to remove weather helm
Good Reaching –Wind on the quarter Poor,try reducing and/ or adjusting rig.
Good Light Wind Good, on a flat sea
Very little loss in windward performance due to small rudder and vane. The Neptune is capable of tacking itself when the airfoil is rotated 180 degrees. It simply drives the ship around onto the opposite tack. The vessel sheets require releasing and hauling in.  |  Good Sailing close to the wind remember that large vane+ auxiliary rudder increases drag
Use the main helm. Disconnect control lines. Rotate the servo rudder out the water.   |     Good Manoeuvrability using Engine: Auxiliary rudder hinders use of main helm.
Rotate the servo rudder out of the water.  |  Easy Removing Rudder: A lanyard is attached, the locking device unlocked then the rudder should slip downwards off the rudder shaft bottom end
Rotate Servo Rudder back into the water. |  Easy Installing Rudder When under way almost impossible