page_title: Self-steering gear
section_title: Mechanical
hierarchical_section_title: Self-steering gear / Mechanical
caption_attribution_description: English: A hand-drawn picture of a windvane self-steering system, drawn after a model from within the book "The Sailors Handbook" by Halsey C. Herreshoff.
context_page_description: Self-steering gear is equipment used on sail boats to maintain a chosen course or point of sail without constant human action.
context_section_description: The main goal of a mechanical self-steering gear is to keep a sailboat on a given course towards the apparent wind and to free the helmsman from the steering job. An advantageous side effect is that the sails are kept in optimal angle towards the apparent wind and deliver optimal propulsion force by that. Even in sailboats running under engine, the self steering gear can be used to keep the boat heading into the wind to easily set or change sails (exception: sheet-to-tiller principle).
  
  As wind direction sensors are used 
  
  a) a wind vane mounted on an axis being tilted more or less towards the horizon (wind vane self-steering)
  
  b) the pressure of the wind in the sail(s) and by that the force on the sheet (sheet to tiller self-steering).
  The different mechanical principles of coupling a change in apparent wind direction mechanically with a course changing actuator (rudder) can be roughly grouped:
  Trimm-Tab (Flettner Servo tab) systems, wind vane coupled with a small flap attached at the main rudder, an auxiliary rudder or a servo pendulum rudder
  vane to auxiliary rudder (Windpilot Atlantik, Hydrovane) with a wind vane directly coupled to an auxiliary rudder
  vane to rudder (only applicable for very small boats, a large wind vane is directly coupled to the ship's rudder)
  servo pendulum rudder (a wind vane turns an immersed blade around its vertical axis, the blade swings out to the side due to the movement through the water and turns the ship's rudder with that)
  servo pendulum with auxiliary rudder (like above, but the servo pendulum blade acts on an auxiliary rudder and not on the ship's rudder)
  sheet-to-tiller (a spring load at the tiller is counteracted by the pulling force of a foresail and/or main sail sheet)
caption: A windvane self-steering with auxiliary rudder and trim tab servo
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