Wind Vane Autopilot

In the construction of the wind vane self-steering gear for our yacht, the book "Wind-Vane, Self-Steering, How to plan and make your own" by Bill Belcher proved to be extremely helpful. It shows the types of self-steering mechanisms, but also discusses how to calculate the size of components in relation to the size and weight of the yacht, along with examples of making such mechanisms from wood. 

A pendulum wind vane type autopilot was suitable for the Albin Vega yacht. Unfortunately, simpler autopilots require a rudder placed directly behind the stern (like in a typical "Volksboot"), not under the hull, as the Albin Vega does. In this type of autopilot, the wind acts on a vertical blade. It can be adjusted to the wind using two lines wound on rollers. When the blade is aligned with the wind, it does not deflect. When the wind acts on one side or the other, it causes it to deflect sideways. Through a pushrod system, it acts on a blade submerged in water. The submerged blade resembles an ordinary rudder (it has a vertical axis of rotation, like a rudder). However, it also has a horizontal axis of rotation above the water and can swing sideways like a pendulum. When the wind blade deflects, it causes the submerged blade to turn on the vertical axis (as if steering with an ordinary rudder). The turn does not require much force because the submerged blade is constructed so that the center of water pressure falls exactly on its vertical axis of rotation. Then, the stream of incoming water begins to exert force on the side of the submerged blade, causing it to deflect on the pendulum axis. This way, a small wind force is converted into a large water stream force. Here, an important technical aspect is the so-called "feedback." When the blade deflects to the end of the pendulum axis range, the feedback in the pushrod system (implemented through their appropriate arrangement relative to each other - the "fork" rotation axis is below the pendulum rotation axis) causes the blade to straighten on the vertical axis (relative to the incoming water). As a result, the water no longer exerts lateral force on it, and the blade will not pop out of the water or be damaged by pressure on other structural elements. This mimics the action of a helmsman who, after the yacht veers off course, deflects the tiller at the required angle and waits for the yacht to return to course but does not pull the rudder further than the available range. Ultimately, the pendulum blade's deflection is transmitted through a system of blocks and lines to the main rudder tiller, and the yacht turns in the desired direction. 

A contraption as strange as a fairy tale but works wonderfully. 

For those interested, we provide detailed photos and videos showing how our autopilot works.

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