Windvane pilots vs electric autopilots: all you need to know

A boat’s autopilot is its most expensive electronic component. So it is important to know it well and know how to use it to get the best out of it. However, autopilots have not always been electric, their evolution has required years of refinement. At the dawn of ocean sailing there was nothing but windvane pilots. Being mechanical and not dependent on electricity, they have been the heart of offshore sailing for decades.

Windvane - Monitor Windvane - diagram
Windvane – Monitor Windvane – diagram


However, the windvane pilot has limitations that do not make it ideal in all circumstances. The world of races has therefore given impetus to the development of electric autopilots. At first they were very simple, but a modern autopilots are really very sophisticated. On modern racing boats, windvane pilots are no longer seen, however they still have a large market in the cruisers’ world. In this article we try to understand its pros and cons and evolutions over the decades.

Windvane - Pen Duick II
Windvane – Pen Duick II


Mechanical windvane pilot and electric autopilot

Before electronics invaded our boats, there were only mechanical autopilots. A mechanical autopilot is called a windvane pilot. In English they are called windvanes or windpilots. Their story is very fascinating, before a commercial version was produced they were all self-built. At the first edition of the OSTAR in 1960 all competitors had one of their own engineering.

OSTAR - The founders
OSTAR – The founders

The windvane pilot

When Francis Chichester completed his first sailing circumnavigation in 1967 he became a hero. Sailing with a sextant and a windvane on the stern of Gipsy Moth IV he became a legend. The following year the Golden Globe started, the first non-stop round-the-world race. Robin Knox-Johnston became the first man to complete a non-stop sailing circumnavigation. Bernard Moitessier was also at the start and his photos with the sextant in hand made history. His boat was also equipped with a self-built system.

Windvane - Francis Chichester - Gipsy Moth IV
Windvane – Francis Chichester – Gipsy Moth IV 

The principle of operation of the windvane pilot

The operation of a windvane pilot is more complex than you think. These systems too have evolved over time trying various solutions. There are effectively two methods, one that uses a servo-pendulum blade (e.g. Monitor) and one that drives a secondary boat rudder (e.g. Hydrovane). The sail, or blade, of the windvane rudder certainly cannot have the strength to steer a large boat of many tons and in such cases those pilots that use a secondary rudder need a twin pilot installation. On a servo-pendulum system the small oscillations of the blade are trasformed into a force sufficient to steer the boat but work best with tillers rather than wheels and their installation is not always possible.

Aries windvane pilot - Transmission of rotation
Aries windvane pilot – Transmission of rotation


To do this, the airblade is connected to a blade immersed in the water that looks like a rudder. However, it must be immediately clarified that this blade does not act as a rudder on servo-pendulum windpilots, it is so only on winvanes like the Hydrovane. On servo-pendulum systems, the blade is mounted on a vertical tube with a fulcrum point and can swing from left to right. On a Hydrovane or auxiliary rudder system the rudder steers the boat and does not oscillate. On servo-pendulum systems what makes the blade swing is the airblade, causing it to rotate slightly, but this does not alter the course of the boat, as the pendulum is connected then to the boats rudder. On auxiliary rudder the same rotation turns the auxiliary rudder to steer the boat directly being independent of the boat’s rudder. The airblade is adjusted to a certain angle to the wind and remains vertical in the absence of other forces. When the wind instead of flowing along the axis of the blade hits it sideways, it knocks it down on one side. The airblade in the air has a counterweight, so even a little air is enough for this to happen.

Wind pilot - Construction scheme
Wind pilot – Construction scheme 

The blade oscillating causes a rotation of the axis of the immersed blade. This is either to generate a force that will be used to move the boat’s rudder on servo-pendulum systems or to steer the boat directly on auxiliary rudder systems. On servo-pendulum systems the rotation causes the blad to swing left or right by the flow of water that hits it. On auxiliary rudder systems the blade acts as rudder and steers directly the boat. Water being much denser than air has a much higher strength, this one principle that has led to the development of servo-pendulum systems, which transform a small force into a large force by the difference of density of air vs water. On auxiliary rudder systems a very well balanced rudder blade mades it possible to steer even a large servo-rudder with little force, it is all down to the use of a properly balanced neutral rudder blade. On a servo-pendulum system the two lines tied to the tube which hold the servo blade are then led back to the tiller. On auxiliary rudders systems such as Hydrovane there are no further lines or complications. On a servo-pendulum system, the two control lines are usually tied to a chain which has coupling point on the tiller bar. The chain allows for fine adjustment if you want to keep the bar slightly off-center. On an auxiliary rudder system the main rudder is not used to steer the boat, rather it is locked in place and can be used as a trim-tab to make the boat as neutral as possible to the windvane auxiliary rudder so that it will need little forces to steer the boat.

The pros of the windvane pilots

The flow of water that hits the blade immersed in water is capable of generating an enormous force – this is very important on servo-pendulum systems that have to steer with the original boat rudder. Less important for the auxiliary rudder systems as the boat’s rudder is not used to steer the boat. With servo-pendulum systems the force of the water is transmitted to the lines led back to the cockpit thus capable of moving the tiller. The second strong point lies in the fact that these systems have no electrical component. As long as it does not break down, we have to worry only about accidents such hitting semi-submerged objects or breaking the airblade.

Windvane - sacrificial tube
Windvane – sacrificial tube

The blade in the water is usually connected to the main pipe with an intentionally weaker section of pipe. In the event of a collision with an object the blade will bend the sacrificial tube section. The blade itself, tied to the boat, will not be lost, and it will be possible to replace the sacrificial tube. As for the airblade, this too can be damaged in very strong winds. Being very light just bring spares and the problem is solved.

Apparent wind and beating with a windvane

The enormous strength of the windvane pilot is to be able to steer even boats of important tonnage. The forces involved are not indifferent and it is necessary to buy a system of the appropriate size for your boat. However, it is truly impressive to observe the ability of one of these winvanes to steer a boat even in a storm.

Windvane - Apparent wind
Windvane – Apparent wind 

By definition, the blade in the air responds only to the air hitting it. The windpilot can therefore lead a boat only relative to apparent wind. For traditional displacement sailboats this does not present major problems at any speed. However, it is important that the boat is well balanced and you can say that your windvane will teach you how to balance and handle your boat better. The strong point of the windpilot however remains when beating or broad beating, where it really gives its best. With a strong apparent that controls the blade precisely, the boat responds and sails very well.

Weaknesses of windpilots

The large forces involved can cause the windvane to break. Damage to the blades in the air or water are easily remedied. Any damage to the mechanical parts are difficult to solve. The structure itself is susceptible to damage in particularly harsh conditions. Some models have an aluminum body and if this breaks it will not even be possible to weld it later. For those in steel, even though you might not be able to fix them at sea, it is always possible to repair them later.

Servo-pendulum winvane - control lines led to the cockpit