Auxiliary rudder systems

An auxiliary rudder system is a discrete steering unit which steers the boat independently of the main rudder. The windvane turns a rudder blade on a rigid shaft directly via a linkage, maintaining the corrective rudder movement until the boat returns to the desired course.

Steering impulse



Steering force



Steering element


Auxiliary rudder

Power leverage (PL)


0 cm

The main rudder is fixed in place and used to fine tune the gear. It counters weather helm, allowing the auxiliary rudder to concentrate just on actual course corrections. Auxiliary rudder systems are only effective if the ratio of the area of the main rudder blade to that of the auxiliary rudder blade is no greater than 3:1. This ratio is easily calculated for any known main rudder dimensions using the auxiliary rudder blade dimensions given in the specifications of the individual systems.

The steering force produced by auxiliary rudder systems is limited by the lack of any servo-assistance, and they are unable to provide effective steering on larger boats. Windpilot auxiliary rudder systems of the NORDSEE and ATLANTIK ranges were used successfully on boats of up to 11 m / 36 ft, but beyond this they could function only as an aid to steering. For this reason Windpilot retired them in 1985 and moved on to other systems.

Hydrovane auxiliary rudder systems were recommended for steering boats of up to 15 m / 50 ft. The cut-off point with respect to 'effective steering' was probably somewhat lower than this though, because the systems were not servo-assisted and the ratio of auxiliary rudder area to main rudder area on a larger boat would have been rather unfavourable.

V vane only, on board a 5m/16ft Van de H vane only, QME windvane. This acts Stadt design more as a steering aid than a full selfsteering system

This Windpilot auxiliary rudder The Hydrovane auxiliary rudder system is suitable for boats up to system: the H vane generates 11 m/36ft in length. more power than Atlantik V vane

Effective steering

We referred to this term briefly in the previous chapter. It is used here to express whether a windvane gear is capable of reliably steering a boat of a particular length in virtually all sailing conditions or is just an aid to steering up to a certain wind strength, sea state and range of apparent wind angles. As a rating of the capabilities of a windvane steering system it is of fundamental importance; a steering gear which cannot do its job properly is no good to anybody.

Any rating of a steering gear should of course be considered in the context of the type of sailing the gear is likely to be used for. A system which is only reliable for upwind sailing, for instance, might be perfectly acceptable to the weekend and holiday sailor. The priorities aboard blue water yachts are rather different: steering by hand for days on end will often exhaust a small crew and bring a premature end to the voyage.

Categories of auxiliary rudder system

Auxiliary rudder with V vane

The vane in a V vane operated auxiliary rudder system (e.g. ATLANTIK) turns the rudder directly via opposed toothed gears in a ratio of 1:1. The damping characteristics are good. Systems of this type are suitable for boats of up to 11 m / 36 ft.

Auxiliary rudder with H vane

These systems (e.g. Hydrovane) have less effective damping than V vane operated auxiliary rudder systems. To resolve this, they have a reduction gear which provides three options for the amount of turn transmitted to the rudder. They do, however, produce rather more effective steering force than a V vane and can therefore be used on larger boats.

The Hydrovane linkage has step-down gearing for better damping

The advantages of auxiliary rudder systems

Because the auxiliary rudder functions completely independently of the main rudder it makes an effective emergency rudder. This is a useful safety feature, particularly on modern fin keel yachts where the balanced rudder has no skeg to protect it. The additional lateral area of the auxiliary rudder right at the very back of the boat not only helps to calm the motion of the boat in heavy seas but also reduces weather helm.

The simple, solid construction of auxiliary rudder gears gives them a long working life. They can only really suffer serious damage if the boat is rammed hard from astern - and even then there is the consolation that steering gears cost much less to repair than the transoms they are mounted on!

Operating procedure:

• bring the boat onto course,

• fix the tiller in position,

• turn the windvane to face into the wind,

• connect the windvane to the auxiliary rudder,

• fine tune the course using the main rudder.

The disadvantages of auxiliary rudder systems

Nobody ever stood up on the harbour wall and proclaimed the beauty of their auxiliary rudder gear. The systems are tall, bulky and heavy, and the extreme end of a boat, particularly a small one, is not the ideal place to add 30 - 45 kg / 66 - 100 lb of extra weight.

The limited steering force obtainable without any servo-assistance means that this type of system is unable in practice to provide effective steering for longer boats (see above).

The auxiliary rudder is generally fixed amidships when not in use. Here it impairs the vessel's manoeuvrability and increases its turning circle. Curiously this apparent drawback is actually a bonus for some: the additional lateral area behind the main rudder makes boats with long keels more obedient to the helm when reversing because it partially offsets propeller throw which tries to push the stern sideways.

The large windvanes of auxiliary rudder systems makes them awkward to operate on ketch or yawl rigged boats when the mizzen is in use.


Auxiliary rudder systems can be mounted either on the centre of the transom or offset to one side, for example to avoid a swim ladder. As the Vikings discovered a long time ago, mounting the rudder to one side has only a very minor effect on steering performance. The rudders on their longships were always mounted on the starboard side and the helmsman steered with his back facing to port.

Considerable lateral forces act on the auxiliary rudder in certain sea conditions so its attachment to the transom must be strong and solid. Traditional overhanging transoms will require the gear to be supported at the bottom by a V-shaped bracket. An angle flange at the bottom is sufficient for modern forward-raked transoms.

The auxiliary rudder should be at least 20 - 30 cm / 8 - 12 in behind the main rudder (this can be a problem on modern open-transom boats where the rudder is positioned far aft). Any less than this and the auxiliary rudder blade will be in the turbulent wash of the main rudder, which prevents it from bringing its full force to bear and consequently impairs the efficiency of the system.

Offset mounting next to a swim ladder. The Viking ships also had their steering system positioned to one side.

Off-centre mounting on boats with an outboard main rudder is only practical if the lateral distance between the main and auxiliary rudders is at least 30 cm / 12 in. Such a large offset reduces the efficiency of the system going to weather because some of the auxiliary rudder area will lift out of the water on one tack when the boat heels.

This BWS-Taurus system would better with a V-shaped bracket at the bottom

Offset mounting next to an outboard rudder. The minimum distance to the main rudder is 30cm/12in.

Auxiliary rudder systems function best on traditional boats with long keels and big overhanging transoms. The auxiliary rudder is so far behind the main rudder in boats of this design that it encounters hardly any turbulent wash, allowing it to achieve maximum efficiency. The large distance from the main rudder also gives it considerable leverage.

Auxiliary rudder system manufacturers:

Windpilot and Hydrovane.

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