SELF-STEERING UNDER SAIL

Autopilots and Wind-steering Systems

Peter Christian Förthmann

Imprint

SELF-STEERING UNDER SAIL (Autopilots and Wind-steering Systems)

Peter Christian Förthmann

Copyright: © 2013 Peter Christian Förthmann

Published by: epubli GmbH, Berlin

www.epubli.de

ISBN 978-3-8442-5640

Foreword

Throughout human history people have been taking to the water in sailing boats, be it for trade, exploration or war. Not until our own century did the idea first surface that a sailing boat might be able to steer itself. In the heyday of the tall ships and even well into the modern era steering meant hands on the wheel. Crew were plentiful and cheap, and all the work on deck, in the rigging or with the anchor was performed manually. Where brute force was insufficient there were blocks and tackle, cargo runners and, for the anchor, the mechanical advantage of long bars and a capstan. Some of the last generation of tall ships, engaged in their losing battle with the expanding steamship fleet, did carry small steam-powered engines to assist the crew, but steering nevertheless remained a strictly manual task. There were three steering watches and the work was hard - even simply lashing the helm with a warp gave considerable relief. The great square-riggers plied the oceans without the help of electric motors or hydraulic systems.

In the early part of the twentieth century, recreational sailing was the preserve of the elite. Yachting was a sport for wealthy owners with large crews, and nobody would ever have thought of allowing the ‘prime’ position on board, the helm, to be automated.

It was only after the triumph of steam and the ensuing rapid increase in international trade and travel that the human helmsperson gradually became unnecessary; the first autopilot was invented in 1950.

Powerful electrohydraulic autopilots were soon part of the standard equipment on every new ship, and although the wheel was retained, it now came to be positioned to the side of the increasingly important automatic controls. Commercial ships and fishing boats quickly adapted electric or hydraulic systems to just about every task above and below deck, from loading gear, anchor capstans and cargo hatch controls to winches for net recovery and making fast. Before long ships had become complex systems of electric generators and consumers and as long as the main engine was running there was power in abundance.

Today, the world’s commercial and fishing fleets are steered exclusively by autopilots; a fact that should give every blue water sailor pause for thought. Even the most alert watchperson on the bridge of a container ship at 22 knots is powerless to prevent it from ploughing ahead a little while longer before gently turning to one side. A freighter on the horizon comes up quickly, particularly since the height of eye on a sailing yacht is virtually zero. Collisions at sea are not infrequent, and the sailing yacht seldom wins.

Modern freighters and ferries rely on autopilots even close to shore - Stena Line’s large ferries steam at full speed through the narrowest channels with only the Decca pulses of their purpose-designed software at the helm.

1. The history of self-steering

Shorthanded long-distance sailing started with just a few hardy pioneers. Joshua Slocum was one of the very first with his legendary Spray. It is said he could keep the boat on a fairly steady course with an ingenious sheeting arrangement or simply by lashing fast the wheel. This manner of self-steering willingly sacrificed a certain amount of sail power to free up a portion of the sail area just for steering trim. Of course Spray had a natural tendency to sail straight, as her keel was almost as long as her waterline.

Hambley Tregoning described in a letter to Yachting Monthly in 1919 how the tiller of a boat could be connected to a windvane. Upon publication of his letter model boat owners rushed out to fit their craft with wind-guided steering. They found they could achieve admirable results with even the most simple mechanical connection between the tiller and a windvane. This type of system did not transfer very successfully, however, since the forces generated by a windvane are too small to move the tiller of a full-size vessel directly.

The First Windvane Steering System

The first windvane steering system, rather ironically, was installed on a motorboat. Frenchman Marin Marie used an oversized windvane connected to the rudder by lines to steer the 14 metre motor yacht Arielle during his spectacular 18 day singlehanded crossing from New York to Le Havre in 1936. His windvane steering system is now on display at the Musée de la Marine in Port Louis.

British sailor Ian Major took Buttercup singlehanded from Europe to the Antilles in 1955 using a small windvane to control a trim tab mounted on the main rudder. This was the most common system in the early days of windvane steering. 1955 was also the year Englishman Michael Henderson fitted a personal creation, nick-named “Harriet, the third hand”, to his famous 17-footer Mick the Miller. His approach was to centre the main rudder and use the windvane to move a small, additional rudder blade. The system was a complete success and was able to handle more than half the steering duties. Bernard Moitessier also chose a trim tab for Marie Thérèse II in 1957, and used a simplified version of the same system on Joshua from 1965 onwards. In this second version, the windvane was fastened directly to the shaft of the trim tab.

The starting gun of the first OSTAR (Observer SinglehandeTransatlantic Race) in Plymouth on the 11th of June 1960 signalled the real beginning of the windvane steering era. Without some form of self-steering none of the five participants, Frances Chichester, Blondie Hasler, David Lewis, Valentine Howells and Jean Lacombe, could have reached the finish.

Frances Chichester’s first windvane gear, christened “Miranda”, consisted of an oversized windvane (almost 4 m2) and a 12 kg counterweight and was connected directly to the tiller via lines and turning blocks. The giant windvane had anarchic tendencies and Chichester was soon contemplating a change to the windvane/rudder proportions.

Aboard Jester, Blondie Hasler was using the first servo-pendulum gear with differential gearing. David Lewis and Valentine Howells both used simple trim tab systems driven directly by a windvane. Jean Lacombe used a trim tab gear, developed jointly with Marcel Gianoli, which had a variable transmission ratio.

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HASLER servo-pendulum system on an S & S 30

Hasler and Gianoli, an Englishman and a Frenchman, were to play a considerable role in the development of windvane steering systems. The principles they established are still used today, and we will consider both their systems later on.

The second OSTAR was held in 1964. Once again all the competitors used windvane steering systems, six of them opting for servo-pendulum gears built by HASLER, who had already undertaken a small production run. Windvane steering gears were virtually standard equipment for the 1966 and 1970 Round Britain Races as well; electric autopilots were still banned.

The field for the 1972 OSTAR was so large that the organisers had to set an entry cap of 100 boats for the 1976 race. Electric autopilots were allowed, but could not be powered by inboard motors or generators. By now, many of the participants were using professionally built windvane steering gears. There were 12 from HASLER, 10 from ATOMS, 6 from ARIES, 4 from GUNNING, 2 from QME, 2 electric, 2 auxiliary rudder gears, 2 from QUARTERMASTER and 1 HASLER trim tab.

The rise of the great solo and short-handed blue water races, none of which would have been feasible without the windvane gear, stimulated the professional development and construction of a wide range of different systems in England, France, Italy and Germany. The early pioneers are still familiar names: HASLER, ARIES, ATOMS, GUNNING, QME and WINDPILOT.

Several factors contributed to the rapid spread of windvane steering systems, in particular the economic miracle of the post-war years, the increasing number of series-built sailing boats and the shift in boat building away from one-at-a-time construction in wood towards mass-production with modern materials. Sailing was no longer a sport for obsessive loners or the elite and its popularity was growing.

The first companies producing professionally designed and built windvane steering systems appeared in Britain, France and Germany in 1968, and in the Netherlands not long after.

Windvane steering systems and the year they were launched:

1962: Blondie Hasler, HASLER
1962: Marcel Gianoli, MNOP
1968: John Adam, WINDPILOT
1968: Pete Beard, QME
1968: Nick Franklin, ARIES
1970: Henri Brun, ATOMS
1970: Derek Daniels, HYDROVANE
1972: Charron/Waché, NAVIK
1976: Boström/Knöös, SAILOMAT

The First Cockpit Autopilot

The first electric autopilots on non-commercial vessels probably appeared in the United States. The first TILLERMASTER, a miniaturised autopilot developed for small fishing boats, was produced in 1970.

British engineer Derek Fawcett, formerly employed at Lewmar, launched his AUTOHELM brand in 1974. AUTOHELM soon dominated the world market, its small push rod models being particularly successful. The systems were manufactured in large production runs by a work force which quickly expanded to 200.

2. Windvane Steering

Systems versus Autopilots

Our aim with this book is to investigate the functioning and the pros and cons of the various systems, and to help the reader decide which is most suitable for his or her particular needs. The two main categories of self-steering system are the autopilot and the windvane steering gear. Autopilots are electromechanical systems which obtain their steering impulse from a compass whereas windvane gears use wind and water power and obtain their steering impulse from the apparent wind angle. We will consider each in turn.

A sailing yacht generates all its drive from the position of the boat and the orientation of the sails with respect to the wind; trim the sails poorly and there will be no drive. This simple relationship explains why a windvane gear is so ideal for steering a sailing yacht. The wind angle it uses is exactly that which gives the boat drive; set this angle once and drive is assured. The benefits of steering to the apparent wind angle are particularly pronounced when sailing to weather. Even the slightest shift in the wind is immediately translated into a course change and optimum drive is ensured - a degree of sensitivity beyond even the best human helm.

Why autopilots?

Simply put, they are compact and discreet. When it comes to buying a self-steering system, probably the largest single factor counting against windvane gears is their incongruous appearance. They are generally large and bulky - hardly the ideal transom ornament. Not only that, but some are also rather unwieldy and heavy and tend to get in the way when manoeuvring in harbour under engine.

Autopilots, in contrast, are virtually invisible in the cockpit and may even be completely concealed below deck. Once installed they are simple to operate, only requiring mastery of a few buttons. Cockpit autopilots are light and generally inexpensive and they steer a compass course. For some sailors this argument is compelling; autopilots were programmed to succeed.

Over many years the sailing world polarised into two camps. In the 1970s windvane steering systems became a common sight on blue water yachts, where they were indispensable. Only in exceptional cases were they to be seen on holiday and weekend boats (and some of these can almost certainly be put down to wishful thinking!).

The debate over the last 25 years between advocates of the two different systems has been heated. One particular bone of contention was the repeated insistence of some that vessels of several tonnes or more are ‘easily’ steered with just fractions of an ampere. Views today are more realistic. There is no getting around the laws of physics: every desired ‘output’ (steering force) requires a certain ‘input’ (current/energy). Who could forget the ‘Conservation of Energy’ law so familiar from school physics lessons?

005_01kThe traditional Monitor servo-pendulum system

3. Autopilots

How they work

Autopilots depend on a compass. A steering impulse produced by the compass actuates an electric or hydraulic motor which extends or retracts a rod or hydraulic cylinder, moving the rudder so as to bring the boat back on course. The compass carries out a desired/actual value comparison and continues the steering operation until the vessel is back on the desired course. There is a direct relationship between

· the steering force;

· the speed with which the steering force is exerted; and

· the current consumption.

The physical constants between these factors are fixed, so the only relationship which matters on a sailing yacht, steering performance (output) / current consumption (input), is always a compromise. It is never possible to obtain maximum steering performance for minimum power consumption.

This gives rise to a dilemma, since an electric motor can be geared to produce either a lot of power slowly or a little power quickly (this is analogous to the way in which a car can manage a steep gradient slowly in first gear, but not at all in top).

Autopilots are distinguished by motor capacity, this automatically fixing the relationship between the force applied by the push rod and its speed of operation. Virtually all autopilot manufacturers rely on this proven arrangement, and none has yet produced an autopilot with more than one transmission ratio and the facility to change gear.

Such pronounced gearing-down of the force from the electric motor (to produce more force at the push rod) is not practical anyway, since the corrective movement of the rudder would then be effected too slowly to bring the vessel efficiently back to the desired course. Choose a low power consumption model for a relatively heavy boat, and the steering performance will be less than wonderful. Choose a powerful autopilot, on the other hand, and no battery in the world will be able to meet the power demand without regular recharging.

Cockpit Autopilots for Tiller Steering

Push rod systems, in which an electric motor is connected via a transmission directly to a push rod, are the most straightforward form of autopilot. The push rod is extended or retracted to move the tiller.

Simple cockpit autopilots consist of a single module which includes the compass, the motor and the push rod. In larger cockpit models, the control unit and compass are separate modules which may be linked to other external transducers via a data bus. Autohelm uses the ‘ST’ (SeaTalk) designation to indicate its network-compatible systems.

Tiller push rod systems are not particularly powerful, and are therefore only suitable for smaller boats. They use relatively small (power-saving) electric motors whose force has to be multiplied by major gearing down before it is applied to the push rod. This makes them noisy and the sound of a cockpit autopilot inoperation is quite pervasive. Although they consume little power, cockpit autopilots are ponderous in their movements.

The following systems are available:

AUTOHELM 800
AUTOHELM ST 1000,
AUTOHELM ST 2000,
AUTOHELM ST 4000 Tiller,
NAVICO TP 100,
NAVICO TP 300.

Cockpit Autopilots for Wheel Steering

Wheel steering autopilot systems are similar to those described above, except that the course corrections are effected by a driving belt, toothed belt or toothed wheel acting on a pulley attached to the vessel’s wheel. Cockpit autopilots for wheel steering may be linked to a data network.

The following systems are available:

Navico WP 300 CX Wheel autopilot
The AUTOHELM ST 800 Tiller autopilot

Inboard Autopilots

Inboard autopilots use push rod or hydraulic systems with powerful motors which are connected to the rudder post or quadrant and turn the main rudder directly. It is also possible to replace the mechanical linkage and shaft with a hydraulic system in which a hydraulic pump provides oil pressure to drive a hydraulic cylinder which in turn moves the main rudder. This type of system is suitable for larger boats. Vessels over 60 feet in length with sizeable hydraulic rudder arrangements use constantly running pumps controlled by solenoid valves for the autopilot.

The Three Modules of an Inboard Autopilot

Control unit

The control unit is used to call up all the functions of the autopilot and any other modules linked via the data bus. It is usually possible to mount additional control units wherever they are needed, so the operator is not restricted to the main cockpit. A hand-held remote control unit provides even more freedom to move about the deck. Joysticks offering direct control of the autopilot drive unit are also available.

Central processing unit

The central processing unit consists of:

a. Course computer

The course computer, installed below deck, is responsible for processing all commands and signals, for calculating the rudder movements necessary for course correction and for actuating the drive unit.

b. Fluxgate compass

An autopilot can only steer a good course if the steering impulse from the compass is accurate and clear. Fluxgate sensors, which supply the course computer with precise course data, are used by all manufacturers. Steering performance in testing conditions can be optimised by installing special additional fluxgate systems. Autohelm uses a ‘GyroPlus’ transducer while Robertson has a novel electronic compass, a modification of the conventional magnetic compass, which promises to help the autopilot steer more smoothly.

c. Rudder position indicator

The rudder position transducer is arranged on the rudder and informs the course computer of the position of the rudder.

d. Windvane (optional)

e. Peripherals

Signals from additional navigation equipment such as Decca, GPS, Loran, radar, log and depth sounder can also be fed to the course computer for consideration with regard to steering movements.

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The modules of an inboard pilot; a Brookes & Gatehous example

Drive unit

There are four alternatives.

a. Linear drive unit:

An electric motor operates the push rod mechanically via a transmission.

These drives are similar in principle to cockpit autopilots, but are considerably more powerful. Depending on the particular use and the size of the system it may be advisable to use metal for the transmission components since plastic is not always able to withstand the heavy loading associated with extended operation. Autohelm offers the ‘Grand Prix’ package as an upgrade for its linear drive units and Robertson uses metal transmission components as standard.

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Autohelm mechanical linear drive unit aboard the 18m/ 60ft ULDB Budapest

b. Linear/hydraulic drive unit:

The push rod is operated by a hydraulic pump. Linear/hydraulic drives appear on large yachts with particularly high rudder forces. The drives may be supplied either by separately installed hydraulic pumps (Autohelm, VDO) or by pumps directly incorporated into the push rod system (Brookes and Gatehouse, Robertson). Robertson also offers ‘dual drives’, in which two linear drives double the force applied.

c. Hydraulic drive units:

These electromechanical hydraulic pumps tap directly into the existing wheel steering hydraulic system. A constantly running pump may be used to supply the force required to steer boats of 25 tonnes or more.

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Robertson hydraulic linear drive units

d. Chain drive unit:

An electric motor operates the main rudder via a chain. Chain drives are preferred where space is limited or where the rod-operated or geared wheel steering system on an older boat precludes the use of other drive units.

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Blue Papillon, a 29m/ 95ft Jongert steered by a Segatron autopilot

Integrated Systems

Until a few years ago it was generally the case that boat owners acquired their instruments one by one. Depth sounder, radar, compass, wind instrument, Decca, GPS, plotter, boat speed indicator and autopilot might easily be individually installed stand-alone units from several different manufacturers.

The situation today is very different, with a few major suppliers offering complete systems from which the sailor can choose as few or as many instruments as desired. Essential to this advance was the development of a specialised data protocol (data bus): functions such as the steering performance of an autopilot module can now be optimised in more demanding systems by connecting a dedicated course computer. An autopilot steering a boat between two waypoints obtained from a GPS interface can thus correct for cross-track error caused by currents running perpendicular to the boat’s course.

The changing role of companies within the industry from instrument manufacturers to system suppliers explains the current extreme concentration of the market on just three major players.

Autopilots may be divided into three groups:

a. Stand-alone systems which operate solely on the basis of a windvane or compass signal (e.g. AUTOHELM 800),

b. Systems which are linked to other modules via a data bus (e.g. SEATALK from Autohelm, NETWORK from B&G),

c. Intelligent systems in which the data of the individual modules is optimised by a relatively powerful computer (e.g. ROBERTSON AP 300, AUTOHELM 6000/7000, B&G HYDRA/HERCULES).

013_01Module integration options with ROBERTSON

Today most autopilots operate as one module within a complex system. NMEA (National Marine Electronics Association) interfaces offer the prospect of expanding such a system to include instruments from other manufacturers. In reality, however, the claim that instruments from different system suppliers can communicate with each other using the same interfaces has proven to be something of a fallacy. There are, as many sailors have already discovered to their cost, several standards in existence even for NMEA interfaces. Of course no instrument manufacturer is to blame for any incompatibility; serious communication problems are always the fault of the instrument on the other side of the interface!

Provided with a fluxgate compass signal optimised by integrated navigation modules, an autopilot is perfectly capable of steering a boat from waypoint to waypoint - assuming of course that the wind decides to cooperate.

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Navigating down below with the AUTOHELM NAVPLOTTER 100

The Windvane Transducer

Almost all autopilots can be linked to a windvane transducer. This enables them to take the apparent wind angle signal as steering impulse. The signal comes either from the masthead unit or from a small windvane at the stern. Neither alternative produces particularly satisfactory results in any kind of swell, since the movements of the masthead unit caused by the motion of the boat or the confused readings of the stern-mounted unit caused by disturbed air have to be damped and processed considerably to obtain a useful signal. The small size of autopilot windvanes often contributes to such problems.

The volume of data required to produce precise and practicable course commands for the steering module when using the course computer to calculate the apparent wind angle is substantial: rolling, pitching, speed, acceleration, wind angle and possibly also true parameters (true wind angle etc.) must all be processed. The importance of sailing to the apparent wind angle cannot be understated; ignore it and the boat loses all its drive.

Power Consumption

The power consumption of an autopilot is determined not only by the rating of the model chosen but also by the following factors:

a. Length and displacement of the vessel

The more boat there is to move, the greater the power consumption.

b. Type of rudder

A keel-mounted rudder requires more force because it is impossible to balance. A rudder on a skeg can have a balance portion below the skeg and is therefore easier to steer. A fully balanced spade rudder without a skeg is lightest on the helm.

c. Speed with which corrective rudder movements must be made

This depends on how well the boat holds a course, and is therefore also influenced by its shape below the waterline.

d. Sail trim, weather helm

Poorly trimmed sails and continuous weather helm are always more of a drain on the autopilot than a well-balanced boat.

e. Sea conditions

Bigger seas and increased yawing require more frequent steering interventions by the autopilot.

f. Desired steering precision

The more exactly the course must be held, the greater the amount of work there is for the autopilot.

Conserving power

Optimising the vessel with respect to the above points can considerably reduce average power consumption. Once this has been done, the only remaining measure is to reduce the frequency of course corrections. This amounts in practice to increasing the angle by which the boat may deviate from the set course before the autopilot responds, in other words allowing the boat a greater range of movement between active steering interventions.

All modern autopilots are programmed to recognise certain regular patterns of yawing. This helps them shorten their operating cycle and reduce the length of time for which the motor is running. It also enables them promptly to correct the course early on in a recurrent motion, so avoiding more vigorous rudder movements later on. Unfortunately we have now reached the end of the list of power saving measures.

The manufacturers base their average power consumption figures on a 25% operating cycle. This assumes in terms of actual autopilot running time that per hour the boat is actively steered for 15 minutes and holds itself on course with no action at all from the helm for the other 45 minutes. These figures may seem just a little optimistic; actual power consumption, therefore, will often be higher.

Fitting out for an extended voyage really brings home the gulf between the theory and practice of power consumption. Energy management is essential here since all the power consumed on board must first be generated on board. The difference between the manufacturers’ rated average power consumption and the actual autopilot motor running time can be enormous; real situations are never ‘average’ and the actual power consumption is always higher. A boat equipped with just a depth sounder, a handheld GPS, paraffin cabin lights, a windvane steering system and without an ice box - that is to say one whose power consumption is reduced to the minimum - will hardly ever run its batteries close to exhaustion. This boat does not, however, bear much resemblance to the average passage yacht. The ARC fleet which passes through the Canaries every Autumn shows a clear trend: in the last 10 years alone the average length of participating yachts has grown to around 44 feet while the number of sub-33 footers has dwindled to barely a handful. The boats are generally equipped to a very high standard as well, with most carrying navigation instruments such as GPS, plotters and radar, short wave, SSB and VHF radios, refrigerator, pumps, water maker and interior and exterior lights.

Combining the 24 hour average power consumption of each of these appliances for a 44 foot boat in warmer latitudes gives a total of 120 ampere-hours (Ah) - even without an electric autopilot running. This example clearly illustrates the care needed in budgeting for energy aboard a sailing yacht. The impact of an autopilot on this energy budget is very substantial, particularly if the system has been chosen for its high performance rather than low power consumption. There are whole books devoted solely to the subject of energy management on board: pay too little heed to this complex issue before you cast off and you can count on a nasty reminder somewhere out at sea.

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Navigating on deck with AUTOHELM

The manufacturer’s recommended autopilot for our exemplary 44 foot boat draws between 2.7 and 6 A per hour, which means that if run continuously it will push up the vessel’s total power consumption by at least another 50% over a 24 hour period. We should also bear in mind here that some units in the vessel’s electrical system will fail if the voltage falls below 10.5 V. Against this background a seemingly large battery capacity of 600 Ah begins to look less impressive.

Wind, water, wave and solar generators can help but depending on the conditions even these are no guarantee against a few hours of enforced motoring every day (as well-known circumnavigator and race organiser Jimmy Cornell confirmed after debriefing skippers at the end of his EUROPA 92 race). Whenever one of the additional generators malfunctions or fails, increased engine running time inevitably results. Without good sound-proofing, the iron sail can rapidly become an unwelcome intrusion into life aboard. The extra heat from the engine is often a bonus as well, just right to ease the afternoon chill in Bermuda...

Energy matters are of course less critical on boats used mainly for weekends and holidays since this kind of sailing normally involves plenty of motoring and shore power is always at hand for recharging.

Range of adjustment of an autopilot

(Example: Autohelm 6000/7000)

1. The Rudder Gain, which has 9 settings, specifies how much the rudder should be moved to return the boat to a desired course. Oversteering will result if the angle is set too high, understeering if it is set too low.

2. The Rudder Damping function has 9 positions and serves to damp yawing motions.

3. The rudder amidships position in the rudder reference transducer has an adjustment range of -7 to +7 degrees.

4. The Rudder Limit function prevents the autopilot reaching maximum lock at full power, which could cause mechanical damage.

5. Boat Turn Rate determines how quickly the boat turns when the autopilot makes course corrections.

6. The autopilot can be set for an average Cruise Speed of anywhere between 4 and 60 knots (sailing boat or powerboat).

7. The adjustable Off-Course Alarm sounds when the vessel’s course deviates from the desired course by more than a set maximum (in degrees) for longer than 20 seconds.

8. There are four Trim settings. This function controls the additional rudder movement necessary to counter off-centre thrust (e.g. when operating a propeller mounted to one side, only used when motoring).

9. The Joystick has two settings, but these are not particularly relevant for sailing boats.

10. The control unit can be set for linear or hydraulic drive.

11. The response angle function has 9 positions. It ensures that the response of the autopilot is appropriately delayed if there is slack or play in the steering system.

12. Compass deviation taken from a chart can be input.

13. The adjustable Northerly/Southerly Turning Error Compensation feature is used in areas where the orientation of North is uncertain to ensure the compass receives an accurate signal.

14. There are three settings for the reaction speed of the autopilot; the higher the value set, the greater the steering precision and, consequently, the power consumption.

All the functions mentioned are initially set at the factory. They can all be adjusted on board and it is essential that they are individually matched to the characteristics of the vessel.

To summarise, each model of autopilot gives a certain level of steering performance which is dictated by its range of technical features and which cannot be improved. All that is left once the autopilot is correctly set up is to increase the time between steering corrections, and hence save power, by ensuring the boat is balanced and the sails are properly trimmed. It should be obvious that selecting a greater degree of steering accuracy will lead to more frequent rudder movements and increased power consumption.

The Limits of Autopilots

Even the very best autopilots struggle beating into a shifting wind. This is because they do not detect small changes in wind direction (the sails back). The only solution is to set a lower course which, unfortunately, means losing distance to windward. It is possible to connect a windvane to the course computer but, as we discussed above, this does not always produce satisfactory results.

Blue water sailing though means winds from astern. The passage routes around the world are universally known; every long-distance sailor heads straight for the all but infallible trades, dreaming of pleasant sailing before the wind. It is therefore imperative that autopilots, and indeed any type of self-steering, can hold an off-the-wind course. No experienced sailor expects miracles of the autopilot: a steering accuracy of 5 degrees in the trades with a big following sea just is not realistic. Equally, it is no good if your autopilot follows the general course with occasional 100 degree excursions - you may still arrive, but probably not where you intended.

The only way to be sure of good steering from an unassisted autopilot is to buy a fast and powerful system. While nothing else will be able to guarantee adequate steering performance in all wind and sea conditions, this solution does inevitably lead us back again to questions of power consumption. Ultimately each skipper has to decide, in light of energy budgets and daily power requirements, which answer best suits his or her particular needs.

Issues of power consumption often tempt a skipper to risk a slightly undersized autopilot. There is no avoiding the loss of performance such a system will suffer as conditions deteriorate. With no reserves of speed or power to meet the increased demands it will eventually be overwhelmed, reacting too slowly and with too little force to keep the boat on course.

The rated operating speeds and drive unit thrusts of the various cockpit autopilot systems are a good indicator of the steering performance you can expect.

Electromagnetic Interference

Electromagnetic interference originating from onboard high-frequency transmitters and receivers was once a common problem, causing autopilots to make sudden anomalous course changes. The European CE (Electromagnetic Compatibility) Standard should prevent this kind of disruption of the autopilot in future. Existing electronics systems can best be protected by ensuring that all power cables are well insulated.

Extreme Sailing

Autopilots are unable to steer in areas where North is uncertain. Extreme sailors in races like the BOC and Vendée Globe run into problems in the high latitudes of the South Pacific with the autopilot suddenly cutting out after losing its fix on North. Nandor Fa, skipper of the Hungarian yacht K & H BANK in one Vendée Globe (singlehanded non-stop around the world) received the following answer from the manufacturer of his Robertson system after faxing for help with his confused autopilot: “Please perform 3 complete circles in calm water within a few minutes - this will enable the compass to reorient itself”.

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Nandor Fa onboard K & H Bank

Given the chaotic sea conditions in the Southern Oceans this was not the most practical piece of advice. Only after several days of steering by hand did Fa come upon the idea of removing the compass and rotating it as gently as possible in his hand. Since then he has used Autohelm systems, which now have special GPS-supported software to help the compass maintain clear steering signals even when North is uncertain. The close collaboration between manufacturers and extreme sailors in events like the BOC and Vendée Globe ensures continued development of the systems. Virtually all the boats in these races are now steered by Autohelm.

One result of this collaboration has been the development of stronger drive components for blue water use. Autohelm introduced the ‘Grand-Prix’ upgrade package for its 4000/6000/7000 series in 1996. The standard Delrin (plastic) load-bearing components in the drive are replaced with metal equivalents. Plastic, as several long-distance skippers have had the misfortune to discover, sometimes fails to measure up to the high stresses placed on drive components. For holidays and day sailing however, when extreme loads are rare, plastic components are perfectly adequate. Hydraulic systems are immune to overloading problems of this nature as they have no mechanical drive components (Autohelm 6000/7000 with hydraulic or hydraulic/linear drive, B&G NETWORK, HYDRA 2, Robertson, VDO).

Autopilots for Different Purposes

Holiday and weekend sailing

Most sailors use their boats primarily at the weekend or for holidays, which partially explains the rapid spread of electric autopilots. Power consumption is not really an issue on one day trips and the quality of steering performance is also relatively unimportant since it is always possible to steer by hand if necessary. Sea conditions rarely impair steering quality as the majority of weekend sailors do not venture into exposed waters. Taking the helm in any case forms part of the fun for the average sailor, so the autopilot is really just a convenience. It sees to the tedious work (steering while under engine) and gives the crew the freedom to eat together, for example. Autopilots, at least the cockpit models, are also within the financial reach of the average sailor.

The significance of a yacht’s autopilot grows with the length of the voyage. There will generally be no problem finding volunteers to steer on a shorter trip, but on a longer trip manual steering becomes tedious and the autopilot will eventually be called into action. The average weekend and holiday sailor has a good autopilot but makes relatively little use of it.

Autohelm has devoted far more effort to the weekend and holiday sector than any other manufacturer and is the world-wide market leader; thanks in particular to its cockpit-mounted range the company has captured around 90% of the market.

Coastal Sailing

Coastal sailing in unprotected waters normally involves longer voyages. A small crew soon tires of steering and it is here that the steering quality of the autopilot starts to matter. Sea state and factors such as tidal streams, shallows, narrow channels and winds from forward of the beam all impair the performance of autopilots. Rough seas make life difficult for them and as the waves increase in height and frequency the limits of a particular system quickly become apparent. Not surprisingly, intelligent and adaptive systems cope better with trying conditions than factory-set units which cannot be adjusted.

The general standard of equipment in this type of sailing is very high. The importance of good steering performance means that powerful inboard pilots connected directly to the main rudder are much more common; underpowered systems are soon exposed on the open sea. Although more powerful autopilots are inevitably hungrier, this rarely leads to battery problems since coastal sailing includes fairly regular motoring.

Blue Water Sailing

An autopilot stands or falls on its blue water performance. An underpowered system on the ocean reacts too slowly, too weakly and with too much delay to keep the boat on course, with increased yawing the result. The fear of losing steerage, of rounding up into the wind or worse and damaging the rig or boat, gives every sailor nightmares. If your autopilot is untrustworthy in a sea you could find yourself at the helm for a very long time.

The choice of autopilot becomes a survival issue for short-, double- or singlehanded sailing: a thousand miles at sea is more than enough to reveal the gulf between theory and reality, and choosing the wrong system could jeopardise the whole voyage. This is evidenced by the large number of would-be passage sailors who, reminded of the enormous importance of good self-steering on the initial leg of their voyage, stop off at Vilamoura, Gibraltar or Las Palmas to fit back-up systems, buy spare parts or add a windvane gear to supplement their autopilot. It is no coincidence that companies like Hydrovane and Windpilot deliver so many of their windvane steering systems to these strategic European jumping-off points!

Although autopilots are standard on blue water yachts, the limitations of the different models (underpowered system, mechanical failures) dictate that they do not in fact steer continuously. A certain amount of manual steering is therefore unavoidable, something which is not always pleasant for the person on watch and which disrupts life aboard. The performance of electric autopilots drops sharply as wind and waves increase, so heavy weather steering often falls to a human helm as well. He or she of course has the advantage of being able to see (and hopefully avoid!) breaking waves.

Jimmy Cornell, organiser of races for long-distance recreational sailors, established in his debriefing after the EUROPA 92 round the world race that automatic systems steered for only 50% of the total time at sea. Manual steering was preferred the rest of time, either to improve speed and carry more sail area or because self-steering systems just were not able to cope with the conditions. Some crews simply did not trust their technology. Almost all the skippers used the autopilot when motoring through calms even if they chose to steer by hand when there was enough wind to sail.

The combination of off-the-wind sailing and long following seas characteristic of blue water passage making sets the stiffest challenge to any autopilot. The need for quick and forceful corrective rudder movements drives up the pilot’s power consumption and saps away at the vessel’s energy budget. This once again highlights the fundamental importance of responsible energy planning for any vessel intending to rely solely on an autopilot. The average power consumption of the autopilots used in the EUROPA 92 race was approximately 4.9Ah (average boat length 42 to 50 feet).

We must add at this juncture that the electromechanical reliability of autopilot systems still leaves something to be desired, particularly under the conditions likely in blue water sailing. This means in practical terms that sooner or later every autopilot is going to fail completely and manual steering will be unavoidable. One look at the list in the Las Palmas ARC office of the skippers requesting autopilot repairs is enough to set anybody thinking. Not surprisingly, bigger electric circuits with a larger number of components are more susceptible to gremlins, and the failure of a single, tiny component can be enough in some cases to cripple a whole system. Autohelm’s choice of black for its cockpit autopilots is particularly problematic in tropical climes since the colour causes thermally-induced operating temperatures to rise to the point where faults can occur. The sailor’s only remedy here is a tin of white paint!

It is striking that those who live aboard their boats tend to revert in the end to the most basic level of equipment, dispensing with any unnecessary gear and reducing clutter aboard; that a good self-steering system still merits a place underlines its importance. One-time pharmacist Lorenz Findeisen has been roving the Caribbean for years. His answer to the question of how his level of equipment has evolved?: “...Most of it broke a long time ago, but I’m not really bothered. As long as the anchor tackle, cooker and my windvane gear keep going I can carry on sailing.”

Autohelm is the market leader for inboard autopilots. Robertson has considerable experience as a system supplier for merchant vessels and is probably second. B&G, which concentrates mainly on precision transducers for racing boats, supplies quite a few of its NETWORK and HYDRA 2 systems to boats in this sector.

Racing

For our purposes races fall into two categories:

A. Fully crewed boats:

These are always steered by hand. This applies in all races, from round-the-buoys to the most famous of all, the Whitbread Round The World Race. Whitbread boats and others for the same kind of racing are extreme in all respects: extreme in their ultralight construction (ultralight displacement boats or ULDBs) which allows them to surf at great speed; extreme in their rigs, which are oversized and infinitely tweakable; and extreme in their aim of constantly maintaining absolute maximum speed. Extreme racing is an exhausting sport which pushes crews to their limit and, in the biggest races where expectant sponsors demand success and publicity, often beyond. When autopilots are used on boats of this nature (on delivery passages, for example), only computerised systems with ‘intelligent’ steering measure up (e.g. B&G HYDRA/HERCULES, AUTOHELM 6000/7000, ROBERTSON AP 300 X).

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Racing with a large crew

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Start of the Vendée Globe in November 1992

B. ULDBs in singlehanded races:

Competitors in the Vendée Globe, the singlehanded non-stop sprint around the world which starts from Les Sables d’Olonne in France every four years, rely exclusively on electric autopilots. The race, which includes 50 and 60-foot classes, is viewed by autopilot manufacturers as the ultimate test; the harshest conditions are guaranteed and the use of windvane steering systems is virtually out of the question (see Ocean racing section). Some older, slower vessels in the BOC Race (singlehanded around the world in stages) carry windvane steering systems as back-up, but here too autopilots do most of the steering.

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60 ft ULDB Charente Maritime

ULDBs, which rarely have any kind of engine, rely on generators, solar cells or wind generators to maintain the power supply. The boats can reach speeds of 25 knots, so only the most powerful, ‘intelligent’ computerised systems are strong and fast enough to keep them on course. Autopilots are installed on every boat and steer most of the time. Although competitors in the long singlehanded races tend to follow a

10 minute waking/sleeping cycle, they never for one moment stop thinking about safety and boat speed. Nandor Fa lost about 12 kg in one Vendée Globe and knows only too well how the effects of this kind of deprivation endure.

Autohelm has a very big presence on the extreme sailing scene. The company has devoted particular attention to this area and has earned its success by maintaining a continuous presence before, during and after races, by making considerable service efforts and by cultivating its close relationship with the participants.

4. Windvane Steering Systems

Windvane steering systems obtain their steering impulse from the apparent wind angle. The advantage of this is that a sailing boat likewise generates its drive from its position relative to the apparent wind. Once the sails and windvane have been set at the appropriate angle to the wind, the boat will continue to steer this angle indefinitely and the sails will always be properly trimmed.

Wind direction is the key consideration when planning any voyage. If the wind blows from astern it is possible to set the rhumb-line course and enjoy a comfortable trip from A to B via the shortest route. When the wind is on the nose, however, tacking is unavoidable and a compass course is useless; the direct route is not the quickest if the sails are backing.

The three elements of a windvane steering system are the windvane, the linkage and the rudder. We cover each in turn below:

The Windvane

The steering impulse in a windvane gear comes from the windvane. The vane takes its energy from the apparent wind flowing across its surface at the angle set. There are two types of vane, the horizontal vane and the vertical vane.

The Vertical Vane

How it works

The Vertical or V vane rotates about a vertical axis (the same principle as a weather vane). It always points directly into the wind, so the effective windvane area (the area actually subject to the action of the wind) is never very big. When the boat strays off course the windvane is deflected by no more than the amount in degrees of the deviation. The steering impulse generated by this deflection can only deliver a limited amount of force since a V vane generates little torque.

Adjustment

Adjusting a V vane to the wind direction could hardly be easier: when free to rotate, it always points exactly into the wind and requires no special setting. It can be adjusted for different wind strengths just by moving it in or out along its mounting bracket. Increasing the distance between the vane and its shaft (longer lever) gives increased power for light airs. Reducing the distance (shorter lever) helps to reduce vibrations in the vane gear in heavier airs when power is not a problem.

Shape

Air flow across a vertical windvane is always laminar, so aerodynamic sections or wedge-shaped designs with flow separation edges are the most efficient shapes. Not only are both alternatives heavy but they are also complex and expensive to build, so almost all manufacturers prefer simple flat designs.

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V vane V vane, WINDPILOT ATLANTIK

Area

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Wedge-profile V vane, SAYE’S RIG

V vanes need to be quite large in area (up to 1m2) to enable them to deliver satisfactory steering impulses as well as the necessary steering force. They take up a considerable amount of space on the transom owing to their size and turning circle, so permanent backstays, mizzen masts and davits can easily get in the way.

Counterweight

Because of its substantial size and weight, a V vane should be perfectly balanced by a counterweight. This is particularly important in the light air position since otherwise steering impulses can be generated by the heel of the boat. It is less critical in the heavy air position when the vane is up against its shaft because the stronger winds will exert enough force to counter any disturbance from the motion of the boat.

Availability

The following use vertical windvanes: HASLER, RVG, SAYE’S RIG, SCHWINGPILOT, WINDPILOT Atlantik/Carabik.

The Horizontal Vane

How it works

A horizontal or H windvane rotates about a horizontal axis. When it is pointing directly into the wind it stands upright. When the wind strikes it from the side, i.e. when the boat is off course, it tilts to one side. What distinguishes this type of vane is the fact that when a course deviation occurs the wind strikes it over the whole of one face rather than just along the leading edge. As a result it has a substantially larger effective windvane area. H vanes are therefore able to exert considerably more leverage than V vanes and are said to be about 5.6 times as efficient.

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H vane, WINDPILOT PACIFIC

Adjustment

Almost all horizontal vanes have adjustable fore and aft inclination. The upright position offers maximum effective area for the wind, which is desirable in light air. Inclining the vane aft, away from the wind, as the wind strength increases helps to reduce lateral swinging movements, allowing the gear to operate more smoothly.

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H vane, WINDPILOT PACIFIC

Shape

Because a horizontal windvane obtains its force from the wind striking the side of the vane, there is nothing to be gained by using anything other than a flat section.

Mounting and removal

Many of today’s horizontal vane systems use plywood vanes fastened to some kind of mounting bracket. Plywood is a relatively soft material so to prevent damage in strong winds there should ideally be a large contact area between the mounting bracket and the vane. The vane should also be easy to remove as the lazy skipper will otherwise be tempted to leave it fitted even in harbour, leading to unnecessary wear or breakage when not even in use. Many ARIES vanes have been left in place for years once the skipper realised removal entailed disassembling the entire locking device. The SAILOMAT 601 gear has the windvane inserted into a slotted aluminium tube, an arrangement which provides very little contact area between the mounting bracket and the vane. MONITOR vanes are removed by undoing a pair of bolts. The WINDPILOT PACIFIC mounting bracket provides a large contact area with the vane and has a slot which allows quick removal of