- 10 -

Hasler servo-pendulum system on an S & S 30 Hasler and Gianoli, an Englishman and a Frenchman, were to play a significant 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, for 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.
- 11 The first companies producing professionally designed and built windvane steering systems appeared in Britain, France and Germany in 1968, and soon after in the Netherlands. Windvane steering systems and the year they were launched: 1976 Blondie Hasler Marcel Gianoli John Adam Pete Beard Nick Franklin Henri Brun Derek Daniels Charron/Wach Bostrm/Kns Hasler MNOP Windpilot QME Aries Atoms Hydrovane Navik 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, with 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.

The AUTOHELM ST 800 Tiller autopilot
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 vessels wheel. Cockpit autopilots for wheel steering may be linked to a data network.
- 16 The following systems available: Autohelm ST 3000 Autohelm ST 4000 Wheel Navico WP 100 Navico WP 300 CX are
Navico WP 300 CX Wheel 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 21m / 60ft 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 operated via push buttons (Autohelm) or turning knobs (Robertson). Display sizes vary and, not surprisingly, larger displays are generally easier to read. Modern high-contrast LCD displays will fade if exposed to excessive direct sunlight, so they should ideally be mounted vertically and never flat on the deck. It is usually possible to fit 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: course computer, compass, rudder position indicator, windvane transducer, and peripherals. 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. In short, it links software and hardware and converts signals into actions. There are two kinds of course computers:
- 17 The manual version which is adjusted and set up by the user and/ or installer; The auto-adaptive version which learns from recent operations and from recorded data. Both have their advantages, but sailors may well prefer the ease of the auto-adaptive black box. Aside from seeing to a few basic decisions (mode of gain, auto tack, compass or windvane), the user has only to sit back and watch that the software carries on doing its job. The overriding aim is to combine high performance with reduced power consumption and neither option is perfect: factory programmed units are never properly set up for real conditions, and manually-adjusted units are also unlikely to deliver their full potential unless the user is a professional. Compass Compasses work best on land. Once afloat, the trouble starts: pitching, rolling, heeling, acceleration and deceleration all make things difficult for a compass. The course computer needs a clear, readable signal from the compass to control the drive properly an autopilot course can only be as good as the steering impulse from the compass. The position of the compass is very important. Consider the following points prior to installation: The further the compass is from the boats centre, the greater the number of movements which will have to be filtered out. Any variations in local magnetic fields will prevent an accurate signal. The compass should be kept well away from electric motors, pumps, generators, radios, TVs, navigation instruments, power cabels and metal objects. Compasses prefer constant temperatures; avoid sites exposed to sunlight or heat from the engine, cooker or heater. Below deck near the base of the mast is a good spot for most cruising designes, provided they do not have a steel hull. The most stable point on more extreme modern yachts is further aft, normally about one third of the way from the stern to the bow. On steel boats there are different ways to get proper steering signals. An arrangement in which a magnetic compass with course dectector is fitted under the compass bowl detects changes in magnetic fields and has been use most successfully by Robertson on commercial fishing vessels. Other manufacturers position their fluxgate compasses above deck or even in the mast, not always the ideal location because of its accentuated motion. Careful installation and thorough calibration of the compass are particularly important on steel boats ( a fluxgate compass cannot be used below deck on a steel boat ). The distance from the compass to the course computer should be kept as short as possible to minimise the problem of voltage drops. The longer this distance, the thicker the cables that will be needed. One final point to bear in mind regarding installation: the compass should ideally be easily accessible in its final position. There are three types of compass to choose from, the magnetic compass, the fluxgate compass and the gyrocompass. Fluxgate sensors which supply the course computer with electronic course data are standard with nearly all manufacturers. Steering performance in testing conditions can be optimised by installing a special fluxgate system. Autohelm uses a GyroPlus transducer while Robertson has a novel type of compass in which fluxgate signals are translated into frequency signals whose variations can more easily be monitored. Further optimisation measures include fluid damping and electronic averaging. The quality of the final signal for actual steering actions is directly related to the price and quality of the sensor unit. You really do get what you pay for, and unfortunately the price range, which starts around 200 for an ordinarily fluxgate compass and 240 for a magnetic compass and course detector, extends the way up to 9000 for a high-tech gyrocompass unit.

- 18 Rudder position indicator The rudder position transducer is arranged on the rudder and informs the course computer of the position of the rudder. It can be fitted inside the drive unit ( protected from errant footsteps ) or externally at the rudder post (more vulnerable). Windvane transducer A transducer attached to a windvane or to the masthead passes information of the apparent wind angle to the course computer. Peripherals Signals from other navigation equipment such as Decca, GPS, Loran, radar, log and depth sounder can also be fed to the course computer to give additional data to aid precise steering.
The modules of an inboard pilot; a Brookes & Gatehous example

Drive unit

There are four alternatives. 1 Mechanical 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. The electric motor can be constant speed ( simple and cheap but power-hungry ) or variable speed ( more efficient). The mechanical linear drive is more energy efficient than its hydraulic linear sister but is also more susceptible to mechanical overload under extreme conditions. Wear and tear on this kind of mechanical drive also increase the operating noise of the unit under load, so it will get louder as it gets older and could eventually irritating. 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; Robertson and almost all other manufacturers fit metal transmission components as standard. A hydraulic linear driving unit needs more installation space than a simple mechanical unit to accommodate the balancing ram which protrudes from the back. Mark Parkin of Simrad UK has observed that quite a number of naval architects forget about the bigger space required by hydraulic rams and so end up having to fit a linear drive.

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Autohelm mechanical linear drive unit aboard the 18m/ 60ft ULDB Budapest 2 Hydraulic linear drive unit The push rod is operated by a hydraulic pump. Hydraulic linear 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. Hydraulic drives are protected against mechanical overload by an overload valve, which opens above a certain oil pressure, and by the inherent oil cushion. A hydraulic linear drive produces far less operating noise than a mechanical linear drive and will remain smoother and quieter, and hence more pleasant to have aboard, throughout its life. Hydraulic linear drives also last much longer, an important advantage for long distance cruising, and only a replacement set of seals needs to be carried as spares. As mentioned, hydraulic linear drives have a balancing ram which protrudes from the back of the unit. They therefore need to be mounted higher up to prevent the balancing ram striking inside of the hull. 3 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. The constantly high pressure introduces sudden high loads into the steering system with every rudder movement, and the resulting noise has earned this type of drive the name bang-bang pilot.

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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 bus and a data transfer protocol: 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 boats 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 a few major players. Autopilots may be divided into three groups: 1 Stand-alone systems which operate solely on the basis of a windvane or compass signal (e.g. Autohelm 800); 2 Systems which are linked to other modules via a data bus (e.g. SeaTalk from Autohelm, Robnet by Robertson) and/ or an NMEA 0183 interface; 3 Systems in which individual modules are linked exclusively by the manufacturers data bus (B&G).

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Module integration options for ROBERTSON autopilots. By courtesy of Simrad 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. The claim that instruments from different system suppliers could communicate with each other using the same interfaces seemed rather optimistic at one time. There were as many sailors have already discovered to their cost, several standards in existence even for NMEA interfaces, and of course no instrument manufacturer was to blame for any incompatibility; serious communication problems are always the fault of the instrument on the other side of the interface! These problems have now for the most part been resolved. Company-specific data buses do still tend to work much faster than NMEA interfaces, however, and the importance of speed cannot be exaggerated. The delay in the transmission of a steering impulse from one sensor unit to another can never be too short. Provided with a fluxgate compass / gyrocompass 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 co-operate.

- 24 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 for cockpit autopilots 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 a vessel 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 13m / 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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V vane
V vane, Windpilot Atlantik auxiliary rudder system
Area V vanes need to be quite large in area (up to 1m2 / 10 ft2) to enable them to deliver satisfactory steering impulses as well as the necessary steering force. They take up a quite alot 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.
Wedge-profile V vane, Sayes Rig 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: Halser, RVG, Sayes Rig, Schwingpilot, Windpilot Atlantik/ Caribik.
- 35 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. 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. 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 todays 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 it is not even in use. Many ARIES H vane, Windpilot Pacific Plus double rudder system 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 that 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 the vane once the locking device has been loosened one complete turn.

The ratio of main rudder area to auxiliary rudder area is ideally 3:1 Pendulum Rudder A pendulum rudder generates servo forces by swinging out to one side. These forces are transmitted to the main rudder. The amount of force produced is determined by the length of the pendulum arm from its pivot point to bottom end of the pendulum rudder. This distance, known as the power leverage (PL), is usually somewhere between 150 and 200 cm / 60-80 in. Pendulum rudders are about 0.1 m2 in area.
Pendulum rudder to main rudder proportions: the lever effect is the key to this system
- 38 Trim Tab A trim tab pivots sideways to move the trailing edge of the rudder to which it is attached. Trim tabs are normally less than 0.08 m2 / 0.85 ft2 in area and can be attached to main or auxiliary rudders or pendulum rudders. Pre-balancing the rudder Prebalancing a rudder blade, which involves moving the rudder shaft to a position about 20% aft from the leading edge, reduces the force needed to turn the rudder. This effect is the same as the sudden increased weight on the tiller when a dinghy rudder pivots up after touching the bottom. As soon as the rudder drops back into its vertical position, the balance is restored and the load on the tiller drops to almost nothing again. Almost all modern yachts have a pre-balanced rudder blade. This is a bonus for all types of windvane gears because a more easily turned rudder allows the gear to work properly with weaker windvane steering impulses. The obvious result of this is better light air performance. If the pre-balancing procedure is overdone and the shaft is positioned between 22 and 25% aft, the rudder blade will be unsettled and will tend to swing out. In extreme cases the rudder blade may end up turning the windvane instead of the other way around. Trim tab to main rudder proportions: this system type can make reversing under power awkward.

Damping

One of the first lessons of helming a boat is to steer as little as possible. Vigorous use of the tiller or wheel to correct the course tends to be ineffective because the boat always turns too far, immediately necessitating another course correction in the opposite direction and leaving a snake wake trailing astern. An experienced helmsperson, with greater awareness of the behaviour of the boat, keeps steering movements to a minimum, following one of two mental steering programs: 1. He or she tries to steer the optimum upwind course or, given another point of sail, precisely hold a desired compass course. A picture of concentration, our experienced helm studies the wind direction indicator, the sails or the compass closely, giving almost continuous small, occasionally larger, steering impulses to keep yawing and course deviation as small as possible; 2. he or she prefers a more relaxed attitude at the helm, correcting the course rarely and with small movements; the course varies over a greater range of angles. How a boat responds to the helm is determined chiefly by design; a long keel boat will always be more sluggish than one with a fin keel and a balanced rudder.

- 39 Experienced helms develop an internal damping program which ensures that, almost without having to think, they are sparing in their use of the rudder. Rudder movements not only turn the boat, they also brake it, so minimising them preserves boat speed as well. A windvane steering system lacks the wisdom of experience and, unless damped, will always turn the rudder too hard, too far and for too long, i.e. oversteer. Damping must therefore be designed into system to replace its clumsiness with the gift of delicate steering and enable it to equal or even exceed the steering performance of our experienced helm. This can be done. Principle 1: More damping equals better steering (although obviously not to the point where the system is so well damped that it does not move at all). Conceiving and building a system which properly balances damping and steering is the toughest challenge before any windvane steering designer. Systems must be powerful but must deliver their power in a controlled way. Principle 2: The less damping there is built into the system, the more additional measures the helmsperson will have to take to offset this steering deficit and cajole the system up to a level where it can cope with a particular boat. This entails not only maintaining perfect sail trim but also reducing canvas early to cut the steering demands placed on the windvane gear. Poorly damped systems make particularly hard work of reaching and downwind courses and often surrender full control to the elements. Principle 3: With no damping at all, self-steering is only possible if sail trim and sail area are so perfectly set that the boat steers straight ahead entirely of its own accord. Of course if your boat tracks along a straight line all on its own you might as well jettison the windvane gear altogether. Completely undamped systems can steer properly at just a few specific wind angles and are only really suitable as an aid to steering. A well-balanced windvane gear will always put up the most satisfactory steering performance; it is best equipped to steer the boat under all sailing and weather conditions. Indeed, a good gear of this nature inevitably steers better than even an alert helmsperson because the continuous damping of all rudder movements keeps yawing angles permanently small and with a windvane, optimum heading with respect to the wind is guaranteed all the time. Such a gear can be rated as providing effective steering. The term effective steering is used to indicate the range of a particular windvane steering system. What use is a gear which can manage only 70% of given conditions or courses if it always retires precisely when manual steering appeals least, i.e. in heavy weather! Squeezing satisfactory steering performance from a poorly equipped windvane gear means extra work for the crew. Eventually it makes more sense to steer by hand than keep running round the boat tweaking everything to prop up the gear. Damping can be provided: at the windvane; at the linkage; at the rudder. Damping at the windvane V vane: A V vane rotating about a vertical axis (weathervane principle) is deflected very little by the wind, at most by the amount in degrees of the deviation from course, and there is almost always wind flowing along both sides of the vane. This gives a high level of damping.

Trim-tab-on-main-rudder system manufacturers: Atlas, Auto-Steer, Hasler, Sayes Rig, Windpilot The Sayes Rig is a hybrid pendulum/trim tab system in which the power leverage (PL) is increased by a bracket attached directly to the main rudder.

Servo-pendulum systems

Since this is the most popular system today we shall devote the next few pages to a detailed look at its various features. How they work The windvane rotates the rudder blade via a linkage. The rudder blade is mounted on a shaft which is able to swing from side to side like a pendulum (hence the name). When the rudder blade is rotated, the force of the water flowing past pushes against it and swings it out to one side. The shaft on which the pendulum rudder swings is connected to the tiller (or wheel) via lines, so the lateral movement of the rudder blade is translated into a pulling force on the tiller (or turning force on the wheel) which effects the course correction. Once the boat is back on course, the windvane returns the pendulum rudder blade to the centre. Steering impulse Steering force Steering element Power leverage (PL) = = = = wind water main rudder up to 200 cm / 80 in
The enormous power leverage of the servo-pendulum design compared with other gears clearly reflects the considerable steering and servo forces it is able to generate.

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This Windpilot Pacific V vane servo-pendulum system MKI (1969), is made of sstainless steel. The servo principle
The traditional Monitor H vane servo-pendulum system.
Imagine you are standing at the stern of your boat doing 6 knots holding a 2 m / 6 ft long wooden plank in the water. Align the plank directly on centreline and you can just about hold it with 2 fingers. Rotate it slightly, however, and it swings powerfully to one side (your shoulder joint represents the pendulum axis). Using this principle the hydrodynamic force of the water flowing past can be harnessed to generate a tensile force of up to 300 kg / 660 lb. This explains how servo-pendulum systems are able properly to steer large, heavy boats: not only does a bigger boat require more steering force, it also inherently produces greater hydrodynamic force for the steering gear to exploit.
- 55 Fig 5.14 This figure shows how the torque at the pendulum arm of a servo-pendulum gear on a displacement boat reaches a natural limit defined by the maximum speed of the boat. ULDBs have no such limit because the boat speed can rise rapidly during surfing. The formula is applied here to a Windpilot Pacific gear with a 12x90 cm/ 4.8x36 in rudder blade and a standard power leverage (PL) of 190cm/ 76 in.

The Windpilot Pacific (1998 model) has an infinite transmission force facility.
- 64 Setting the wheel adaptor Most wheel adaptors conform to the same basic design. The various models do, however, differ substantially in their technical features, as we shall now explain: 1. The fixed drum - no adjustment possible (Sailomat Cap Horn). Both steering lines have to be disconnected from the adaptor and shortened/lengthened in order to finetrim the course. This is not a straightforward procedure and fine trim is often ignored, resulting in less efficient sailing. Providing sufficient scope for such adjustments also means that the lines have to be longer and additional turning blocks may be needed. 2. Adjustable track adaptor (Monitor). A spring-loaded pin engages in a hole in the track to hold the drum in the desired position. Fine trim involves pulling out the pin and rotating the drum until the pin aligns with a hole in the new desired position. 3. Gearwheel adaptor (ARIES). The adaptor is mounted via a finely-toothed gearwheel and is engaged/disengaged using a clutch. It must first be disengaged for fine-trimming. 4. Disc brake style infinitely adjustable adaptor (Windpilot Pacific). The adaptor is mounted via a disc on which it can be rotated and then fixed in place with a locking brake. The locking brake should be tightened no more than necessary to hold the adaptor in place. The adaptor is then able to slip on the disc when overloaded, for example in a sudden squall, preventing damage to the transmission components. This type of adaptor is very simple to adjust, a little slack in the locking brake while the wheel is repositioned being all that is required. 5. The fixed drum - no adjustment possible (Sailomat Cap Horn). Both steering lines have to be disconnected from the adaptor and shortened/lengthened in order to finetrim the course. This is not a straightforward procedure and fine trim is often ignored, resulting in less efficient sailing. Providing sufficient scope for such adjustments also means that the lines have to be longer and additional turning blocks may be needed. 6. Adjustable track adaptor (Monitor). A spring-loaded pin engages in a hole in the
- 65 track to hold the drum in the desired position. Fine trim involves pulling out the pin and rotating the drum until the pin aligns with a hole in the new desired position. 7. Gearwheel adaptor (ARIES). The adaptor is mounted via a finely-toothed gearwheel and is engaged/disengaged using a clutch. It must first be disengaged for fine-trimming. 8. Disc brake style infinitely adjustable adaptor (Windpilot Pacific). The adaptor is Three wheel adaptors (top to bottom): mounted via a disc on which it can be Monitor, Aries and Windpilot. rotated and then fixed in place with a locking brake. The locking brake should be tightened no more than necessary to hold the adaptor in place. The adaptor is then able to slip on the disc when overloaded, for example in a sudden squall, preventing damage to the transmission components. This type of adaptor is very simple to adjust, a little slack in the locking brake while the wheel is repositioned being all that is required. The mounting diameter of a wheel adaptor may be a problem if it clashes with the mounting diameter of an autopilot already present.

- 73 Experience, of course, is the real test. If wave action really could bring damagingly large forces to bear on a trailing pendulum rudder blade and its mounting, we would expect to find at least a few instances amongst the thousands of Aries and Monitor systems in use of the pendulum arm being bent against the steering line guide tubes which extend at the bottom of both these systems. This type of damage turns out to be all but unheard of. The configuration of the bevel gear linkage in both systems ensures that the pendulum arm is always brought back into parallel with the keel, i.e. is damped, before it can travel so far sideways. This remains true regardless of wave action or even capsizes.
An offset mounted servo-pendulum system will not function effectively Wooden, steel, aluminium and solid laminated GRP hulls need no extra reinforcement on the inside of the transom. Only on sandwich construction hulls is it recommended to fit additional wooden blocks or aluminium plates rather than sandwich material at load bearing points. The apparently greater load distribution provided by the larger number of bolts (up to 16) on conventional servo-pendulum systems (Aries, Monitor) is not technically necessary and the mass of bolts contributes to the visual pollution of the stern. The loads may simply have been overestimated by the designers at the time these traditional servo-pendulum systems were conceived.
This mounting for a Windpilot Pacific on a 25 tonne gaff cutter has worked well for 12 years.

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Mounting on a 20 tonne Colin Archer Ease of use
Mounting on a HELMSMAN 49
Removal The ease with which a servo-pendulum gear can be removed seems fairly irrelevant for a blue-water voyage. In other situations, for example if a protruding gear is likely to be hit or to prevent theft during winter storage, it is helpful if the system can be removed without too much trouble. With the Pacific and Sailomat 600 models this can be accomplished by undoing just a single bolt. Most other systems are retained by several bolts. Operation A good servo-pendulum system should be simple to set up and, most importantly, should permit the user to raise the pendulum rudder up out of the water very quickly. Operation should be straightforward enough that a helmsperson will engage the system even for short absences from the helm, for example during a quick trip to the nav-station. Along with their visual drawbacks, the difficulty of operating conventional servo-pendulum systems is probably the main reason why many sailors initially opt for an autopilot. A pendulum rudder cannot be prevented from moving around. Consequently, unless raised before motoring in reverse it will interrupt the manoeuvre as soon as the flow from astern is sufficient to deflect it. Rudder blade not in use, Monitor.

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Technical information
Technical specifications of selected cockpit autopilots

Autohelm

AH V ST V ST V ST 4000 T 12 V ST 4000 TGP 12 V ST V ST 4000 W 12 V

Navico

TP V TP V
Voltage Average power cons. standby 25 % duty Helm speed lock to lock no load 20 kg load 40 kg load Drive unit thrust Push rod travel Wheel speed Max. wheel torque Max. revolutions Remote control operation Suitable for boats up to Price

0.06 A 0.5 A

0.06 A 0.7 A

0.06 A 0.75 A

6.7 sec 9.6 sec 57 kg 25 cm -
6.7 sec 9.6 sec 57 kg 25 cm +
4.1 sec 6.4 sec 77 kg 25 cm +
3.9 sec 5.8 sec 84 kg 25 cm +
4.3 sec 5.5 sec 93 kg 25 cm +
3.3 rpm 70 Nm up to 3.5 +
5.5 rpm 75 Nm up to 3.5 +
6.5 sec 9.0 sec 65 kg 25 cm +
4.2 sec 6.0 sec 85 kg 25 cm +

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The 12 types of windvane steering system

1 Windvane only V vane

2 Windvane only H vane
3 Auxiliary rudder V vane
4 Auxiliary rudder H vane
5 Trim tab on auxiliary rudder V vane 6 Trim tab on auxiliary rudder H vane

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7 Trim tab on main rudder V vane
8 Trim tab on main rudder H vane
9 Pendulum trim tab V vane

10 Servo-pendulum V vane

11 Servo-pendulum H vane

12 Double rudder H vane

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Summary of the 12 types of system
Still in production no no no no yes no no yes yes yes no no no yes no yes no no no no yes no no no no yes yes yes yes yes yes yes no yes no yes yes yes no yes Bevel gear Vane type No Type Brand Country of origin Power leverage Servo power Vessel size
vane only vane only auxiliary rudder
auxiliary rudder trim tab/ auxiliary rudder trim tab/ auxiliary rudder trim tab/ main rudder trim tab/ main rudder trim tab/ pendulum rudder servopendulum rudder servopendulum rudder
Windpilot Nordsee QME Windpilot Atlantik 2/3/4 Windpilot Caribic 2/3/4 Hydrovane Levanter RVG

Ger GB Ger Ger

V H V V

no no no no

< 6m/20ft < 7m/23ft < 10m/33ft < 10m/33ft

GB GB USA

no no yes

< 25cm/10in

no no no
< 15m/49ft < 12m/39ft < 12m/39ft
Auto Helm BWS Taurus Mustafa Hasler trim tab Windpilot Pacific trim tab Atlas Auto-Steer Viking Roer Sayes Rig Quartermaster Hasler Schwingpilot Windpilot Pacific Mk I Aries Standard Aries Lift-Up Aries Circumnavigator Atoms Atlas Auto-Steer Bogassol Bouvaan Cap Horn Fleming Monitor Navik Super Navik Sailomat 601 Sirius Windtrakker Windpilot Pacific Light Windpilot Pacific
USA NL I GB Ger F GB S USA GB GB Ger Ger GB GB GB F F GB E NL Can NZ USA F F S NL GB Ger Ger
H H H V V H H H V V V V V H H H H H H H H H H H H H H H H H H
yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes yes

Sistemi uomo in mare

Emergency Guard Jonathan GmbH Usedomstr Hamburg, Germany Tel: ++Fax: ++Mobile: ++Bogasol Egui Disney Calle Provensa 157 bis E 08036 Barcelona, Spain Tel: ++79
Aries (pezzi di ricambio per tutti i modelli esistenti) Aries Spares Helen Franklin 48 St Thomas Street Penyren, Cornwall TR10 8JW UK Tel: ++377467 Fax: ++378117 Aries Standard Peter Matthiesen Mollegade 54, Holm DK 6430 Nordborg, Denmark Tel: ++Fax: ++Auto Helm Scanmar International 432 South 1 st Street Richmond CA 94804-2107 USA Tel: ++2152010 Fax: ++2155005 E- mail: selfsteer@aol.com Website: www.selfsteer.com Auto-Steer Clearway Design 3 Chough Close Tregoniggie Ind Estate Falmouth, Cornwall TR11 4SN UK Tal: ++376048 Fax: ++376164
Bouvaan Tjeerd Bouma Brahmstraat 57 NL 6904 DB Zevenaar Nederland Tel: ++25566 BWS Taurus Scheeosbouw & Uitrusting Nijverheidstraat 16 NL 1521 NG Wormeveer, Nederland Tel: ++62 Fax: ++21 Cap Horn Cap Horn 316 avenue Girouard OKA JON 1EO, Canada Tel: ++4796314 Fax: ++Fleming Fleming Marine USA Inc 3724 Dalbergia Street San Diego CA 92113 USA Tel: ++Fax: ++557 0476
Levanter Levanter Marine Equipment Gandish Road East Bergholt, Colchester CO7 6UR UK Tel: ++298242
Hydrovane Hydrovane Yacht Equipment Ltd 117 Bramcote Lane Chilwell, Nottingha m NG9 4EU UK Tel: ++Fax: ++Monitor Scanmar International 432 South 1 st Street Richmond CA 94804-2107 USA Tel: ++2152010 Fax: ++2155005 E- mail: selfsteer@aol.com Website: www.selfsteer.com Mustaf EMI SRI Via Lanfranchi 12 I 25036 Palazzolo Italy Tel/Fax: ++7301438 Navik Plastimo France 15 rue Ingnieur Verrire F 56325 Lorient France Tel: ++Fax : ++RVG International Marine Manufacturing Co 8895 SW 129 Street Miami FL 33176 USA Tel/Fax: ++Sailomat PO Jolla Californien CA 92038 USA Tel: ++Fax: ++454 3512
Sayes Rig Scanmar International 432 South 1 st Street Richmond CA 94804-2107 USA Tel: ++2152010 Fax: ++2155005 E- mail: selfsteer@aol.com Windpilot Windpilot Bandwirkerstrasse 39-41 D-22041 Hamburg, Germany Tel: ++44 Fax: ++15 Mobile: ++Email: Windpilot@t-online.de Website: www.windpilot.com Windpilot USA PO Box 8565 Madeira Beach, Fl 33738 USA Tel: ++Fax: ++Toll free: ++Windpilot Email: windpilot@compuserve.com