SELF-STEERING UNDER SAIL - Peter Foerthmann - ebook


Peter Foerthmann

13,42 zł


Windvane or autopilot - it is one of the eternal questions of long-distance sailing. This practical guide brings clarity to the debate: it investigates the technologies behind all of today's common self-steering systems, explains which solutions are best suited to which type of boat with respect to size and construction, describes how to make the most of the various options on offer and examines the relative advantages and disadvantages of each. Which systems are good for racing and which for cruising? What are the limitations of each in terms of sea conditions and power consumption? Why is proper sail trim so important for good self-steering? Peter Förthmann answers these questions and more without resort to complicated diagrams and impenetrable technical speak. A comprehensive resource written from a wealth of personal experience, this book is full of clearly explained tips to help you choose the right self-steering solution and bring the best out of it in use. An overview of the market and a directory of almost all the self-steering systems available right around the world complete the picture.

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Autopilots and Wind-steering Systems

Peter Christian Förthmann


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

Peter Christian Förthmann

Copyright: © 2013 Peter Christian Förthmann

Published by: epubli GmbH, Berlin

ISBN 978-3-8442-5640


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.

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?

The traditional Monitor servo-pendulum system


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:


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.

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.

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.

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.

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).

Module 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.

Navigating down below with the AUTOHELM NAVPLOTTER 100