ction>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.
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,
