INDEX TO ARTICLES
- Derek Daniels Article 1984
- An Overview of Mechanical Self Steering– by John Curry
- Three Pairs of Hands – by Don Gilchrist – courtesy Australia’s Cruising Helmsman
- How Safe is Your Rudder?– by Andrew Simpson – courtesy UK’s Paractical Boat Owner
- Sailing Downwind? Set a Whisker Pole – by Andrew Burton – courtesy US’s Cruising Worl
- YM_Learning_Curve Jeanne Socrates – ‘Shipwrecked 60 Miles Short of Triumph’ – courtesy to UK’s Yachting Monthly
- Get Your Boat to Self Steer Under Sail – From Bluewater Sailing’s ‘Cruising Compass’
- No-Power Steering – Yachting World August 2012 Feature
Get Your Boat to Self Steer Under Sail – From Bluewater Sailing’s ‘Cruising Compass’
In the days of coastal shipping under sail, the old schooners or gaff headed cutters were often sailed by a “man a boy and a dog.” How did this small crew handle the 50 to 70 foot cargo ships that were laden with lumber, coal, granite, grain and other commodities that were hard to ship overland? The trick that made this possible was the ability of the skipper to get the vessel to steer itself under sail for long periods at a time. Those boats had long straight keels and sail plans with low centers of gravity; plus, they had numerous sails to trim so the boat could be balanced with many fore and aft adjustments, including square sails for down-wind running.On modern fin-keel, spade-rudder designs that most of us sail, the trick of getting a boat to steer itself can be a little more complex because the hulls have lower built-in directional stability and the sail plan usually consist of only two fore and aft sails that are normally flown on one side of the boat or the other thereby creating a natural imbalance.
Down wind, you can get a modern sloop to sail straight by running dead downwind wing ‘n wing – that’s with the mainsail on one side and the genoa poled out on the other. The boat will steer before the wind for hours this way as long as the helm is balanced and neutral. You can adjust the balance by reefing or unreefing the sails as necessary.
Up wind, modern boats can be made to steer themselves for many minutes if you can get the sails completely balanced so the helm is neutral. You do this with sail trim by adjusting the sheets, the cars on the genoa leads, the traveler and the main outhaul. Once the sail plan is balanced, the boat will slip along without rounding up or falling off and will maintain a constant angle to the wind.
Balance the rig, trim the sails carefully and you will find your boat will go where you want it to all by itself.
Jeanne Socrate’s new Najad 380 – see http://www.svnereida.com/
An Overview of Mechanical Self Steering and Autopilots – By John Curry
In 1898 Joshua Slocum started it all by completing a three year circumnavigation, from Boston to Newport, RI covering 46,000 miles in his 37 foot, nine ton sailboat all by himself. He devised self steering systems by connecting lines from sails to his tiller. His boat Spray had a particularly long and straight shape with a similar keel which made it easier for the boat to stay on course – easier than would be for our modern hulls with their little keels and rudders.
After WWII the world’s oceans started to see a growing fleet of independent adventurers exploring the earth for themselves from their little boats. These self made explorers readily adopted self steering devices for their boats. In fact, the prime reason that the trickle of explorers in the 1950s has become a full armada of pleasure seekers can be attributed to two devices: GPS and self steering.
The self steering is handled by both the electronic autopilots and the mechanical windvane driven self steering devices. Most experienced cruisers have both – an autopilot for motoring and mechanical self steering for sailing. A discussion of autopilots versus non-electronic self steering is found at the end of this paper.
For week-end sailors that make the transition to become off-shore cruisers there are decisions to be made about upgrading autopilots or acquiring a mechanical self steering. Like the around the world sailboat racers, experienced cruisers have learned that confidence in autopilots can only be achieved by investing heavily in quality – preferably with a back-up and infallible power generation systems. The lack of any electrical power requirements makes the self steering devices most appealing to the offshore sailor – no mysterious black boxes and no consumption of amp hours ….. and there is something symmetrical about a sailboat being guided by the wind and not dictated to by a pulsating electrical device.
TYPES OF SYSTEMS – Servo Pendulums, Auxiliary Rudders and Trim Tabs
There are a variety of types of devices available although most are either of the ‘auxiliary rudder’ or the ‘servo pendulum’ style. The ‘trim tab’ type of system is also worth note. The systems and some of the more common brands can be classified as follows:
- Auxiliary rudder – Autohelm, Hydrovane, Sailomat, Windpilot
- Servo pendulum – Aries, Cape Horn, Fleming, Monitor, Sailomat, Windpilot
- Trim tab – Auto Steer, Sayes Rig
There are numerous other brands available. To find them simply do a search on the web for “self steering” or “wind vane self steering”.
Of all these units only the Hydrovane and Aries have their roots in the ’60s with Hydrovane’s founder, Derek Daniels, being the last of a generation of self steering pioneers when he retired in 2002.
HOW THEY WORK
Operation of Wind Vanes – All of the mechanical self steering systems use some sort of a vane which is like a little flat sail without any shape or curvature. Originally plywood was used but now many are made of synthetics or even sailcloth on an aluminum frame for greater size and strength. The vane is set in an ‘on course’ position with its leading edge pointed straight into the wind. Imagine holding a big piece of plywood up in the air. If one edge is faced directly into the wind then it is relatively easy to hold but as you gradually turn it sideways so that the wind blows against a larger and larger apparent surface then there is more and more force pushing against the plywood. That is how the vane functions. To maximize leverage the vane is usually fixed on a horizontal axis. As the vessel goes off course the vane is pushed over which causes the linkage to do the rest – as explained below.
Auxiliary Rudders – An auxiliary rudder system involves a completely separate rudder from the main rudder. Hence vessels with such units end up with two entirely separate steering systems – a most compelling virtue – an emergency steering system already in place. The technique is for the main rudder to be locked in a neutral position, or actually locked in a balancing position that compensates or eliminates any weather helm, and then the auxiliary rudder does all the steering. The deflection of the vane is the impulse that directs the rudder via various systems of linkage.
Examples of the differing methods to drive their rudders: The Autohelm uses a trim tab on a large unbalanced rudder. Its virtue is the ability to have the vane installed nearby but not directly attached to the drive shaft. The Hydrovane uses a balanced rudder and a particularly large vane with some unique linkage to get its power. Hydrovane has achieved a larger and more powerful vane by using an aluminum pipe frame covered with nylon cloth. Sailomat and Wind Pilot both have added to their product lines a servo pendulum system that powers an auxiliary rudder. A balanced rudder is a significant component of the systems of Hydrovane, Sailomat and Windpilot as it takes such little effort/power to cause it to move.
Strengths of the auxiliary rudder systems:
- The vane is set pointing into the wind – it’s leading edge to windward
- The main wheel/tiller is locked off at the position that balances the boat for any weather helm
- As the vessel goes off course the vane, in turn, deflects which causes the rudder to turn and bring the boat back on course
Strengths of the auxiliary rudder systems:
- A complete back-up steering system for emergency use
- Can be installed off-centre to accommodate swim platforms and ladders – except the servo pendulum units
- Less yaw due to immobile main rudder
- Fixed main rudder predetermines a ‘balanced boat’ as any weather helm is compensated for
- No tense lines through the cockpit
- Main rudder system is less prone to break-down as it would be used far less
- In collision avoidance situations it is easy to turn the wheel/tiller ‘hard over’
- Suitable for most boats
Weaknesses of the auxiliary rudder systems:
- Appendage on the transom that adds to the boat length and is an obstacle when maneuvering in tight quarters
- Drag – another rudder or two in the water – creates more wetted surface
Servo Pendulum Systems
These units are unique for their blade or paddle that seems to reach out in the water. The off-course deflection of the vane, through the leverage of some linkage or gears causes this paddle/blade in the water to twist. That twisting presents a face of the paddle to the water flowing by forcing the paddle to swing with force to one side or the other. The motion of the paddle causes connecting lines to the main steering wheel/tiller to move which in turn causes the main rudder to change course. These systems require somewhat intricate installations involving a number of blocks that are positioned to minimize friction for the connecting lines to the wheel/tiller. The tensioning of those lines is critical as is the tuning of the systems.
To summarize that connectivity:
- by going off course the vane deflects
- causing the paddle/blade in the water to turn
- the passing water then pushes the paddle/blade face to one side
- the swinging sideways of the paddle/blade pulls on connecting lines to the wheel/tiller
- causing the wheel/tiller to move
- hence the rudder moves to alter course
Strengths of servo pendulum systems:
- Power is derived from the boat speed through the water – producing great power as the boat gains speed
- Break-away feature of most paddles
- Paddles are usually removable when not in use
Weaknesses of the servo pendulum systems:
- Tensioning and tuning of the connecting lines that can suffer from stretch, binding or chafe
- Obstacle in the cockpit of those tensioned connecting lines
- Breakage of the paddle/blade from hitting floating objects as it swings from side to side – most units have break-away features to accommodate such pressure or impact
- Can have difficulty in light airs – friction can vary enormously, especially in the types of rudder mechanisms – result can be non-functioning in light airs due to insufficient power – especially downwind – works better on boats with balanced rudders and lighter/faster boats
- Appendage on the transom that adds to the boat length and is an obstacle when maneuvering in tight quarters
- Drag of the paddle in the water
The servo pendulum systems are not adaptable to all sailboats. Some of the situations that are not suitable are:
- Vessels with hydraulic steering
- Center cockpits or when the connecting lines must be very long or travel an indirect route to the wheel/tiller – friction and tensioning become more challenging with the addition of more turning blocks or longer lengths of line
- Steering wheels/tillers that require considerable strength to move
- Wheels/tillers with too few or too many rotations required to move the rudder its full radius
Trim Tabs – A trim tab is a mini rudder that is attached to a larger rudder. Through the windvane and leverage via certain linkage, the trim tab is caused to move in the opposite direction than the desired direction for the larger rudder. So as the trim tab turns it forces the rudder to which it is attached to move in the opposite direction – effectively, it drives the larger rudder over. Trim tabs prove to be very simple and powerful although they do create a certain amount of drag as the face of the tab (mini rudder) can be nearly 90 degrees to the direction of the rudder to which it is attached. The Sayes Rig is a fairly large rudder/trim tab that is connected to the main rudder by a hoop that is installed on the main rudder. The Auto Steer is meant for vessels with transom hung rudders. The Autohelm is a trim tab onto an auxiliary rudder whose vane may be located some distance from the rudder – attached only by cables.
Sensitivity and Power – All the above systems do the job – to varying degrees. To differentiate between the various systems an assessment must focus on their 1) sensitivity 2) power and 3) durability. The challenge of the design of a system is to utilize the right mixture of power and sensitivity. The requirements of the systems vary with the wind speed and for each point of sail. A boisterous sea can also add challenges as it throws, with great force, the boat and its sensitive vane, in all directions. The de-sensitizing of self-steering is called ‘damping’. The damping is defined as a virtue peculiar to windvane self-steering – an ability to slow the rate of course change when making course corrections – hence not over steering in order to produce a gentle return to the desired course. The ‘S’ pattern of the wake tells the story. Ideally a good helmsman strives to keep the vessel heading in a straight line. In heavy seas it is impossible to achieve anything like a straight course but, in those conditions, the capacity of the steering system to ‘automatically’ apply the right amount of steerage with appropriate force is of paramount need. Excess power or correction exacerbates the need for an even stronger reaction in the other direction and so on. Insufficient power is not even workable. Neither brute power nor extreme sensitivity are the answer.
In conclusion, the system must be:
- adjustable to varying degrees of ‘damping’
- adequately powered in light and heavy air
Durability – Second only to the vessels’ ability to float is the importance of steerage. Bad weather in the open sea puts enormous demands on the entire vessel but especially on the steering systems. It is no time for a breakage – but that is exactly the time when the weakest link will give way – and a time when the crew is least able to deal with it!
MAINTENANCE AND TROUBLESHOOTING
Friction – In light winds the amount of friction in a system determines at what point it becomes effective or ineffective. The servo pendulum systems have much more potential and inherent friction. The lines and turning blocks should be cleaned of salt and grit and regularly re-tensioned – but not over tensioned as that can cause binding. Blocks should be of the higher quality with roller bearings. Not much can be done about the boat’s actual steering mechanism although it should be reviewed to see if there is unnecessary stiffness. Auxiliary rudders have much less potential for friction with the Hydrovane having perhaps the least of all as it does not have any of the external paraphernalia as the others: lines, cables, trim tabs or paddles in the water.
Damage from Collision – All devices strapped onto transoms are vulnerable to collision – with other boats, docks, pilings etc. The rudders and blades in the water are also exposed to any passing floating debris and fishnets. The servo pendulum blades have proved to be the most vulnerable as they swing from side to side – away from the protection of the keel and main rudder. For that reason they are generally designed with a break-away feature.
Breakage and Wear – Each product will have certain parts that are either vulnerable to breakage and wear or prone to fail or simply fall off and be lost overboard. The suppliers often provide a ‘spares kit’ that includes all those items. It is worth enquiring about the durability of vanes, rudders, paddles, gear mechanisms and any other items.
Finally, perhaps the greatest problem comes from installing too small a unit for a given boat in order to cut costs. Not only will performance be unsatisfactory, but the unit will be overstressed and likely to fail. It is far better to err on the conservative side, especially if you are considering ocean crossings. Steering by hand on long passages becomes a monumental chore.
Balancing a boat – Despite the dramatic force amplification achieved hydrodynamically, the end forces generated by self steering devices are still not that powerful, especially in light winds and at slow boat speeds. No self-steering apparatus will operate effectively unless the boat is balanced first. This is largely a matter of sail trim, although where an auxiliary rudder is used the main rudder will be locked off in such a way as to correct for helm imbalance e.g., weather helm.
Most boats will self steer hard on the wind without a self-steering device. But as the boat comes off the wind, balance is harder and harder to achieve. On a beam reach it may be necessary to sacrifice optimum sail trim – e.g., by letting the mainsail luff somewhat – in order not to overpower the self-steerer.
When broad reaching and running, the more the center of effort can be concentrated in the headsails the easier the boat will be to control – eg – either no main (or mizzen) with only twin jibs set or a ‘wing-on-wing’ configuration with main sheeted out as far as possible and the jib poled out to the weather side. Since apparent wind speed is much reduced when running, the wind vane exerts less force than on any other point of sail; combine this with the fact that, when headed downwind, sea conditions can be unrully, then it is easy to see that the self steering system will need all the help it can get. Downwind sailing in ocean swells is the acid test of any self-steering device.
Yaw. A self-steerer reacts to a change in course and can never anticipate wind shifts or wave action. It is therefore, a built in tendency to cause the boat to yaw from side to side around the course line. The further the boat is off the wind, the greater the tendency to yaw. Better systems have a degree of yaw damping capability. The gear is designed in such a way that as the boat’s rudder or auxiliary rudder turns in response to ‘instructions’ the force exerted is lessened or ‘dampened’ to achieve a gentler return to course. An ‘undampened’ steerer will effectively have only an ‘on’ or ‘off’ mode which results in more violent course corrections – hence more yaw. But even so, no self-steering will hold a downwind course in following or quartering seas without a fair degree of yawing – just as no helmsman can.
ADVANTAGE OVER AUTOPILOTS
When comparing a good autopilot to a good windvane self-steering device what are the separators?
An expensive autopilot is a most impressive piece of machinery. Push a button and watch it go. There is nothing easier – supposedly. The most rigorous test of autopilots is done every year or so by the around the world ocean racers. A decade or so ago the windvane got instant fame when the arriving fleet in Australia, in frustration over the non-performance of their autopilots, in masse ordered self steering systems for the next leg of the race. Since then the autopilots have made vast improvements and the boats themselves have become flying carpets that can average speeds of over 20 knots for long periods of time. A boat that accelerates from a hull speed of 8 knots to a constant surfing speed of 20+ knots is beyond the range of any of the mechanical devices – not to mention the sail loads that they carry. Of more importance is the method that these racers use to manage their most critical self steering – and that is to have multiple autopilots and generators. The norm for them now is to have as many as two autopilots operational and at least that many as spares. As well, they require a totally redundant set-up to provide electricity. This would include at least one if not two generators as well as the main engine. The proper functioning of an autopilot means not only that its black box and mechanics must stay healthy but that the supporting power generating systems must as well be fully operational. A single glitch in any one of thousands of parts can stop the autopilot: fuel pumps, fuel filters, starter, alternator, regulator, batteries, engine valves and on and on. The point is that reliability can only be achieved with considerable redundancy – and enormous cost.
Today, as local sailors graduate to become offshore cruisers there is a tendency to stick with the devil they know – the autopilot. Certainly there are many circumnavigators who have happily sailed the world relying on only an autopilot for self steering. Too bad that they have never come to know the independence that can be gained when using a mechanical self steering device …… something about teaching an old dog new tricks…..or maybe they are not that comfortable sailing and prefer to rely on the iron staysail.
A mechanical self steering device is blissfully independent of all other systems and its very simple parts carry on in a most un-mysterious fashion. So the real difference between autopilots and mechanical self steering is simplicity, reliability and lack of power consumption…..
And, of course, there is something symmetrical about a sailboat being guided by the wind and not dictated to by a pulsating electrical device.
The Third Pair of Hands – By Don Gilchrist
A critical analysis of self steering concepts and their application in the cruising lifestyle.
Don Gilchrist is back practicing dentist (orthodontics) in Cairns, Queensland, Australia. He and his wife, Robyn have lived aboard their Oceanic 42 for ten years and have just completed a seven year circumnavigation. This article appeared in the June 2003 edition of Australia’s ‘Cruising Helmsman’ yachting magazine. According to Don cruising is like Hotel California: “You can check out any time you like but you can never leave”.
When I grafted an extra 1.5 meters on the back of “Stylopora” not only was I turning my back on Jack Savage’s original idea of davits on the Oceanic 42 but I felt I was cutting wind vane self steering out of the script as well.
So far I have not felt the lack of davits but I was always ambivalent about foregoing wind vanes. In any collection of yachts a wind vane on the transom is as good a guide as any to the division of the serious cruisers from the rest. Initially I supposed there was a reason for this but I was carried along on a wave of high-tech euphoria. Wasn’t the boffins latest brainchild GPS a triumph ? Hadn’t our original electronic autopilot shown itself a proven performer? Didn’t wind vanes steer yachts onto the rocks after a wind shift.?
So Stylo grew and wind vanes were reluctantly forgotten. Certainly backup was needed for our original wheel pilot and I chose a below decks model driving a hydraulic ram direct to the quadrant thus bypassing any future problems with the steering mechanics from the wheel back to the quadrant. Little could be worse than steering the boat across an ocean sitting in the aft cabin clutching the emergency tiller, hand bearing compass in your lap.
Unusual Trim Tab self steering
Our Coursemaster 450 has proven a strong performer but not without teething problems. “Electrical overload” and a “compass fault” were solved with a few electronic components in Ambon under faxed instructions from Richard Chapman at Coursemaster whose customer support has always been excellent and a hydraulic problem, which could have been solved in 30 seconds, had I perceived it correctly, saw us swap to the wheel-pilot for the top half of the Red Sea.
By this stage, particularly after the tragedy of the US yacht “Melinda Lee” being run down by a ship with loss of life off NZ, I had become aware that ships at sea are, to all intents, oblivious to the existence of cruising yachts. Forget all that nonsense of power and sail, port and starboard: they simply do not know you are there. If such an unhappy conjunction should occur the odds are that the yacht will simply disappear with all hands and no one will ever know why. If it were not for the miraculous survival of Judith Sleavin no one would have ever known about this one either.
The most effective defences against shipping on passage are a diligent watch and liberal use of radar. When the weather is bad no one wants to sit in the cockpit for their entire watch when the dodger is opaque with salt spray or rain and the cockpit cushions sodden. Amongst the heaving, foam-flecked seas any chance the watch on the ship has of seeing yacht navigation lights is minimal indeed. With the sea up and a few showers and squalls about a yacht just disappears into the background clutter for both eye and electronics on the bridge of the ship. But it is hard to hide 20,000 tons of ship from the yacht’s radar within 15 miles in any degree of dirty weather. For radar to be useful it needs to be kept on, at least on standby, all night. At about 3 amps on standby and at least double that on transmit it’s a fair drain. Add another 3 or 4 for GPS, nav lights, instruments etc. and a whopping 10 plus for a busy autopilot and you have a demand problem that few battery banks can cope with day after day. Such is the tyranny of the helm that crews scrimp to keep the autopilot working: radar, navlights, radio, … everything takes a backseat to the autopilot and an autopilot that leaves its amps for the radar has lots of appeal.
Lying awake in the aft cabin as the Coursemaster grunted away, fretting about the rudder falling off, shipping and power consumption aboard yachts I decided to review the situation. I looked at many installations and quizzed their owners as I reached into my own mind to determine what I wanted a wind-vane to do for “Stylopora”. 95% of self steering may be divided into two broad groups, each divided again into two subgroups:
Group A. Electronic / Electrical
- Above deck eg. tiller & wheel pilots
- Below deck eg. Coursemaster
Group B. Wind Vanes
- Servo pendulum eg. Aires, Monitor & Fleming
- Auxiliary rudder eg. Hydrovane
ABOVE DECK: The plusses for this group are cost and convenience in that they are reasonably cheap and amenable to owner installation. There is minimal work below decks apart from getting power to the unit and putting the control head in some place where it is not too vulnerable to gratuitous trauma or the vagaries of weather. If they’re cheap and you can put it in yourself then the spares/backup question is easy to answer: simply carry another one. Harder to answer are questions related to their limitations. Size and weight of vessel is not the problem. Inherent helm weight and system friction are. A 12 metre centre cockpit yacht with pull-pull cable steering and a large unbalanced skeg hung rudder will be beyond the capacity of the strongest wheel pilot in any developed sea. But a 12m aft cockpit cruiser/ racer with light steering and a balanced spade rudder will be quite manageable in most conditions. Broad reaching in fresh breezes with a lumpy quartering sea will be beyond this pilot type in any vessel. Speed and power of response will be lacking leading to an erratic course as the boat yaws around the ocean. At worst a crash gybe all standing could take the rig out of the boat and kill anybody in the way.
This type is totally dependent on the main steering system . If there is failure between the pedestal and the rudder shaft, hand control as well as autopilot have both gone for a Burton. For this category tiller steered boats have an advantage. But few production boats have tillers and effectively none over 11metres (36 ft) which excludes most yachts suitable for cruising and passage making. Centre cockpit designs are deservedly popular for cruising and they possess all the features that one should be cautious about. Wheel steering, unbalanced rudders and high friction mechanics severely limit the application of cockpit/electronic pilots for blue water cruising.
For day boats and weekend cruiser-racers they may however be ideal. The tyranny of the helm is not an equivalent threat for a friendly foursome between Pittwater and Sydney Heads as it is for a cruising couple mid-Atlantic.
BELOW DECKS: Such pilots can be powerful indeed. They may activate some part of the steering mechanics via a chain and sprocket or a hydraulic pump (this type is one of the few that can be adapted to hydraulic steering). The more direct route is onto the rudder shaft via the quadrant or its own dedicated tiller with some sort of linear drive.
These pilots can handle the heaviest loads on the biggest boats in any weather conditions … IF you can keep the amps up to them!. Having high power outputs they have large power appetites. In heavy conditions up to 15 amps continuous is not unheard of. Because of their power they require sophisticated installation in an engineering sense. Flimsy supports and light weight fastenings will self destruct in no time. They are much more complicated for the novice owner to install and few are supplied with recommendations or instructions to that effect.
Instead of a control head and drive unit we are faced with drive unit, rudder sensor, fluxgate compass, junction box, at least one control head, often a hand held remote control and sometimes even a wind sensor. All of which has to be found an appropriate location and installed with its cabelling to enable periodic servicing. As well as being tidy and decorative enough to satisfy the mistress of the accommodations.
Most can be interfaced with the rest of the ships electronics through NMEA ports if you like that kind of thing. We do not. The meeting place for all nav info on Stylo is a paper chart interfaced by the human brain.
As well as their additional power they usually have some limited “intelligence ” in that they are programmed to learn how to best control the boat as they go along . The increased economy of movement of our CM 450 is noticeable over the first 15 minutes. Above deck pilots sound busy. Below deck units can be decidedly noisy as they shove things to and fro. Ours is not nicknamed “Moose” for nothing. In our aft cabin Oceanic 45 his mechanicals are right under the bed and disturbance to the off watch can be significant.
Cost is a detractor as outlay approaches A$5000 or more. However if the vessel is used regularly for short handed cruises of a week or more the expense becomes justifiable. A combination of wheel pilot backing up a below deck unit would satisfy almost all of the requirements of full-time live-aboard coastal cruising.
SERVO-PENDULUM WIND VANES: This type are the most common wind vane with Aires, Fleming and Monitor being seen in any collection of blue water yachts. The idea was started by an adventurer, “Blondie” Hasler, who sought a system powerful enough to cope with the large, heavy , unbalanced, keel hung, tiller steered rudders of his time. He used a wind vane geared to angle a pendulum blade to the water flow which would drive the blade to one side or the other with great force. This could be coupled to drive the main steering gear to counter the change in apparent wind on the vane that started the process.
Older Aries ………………………………… Fleming – lines to wheel
Servo pendulums are busy looking structures, amounting to a modest facsimile of an offshore oil platform on the stern. They work so powerfully that more than one user has told me “in fresh conditions when the pendulum feels the water flow human force cannot hold against it “. Consequently they have the power to shift the large, unbalanced rudders of big cruising yachts and overcome the friction of complex, centre-cockpit steering systems.
Monitor Servo Pendulum
On the down side they tend to dominate the back of the boat to the exclusion of all else. They are vulnerable to damage and the connections from the pendulum drive unit to the main steering can be cumbersome and inconvenient. Light wind and sloppy sea conditions are the nemesis all wind vanes, servo pendulums uppermost among them. Low water speed equals low power output which comes up against a steering system undiminished in its friction or power requirements. When the rolling motion of the boat takes over as the main contributor to the apparent wind felt by the vane all wind vane control becomes ineffective.
Wind vanes tend to be ineffective motoring, unless some sort of electronic pilot takes over the input into the wind vane from the wind itself.
Servo pendulums are totally dependent on the main steering gear for their function. I do note however the German Wind Pilot sometimes combines a servo unit driving an auxiliary rudder. Servo pendulums tend to be vulnerable to damage as they swing out away from protection by hull, keel and rudder. To offset this they are provided with a fail-safe system in the form of a sacrificial sleeve or shear pin.
AUXILIARY RUDDER WIND VANES: Hydrovanes have been around for more than 20 years and have evolved steadily since their origin. Initially they came about to offset various intractable problems of servo pendulums: mainly dependence on the main steering, the complexity of connection to it and the servo machines poor performance in light air.
The theory of auxiliary rudders is that the vessels main rudder is locked to provide the basic balance, or “weather helm”, on that point of sail. The auxiliary rudder then merely provides the trim corrections to keep the vessel on course. The auxiliary rudder can thus be much smaller than the main and fully balanced to minimise the power needed to move it. Thus allowing it to work in light conditions as well as heavy.
On the down side of auxiliary rudder types is cost. While they are visually less flamboyant than servo pendulums the engineering is reputedly more expensive.
They too tend to be vulnerable to damage and take over the back of the boat but not to the same extent as servos. Because the wind vane provides not only the control but also all of the force required to keep the vessel on course the wind vane itself is much bigger on Hydrovanes, complicating clearance of solar panels and mizzen booms as well as stowage.
Spinnaker work in light and sloppy conditions is not for wind vanes of any type. At such times things are better handled by “Moose”. When things go a bit flappy there are fewer variables.
Their big plus is that they are independent of the main steering and indeed provide an effective emergency rudder in case of catastrophic failure of the main gear. There is on record in ARC rally archives an account of a boat of popular production design that lost it’s spade rudder entirely mid-Atlantic yet finished the rally without fuss solely as a result of it’s Hydrovane self steering gear.
Any kind of self-steering has the power to communicate back to the helmsman. If your electric model has 90 deg. of weather helm and is grunting away as while the vessel slews about the ocean. Or your wind vane is fully over to one side all the time with a noisy gurgle coming from astern the rig is out of balance and it is up to you to put it right. ALL auto pilots reward the balanced boat handsomely with longer trouble free service, better course keeping and more peace of mind. Nothing on a boat is set-and-forget and that is as it should be. Sail plan, course keeping, speed and comfort are all interrelated and the meeting point is boat balance DO NOT IGNORE IT.
Whatever the pilot, it is nice to be able to control it from a position close to the helm. Within the limits of weather resistance the control heads of all electronic types are flexible in this regard: although all the manuals say “Keep out of rain, spray etc.” How you are supposed to do this and have it within reach of a yacht’s helm at the same time is beyond me. Most windvanes have some kind of remote control, our Hydrovane Derek certainly does and it was no problem to route it to the centre cockpit for night use on passage and it was easy to stow when not in use. There are some adjustments that need to be done aft, at the unit itself but once “Derek” was set up for the general conditions in terms of windvane axis angulation he seemed to look after himself. We never had the need to go aft and do any of it at night on passage or in adverse conditions. All servo pendulums come with a wheel or tiller quick disconnect. Hydrovanes do not because the auxiliary rudder is so much smaller than the main and independent of it. In a crisis the main rudder overrides the auxiliary and you can sort it out later after the panic is over.
In the end our auto-pilot set up was: Plastimo wheel pilot, Coursemaster 450 electronic/electric/hydraulic and in Malta I fitted a Hydrovane for the long trans-oceanic passages and I have never regretted any of them. The back-up that each provides the other is unique and valuable in its own right. For a quick third pair of hands in tight pilotage or coast hopping on a light day the wheel pilot is great. When there is a long motoring job and the pilotage requirements are precise, with the kite up or the wind variable the CM 450 comes into it’s own. The power and precision in any circumstance of weather is irreplaceable. But for a long haul of trade wind sailing in shipping lanes when you want to use radar a lot. Of knowing that no electrical failure can rob you of your auto pilot and sentence you to the tyranny of the helm for the duration. When you want quiet and peace for sleeping off-watch and the tranquillity that comes from knowing that you are carrying an entire spare steering system with you, the Hydrovane is peerless.
Having one each of 3 categories on board Stylo, have I overdone things? Perhaps and only perhaps and I think not anyway. After the structural integrity of the hull and rig and the reliability of the motor there is NO system on a cruising yacht more important than that which allows it to maintain its course without full-time hands-on human control.
All systems overlap yet none is complete. Only in the application of all of them, in their place, does the cruising yacht allow its crew to approach those peaks of freedom, comfort and peace of mind that are part of going cruising in the first place. There is plenty to do aboard a cruising yacht without having to hand steer her every inch of the way.
copyright – Don Gilchrist 1997 all rights reserved.
HOW SAFE IS YOUR RUDDER – By Andrew Simpson
..from the April 2007 issue of UK’s Practical Boat owner
Andrew Simpson is a yacht designer, builder and surveyor specializing in fast cruising and racing yachts. He is PBO’s consultant editor.
Rudders are subject to incredible stresses and loads and if they break, the consequences can be disastrous. So how safe is your’s? asks Andrew Simpson
Towards the end of last year, the Jubilee Trust’s magnificent three masted barque, SV Tenacious, on passage from the Canaries to Antigua, responded to a distress call. A French yacht called Zouk – a 13m (43 ft) Jeanneau Sun Odyssey – had lost its rudder and had been adrift for nearly a week.
Isolated mishap? Not really. In the Atlantic Rally for Cruisers (ARC) of 2002, a Hunter Legend 450, known as F2, met a similar fate and got help from. would you credit it. Tenacious again!
Onwards to the ARC of 2006 and the storey quickens. This time Y Not, a contest 48, and Arnolf, a Bavaria 35, both lost their rudders.
In the course of my research for this article I heard of other casualties, including the Hanse pictured above, a Catalina 42, J44, Wylie 38, Hunter (Legend) 466, and a quartet of Cal 39s. I have personal knowledge of an Excalibur 36 (I built its replacement rudder), a Rival 38, a Dehler 34, a couple of Trident 24s, various Westerlies and some earlier Moodys. When you think of how many boats are out there, this is hardly a mechanical epidemic, but considering how important rudders are it’s certainly a cause for concern. Most were spade rudders, and the most common failures were stocks breaking where they emerged from the hulls – always areas of highest stress concentration. It’s this type we’re mainly concerned with here.
So what were the causes? In most cases we’ll never know.
It’s surprising how many skippers claim they hit something. ‘There was a hell of a bang,’ one once told me. ‘Just one bang?’ I queried. ‘Surely it would have hit the keel first.’ Of course, this sort of conjecture is very circumstantial. Boats do hit submerged objects, but it may be simply that the rudder flailed and as it came adrift, banged up under the hull. It seems to me that so dramatic is the transition from business-as-usual to ‘Houston we have a problem,’ that in the absence of an indignant whale or a tree trunk in the wake we may never identify the cause.
To question precisely how such an event occurred might seem like nitpicking – but it’s really very important. No rudder will take extreme punishment, but if it gives up the ghost in normal service we have something to worry about. For what we are then talking about is structural inadequacy from the outset.
Safety in numbers?
This is a concern which pops up again and again. PBO last covered the topic in depth 10 years ago in (PBO 352-354 – see panel bottom of page 88) written by the eminent hydrodynamicist Tony Marchaj, in which he described how ‘normal’ loadings on rudders could be grossly exceeded. The maths can be heavy going but my intention here is not to delve too deeply – to review the various points without too much reference to complex sums.
But not entirely. Any calculation must start by estimating the maximum side force (F) on a rudder. Marchaj referred to the old Lloyd’s-based formula which for our purposes can be written as:
F = 1.1 x Vs² x A
Where Vs is hull speed and A is blade area. It can be seem that V is squared to conform with the axiom that lift on a foil increases by the square of its speed, relative to the fluid in which it’s immersed. This leaves the designer to estimate – some would say ‘guess’ the value of V.
But Lloyd’s lost interest in yachts years ago and most designers switched to the American Bureau of Shipping (ABS) Guide for Building and Classing Racing Yachts. Their formula for estimating side force took a different tack
F = 984 x C x Lwl x A x N
Both are imperial versions of the formulae but it doesn’t matter. Note that ABS have abandoned hull speed and are simply inferring it from the waterline length (Lwl). A is again the area and C is a lift coefficient which is 1.5 for rudders of moderate aspect ratio. The value of N is usually 1.0v – and therefore has no effect on the result – but rises in calculations for lighter-than-average boats to allow for their higher potential speeds.
Following Lloyd’s departure, ABS decamped from involvement with yachts of less than 24m (79 ft) and the world now awaits the completion of a new ISO Standard. It is understood that it will be based generally on ABS.
Anyway, having estimated the side force, the next steps would be to determine the bending moments, then onwards to establish what size of stock would be up to the task. But this is a process too grindingly tedious to pursue – most designers use a spreadsheet, hardly riveting reading. Instead, let’s move towards the source of all those loads.
Beating to windward is thought to be the hardest point of sailing. There’s lots of spray, the boat heels abominably and the crew takes a hammering. The forces acting on the sails, spars and rigging can be savage and these are opposed by the keel and rudder below the waterline.
But, consider this: despite all the apparent drama, the boat’s speed will be low – maybe no more than three quarters maximum hull speed. It follows, therefore, that since the rate of waterflow over the rudder is moderate, according to all established methods of computation the side force will be moderate as well. Despite being counter-intuitive, the fact is that rudders are relatively at peace upwind and more stressed when running or broad reaching, as you might expect in a trade wind crossing. And it’s quite easy to understand why.
The Greek work for wheel -‘trochus’ -lends its meaning to ‘trochoidal wave theory’, first advanced in 1862 by William Rankine. It describes a mechanism in which each molecule within a deep water wave follows an almost perfect circle, returning to pretty much its original position once the wave has passed. The diameter of the ‘wheel’ followed by the outermost molecules is equal to the wave height, and the time taken for it to turn a full circle will be the wave’s period – more commonly expressed as the time in seconds between two consecutive wave crests passing a fixed point. Of course, the whole body of water isn’t moving at the speed of the wave train. Waves are the manifestation of the advance of energy, not the horizontal flow of the sea. The orbital action is localized for all intents and purposes. But that doesn’t reduce its significance to sailors who can be dramatically affected by the fact that the water on each wave’s surface moves in different directions and velocities depending on which part of the wave you occupy.
Let’s take the case of a boat running before the trades towards the West Indies. It is December – a good time to cross. The average wave height in that region for that month is about 1.5m (5 ft) but ‘averages’ are simply that, and waves of twice the average and more are common.
So, our boat is keeping up a good lick under twin head sails. It’s exhilarating sailing. She rises to the top of a particularly large wave and the surface flow at the crest propels her forward over the lip. And, in case you think such a boost would be trivial, the maximum orbital current for a 3m wave with a period of six seconds would be nearly 4 knots. At this point, with the boat having first slowed, climbing the wave, she enters the orbital current and the helm goes light. The input velocity has fallen to almost zero, the rudder is ineffective and remains so as our boat starts its decent down the wave face. The helmsman does what he can but yaws off track. Speed increases. The boost from the surface flow, plus the impetus provided by gravity – very considerable if the wave is steep – is now augmenting the boat’s own speed. A lightish 12m (40ft) monohull could be well into double figures of knots by the time it reaches the trough when – lo and behold – it finds the orbital current rushing up to meet it – at four knots, to take our specimen wave.
By now those formulaic estimations of Vs based on hull speed plus a bit are starting to look pathetic. In those brief moments before the counter current again slows the boat, the inflow velocity peaks alarmingly. But there could be worse to come, for this is the classic broach situation. Reaching the trough slightly askew, the bow now meets with strong resistance while the stern is still on a charge. The helmsman, naturally, senses he’s losing it and puts the wheel hard over in an attempt to avoid the inevitable. He fails. Instinctive though his actions are, this is not good news.
To understand why, we have to think a bit about foils. Symmetrical foils – such as rudders – obtain their lift my maintaining an angle of incidence with the fluid in which they’re acting – seawater in our case. If the angle of incidence is increased gradually, both lift and drag slowly build to the point where the foil stalls – that’s to say, the flow breaks down on the low pressure side of the foil. This is a comparatively mild event, usually with no serious consequences. However, if the angle of incidence is increased rapidly – as in putting a rudder hard over – the foil can experience what’s known as a ‘dynamic stall’ where the speed of the event almost seems to take it by surprise. This creates a momentary spike of lift, well above that generated in the steady state, before the flow breaks down as before.
Are autopilots guilty?
It’s also been suggested that modern autopilots might have a hand in our rudder problems. The argument goes that, despite sophisticated control algorithms, they have no anticipatory capabilities. Whereas, for example, a skilled helm would see a monster wave ahead and could prepare to mitigate its effects, the autopilot would be oblivious until its sensors recorded a crisis, whereupon its tiny brain would go into overdrive to put matters right. It’s also possible that autopilots simply ‘work’ the rudder more. Even the best helmsman don’t correct for every swerve off course whereas autopilots are constantly vigilant.
The majority of stocks are made of stainless steel but some builders favour aluminum. Some Swans and Bénéteaus use composite stocks and doubtless there are others that do likewise. But the choice of material is catered for in the formulae. When calculating stock diameter, the materials ‘minimum tensile strength’ or the ‘minimum yield strength’ is used, whichever is the lesser. Safety factors are built in but these are based on their structural characteristics when new.
Unfortunately, subjecting a material to repeated load cycles will weaken it with time, and will do so all the more rapidly if those loads approach its ultimate strength. In practical terms this means that a marginally spec’ed stock will fail before a stronger one and that all of them will weaken with age. Corrosion can also be a problem, as you can see on page 25.
If this catalogue of events seems alarmist, then I must admit it is. But it serves to demonstrate how a combination of factors can conspire to overload accepted practices. At least Lloyd’s methods of estimating side loads allows the designer to specify the value of Vs but the ABS formula – and, presumably the ISO standard that will replace it – decides this for itself rather simplistic way, perhaps without full regard to all that might befall. Yes, of course a formula can be tweaked to err grossly on the pessimistic side, but that’s only possible if all the issues are fully understood.
Before we move on to what can be done about all this, Tony Marchaj quoted the chairman of a branch of Britain’s Institute for Structural Engineers, who seems unusually wise in that respect. He said: ‘Structural engineering is the art of modeling materials we do not wholly understand into shapes we cannot precisely analyse as to withstand forces we cannot properly assess in such a way that the public at large has no reason to suspect the extent of our ignorance.’
Understanding the problems is one thing; doing something about them, quite another. Since most of the responsibility rests with the designers and builders, it leaves us as little more than passive bystanders. But at least foreknowledge allows us to make informed choices.
Given that heavier, slower boats with their greater inertia are less prone to the sort of breakaway speeds demonstrated by their flightier brethren, could they be the better choice? Well, there’s certainly a body of opinion that would say so, but that seems to fly in the face of design development and – what’s more – you would have to pay for all the extra material that goes into them.
Spade or skeg?
Then there’s the issue of spade rudders. Undoubtedly, these are the most vulnerable, so should we choose skeg-hung rudders? Here I think there’s a stronger case. Manufacturers love spades because their efficient, inexpensive to make and easy to fit. My own preference is for partial skegs, which add valuable support, allow the rudder to be semi-balanced and also improve directional stability – again, alas, at more expense and with some loss of nimbleness when maneuvering.
But no boat can be made entirely immune, so maybe we should think about back-up systems. Cobbled together jury rigs are a possibility – drogues and the like among them – but I wonder how many of these notions have been tested at sea and how many are just theoretical. Lying helplessly beam-on to a large swell is no time to be scratching one’s head.
One way forward would be to fit wind-vane self-steering gear that can be adapted for emergency steering – several types are available. The Hydrovane with its auxiliary rudder is one example and Scanmar’s Monitor pendulum servo gear is another – once converted to its manual steering mode by replacing the pendulum with the ‘M-rud’ blade. Indeed, Scanmar have gone further. Recognizing a growing concern among offshore sailors, they have recently introduced their ‘SOS Rudder” – a dedicated emergency rudder that mounts on the transom and can be hinged up out of the way until needed.
Is your’s too old?
But it could be that it’s just unreasonable to expect our rudders to soldier on for ever. The Excalibur 36 mentioned earlier had given 30 years of staunch service before the stock let go. Time had simply taken its toll. We all know that metal fatigue limits the life of our standing rigging; most of us are reconciled to replacing it periodically. So why not our rudder stocks?
At the end of the day, it will all be down to personal choice. The risk of losing your rudder isn’t high and is probably a risk worth taking for the sort of inshore cruising many of us do. But for those proceeding offshore, where self reliance is everything, it’s certainly worth a pause for thought.
Sailing Downwind? Set a Whisker Pole – By Andrew Burton
Take some time to rig the necessary control lines and you’ll get better performance on the downwind leg.
Many cruisers don’t carry a pole because they feel it’s difficult to set up and use.
NO MATTER WHETHER THE JOURNEY is a trade-wind romp across a thousand miles of ocean or a daysail up the bay, a cruising boat that’s not equipped with a whisker pole loses the ability to sail efficiently when the destination is dead downwind.
In any chop or waves, it’s difficult, if not impossible, to wing the jib out unsupported, and with the wind farther aft than about 140-degrees apparent, the main will blanket the Jib or genoa. That’s a total of about 80 degrees of apparent wind that you can’t use efficiently without a pole. But many cruisers don’t carry a pole because they feel it’s difficult to set up and use. That’s not the case if you follow a few simple steps. Let’s go through what it takes to wing out your jib with a pole.
Your equipment needs? A topping lift to raise the pole to the correct height, and a downhaul, or foreguy, to pull the pole down and forward. The foreguy runs from the outer end of the pole through a block near the bow and back to a winch or cleat in the cockpit. Along with the jib sheet, these two controls stabilize the pole so it won’t move after it’s set. You can also set up an afterguy, a line from the end of the pole to the cockpit, to pull the pole back and hold it steady before sheeting the jib home. I always set the pole with the jaws up, but that’s not critical.
STEPS TO SETTING THE POLE
- While the pole is still stowed on deck, attach the topping lift and foreguy. Take up the slack in the topping lift. Leave a few feet of slack in the foreguy. If you’re already sailing deep off the wind, the jib at this point could be furled.
- Release the pole from its chocks. Place the windward jib sheet in the upturned jaws. If you’re sailing on the wind, put the lazy sheet into the jaws.
- Now you’re ready to set the pole. Lift the forward end so it’s above the pulpit and lifeline and push it forward, making sure that it’s on the windward side of the forestay, The tight topping lift will help to keep it off the deck. Then attach the inboard end to the mast.
- Adjust the outboard and inboard ends of the pole so they’re the same height as the jib clew.
- If you’re already sailing close to dead downwind, make sure there’s plenty of slack in the foreguy, then unfurl the jib and sheet it home, being careful that you stop winching before the pole touches the shrouds. If you’re sailing on the wind, turn downwind; when the breeze is nearly dead behind the boat, jibe the jib to the windward side and sheet it in, as above.
- Now pull the foreguy tight; this sets you up to run wing and wing. Using this setup, you should be able to sail with the wind as far forward as 130grees apparent, although you may need to ease the pole forward a bit and furl some of your jib. Once the sail is set, watch that your jib sheet and foreguy don’t chafe on the lifelines; relead them if they do. To stow the pole, simply reverse the process.