SELF STEERING FOR YACHTS
Basic principles of four types by Paul
I have seen
and often modified wind vane controlled self steering gears that have
been owner built. Although well constructed many of these units did not
work well, This was because there had been little understanding of the
basic principles that must be adhered to. In this paper I set out the
basic dimensions and geometry of the four most common types built by the
home constructor, these are:- Vertical vane to trim tab, Horizontal vane
to trim tab, Auxiliary rudder and also the Pendulum servo. This will
guide the owner to construct a wind vane self steering unit that can
work as well as any proprietary model.
that all four methods are examined as there are common rules that apply
to all types and after a little consideration, it may be found that one
of the simpler methods is best for your yacht.
are clearer if downloaded to your computer and opened in Windows picture
and fax viewer.
all types of self steering gears manufactured, from the simple wind vane
direct to tiller type, to the complicated wind vane to pendulum servo
which then drives an auxiliary rudder. It is not only the complicated
linkage that gives one a headache but it is also the price tags that run
into thousands that can hurt.
sailor will therefore be asking himself:- What type will suit my yacht?
How much will it cost? Can I make one for myself? Will it work in a
to these questions are :-
sailor with basic practical skills can make one for themselves. They
can successfully be built entirely from wood, simply using bolts and
dinghy fittings as pivots. With simple metal working tools and a welder,
an extremely strong low maintenance system can be built. One of the
secrets is to keep it as simple as possible.
Yes, it will
work well so long as a few basic principles are adhered to. A wind vane
does not steer a compass course quite as accurately as an electronic
autopilot, but even in awkward conditions such as when running in a
disturbed sea, should only allow the yacht to wander 10 or 15 degrees
maximum. Some people worry about this, but, if you actually work out how
much this adds to a passage you will see that it is negligible. An
advantage of wind vane controlled steering gears over electronic types,
is that on a long passage once the sails are set, the wind vane will
follow any small changes in wind direction. This means that it is easier
to keep the yacht sailing at it's optimum without constantly re-trimming
The cost can
be virtually nothing if scrap materials are used, or, if all the
materials are bought new should only cost a fraction (Perhaps 5%) of a
If you are
buying or building a new yacht on which you intend to fit a wind vane
steering gear then consider the design of the yacht carefully. On any
short handed yacht such as one sailed by a family, the ability to easily
steer itself is very important. This frees the crew from the tyranny of
having to helm for long periods. If a wind vane system is used rather
than relying on an electronic type then running the engine for battery
charging will be kept to a minimum.
wind vane self steering unit will steer in winds as low as force 2 when
the vessel is likely to start motoring anyway. This means that the only
time that an electronic self steering system is necessary, is when the
winds are light. Under these conditions an electronic unit, considerably
smaller than normal will suffice.
broadly fall into two categories, those with inboard rudders and those
with transom hung rudders. On a yacht with an inboard rudder there are
three basic choices.
If she is
very small and exceptionally well mannered then a simple wind
vane to tiller may work, but they are seldom successful so I will
be ignoring them.
The other two
choices are pendulum servo to drive the main rudder, or one of the
auxiliary rudder types.
A yacht with
a transom hung rudder may use any of these steering gears. However, on a
yacht of this type, using any system other than a trim tab on the main
rudder, appears to be an unnecessary
available, your own expertise and your tools will determine the exact
design. The problems that occur with many self made gears, are normally
caused because the builder did not understand the basic principles.
These are vane, trim tab, pendulum and auxiliary rudder size. The
geometry of the parts and the little understood principle of 'feed
READ ON, you don't need to understand any
of them!! If you are an engineer and want an in depth understanding
there are several books available which explain it all in great detail.
Most yachtsmen don't require this, so in this paper I simply describe
the systems that a home builder can produce giving sizes and
measurements, without delving deeply into the design principles.
quoted, are for average 30 to 40 foot yachts and can be increased or
decreased as necessary. The geometry must be closely followed for them
system to build is the first (design 1) increasing in difficulty until
finally the last (design 4) is the most difficult.
TEXT SHOULD BE READ WITH THE DRAWINGS ALONGSIDE TO MAKE THINGS CLEAR
ON THE THUMBNAIL FOR A PRINTABLE PICTURE
PIVOTED VANE TO TRIM TAB (Design 1)
This is a
very simple gear to construct and control. The yacht will wander a
little more than if a horizontally pivoted blade is used, but it is more
than acceptable and is favoured by many long term ocean voyagers because
of it's simplicity and ease of use.
should transfer one degree of vane movement into one degree of trim tab
It should act
80% forward of the distance between trim tab pintles and rudder pintles.
This is very important to provide 'feed back', which stops the system
over steering. (This actually means that when 15 degrees of trim tab is
applied, the rudder will move 15 degrees and at this point the rudder
and trim tab will realign, so exerting no more force). If the two sets
of pintles are not parallel, (i.e. if a line extended vertically through
both sets of pintles will meet at some point above the yacht) then the
linkage should act 80% forward of the aft pintle line, wherever the trim
tab tiller is fitted.
The air vane
should be as large as reasonable. A shaped blade cut from 4' by 2' by
4mm (3/16") plywood is often used, (This size of blade will also suit
considerably larger yachts). The centre of this should be 18" behind the
pivot point. On the opposite side of the pivot there must be a weight to
balance the vane around its axis. This means that if the blade is laid
horizontally on one side, only supported by the pivot point, the weight
shown in the drawing exactly balances the weight of the blade. This
stops the blade swinging due to gravity as the yacht rolls.
tube that carries the air blade will need to have a diameter of at
least one inch to be strong enough and this can be considerably greater
without adversely affecting the performance, due to inertia.
A method of
course setting between the vane and the rest of the linkage must be
provided. There are several methods of achieving this but one of the
simplest is to use two discs that can be locked together to start the
system. They can either be locked by using holes around the edge that a
pin drops into, or a type of 'G' cramp can be employed. With the locking
pin removed or the clamp released the vane is free to 'weathercock' into
the wind when the system is not in use. As it is unlikely that the
linkage will be able to accommodate the large movements of the rudder
during manoeuvring, there needs to be a method of disconnecting the
linkage from the trim tab tiller. This is not only the easiest steering
gear to construct, but is also the easiest to operate.
The trim tab
will be 20% or 1/5 of the total rudder chord. This means that if the
rudder measures 25 inches from front to rear, the trim tab will be 5
inches. It is best if this is not an addition to an existing rudder, as
this will make the rudder oversize and difficult to control. If an
existing rudder is being modified, a section of the trailing edge should
be removed and either re-used as the trim tab or a new trim tab
constructed. The trim tab stock can be made from 3/4 inch stainless bar
with lugs welded on. The tab is finished by having shaped plywood
sandwich the lugs.
If you are
building a new yacht consider partially balancing the rudder by 10 or 15
percent, ( I now use roughly 18%) as this helps it to work easier and is
now favoured by many modern designers. The maximum balance used on a
sailing yacht must not exceed 20%. It may well be worth modifying an
existing rudder to improve the performance after checking with a yacht
A method of
locking the trim tab in line with the rest of the rudder must be
provided. This is for when you are hand steering and reversing. A drop
in pin or locking clamp can be employed which must lock the trim tab
exactly in line with the forward part of the rudder. When locked, the
trim tab will need to be accurately aligned with the main part of the
rudder, otherwise the trim tab will constantly try to apply helm. Also
this locking device must be strong as the loads when reversing can be
reasonably easy to link an inexpensive tiller type electronic self
steering to a trim tab. This would give accurate steering with minimal
power drain on the batteries.
I want to
mention the bearings at this early stage, as apart from the design
principles, sticky bearings can spoil an otherwise perfect gear. In fact
many of the problems experienced with expensive manufactured steering
systems after a few years, is caused by debris build up in the bearings
and bushes making things tight.
of each part of a self steering gear is very small. The only part that
has to go full circle is the course setting disk which doesn't need any
I never use
any ball or roller bearings in my steering gears. I have found that
simple metal to metal, or better, metal to nylon bushes are more than
When I built
my first steering gear, which was a pendulum servo type, I originally
made all the bearings a good fit, but I found that after a while the
movement tended to stick, leading to erratic course keeping.
across the Atlantic I dismantled it and ran a drill through all the
bearings, making them all quite sloppy. It worked like magic! The water
flowing past the blade caused the whole unit to gently vibrate, stopping
any tendency for the bearings to stick even in light winds.
Since then I
have often heard people say that as their bought units get older and
more worn they seem to work better. Now when I build a unit I always
make sure that there is plenty of 'slop' in the bushes. Because there is
little movement between parts it takes tens of thousands of miles to
cause any appreciable wear.
VANE TO TRIM TAB (Design 2)
This type is
a little more complicated to design, construct and use. The advantages
are that it will steer a slightly more accurate course, works a little
better in light winds and needs a smaller vane.
The air vane
needs to be 1 foot wide by 4 feet high and cut from 4mm ply. The blade
pivot can be fixed horizontally or can be set at an angle of up to 15
degrees to allow the blade to trail away from the wind. It is
advantageous if the blade can be adjusted to either be more upright for
light winds, or be angled backwards for stronger winds. This can be
achieved in two ways. The first and easiest is to have the air blade
attached with one bolt and 'wing' nut at its base. This allows it to be
adjusted. The second and very complicated method (not recommended) is to
construct the linkage so that the whole pivot assembly is adjustable.
length of 1/2 inch stainless bar running in plastic bushes, a set of
dinghy rudder pintles, and the front wheel hub and bearings from a pedal
cycle have all been used successfully as the pivot.
The air vane
must be able to ' flop over ' 45 degrees and there must be a counter
weight just heavy enough to bring it back to the vertical. It is
advantageous if the balance weight can be adjusted up and down by a few
inches to increase or decrease its effect on the vane in differing wind
A method of
rotating the blade must be provided for course setting. This can easily
be made by mounting the blade on a disk with a hole in the centre. The
disk will rotate on a framework and will need a method of fixing or
clamping once on course. This can either be a series of holes with a
drop in pin or a clamp.
A lever on
the side of the blade will operate a push / pull rod which transfers the
movement through a bell crank to the trim tab.
The air vane
must move 45 degrees which must move the trim tab 15 to 18 degrees.
(Approx. 3 to 1) It should act 80% forward of the distance between trim
tab and rudder pintles. This provides the feed back to stop
A method of
disconnecting the vane from the trim tab must be provided. This is to
stop the rudder operating the vane when it is not in use, as this will
break the system.
steering and reversing the trim tab must be securely locked in line with
the main rudder.
RUDDER WITH TRIM TAB (Design 3)
transom hung rudder and trim tab, which is often preferred by many long
distance sailors as there is very little load on any of the parts, must
come the auxiliary rudder.
advantages of this system are that like the transom hung rudder it is
acting at the extreme rear of the yacht and so has great leverage. It is
a totally independent system and the main rudder and steering gear are
locked and therefore are not being worn out.
are beginning to become more complicated to design, build and use. This
is because we also have to construct a new rudder with pintles and a
very strong mounting.
of vane may be used, but for the sake of simplicity it is shown in the
drawings with a vertically pivoted blade.
principles of vane to trim tab linkage remain the same. But as we are
now dealing with a semi balanced rudder it may be possible to reduce the
size of the vane slightly. The best thing is to try it with the sizes
quoted, if it proves too sensitive it is much easier to cut the wind
vane down, than it is to add extra area.
The vane must
turn the trim tab at a point 80% forward of the distance between the
trim tab and rudder pintles, to provide feedback and stop over-steering.
A method of
locking the trim tab to the rudder and of locking the rudder
centrally must be provided. This is best achieved by fitting tillers to
both the trim tab and the auxiliary rudder, which can be locked in
must be very strongly mounted onto the transom. The sideways loads can
be enormous when the yacht is in big waves.
stock will need to be at least 1 1/2 inches thick stainless steel to
take these loads. I have shown an alternative rudder which is probably
easier to make and will be stronger if the whole rudder is made by
gluing sheets of plywood together. This would also have the advantage of
being able to be lifted off its pintles for storing or working on.
should be immersed by around 32 inches below the load water line. It
should also extend above the LWL to cater for the yachts stern wave. A
total blade depth of 40 inches is about right.
should be 3 inches thick at its widest point, which must be just behind
the pintle line. The leading edge will be rounded off and the rest of
the blade including trim tab will taper to about 1/2 inch thick at the
rudder will have a 15 inch chord. The balance area forward of the
pintles or stock is 3 inches ( 20% ) and the trim tab is also 3 inches (
type of self steering the yacht is put on course, the main rudder is
locked centrally, then the self steering is engaged and adjusted to just
balance the forces trying to push the yacht off course.
SERVO (Design 4)
If you decide
to opt for a pendulum servo type then you have chosen not only the most
complicated gear, but also the one that is often considered to be the
most powerful. So if you have a yacht that is heavy to steer, with an
inboard rudder, perhaps this is the one for you.
servo takes its direction from the wind using either the vertical or
horizontal air blades already described. This movement is used to twist
a blade suspended over the stern. Depending which way it twists it will
move either to port or starboard, rotating around its attachment point.
This movement is transferred to the main rudder by ropes, steering the
yacht back on course.
blade will have a chord of 5 inches. It will be immersed 30 inches below
the LWL, the total length will be designed to suit the yacht, depending
on the height of the transom.
will have a 20% balance. This means that 1 inch will be forward of the
plywood is a good material and should be around 1 1/2 inches thick above
the LWL and can be tapered to 1 inch at its end if you wish. It should
have a rounded leading edge, with its thickest point 1 inch back, then
gently taper to the trailing edge.
horizontally pivoted air blade is best with this system as it is more
accurate and gives greater deflection for small changes in course. A
deflection of 45 degrees of the air blade must rotate the pendulum by 20
degrees. This will act on the aft edge of the pendulum about 5 inches
above the pendulum axis and 6 inches behind the pendulum pintles to
provide feedback. ( In this case feedback means that once the pendulum
has swung 30 degrees it will realign with the water flow and exert no
more force.) The pendulum must be able to swing 30 degrees, but a little
more is better so that it isn't constantly hitting any stops.
carrier shown in the drawing needs to be very strong. One inch stainless
bar, such as an old propeller shaft, or 1 1/4 inch stainless tube should
be considered as having the minimum strength. Alternatively a pendulum
carrier can be constructed from 2 by 2 inch timber or cut out from
plywood and then use the gudgeons and pintles from a small cruiser or
dinghy rudder as the pivots, (excess weight in this part of the system
has no adverse effect).
It rotates on
a horizontal axis on the centre-line of the yacht. (Or as close as
practical). The pendulum blade must be at 90 degrees to the waterline or
angled a few degrees back at the base away from the flow of the water,
(trailing). If the pendulum blade is angled forward at the bottom it
results in uncontrollable oversteer. As the aft deck of many yachts
slopes down towards the transom the aft mounting of the servo carrier
may need packing to correct this angle.
go to the yachts tiller attach 13 to 15 inches above the axis of the
pendulum. These tiller ropes must be very flexible 6mm dia. (multi-plat
rope is best). The ropes must be guided by very free running blocks and
there must be minimal friction in the system.
blocks need to have strong mountings as this system can exert very high
attach to the tiller approximately 15 inches forward of the rudder
pintles. A method of releasing them quickly must be provided, for when
you need to steer by hand. This can be achieved by attaching the ropes
to the tiller with 'jam' cleats.
On a yacht
with wheel steering many people prefer to attach these ropes to a short
tiller provided for just this purpose. Where the yacht has no tiller,
the steering ropes will need to operate on the ships wheel. This is
achieved by fitting a rope drum to the middle of the wheel and the
steering ropes then normally need at least two turns around the drum.
The ropes can both be led through guide blocks to one side of the
cockpit, which helps keep the cockpit clear. The diameter of the drum
normally needs to be around 7 to 9 inches for correct control. A method
of releasing the drive from the drum to the wheel is needed. This can be
achieved by constructing the drum as two discs. One is permanently
attached to the wheel and the other rotates on a central bolt. To
mechanically join them use a 'dog' clutch which is engaged by tightening
the central bolt. Or alternatively a simple pin can be used to lock the
drum to the wheel.
at the various types of self steering, there are some points regarding
the linkages and general design that need to be considered.
The rudder of
a yacht is a compromise. It needs to be large enough for manoeuvring in
harbours etc. Yet when the yacht is sailing a much smaller rudder is all
that is required. This means that when the yacht is in a harbour around
40 degrees of movement is needed but when sailing a maximum of 15
degrees is all that is required. This large movement needed when
manoeuvring generally means that any system that uses a trim tab on the
main rudder will need to have a method of being disconnected from the
trim tab tiller to accommodate these large movements.
horizontally pivoted vanes the linkage must be capable of being
disconnected from the trim tab tiller. This can be achieved by having
either the bell crank or the fork slide to disconnect one from the
The air blade
and the connecting linkage of any type of self steering needs to be kept
as light as possible, consistent with adequate strength. The reason is
that as it becomes heavier it tends to respond slower due to inertia.
The air blade will be strong enough if made from 4mm ply, don't apply
too much paint as this dramatically increases the weight.
rods can be made from 1/2 inch dowel or aluminium tube and bell cranks
can be made from 6mm aluminium or plywood.
principles apply to all yachts, but yachts are all different so it is
wise to build in a small margin for adjustment of the system. This can
simply be done by drilling extra holes on each side of a pivot point, to
adjust the length of a lever.
system is in use you may find that your yacht responds too quickly or
too slowly, showing that the system needs gearing up or down slightly.
With a small amount of adjustment built in this is easily
achieved. In practice it has been found that different yachts only need
the linkage to alter the amount of movement of the trim tab or pendulum
by plus or minus 2 or 3 degrees maximum. If a system needs to deviate
from the stated movements by much more than this, then something is
wrong and the 'movements' should be checked.
has shown that using Bowden (push/pull) cables does not normally work
well. They tend to stick, leading to erratic steering.
acceptable for the wind vane to be set to one side of the yachts centre
line. However when going to windward an offset vane will be disturbed by
the air leaving the rear of the mainsail more on one tack than on the
The air vane
will need to be several feet above the deck to place it in relatively
undisturbed air. Do not place it too high, such as on top of an aft
gantry, as it can then become excessively affected when the yacht
show a pin and fork linkage to connect the bell crank to the trim tab
tiller. Although this appears to be a very crude system, it does work
well and on examination has been found to show no appreciable wear after
30,000 miles, which actually represents a complete circumnavigation of
bars or tubes that rotate and need to move freely such as the vertical
wind vane, trim tab and rudder stocks, should sit on a pin end or ball
in a cup to reduce friction and allow them to rotate easily. The bushes
in the centre of rotating tubes or bars should be shaped internally to
have the minimum area of contact and thus reduce friction.
Each of these
types of gears have been successfully built by home builders and have
controlled yachts in varying conditions from near calms to severe storms
without any assistance from the crew. This has led to many short handed
and family crews making remarkable passages that would not have been
thought possible until recently.
understanding of the principles involved is not necessary. So long as it
is kept simple and satisfies the basic principals that have been
outlined you can build your own to suit your boat and your pocket.
MY PERSONAL CHOICE
many thousands of miles. Using many types of wind vane steering, I
became convinced that the trim tab system was the best. If the yacht was
suitable. One of the main reasons for this choice is that there is very
little strain on any of the equipment. On my last 32 foot yacht, the
trim tab system actually steered us downwind in 60 knots and big seas
with very little strain on the gear. I did nervously sit there ready to
take over but never needed to.
when the Fay range of yachts from 32 to 44ft were designed they all had
transom hung rudders. This makes using a trim tab on the main rudder
easy. If I had any other type of yacht without a transom mounted rudder,
I would endeavour to use an auxiliary rudder with a trim tab. On my
latest yacht Ti Gitu which has wheel steering we use a trim tab on the
main rudder. On short passages the trim tab overcomes the friction of
the chain and cable type steering. For long ocean passages the quadrant
on the rudder post, can be disconnected from the steering. This allows
the wind vane to work easier and saves wear on the wheel steering gear.
small tiller autopilot to a trim tab makes very inexpensive electronic
steering possible on even large yachts.
Here at Fay
Marine we are dedicated to increasing the possibilities and pleasure
that can be achieved from long distance sailing and it is our deepest
hope that the information supplied in our plans and design papers will
help more sailors to achieve their dreams.
© Paul Fay
are for the private individual or club to construct a steering unit.
Permission must be obtained from Paul Fay to use these instructions to