Fratcher - Marine Engineer/Captain
Autopilots, known affectionately as “Otto,” or “my
silent crew,” or even “dial a ride,” have been
around for over fifty years. Now considered basic safety gear,
the ability of the crew to hold a course without the need for
a crewmember manning the windswept helm has made the autopilot
standard equipment on most offshore yachts and serious fishing
Autopilots allow short handed crew to single hand when needed
while single handed sailors can catch short bursts of sleep. Racing
teams have found autopilots have a better record of holding course
than a tired helmsman, and fishermen can concentrate on reeling
in the catch while the launch lumbers slowly along guided intelligently,
preventing a line tangle.
Autopilots fall in to three basic categories-
• Portable, stand alone, above deck units
• Below deck systems
Let’s look at each system in turn
Above deck autopilots
Smaller yachts and launches (up to 40ft) can often survive on
a simple, stand alone electric autopilot bought from a local chandlery.
These industrial work horses have come a long way in the last
twenty years since the first “Tiller Pilot” arrived
on the market. Made for both wheel and tiller steered boats, they
are dependable and energy efficient. With a starting cost under
1000NZD it’s no wonder most every small yacht has adopted
and often named an electric self steering device.
Above deck autopilots are built waterproof, with a thrust of
over 80kg, and self learning. In other words a modern autopilot
will quickly learn the response needed to steer each individual
vessel preventing over correction and slewing.
New units contain an internal fluxgate compass, and can be mounted
port or starboard depending on available space. A few extra wires
and they interface to a GPS or wind monitor, all for an electrical
draw of an amp or two.
Most units have one touch “lock on compass course”
or GPS waypoint tracking. Push two buttons at the same time and
the boat tacks leaving a small crew free to handle sheet lines
and winches. Higher quality autopilots have “man overboard
retrieval” programs and downloadable data packs.
Handheld remote controls allow the crew to move around the boat
while adjusting course, dodging obstacles or even holding an accurate
course while reefing.
Avobe Deck Wheelpilots
Above deck wheelpilots are available for smaller yachts and
launches with the same functions as the tillerpilots, they just
couple directly to the boat’s wheel instead of the tiller.
Installation is quick and can be performed by most DIY’s
in a day. Keep in mind most small wheelpilots are belt driven
or direct coupled to the wheel. This means the wheel must turn
perfectly true. Even a small amount of wobble in the wheel or
a slightly bent steering shaft will quickly break the belt or
ruin the drive gears in a direct coupled wheelpilot system.
Note-Adding a Wheelpilots to an old steering system demands a
complete inspection of all steering components. Wheelpilots can
develop tremendous force and don’t have “intuition”
if they are over stressing any part of the steering system. Old
bushings, cables, and support arms can quickly wear with the addition
of a new wheelpilot.
Below deck autopilot
Below deck autopilots are the all weather answer to boats over
40ft. The components are split into four sections-
• Drive unit
• CPU or “brain”
• Control head
Let’s look at each component in turn.
The drive unit is the working end of the autopilot. It does
the actual work of moving the rudder. The drive is typically linear,
or push/pull of mechanical or hydraulic style and can exert incredible
force. Consider the power on the tiller of a medium sized yacht.
If you choked up the tiller till you were just a half meter from
the rudder stock it would be near impossible to control the helm
due to the high loads involved. This is a basic example of the
forces involved in trying to steer a large yacht with a linear
drive and why the installation must be thought out and robust.
The most often overlooked aspect of a drive unit installation
is the securing method of the drive base to the boat. Any mounting
flange movement will cause “wallowing” of the bolts
leading to an early failure.
Tip-Most drive units come with holes to accommodate
four large bolts. To increase the strength consider building a
stopping block, or lip around the mounting flange so the auto
pilot flange has something to butt against.
During installation it is important to check that the drive unit
has a small amount of excess available movement past the swing
of the steering quadrant. We don’t want the drive to act
as a rudder stop.
The connection to the rudderstock can be through the existing
steering quadrant, or better is a separate, keyed arm attached
to the rudder stock. This second arm gives a true backup steering
system for the yacht.
The load on an autopilot drive can be high especially during
rough weather. While the average current draw might be three amps,
the drive motor uses short bursts of high current that average
to a three amp draw, thus large wire should be used to feed the
drive unit motor. Check the wire size charts to be sure of a maximum
3% voltage drop during the high intermittent loads. Remember-low
voltage increases amp draw, shortening the life of the drive motor.
The autopilot drive should have its own breaker (not a fuse)
direct to a reliable power source such as the main power bar in
the electrical panel. Resist the urge to tap into an existing
power source such as the spotlight etc.
Hydraulic drive units
Hydraulic power packs are simple, robust and often used in larger
autopilot installations or outboards. Yachts with existing hydraulic
steering systems may simply add a hydraulic power pack T’ed
into the existing hoses. If the vessel has an existing conventional
steering system going hydraulic means adding a balanced steering
cylinder in addition to the powerpack.
The forces can be regulated through cylinder size and system
pressure. Like a linear drive unit, hydraulic cylinders need stout
mounting and an even stronger connection to the rudder shaft.
Hydraulic systems have very little give and don’t tend to
back feed. This means the rudderstock, quadrant and connections
all must be able to support the full load of a breaking wave or
Central processing unit (The brain)
The central processing unit (CPU) of the auto pilot is often
considered the brain. Modern central processing units interface
with GPS and NMEA signals and have learning programs that quickly
adjust to sea state and boat movement.
Note-While wind and compass data can be gained
through the use of NMEA, or the existing wind instruments, most
NMEA inputs take a few seconds to cycle through the NMEA code
thus the input is not fast enough for auto pilot response. For
this reason it’s important the autopilot CPU have its own
compass and wind sensors.
In the old days the CPU simply monitored the course and turned
the helm to make corrections. This used a lot of power and caused
the boat to zigzag up along the course line. Today the CPU can
be programmed for the type of boat, speed, acceleration, and type
of use, IE fishing, racing etc.
Modern CPU’s even sense lateral movement to know when the
boat is “slewing” down a wave. This is done through
a new gyro style sensor based on a low cost sensor similar to
the anti shake feature used in most video cameras.
The CPU should be mounted below decks in a clean, dry, cool area.
The CPU can build up considerable heat so airflow is a must. Drip
loops should be built into the wire ways to prevent water following
a wire into the circuit board.
Rudder angle indicator
The rudder angle indicator is device that tells the computer
where the rudder is pointed. It also can give an idea of the speed
the rudder is reacting to the commands. The rudder angle indicator
is mounted next to the drive unit with its own connection rod
to the quadrant and electrical cable to the control head.
The rudder angle indicator is often considered a weak link in
an autopilot installation. They tend to be fragile and can be
ruined by an errant foot or a careless line tossed over them.
Most professional installers build a guard over the delicate components
for long term reliability.
Some modern systems, such as Simrad, have virtual rudder angle
indicators for use on outboard motors eliminating the need for
this extra piece of gear and extra wire.
The CPU needs to know where the boat is pointed. This information
is supplied by use of a fluxgate compass. The location of the
compass should be away from metal, and electrical cables.
Note- Place placards or signs around the compass
so crew will know the location when storing supplies. Keep an
eye on the location of stored goods such as steel dive tanks and
canned food that can create, or disturb the magnetic field around
Swinging the compass is a simple task of driving the boat in
a slow circle (follow the manufacturers instructions) while the
computer makes corrections. During the swinging of the compass
be sure to have all high load devices turned on so if interference
is present the computer will attempt to compensate.
The control head is the interface between the sailor and the
autopilot. Careful thought should be applied when deciding on
the type of display to purchase. Most systems allow a variety
of displays to be used. A choice between a rotating knob, push
buttons or even a remote control can be ordered depending on the
desire of the user.
Control heads are similar to a remote helm and can be installed
in place of separate steering stations saving space and money.
Consider a second control head at the navigation station, or near
the fishing area of the boat.
Tip-A repeater unit mounted in the skipper’s bunk can provide
peace of mind. Some repeaters have NEMA outputs so the skipper
can control the helm, and monitor the wind speed all from the
comfort of his bunk.
SSB Radio Interference
SSB radios are notorious for causing interference that can cause
an autopilot to “wonder”. Many a yacht has been lost
when the skipper went below to announce his arrival to friends
over the SSB. The autopilot course was interfered with by the
radio signal causing the boat to veer off course ending a grounding.
Once the autopilot is installed test the system in open, safe
water by making a series of broadcasts on the SSB proceeding through
the various bands verifying there is no interference. If the yacht
is using a Pactor modem for email repeat the procedure on high
power through the Pactor modem.
Wind vanes are the old yacht standby. They are tough, don’t
use any electricity and can be fixed with a basic welding machine
in most outback locations.
In today’s world of high technology, and low autopilot
electrical draw, fewer yachts tend to rely on the old windvane.
A quick survey of yachts crossing the Pacific this year showed
only about 30% had even bothered to install a windvane and less
admitted to using them.
This low usage rate is for three reasons-
• A windvane’s ability to hold a course diminishes
as a yacht turns downwind, thus reducing the apparent wind speed.
Yachts sailing the “milk run” are often faced with
fluky windvane performance.
• Electric autopilots have become amazingly accurate holding
courses to within a few degrees even in rough weather. Windvanes
just can’t maintain the same high accuracy standard as modern
• Windvanes don’t work when motoring. Faced with a
limited budget and the need to motor through the calms many yachts
forgo the windvane altogether.
Some yacht crews have put the windvane into the category of “emergency
backups”. A must have, but hope we don’t have to use
piece of equipment. Still, for those who would rather “deal
with steel” instead of complicated electrical devices the
windvane is a solid, well proven self steering solution.
Windvanes work by monitoring the wind angle through an air paddle
that transfers the wind signal mechanically to a trim tab or water
paddle. Over the years dozens of different windvanes have been
brought to market, but most are either based on the “auxiliary
rudder” or “servo pendulum.”
An auxiliary rudder system is where a second rudder is bolted
to the back of the yacht and controlled through a trim tab. The
advantage is a true complete second steering system has been installed
while the disadvantage is the yacht is steering from a new rudder
location the designer never intended.
The servo pendulum is the more common type windvane encountered
and used by both Aries and Monitor brand windvanes. The yacht’s
original rudder is steered through the wheel or tiller via lines
connected to the “pendulum” that is controlled by
the wind paddle. This means small steering lines crisscross the
cockpit and must be protected against chafe or catching other
gear in the blocks.
Tip-Small amounts of pendulum movement at the
windvane can be lost due to old blocks, and worn out control lines.
Vast improvements in windvane accuracy can be made by use of modern
roller blocks and high tech, low stretch lines.
The windvane to choose depends much on the boat’s configuration.
Boats lucky enough to have an outboard rudder can simply add a
trim tab to the back of the existing rudder and control it from
a simple wind paddle, while boats with long overhangs or double
enders have more difficulty even utilizing a windvane.
Tip-Small linear drive tillerpilots can sometimes
be connected in place of the wind paddle on a windvane to steer
the yacht when motoring (or sailing in extremely light conditions),
thus allowing the smallest (and least expensive) tiller pilot
to steer a large vessel.
Adding self steering to a trailer boat has made a day of fishing
much more relaxing. Simrad autopilots have virtual feedback units
for outboard motors thus eliminating the need for a fragile rudder
Features such as the ability to follow contour lines have made
Simrad a favorite among fishermen. Simply program in the thirty
meter contour depth and begin fishing while the boat “walks
The “No Drift” mode allows the auto pilot to follow
a track line regardless of current.
Simrad is compatible with the new Volvo IPS (and Hamelton jet).
Paul from Volpower tells us the IPS is a fully integrated steering
system that does not need an external steering ram, fittings or
dash panel. It’s simply a matter of connecting the autopilot
control wires at the back of the panel and bringing up the auto
pilot function on the display.
Future of autopilot technology
One of the most difficult things for an auto pilot to deal with
is a sailboat’s quick acceleration and deceleration such
as catamarans and light displacement race boats. This is because
during a quick acceleration the apparent wind angle changes thus
the sails are suddenly not trimmed correctly. Modern autopilots
monitor both wind and a compass course to provide the information
needed to utilize each gust. In the future autopilots will steer
a better course than the best helmsmen due to ability to “learn”
the boat and not fatigue.
In the future autopilots will be able to sense when a boat is
about to surf and “waggle” the rudder for the helmsman.
They will sense when a boat has reached the bottom of the wave
and steer the correct course for the next set of waves. Much of
this improvement will be due to three dimensional gyro sensing
now in use in aircraft and aero space industries.
Some auto pilots even have programs coupled to a small transmitter
carried by the crew on watch. In the event the crewmember were
to fall overboard the CPU will head the boat into the wind and
sound an alarm. Soon such features will become standard on even
the most basic autopilots.
Autopilots installed on multihulls will be programmable to correct
the course moments before the hull flips preventing the ultimate
multihull disaster, capsizing.
In the old days they used to say “autopilots have great
muscle, but very poor eyesight.” In the coming years autopilots
will monitor the radar and chart plotter for obstructions. In
the event of a threat an alarm will sound leaving the autopilot
to make a decision of heading the boat into the wind or dodging
the coming vessel.
autopilot trouble shooting
Check hoses for cracks
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