Jefa 100 KgM autopilot linear drive unit
The Jefa linear drive is a strong and compact autopilot drive
and much more efficient than existing hydraulic and electro-mechanical
autopilot drive units (for the why and how, please see our
Q&A page). With a thrust of 400 Kgs on 250 mm centers it's much stronger than a human being (the max. output torque of
100 KgM is equivalent to 100 Kg force on the end of a 1 meter steering
tiller) and is build for 24 hours per day continuous operation with a
total weight of only 6,6 Kgs. The combination of the flat wound (pancake) electric motor with the ultra efficient
planetary gearbox results in an extremely efficient drive unit to keep
the battery charging time to the minimum. The drive can be used on boats
from 20 to 45 foot l.o.a. (or up to 100 Kgm rudder torque) equipped with a mechanical steering system that can
be back driven.
The linear drive drives the rudder via the existing tiller arm or
quadrant or via an independent tiller arm.
Please click on the picture for a
Due to the telescopic draglink, the overall dimensions are as small as
possible. The below pictures show the two outer positions and the middle
position. Please click on the pictures for a
Please note that the drive can also be mounted upside down when the
installation space requires this.
Correct mounting relative to the rudder
The above illustration shows the correct installation geometry of the
linear drive. It's very important to check if correct rudder stops are
fitted (shown in green) limiting the rudder travel to 2 x 36° (normal
for wheel steered systems). The lack of correct rudder stops will cause
the linear drive to act as travel limiter, resulting in damage to the
internal gears. The linear drive has a maximum travel of 303 mm, so
there is 4 mm of spare travel each side assuring a free run. It’s
advisable to mount the drive with the motor pointing sideways and not up
or downwards (like in above illustration) as this position generates
less friction and also less ware in time.
On most cable steered boats the rudder travel is 2 x 40° and on some
tiller steered boats the rudder angle is even bigger. Please revert to
the table at the right for the correct pin centres and offset distance
in these cases. Please note that the maximum achievable rudder torque
will be lower when shorter centres are used. For example: The maximum
rudder torque for the 50° setup will be 192/250*100= 77 KgM in stead of
the 100 KgM with the 36° setup.
Some mounting possibilities:
The above illustration shows how a rack and pinion system can be
combined with the linear drive on one tiller lever. This solution saves
money and space.
The linear drive can point port or starboard, in front or aft of the
The above animation shows the setup of the linear drive. The drive can be separated in
4 main parts: The electric motor, the two step planetary gearbox,
electro-magnetic clutch and the final spur reduction gearbox. The Jefa
linear drive has multiple
advantages over existing integrated drive units. These advantages will
be explained per section of the drive:
Electric Motor: The flat wound electric motor
(pancake motor) used in the Jefa
drive units is carefully selected for this application. Pancake motors
have multiple advantages over normal electric DC motors:
A large flat wound rotor to achieve a high starting toque and an
immediate response to the autopilot speed control signal.
A motor efficiency of 72,5% to achieve a minimal power consumption
and maximal mechanical power output (compared to max. 50% efficiency
of a normal DC motor).
Compact main dimensions compared to achievable output.
gearbox: To achieve a correct rudder travel speed (hard over time)
the electric motor has to be highly reduced in speed. Some
autopilot drive producers use a worm reduction box, but the efficiency
is extremely low as the gears rub each other. The Jefa linear uses a
planetary gearbox which has following
The highest possible efficiency compared to any other gearbox.
All forces are equally spread over 3 gear teeth in stead of one
allowing a much compacter and stronger solution.
The forces and torques from the motor to the output shaft remain
in the centre line of the drive unit, resulting in a higher
efficiency and extremely reduces the loads on the housing and other
Electro magnetic clutch: On the moment the mechanical steering system on the yacht is manually operated, the autopilot drive
has to be disconnected from the steering system. This is achieved with
the electro-magnetic clutch and controlled automatically by the
autopilot junction box. Jefa has developed a unique engagement clutch. The solution is based on
a electrically operated
spring loaded clutch pin that engage and disengage the outer gear ring
of the planetary gear step. This solution has multiple advantages over
the existing friction plate clutches:
Less friction to back drive the unit.
Lower power consumption (0.7 Amp. at 12 Volt).
When the clutch isn't powered, it's disengaged and engaged when
The clutch doesn't wear in time.
More compact than any friction clutch.
When the autopilot is switched off, the helmsman isn't suddenly confronted
with the full rudder torque, but has to put loading on the wheel to
equalize the forces so the the clutch can disengage, making the manual
take over much safer.
This performance table shows the relation between the consumed power and
the output power and how quick this is done (hard over time). The red
line shows the output torque against the needed amperage. The green line shows the hard over time (time to travel 72° of
rudder travel) of the drive relative to the
output torque. Also visible is the strength of the drive unit related to man
power. The unit is much stronger than a human being and can last much
longer but one should note that when the unit is operated in the red
zone, something is wrong with the trim of the boats and the sails should
be adjusted to achieve lower rudder torques. The above table shows that
the Jefa linear drive will steer the yacht even in the worst
possible conditions. As the drive will mostly operate in the left green
zone and will not continuously rotate, the average power consumption on
12 volts is 1 to 2 amps.
This illustration shows the minimal components for a working autopilot
configuration. Jefa autopilot drives work together with all mayor
autopilot electronics. The connection of the Jefa autopilot drive to the
autopilot junction box is quite simple. The two 1.5 mm² red and black
wires have to be connected to the plus and minus of the autopilot clutch
line. This will make sure that when the autopilot user engages the
autopilot on the control screen, the clutch will engage and allow the
autopilot motor to drive the rudder. The two 2 mm² red and
black wires have to be connected to the autopilot drive output
connection. Now the Jefa autopilot drive is integrated into the system.
Tiller specification form
Please click this to open the tiller
lever specification form in Adobe PDF. This is a great help to specify a
tiller arm. Please sent the form to us.
Compatibility in 12 Volts.
Following table shows the maximum rudder torques that can be generated
by the Jefa linear drive in combination with various autopilot junction
Autopilot junction box
12 Volt version.
Garmin GHP12 sailboat APS (*1)
NKE gyropilot 2 RVP (*2)
not advisable due to lack in speed control and
dynamic braking see this page
B&G h5000 ACP-1/2
not advisable due to lack in speed control and
dynamic braking see this page
B&G Triton Pilot - Low Current
identical to Simrad AC12 - see above
(*1) A special Garmin version of the
linear drive is available under code number DU-LD-12/GA.
The Garmin rudder feedback unit is integrated and special Garmin
cables and plugs are wired to the drive unit.
(*2) Please read the special installation
instructions for the clutch available on our FTP server via
this direct link.
linear drive unit type LD100
Linear drive 100 KgM - 400 Kg thrust, 12 volts
Linear drive 100 KgM, incl. Garmin rudder feedback and
integrated rudder feedback unit for linear drive (*3)
The linear drive is delivered including a Ø16 mm tiller pin and in some cases
you will need a tiller arm. *3: Only
possible for Jefa, Garmin and NKE autopilots (all 10 kΩ).
Please click the left picture to open the Linear drive explosion drawing
with parts list.