International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 2
Number 1
March 2008
55
Gyrocompasses – Their Condition and
Direction of Development
A. Felski
Polish Naval Academy, Gdynia, Poland
ABSTRACT: Gyroscopic compass, the main source of information about the heading on modern ship, is
celebrating its centenary. In fact, nowadays it is commonly used on the ships in the form invented by Herman
Anschutz before the Second Word War. However in the last decade we observe stormy evolution of
completely different installations, which may substitute the well known gyro. Different kinds of devices,
which could be used for heading determination, will be shortly presented and classified. Author’s thesis is that
the new solutions are better than the old ones, nevertheless at the moment they are not in use only because of
the mariners’ conservatism.
1 THE QUESTION OF TERMINOLOGY
The present year may be funded as centenary of
creating of the gyrocompass, as in 1907 Anschutz
received the first patent for apparatus capable to
supersede magnetic one. Meantime a lot of
producers occurred as well as many diversified
structures of gyrocompasses raised so in author’s
opinion it is excellent time to summarize and set in
order the knowledge in this topic.
The discussion should start on sense of the name
“gyroscope” as it has influence on the apprehension
what is the gyrocompass. The term “gyroscope”
originates with Foucault, who demonstrated that
Earth rotates in experimental way. He made it in
1852 in Paris, using a spinning disc. Foucault’s
demonstration was based on the fact that the rotation
axis of the disc must remain fixed in inertial space in
the absence of applied torques. If so, the direction of
the disc’s axis with respect to the Earth changes, as
the Earth rotates underneath it. This is the essence of
the name “gyroscope” which occurs by joining of
two Greek words “gyros” and “skopos”. The first
one means “rotation” and second one - “to view”. So
according to Foucault gyroscope means some
devices to prove Earth rotation, with similarity to
microscope – devices for observing microscopic
objects or telescope – devices for observing distant
objects. This fact is very important from my point of
view, as in common opinion gyroscope is a swirling
body of wheel shape which keeps the constant
direction in the space. So according to this opinion
the gyrocompass is a device constructed on
gyroscope.
The proper interpretation is that gyrocompass is the
device which is capable to show the direction of the
Earth axis by measuring the Earth rotation by means of
the mechanical gyroscopes (in the old manner) or by
any other devices capable to measure the rate of turn.
Mechanical gyroscope has been used as a main
part of gyrocompasses for many years, but at present
the question is more complicated, because of many
different constructions implemented instead of
classical gyroscopes. Momentum wheel gyroscopes
use a spinning mass patterned after the spinning top,
very familiar child’s toy. If the spinning momentum
wheel is mounted inside the gimbals to isolate it
from rotations of the body on which it is mounted,
then its spin axis tends to remain in an inertially
56
fixed direction and the gimbal angles provide
readout of the total angular displacement of this
direction from body-fixed axis directions. Such
devices are now classified as directional gyroscopes
in opposition to rate turn gyroscopes. This second
type of gyroscopes, sometimes called as one-degree-
of freedom (also SDF – single degree of freedom),
has been invented around 1950. A rate gyroscope
provides a signal proportional to rate of angular
velocity of the carrier. The heart of this type of
device is a wheel running at high speed too, but
attached to the instrument case by torsion bar.
Carrier’s rotation enforces the main axis of the
instrument in changing its direction in the inertial
space by some angle. And
this angle provides
the information about the carrier’s rotation, which
could be measured, usually by some electromagnetic
instruments. Flexibility of the torsion bar enforces
the spinning wheel go back to previous position,
after the carrier stops its turning. Instead of torsion
bars sometimes electric pick-off assemblies are
applied.
Then, in the sixties of the XX century
Dynamically Tuned Gyro (DTG) was designed.
Firstly, this kind of gyro was invented around 1920
by Kearfott, but for 40 years it was inadequate for
the market. DTG is a kind of gyroscope that uses a
spinning fly wheel on a specific, flexures universal
joint. Normally that wheel is very unstable, but the
flexure spring stiffness affects on dynamic inertia of
the wheel, so at particular speed these two
interactions cancel themselves. The resulting sensor
is very stable in inertial space, extremely small and
relatively cheap.
Then, development of the laser technology
influenced on the method of angular velocity
measurement methods. So in the seventies devices
for angular velocity determination without any
spinning mass have been invented. There are two
groups of optical devices, which rotational
sensitivity is based on the Sagnac effect. Light acts
as the sensor element in the optical gyroscopes and
there is no commonly known spinning mass.
Because of that, some authors proposed other names,
not gyroscope. Although there is no spinning proof
mass, generally the nomenclature is retained in
deference to convention.
At first, two words have been used: “gyroscope”
for directional devices and “gyro” for rate turn
devices. In present time, the most popular is short
term “gyro” for any devices, which could be used for
proving angular velocity of the basis, as the essence
and common characteristic is spinning or rotation.
Other kinds of no-mechanical and no-optic kinds
of gyros have been invented in the same period.
Generally speaking engineers began to implement
alternatives to the wheel parts, as gyroscopes would
be more reliable and less expensive, if they had
neither spinning wheels nor moving parts. In eighties
of the XX century vibrating elements for providing
gyroscopic torques from the Coriolis acceleration
has been proposed. There are Hemispherical
Resonator Gyros, Vibrating String Gyros and Tuning
Fork Gyros. This group of gyros’ common attribute
is the changing of his shape on influence of coriolis
acceleration, which appears when sensitive element
is stimulated to vibration and simultaneously turned.
Especially Tuning Fork Gyros are very attractive in
form of Micro Electronics Mechanical System
(MEMS), in which the sensor could be produced
from quartz as cheap, small, and need only few
milliwatts of power.
2 VARIETY OF CONSTRUCTIONS
Foucault’s experiments with gyroscopes give us
some revealing statements. For marine community
the fundamental is the conclusion that the gyro with
only two degrees of freedom, or in other words, free
to move in two planes only, will tend to set itself
with its axis of rotation parallel to the axis of the
Earth rotation. These statements are proved at any
place on the Earth’s surface, despite the two poles
and stimulate Dr Anschutz to design a gyro
apparatus as a substitute for Magnetic Compass.
Some years of experiments have clearly shown to
Anschutz that the use of a gyro with only two
degrees of freedom is the correct solution of the
problem. To be practical a gyrocompass must
possess a very large gyroscopic resistance and be
strongly opposed to any attempt to tilt its axle.
Additionally, the friction of the suspension system
must be as small as possible. These two facts lead to
the result that, if the gyroscope is deflected for any
reason out of meridian plane, its swinging motion
takes place for long period and some method of
damping is necessary.
Fig. 1. The cross-section of the first gyrocompass (made on
basis of [6])
57
The first practical solution of Anschutz consists
of strong electric motor hanging below the float
which is dipped in the mercury. Additionally to the
motor, the smart apparatus has been fixed for
correcting the mass arrangement. This second
apparatus has had shape of pendulum, which has
been steered by air stream produced by spinning
motor, which resulted in dumping the compass
oscillations.
The fundamental feature of the Anschutz’
compass is the shifting of the centre of the mass of
the gyroscopic element below its geometric center. It
causes the directive force to aligning gyroscopic
element in the proper direction. Anschutz’
competitor - Sperry in 1911 invented for it the
communicating vessels with mercury. This solution
gives it more flexible source of directive force, as
variable level of the mercury generate the variable
force,
according to different latitude of the ship and
different deflection of the directional element out
of the meridian. Sperry’s solution was so good, that
has been applied up to the end of the XX century
(Robertson RGC11 for example).
Around the 1925 Anschutz modified his one-gyro
construction by introducing the well known two-
gyro sphere (“New Anschutz”), which is the basis of
the most popular modern gyrocompasses and we can
observe only miniaturization of it. Before the Second
World War it weighted about 200 kilos and needed
some 2kWt of energy, when the modern one weight
20 kilos and need only 80Wt (for example Anschutz
Standard series or Plath Navigat series). This is
possible mainly because of the digitalization, so
additionally it results in digital mode of transmission of
the heading.
Common feature of any gyrocompasses designed
after Anschutz or Sperry constructions is the internal
source of directive force, which is originated from
the distribution of the mass of sensitive element. So
the most popular class of gyrocompasses could be
named as gyrocompasses with internal correction.
The bad implications of this are dynamic deviations
of the gyrocompass. New way of gyrocompasses’
development is the idea to influence on three degrees
of freedom gyro from outside, for example by
turning the gimbal circle with electrical engine. It
can be steered by mathematical machine on the basis
of information about the angle of elevation of the
main axis of the free gyro over the horizon. This is
the idea of gyrocompass with external correction.
The examples of this group are Tokimec ES 110 or
Russian Vega compasses. In such construction the
directive force is calculated according to the place of
the ship on the Earth, her speed and heading, and
elevation of the main axis of the gyro over the
horizon, measured by inclinometer. So lots of
sources of deviation are eliminated and naturally the
dynamical quality of presented heading is better than
in case of gyrocompasses with internal sources of
correction.
Regardless of what was mentioned before, as
alteration of inertial systems the analytical
compasses rise in the eighties of the last century.
Although there are produced with mechanical,
Single-Degree-Of-Freedom (SDF) gyros (for
example Navistab), however mainly analytical
compasses based on optical ones (for example
Navigat 2100 or Raytheon MINS). Two fundamental
laser gyroscope types are used: the ring laser gyroscope
(RLG) and the fiber optic gyroscope (FOG), both
which use the Sagnac effect on counter rotating laser
beams and an interferometric phase detector to measure
their relative phase changes. Ordinarily this
modification of gyrocompasses is build with three SDF
gyros and augmented with accelerometers and
computer, so sometimes it is difficult to say: it is
gyrocompass or inertial navigation system. In
contrary to classical gyrocompasses, when the
directional gyro is physically aligned in meridian
plane, in analytical ones the heading is calculated by
computer. It is done by measuring the rate of turn of
meridian and horizontal planes by rate of turn gyros.
In practical, this kind of devices are usually mounted
to the deck (Strapdown) so mentioned turnings of
the planes are measured as the components in the
planes of the ship (down the axis of symmetry,
midship section plane and vertical). As these kinds
of gyrocompasses have no dynamically aligned
parts, there is lack of errors with dynamical
character. Although the strapdown compasses has
the smallest errors, they work in three axes, so this
device is capable to measure the pitch and roll
except for the heading of the ship. The strapdown
systems seem to be the superlative sort of compasses,
ideally fit for some special ships, for example
hydrographic, off-shore activities, submarines etc. It is
not surprising that the strapdown compasses are the
most expensive.
58
Table. 1. Comparison of different gyrocompasses
Classical (directional gyroscopes)
With
internal
correction
Momentum Wheels
Gyroscopes
(directional gyroscopes)
(New Anschutz)
Anschutz (Standard series)
Plath (Navigat I – X)
Kurs, Amur etc.
Settling time – 4 hours
Cost – some thousands $
Weight – about 100kG or more
Power consumption – at least 80W
(Sperry)
RGC11 - Robertson
With
external
correction
ES 110 – Tokimec
Russian Vega
Settling time – 4 hours
Cost – some thousands $
Weight – about 100kG or more
Analytical
DTG
Meridian Standard – SG
Brown
SKR 82 –Robertson
Settling time – ~20 min
Cost – 10 000 $
Weight – about 100kG
Strapdown
DTG
Navistab – Plath
Settling time – ~20 min
Cost – about 50 000 $
Weight – about 30kG
RLG
LSR85 - LITEF
FOG
LFK95 - LITEF
Navigat 2100 - Plath
Gyro-magnetic
Vibrating Gyro plus
fluxgate sensor
SSC200 - Maretron
Sonic Compass - Tecnautic
GytoTrack - KVH
Settling time – ~5 min
Cost - about1 000 $
Weight – about 100G or more
GPS compass
2 antennas and GPS signal
phases measure
JLR 10 - JRC
Satellite Compass Standard
21 – Anschutz Rytheon
HS 50 - Simrad
MX 575 – MX Marine
Settling time – ~5 min
Cost - about 5 000 $
Weight – no more 5kG (with antennas)
Next kind of gyrocompasses is gyro-magnetic
ones. The idea of combining the magnetic compass
with gyroscope has been know from fifties. Such
kind of devices has been utilized on airplanes and
very fast war cutters (torpedo or missiles boats).
Easy accessible “from the shelf” new magnetic
sensors (fluxgate) and MEMS gyros establish the
opportunity to build very sophisticated instrument.
Generally speaking it is one, more often vibrating,
gyro which is augmented by information from
fluxgate sensor with magnetic direction, and with
computer, as it is natural in the nowadays. So for
price on the level of 1000Euro it is possible to buy
gyrocompass with settling time of 5 minutes and
weight much less than 1 kg! It has no dynamical
deviations and is not influenced by any ship’s
maneuver. At the moment this group of devices is
treated as no-professional equipment, so it could be
suggested for any yachts, fishing ships and so on. At
the moment they have no approvals of classification
societies but why it is so? May be the interest in the
field of leisure fleet is so massive, that it is no
interest to pay for receiving the certificate of
approval? At the moment this device fulfills all
records of Convention for Safety of Life at Sea and
IMO Resolution A.424, except for only one point –
there it is not clear is it a gyrocompass or not.
But in the meantime totally new solution rose on
the market, which may be the biggest competitor for
any known compasses. This is GPS compass, which
combines the GPS receiver with opportunity to
measure the heading by combination of two GPS
antennas. At the moment they are approved only as
the secondary source of the information about the
heading, but this could be caused by the few years of
attendance on the market. The GPS compasses have
excellent parameters, because they are the first
compasses that work without any limitations, even
on the pole. GPS compasses work in practice
without deviations, with errors no more than 0.5
degree and settling time no more than 3 min in any
conditions.
59
3 SUMMARY
Nowadays gyrocompasses are a group of navigation
systems, which include much differentiated devices.
In the paper the main group of them has been
presented as well as the most important facts about
their designing and features.
The table presents the four brands of compasses
which are used nowadays, and the most typical
examples of each one.
Summarizing we can say, that the most popular at
the moment are compasses with internal corrections,
but they have the worst dynamical properties and
they are relatively expensive. The other groups have
at least the same accuracy or better, but they are free
of dynamical deviations and they have shorter
settling time.
The strapdown system is the most accurate and
there is only one system which is able to measure
three angles of ship attitude, but this is the most
expensive one. In contrary, the gyro-magnetic one is
the cheapest one dimensional compass, but in
common opinion it is fit for small vessel.
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Jekeli Ch., “Interial Navigation Systems with Geodetic
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