Gyro support the plane of rotation (Marine Insight,
A gyro compass is a type of
gyroscope; it is used commonly on ship using an electrically powered. The main aim
of gyro compass is to determine the ships heading using gyro sphere which is
included in Master Compass (Gyroscope. 2013). In addition, it is designed to find the
direction of the true north by the influences of
gravity and the Earth’s rotation. The important part in gyro compass
systems is the spinning wheel. Gyro
compasses cannot be affected by external magnetic field which comes from the ship. The gyroscope consists of stable wheel arranged to
spin at high speed about axis or axle (Cleonis.nl,2016). A gyroscope can move
freely about three mutually perpendicular axes. The three mutually perpendicular axes are the precession
axis, the torque axis and the spin axis. The gyro compass system is based on two
essential characteristics, known as the gyroscopic inertia and precession. The gyroscopic
inertia is a rotating
body to support the plane of rotation (Marine
Insight, 2017). The gyroscopic inertia is depending on the movement of the
spinning rotor (Dasgupta, n.d.). The precession is a term used to explain the movement of the axle of
a gyroscope by the influence of an external force. If the force is applied to the spinning
rotor, the gyroscope will be moving at an angle of 90 degrees from the applied
force (compass, n.d.). One of the main
feature of gyro compass is shows the true north. Another feature of gyro
compass is unaffected by the external force. On the other hand, one of the main
disadvantages of gyro compass is that it requires electricity to work,
therefore if the electricity falls, gyro compass will fall as well (Navy.memorieshop.com, 2017). The
total number of compass repeaters at Bahri Tabuk vessel are five and it is
located on the bridge, bridge wings and the steering room. Figure 1 shows the
compass repeater in the starboard side. The gyro compass is form of the following units:
detecting ship heading and calculate rate of turn.
Repeater compass / steering repeater compass: receiving the heading signal from master compass and indicates
it is used to control gyrocompass. There are two kinds of operation units. The
operations are C.operation and M. operation.
Control box: it is connected to Master compass and other
external device. This unit drives each heading signals.
Alarm Unit: indicates the
failure of the gyro compass.
maintains constant supply of the ship to the motor generator.
Course Recorder: records the maneuvering of the ship.
powers to the compass equipment. (Marine Insight, 2017)
Maintenance and inspection of gyro compass
Gyro compass must be maintaining and checked to insure that it is working
normally. The officer of the watch is responsible to calculate azimuth error once
a day by using the compass repeaters and checking when is the next annual
service for gyro compass see figure 3 (Marine
Insight, 2017). The
table shows the items which must be inspected:
Gyrosphere drive current
Ship speed value
DC battery input
(manual of magnetic
Gyro compass error
gyrocompass is precise equipment but it has small errors, this errors expressed
as east or west. Gyro compass has two
different types of errors which are static and dynamic errors. The Statics error has two main
issues which are alignment and transmission. Alignment
error is an error existing between vessel lubber line and the indicated heading. However, this error can be minimised
by line up the compass with the ship’s lubber line at installation.
Transmission error is an error in indicates heading between master compass and
repeater compass. It can be minimised by the design of the master compass. One
example of the dynamic errors is Acceleration error and it is caused from the
sudden changed in the ship course and speed. It can be minimised by the design
of the center of gravity of the gyrosphere.
Other example of the dynamic errors is speed error and it is caused when
the course is south or north (Marinegyaan.com,
Start-up and stop the gyro compass
The gyro compass is start up and
switch off by operating the main power switch in the control box or autopilot
stand. The master compass going to
starts north-seeking. The repeater compasses will receive heading signal. The
gyrocompass must start five hours before the ship departure to settle down and
displays true heading.
The Gyro compass is
receiving and sending signals from different navigation equipment. Table one
shows the signals which can be input from external devices to gyro
compass. Table two is showing the
signals which can be output to external devices from gyro compass.
ECDIS, Course recorder
/ Rate of turn signal
compass, GPS, Course recorder
compass heading signal
Heading/ Rate of turn single
Universal data display
Heading /Rate of turn signal
recorder, ROT indicator,
Gyro compass failure
It is important to response for Gyro compass failure quickly and
effectively to insure the ship is going to the right direction. The
first actions of the officer of the watch is take the vessel off auto pilot and
engage hand steering immediately. Figure 111 shows the switch unit which used
to switch from auto mood to hand steering
(Shipsbusiness.com, 2018). The
next actions are call master, avoid any danger nearby and change to magnetic
compass for heading. The final actions are
informing the chief engineer, electrician to check and repair and inform office
by message according to the contingency checklist of the ship.
Identify gyro compass failure
If gyro compass failed, the buzzer will
sound and the failed will blink on the screens of C.operation unit. The c.operation
units show the error code and the cause of the alarm (Marinegyaan.com, 2017). The alarm can be stopped by pressing the
buzzer stop key on C.operation and M.operation. C.operation
Unit is used to controlling the gyrocompass and setting the communication to
connect with external advice. The C.operation unit is equipped on the autopilot stand or on the front
door of control box. M.operation unit is used for operating the master
compass and it is equipped on the front panel of master compass. Figure 2 shows the name
of each part of C. operation unit, The Operation units have two moods which
are normal and command mode. Normal mood is used for showing the azimuth date,
heading and system status. Command mode
is used to show information and the setting on the systems (gyro compass
manual) the type of alarm in gyro compass are:
Power failure alarm.
System failure alarm.
High temperature alarm.
High voltage alarm.
Low voltage alarm (Marinegyaan.com, n.d.).
Alarm LED and buzzer stop key.
Date display area
Command mode, could use to switch from command mode to normal mode.
Select LED and select key
Gyro heading selection key
External heading selection key
Figure 2 spare magnetic in Bahri
Figure 1 Magnetic compass
compass is an important piece of navigation equipment because it operates
independently and it is not relying on Electronic Navigational Aids (ENA). A magnetic compass is mainly used to
steer a course and also to fix a ship position on chart by take bearing of
visible objects. In addition, it used to take bearing of a celestial objects
for navigation and backup for gyro compass failure (Brighthub
Engineering, 2017). The disadvantages of using a magnetic compass is does not
seek for true north. Another important point to be noted
about using magnetic compass is affected by materials (Schenker.net, 2017). All vessels are required to be fitted
with a means of finding direction and heading from the steering position and
independently according to SOLAS rules 22.214.171.124. Therefore, all ship must have
a magnetic compass to fulfil this requirement.
The ships of 150 gross tonnages and upwards must have a spare magnetic
compass according to SOLAS rules 126.96.36.199 (SOLAS, consolidated edition 2014, n.d.) A magnetic compass is
installed above the wheelhouse (monkey island) to keep it away from magnetic
interference see figure (Compassadjustment.com, 2017). In Bahri Tabuk vessel, the spare magnetic compass is
located in the bridge see figure. The
magnetic compass is not linking with other navigational equipment because it is
periscope used to reflect from the magnetic compass into the bridge, so the
helmsman can read the compass when he is steering the ship. The magnetized needle
in magnetic compass is suspended freely, therefore, the forces of earth
magnetic field will make it point at north direction. Since the north direction
is known, the other direction is easily found (Marinegyaan.com, 2017). The design of a magnetic compass is made to be able to
combining with azimuth reading device, binnacles, transmitting systems
according the magnetic compass manual. Binnacle is a stand to keep the Gimbals in
horizontal way, so it will not move when the ship is pitching or rolling. The binnacle is made of welding with cast
aluminum and original aluminum plate. The binnacle is provided with six powerful
magnets and six weak magnets. A reflector tube has a length of two meters. The
viewing mirror angle can be varied and is double sided. The Magnetic compass is composed of the following units:
Compass card: The compass card is 180 mm in diameter and it
is in 360 degrees stating from north clockwise.
glass covers the top and bottom of the compass and it has a thickness of 6mm.
Directional systems magnets: it designed to not produce any sextantal or
Liquid: The liquid is composed of the mixture of
aliphatic hydrocarbons and it is colourless.
The filling plug is on the bowl see figure 2.
gimballing: The angle formed by the outer and inner gimbal axes is 90
degrees. The outer gimbal axis lies in the fore and aft direction.
Centering of Azimuth Reading Device: The rotation axis has a center boss on the
top glass cover of the compass to fit the azimuth reading device.
Pivot Bearing: The pivot bearing is fitted with a vertical
spring suspension, so the directional systems mounting in the compass return to
the original position (magnetic compass manual). (Navyadministration.tpub.com, 2017)
magnetic compass errors
Figure 3 compass rose
a magnetic compass errors cannot be removed but it
could minimised. The two main errors in magnetic compass error are deviation
and variation errors. Deviation is the angle which is between the magnetic meridian and the north and
south axis of the compass card and it measured in degrees west or east (Skysailtraining.co.uk, 2017). it caused by
interference of the vessel structure or any electrical machinery with the earth
magnetic field. In addition, the value of deviation is different from heading
to heading because of the earth and the vessel soft iron magnetism (Compassadjustment.com, 2017). The value of deviation
shows on the deviation table for every 15 degrees of vessel heading annex 2. Variation is the angular difference between the true north pole and
the magnetic north pole and it Measured
in degrees west or east. It
affects the magnetic compass by pointing more or less away from the true
north. It caused by the different
location of the earth magnetic and the geographic poles (Splashmaritime.com.au, 2017). The value of variation for any area can be calculated by the
nearest compass rose on the marine chard. Compass rose is
designed to show the directions and to calculate the variation see figure 2 (Schoolofsailing.net, 2017).
Evidence of celestial compass error
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