Gyro compass Junction box Horizontal stand A gyro compass is a type ofgyroscope; it is used commonly on ship using an electrically powered.
The main aimof gyro compass is to determine the ships heading using gyro sphere which isincluded in Master Compass (Gyroscope. 2013). In addition, it is designed to find thedirection of the true north by the influences ofgravity and the Earth’s rotation. The important part in gyro compasssystems is the spinning wheel. Gyrocompasses cannot be affected by external magnetic field which comes from the ship.
The gyroscope consists of stable wheel arranged tospin at high speed about axis or axle (Cleonis.nl,2016). A gyroscope can movefreely about three mutually perpendicular axes. The three mutually perpendicular axes are the precessionaxis, the torque axis and the spin axis. The gyro compass system is based on twoessential characteristics, known as the gyroscopic inertia and precession. The gyroscopicinertia is a rotatingbody to support the plane of rotation (MarineInsight, 2017). The gyroscopic inertia is depending on the movement of thespinning rotor (Dasgupta, n.
d.). The precession is a term used to explain the movement of the axle ofa gyroscope by the influence of an external force. If the force is applied to the spinningrotor, the gyroscope will be moving at an angle of 90 degrees from the appliedforce (compass, n.
d.). One of the mainfeature of gyro compass is shows the true north. Another feature of gyrocompass is unaffected by the external force. On the other hand, one of the maindisadvantages 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). Thetotal number of compass repeaters at Bahri Tabuk vessel are five and it islocated on the bridge, bridge wings and the steering room. Figure 1 shows thecompass repeater in the starboard side. The gyro compass is form of the following units:· Master compass:detecting ship heading and calculate rate of turn.· Repeater compass / steering repeater compass: receiving the heading signal from master compass and indicatesship heading. · Operation units:it is used to control gyrocompass. There are two kinds of operation units. Theoperations are C.
operation and M. operation. · Control box: it is connected to Master compass and otherexternal device.
This unit drives each heading signals. · Alarm Unit: indicates thefailure of the gyro compass. · Voltage regulator:maintains constant supply of the ship to the motor generator. · Course Recorder: records the maneuvering of the ship. · MotorGenerator: givingpowers 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 workingnormally. The officer of the watch is responsible to calculate azimuth error oncea day by using the compass repeaters and checking when is the next annualservice for gyro compass see figure 3 (MarineInsight, 2017). Thetable shows the items which must be inspected: Inspection items Inspection interval Gyrosphere drive current Once/day Repeater compass alignment Once/ departure Ship speed value latitude Once/day Azimuth error One/day DC battery input Once/ year (manual of magneticcompass) Gyro compass error Thegyrocompass is precise equipment but it has small errors, this errors expressedas east or west.
Gyro compass has twodifferent types of errors which are static and dynamic errors. The Statics error has two mainissues which are alignment and transmission. Alignmenterror is an error existing between vessel lubber line and the indicated heading. However, this error can be minimisedby line up the compass with the ship’s lubber line at installation.Transmission error is an error in indicates heading between master compass andrepeater compass. It can be minimised by the design of the master compass.
Oneexample of the dynamic errors is Acceleration error and it is caused from thesudden changed in the ship course and speed. It can be minimised by the designof the center of gravity of the gyrosphere. Other example of the dynamic errors is speed error and it is caused whenthe course is south or north (Marinegyaan.com,2017). Start-up and stop the gyro compass The gyro compass is start up andswitch off by operating the main power switch in the control box or autopilotstand. The master compass going tostarts north-seeking. The repeater compasses will receive heading signal. Thegyrocompass must start five hours before the ship departure to settle down anddisplays true heading.
Gyro links The Gyro compass isreceiving and sending signals from different navigation equipment. Table oneshows the signals which can be input from external devices to gyrocompass. Table two is showing thesignals which can be output to external devices from gyro compass. Input Signal External devices Ship speed signal Doppler log, GPS Latitude signal GPS, ECDIS, Course recorder Heading / Rate of turn signal Magnet compass, GPS, Course recorder Output signal External devices Repeater compass heading signal Repeater compass Stepper heading single Radar, ECDIS Serial Heading/ Rate of turn single Autopilot, Universal data display Analog Heading /Rate of turn signal Course recorder, ROT indicator, Gyro compass failure It is important to response for Gyro compass failure quickly andeffectively to insure the ship is going to the right direction. Thefirst actions of the officer of the watch is take the vessel off auto pilot andengage hand steering immediately. Figure 111 shows the switch unit which usedto switch from auto mood to hand steering(Shipsbusiness.com, 2018).
Thenext actions are call master, avoid any danger nearby and change to magneticcompass for heading. The final actions areinforming the chief engineer, electrician to check and repair and inform officeby message according to the contingency checklist of the ship. Identify gyro compass failure If gyro compass failed, the buzzer willsound and the failed will blink on the screens of C.
operation unit. The c.operationunits show the error code and the cause of the alarm (Marinegyaan.com, 2017). The alarm can be stopped by pressing thebuzzer stop key on C.operation and M.operation.
C.operationUnit is used to controlling the gyrocompass and setting the communication toconnect with external advice. The C.operation unit is equipped on the autopilot stand or on the frontdoor of control box. M.operation unit is used for operating the mastercompass and it is equipped on the front panel of master compass. Figure 2 shows the nameof each part of C.
operation unit, The Operation units have two moods whichare normal and command mode. Normal mood is used for showing the azimuth date,heading and system status. Command modeis used to show information and the setting on the systems (gyro compassmanual) 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 Enter key Heading display Gyro heading selection key External heading selection key Dimmer Magnetic compass Figure 2 spare magnetic in Bahri Tabuk Figure 1 Magnetic compass A magneticcompass is an important piece of navigation equipment because it operatesindependently and it is not relying on Electronic Navigational Aids (ENA). A magnetic compass is mainly used tosteer a course and also to fix a ship position on chart by take bearing ofvisible objects. In addition, it used to take bearing of a celestial objectsfor navigation and backup for gyro compass failure (BrighthubEngineering, 2017). The disadvantages of using a magnetic compass is does notseek for true north. Another important point to be notedabout using magnetic compass is affected by materials (Schenker.
net, 2017). All vessels are required to be fittedwith a means of finding direction and heading from the steering position andindependently according to SOLAS rules 188.8.131.52. Therefore, all ship must havea magnetic compass to fulfil this requirement.
The ships of 150 gross tonnages and upwards must have a spare magneticcompass according to SOLAS rules 184.108.40.206 (SOLAS, consolidated edition 2014, n.
d.) A magnetic compass isinstalled above the wheelhouse (monkey island) to keep it away from magneticinterference see figure (Compassadjustment.com, 2017). In Bahri Tabuk vessel, the spare magnetic compass islocated in the bridge see figure. Themagnetic compass is not linking with other navigational equipment because it isindependently.
Aperiscope used to reflect from the magnetic compass into the bridge, so thehelmsman can read the compass when he is steering the ship. The magnetized needlein magnetic compass is suspended freely, therefore, the forces of earthmagnetic field will make it point at north direction. Since the north directionis known, the other direction is easily found (Marinegyaan.com, 2017).
The design of a magnetic compass is made to be able tocombining with azimuth reading device, binnacles, transmitting systemsaccording the magnetic compass manual. Binnacle is a stand to keep the Gimbals inhorizontal way, so it will not move when the ship is pitching or rolling. The binnacle is made of welding with castaluminum and original aluminum plate. The binnacle is provided with six powerfulmagnets and six weak magnets.
A reflector tube has a length of two meters. Theviewing 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 itis in 360 degrees stating from north clockwise.
· Glass: theglass 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 oroctantal deviations. · Filling plug Liquid: The liquid is composed of the mixture ofaliphatic hydrocarbons and it is colourless. The filling plug is on the bowl see figure 2.· Compassgimballing: The angle formed by the outer and inner gimbal axes is 90degrees.
The outer gimbal axis lies in the fore and aft direction. · Centering of Azimuth Reading Device: The rotation axis has a center boss on thetop glass cover of the compass to fit the azimuth reading device.· Pivot Bearing: The pivot bearing is fitted with a verticalspring suspension, so the directional systems mounting in the compass return tothe original position (magnetic compass manual).
(Navyadministration.tpub.com, 2017) magnetic compass errors Figure 3 compass rose a magnetic compass errors cannot be removed but itcould minimised. The two main errors in magnetic compass error are deviationand variation errors.
Deviation is the angle which is between the magnetic meridian and the north andsouth axis of the compass card and it measured in degrees west or east (Skysailtraining.co.uk, 2017). it caused byinterference of the vessel structure or any electrical machinery with the earthmagnetic field. In addition, the value of deviation is different from headingto heading because of the earth and the vessel soft iron magnetism (Compassadjustment.com, 2017).
The value of deviationshows on the deviation table for every 15 degrees of vessel heading annex 2. Variation is the angular difference between the true north pole andthe magnetic north pole and it Measuredin degrees west or east. Itaffects the magnetic compass by pointing more or less away from the truenorth. It caused by the differentlocation of the earth magnetic and the geographic poles (Splashmaritime.com.au, 2017). The value of variation for any area can be calculated by thenearest compass rose on the marine chard. Compass rose isdesigned to show the directions and to calculate the variation see figure 2 (Schoolofsailing.
net, 2017). Magnetized needle Bahakim1 Evidence of celestial compass error ReferenceMarinegyaan.com. (2017). Whatare types of error of Gyro Compass? |. online Available at:http://marinegyaan.com/what-are-types-of-error-of-gyro-compass/ Accessed 5Dec.
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