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Compass Flashcards

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1
Q

Do we need a compass?

A

Yes! to be able to steer to our destination. Also to be able to fix our position on the way to our destination.

It is required under Solas Chapter V
Regulation 19.2.1

All ships, irrespective of size, shall have:
* a properly adjusted standard magnetic compass, or other means, independent of any
power supply, to determine the ship’s heading and display the reading at the main
steering position;

This is then bought into UK law via the Merchant Shipping (Safety of Navigation)
Regulations 2020

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2
Q
A
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3
Q

What is True north

A
  • True North is the stationary direction pointing to the Earth’s Geographic North Pole.
  • The planet’s axis of rotation.
  • Marked by converging lines of longitude on a globe or map
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4
Q

What is Magnetic north

A

the name given to the direction in which the “North” end of a magnetic
needle, would point to.

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5
Q

What is Variation

A

the angle between the geographic (true) and magnetic meridians at any place. It
is measured east or west from true north.

Measured in degrees and minutes

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6
Q

What is Deviation

A

The angle between the
magnetic meridian (magnetic north) and the direction in which the needle points
(compass north) is called the deviation. It is measured in degrees east or west from
magnetic north.

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7
Q

How to reduce Deviation

A

By the fitting and adjustment of permanent magnets and softiron Spheres at the compass binnacle.

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8
Q

what i s ment by‘Swinging the Ship’

A

‘Swinging the Ship’ to Establish Residual Deviation. After adjustment of the permanent
magnets and soft-iron Spheres at the compass binnacle, the ship’s residual Deviation is found
by slowly ‘swinging the ship’ through 360° and noting the Deviation for the various compass
Headings. The residual Deviation may be tabulated or drawn as a graph.

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9
Q

What’s on the deviation card?

A
  • Date and location
  • Name of compass adjuster
  • CoC and signature of Compass adjuster
  • Name and signature of master
  • Location of all correctors
  • Residuals coefficients
  • Residual deviation
  • Heeling magnet
  • Flinders bar
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10
Q

Why is deviation dependent on ship’s head?

A

It’s because the ship is long and skinny, hence if you imagine we have a large anchor and
several shackles of cable on the bow which is highly magnetic we could say the ship has a
positive or negative force from the bow!

draw the diagram of the four ships in my head

  • There is no deviation on compass north and south when the pull is in line with the
    compass needle.
  • There is maximum deviation on compass east and west when the pull is at right angles
    to the compass needle.
  • On the other directions of the ships head the deviation varies.

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11
Q

Limitations and sources of error (magnetic compss)

A

Does not work in polar regions

Magnetic compasses are of little value for navigation near the magnetic poles. Large diurnal
changes in variation, sometimes as much as 10°, attributed to the continual motion of the
poles, have been reported.

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12
Q

Magnetic compasses should be
adjusted when:

A
  • They are first installed.
  • They become unreliable.
  • The ship undergoes structural repairs or alterations that could affect its permanent and
    induced magnetism.
  • Electrical or magnetic equipment close to the compass is added, removed or altered.
  • A period of two years has elapsed since the last adjustment.
  • Record of the compass deviations has not been maintained.
  • The compass shows physical defects.

MSN 610

Effects of Changes in Magnetism During the Life of a Ship Because the magnetism of a new ship can be particularly unstable, the performance of Magnetic compasses should be monitored carefully during the early life of a ship.

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13
Q

What is Retention error

A

This error results from the tendency of a ship’s structure to retain some of the induced magnetic effects for short periods of time.

For example, a ship traveling north for severaldays, especially if pounding in heavy seas, will tend to retain some fore-and-aft magnetism
hammered in under these in-duction conditions. Although this effect is transient, it may
cause incorrect observations or adjustments.

This same type of error occurs when ships are docked on one heading for long periods of time.

A short shakedown, with the ship on other headings, will tend to remove such errors. A similar sort of residual magnetism is left in
many ships if the de-gaussing circuits are not secured by the reversal sequence.

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14
Q

When to Monitoring Compass Performance

A

Compass performance should be monitored by frequently recording deviations in the compass deviation book.

Compass errors should be determined:
After every large alteration of
course.
At least once every watch when there have been no major course alterations.

Checking the compass deviation regularly may show the need for repair, testing or
adjustment.

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15
Q

who should do the Adjustments and Repairs on a magnetic compass

A

In the UK, all adjustments should be made by a compass adjuster who holds a Certificate of
Competency as Compass Adjuster issued by the UK Government.

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16
Q

Operational checks of a magnetic compass

A

The performance of all magnetic compasses, including spares, should be checked as follows:

  • Freedom of movement of the gimbal.
  • The card floating freely and level and rotating without any friction.
  • Liquid free of bubbles and clear.
  • Compass card clear and sharp (able to be read) with no distortion or discoloration.
  • Optical system (if any) correctly adjusted and clean.
  • Azimuth reading devices and means of illumination in working order.
  • No liquid leaks around seals or filler plugs.
  • No Tools left in the area or speakers etc
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17
Q
A
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18
Q

What is a Transmitting Magnetic Compass (TMC)?

A

A device used on ships to transmit the vessel’s heading information to other ships or shore-based stations.

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19
Q

What technology does a Transmitting Magnetic Compass (TMC) utilize?

A

Magnetic sensors to determine the ship’s heading.

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20
Q

What is the purpose of a Transmitting Heading Indicator (THI)?

A

To provide heading information and transmit this data to other ships or shore-based stations.

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21
Q

How do TMCs and THIs determine the ship’s heading?

A

By relying on magnetic sensors or compasses.

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22
Q

What type of communication methods do TMCs and THIs use to transmit heading information?

A

Appropriate comm AIS.

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23
Q

True or False: A Transmitting Heading Indicator (THI) is not part of a vessel’s navigation and communication system.

A

False.

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24
Q

Fill in the blank: A Transmitting Magnetic Compass (TMC) transmits heading information to _______.

A

[other ships or shore-based stations]

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25
What does AIS stand for in the context of TMCs and THIs?
Automatic Identification System.
26
What is a Gyro Compass used for?
Gyro Compass is used for navigation on ships.
27
What are the two significant advantages of Gyro Compasses over magnetic compasses?
They find truth north and are unaffected by ferromagnetic materials.
28
What does a Gyro Compass find that is navigationally more useful than magnetic north?
It finds truth north as determined by the rotation of the Earth.
29
How does a Gyro Compass respond to ferromagnetic materials?
It is unaffected by ferromagnetic materials.
30
What can you do with a gyro bearing on a chart?
You can plot a gyro bearing directly to a chart.
31
What is a gyroscope?
A gyroscope is a wheel spinning at a high rate of speed and mounted to turn its axis of spin in any direction.
32
Fill in the blank: A Gyro Compass is navigationally more useful than a _______.
magnetic compass.
33
True or False: A Gyro Compass can be influenced by the ship's steel hull.
False.
34
What are the two unique properties of a free gyroscope?
Gyroscopic Inertia and Precession ## Footnote These properties form the basis of a gyroscope's behavior.
35
Define Gyroscopic Inertia.
The property that causes a gyroscope to maintain the position of its axis in space and resist forces that attempt to change its orientation. ## Footnote Gyroscopic Inertia is crucial for the stability of the gyroscope.
36
What happens when you try to change the orientation of a gyroscope?
It will try to maintain its original orientation. ## Footnote This resistance to change is a key characteristic of Gyroscopic Inertia.
37
What is Gyroscopic Precession?
A rotational movement perpendicular to the applied force when a force is applied to tilt the spinning disc. ## Footnote Precession occurs due to the conservation of angular momentum.
38
How does a gyroscope respond when a force is applied to tilt it?
It experiences precession instead of immediately tilting in the direction of the applied force. ## Footnote This unique response is an important aspect of gyroscopic behavior.
39
What factors influence the direction and speed of precession?
The rate of spinning and the applied force. ## Footnote These factors determine how the gyroscope reacts to external influences.
40
Fill in the blank: Gyroscopic Inertia is also known as _______.
rigidity in space ## Footnote This term highlights the gyroscope's ability to maintain axis orientation.
41
What does SOG stand for?
Speed Over Ground ## Footnote SOG is a measure of the speed of a vessel relative to the ground.
42
What is the significance of latitude in relation to gyros?
Gyros lose functionality at extreme latitudes ## Footnote Gyros are generally reliable up to 75° latitude but are unusable north or south of 85° latitude.
43
True or False: Gyro compasses are fully operational at the poles.
False ## Footnote Gyro compasses lose all horizontal directive force as the poles are approached.
44
At what latitude do gyros become unusable?
85° latitude ## Footnote Gyros are generally reliable up to 75° but should be checked frequently beyond that.
45
What should be done when using gyros above 75° latitude?
Check by the azimuths of celestial bodies ## Footnote This ensures accuracy as gyros lose reliability in extreme latitudes.
46
What is the primary purpose of maintaining a gyrocompass on a ship?
To ensure accurate navigation and heading information.
47
Why are gyrocompasses preferred over traditional magnetic compasses in marine navigation?
They provide stable and reliable directional data, unaffected by magnetic fields.
48
What is the first step in the maintenance procedures for a gyrocompass?
Regular Inspection.
49
What should be included in a routine inspection of a gyrocompass?
Checking for any physical damage, loose connections, or signs of wear and tear.
50
What is the purpose of calibrating a gyrocompass?
To ensure its accuracy by aligning it with true north.
51
When should calibration of a gyrocompass be performed?
At regular intervals and after repairs, significant alterations, or changes in location.
52
What should be checked during routine maintenance of a gyrocompass?
For any errors or deviations from expected readings.
53
How should errors detected in a gyrocompass be addressed?
Through calibration or adjustment.
54
Why is cleaning and lubrication important for a gyrocompass?
Dust, dirt, or debris can affect its performance.
55
What should be followed to ensure proper cleaning and lubrication of a gyrocompass?
The manufacturer's guidelines.
56
What is essential for the power supply of a gyrocompass?
A stable power supply with appropriate backup systems.
57
What backup systems are recommended for a gyrocompass?
Uninterruptible power supplies (UPS).
58
What is crucial for the mechanical alignment of a gyrocompass?
Proper mounting with no misalignments.
59
What should be done regularly to verify the functioning of a gyrocompass?
Routine Testing and performance checks.
60
Who should be trained in using the gyrocompass?
The ship's crew.
61
What should be maintained to track maintenance activities of a gyrocompass?
Detailed records of maintenance activities, calibrations, and adjustments.
62
What is the benefit of proper record keeping for a gyrocompass?
Helps in identifying trends, potential issues, and compliance with regulations.
63
Gyro compass Operational checks ?
Regular Inspection Calibration Check for Errors Cleaning and Lubrication Power Supply and Backup Mechanical Alignment Routine Testing Record Keeping
64
What should always be followed for gyro maintenance?
Manufacturer's guidelines and recommendations for the specific make and model of the gyrocompass installed on the ship. ## Footnote This ensures proper functioning and compliance with regulations.
65
What can affect the maintenance requirements of a gyrocompass?
Type and model of the gyrocompass, ship's regulations, and operational practices. ## Footnote These factors can lead to variations in maintenance schedules and procedures.
66
How often does Sperry Marine recommend gyroshpere maintenance?
Every 18 months. ## Footnote This maintenance should be carried out by authorised service personnel.
67
What is the maintenance frequency recommended by other companies for gyrocompasses?
Annual inspection and cleaning. ## Footnote This may differ from Sperry Marine's recommendation.
68
What activities are performed during the 18-month maintenance of a gyrocompass?
Cleaning of the gyrosphere and inner surface of the container, renewal of all fluids, and exchange of the centring pin if necessary. ## Footnote These tasks are essential for maintaining gyrocompass performance.
69
What is recommended by Sperry Marine every five years?
Exchange the gyro sphere and the centring pin by authorised service personnel ## Footnote This is to ensure continued trouble-free operation and to minimise the risk of failure.
70
What components should be exchanged every five years according to Sperry Marine?
* Gyro sphere * Centring pin ## Footnote These components should be exchanged by authorised service personnel.
71
Why does Sperry Marine recommend exchanging the gyro sphere and centring pin?
To ensure continued trouble-free operation and to minimise the risk of failure ## Footnote Regular maintenance is critical for the longevity of equipment.
72
What direction should the arrow be pointed to take a bearing of a heavenly body using an Azimuth Mirror?
Upwards
73
What direction should the arrow be pointed to take a bearing of a terrestrial object using an Azimuth Mirror?
Downwards
74
What must always be horizontal when using the Azimuth Mirror?
Prism
75
What is the primary function of a Pelorus?
To obtain bearings of shore objects
76
Why is a Pelorus particularly useful compared to an Azimuth Mirror?
When the line of sight of the Azimuth mirror is obscured
77
What is a key feature of the Pelorus that allows it to be used from different locations on a ship?
It is a portable instrument
78
How is the Pelorus lined up to determine bearings?
For and aft
79
What does the Pelorus provide relative to the ship's head?
Relative bearings
80
What type of compass card is found inside the Pelorus?
Graduated 360° compass card
81
If the ship's head is known, what can the Pelorus be used to take?
Compass bearings
82
How To Find the Compass Error by Transit
83
Compass Check via Amplitude of the Sun (Sunrise and sunset only)
84
how to Compass Check via Azimuth of a heavenly body (Any Time of Day or night)
## Footnote LHA is local hour angle. When you’re at the centre of the world (Greenwich), you can work out where the sun should be from the daily pages in the nautical almanac for that moment in time. You can then calculate the LHA if you’re east of Greenwich you always add the degrees East to find the LHA. If west, then it’s subtracted from Greenwich. You might sometimes need to add or subtract 360° to make it work.
85
86
Why do ships need a compass?
To steer and fix position; required by SOLAS V/19.2.1 – all ships must carry a standard magnetic compass independent of power.
87
What are the two main types of navigational compasses?
Magnetic compass & Gyro compass.
88
What is variation?
Difference between True North and Magnetic North, measured East/West of True.
89
What is deviation?
Difference between Magnetic North and Compass North caused by ship’s magnetism.
90
How is deviation reduced?
By permanent magnets & soft-iron correctors (spheres/Flinders bar).
91
What is “swinging the ship”?
Turning ship 360° to check residual deviation on all headings → recorded on deviation card.
92
What’s on a deviation card?
Date, location, compass adjuster details, Master’s signature, correctors fitted, coefficients, residual deviation.
93
Where does deviation change most?
Max on East/West, zero on North/South headings.
94
Limitations of magnetic compass?
Unreliable near poles, subject to errors (retentive magnetism, electrical interference).
95
When must a compass be adjusted?
First installation, unreliable, after major repairs, when equipment nearby changes, every 2 years if not maintained.
96
What are operational checks?
Free gimbal movement, clear fluid, legible card, no leaks/bubbles, working azimuth mirror, illumination okay.
97
Who can adjust a compass in the UK?
A certified Compass Adjuster (UK CoC).
98
What does a gyro compass indicate?
True North (by Earth’s rotation).
99
Advantages of gyro over magnetic?
Not affected by ship’s magnetism, gives direct True bearings.
100
Properties of gyroscope?
Rigidity in space & precession.
101
Where does gyro fail?
Near poles (above 85° lat) – directive force lost.
102
Errors of gyro?
Speed (SOG) error & Latitude error.
103
Gyro maintenance?
Regular inspection, calibration, error checks, cleaning/lubrication, stable power supply, records kept.
104
Manufacturer’s recommended servicing?
Annual inspection; 18-month gyrosphere maintenance; 5-year replacement of gyrosphere & centring pin.
105
What is a Transmitting Heading Device (THD)?
Sends heading info from compass to ship’s systems (radar, AIS, autopilot).
106
What is an Azimuth Mirror?
Device for taking celestial/terrestrial bearings with compass.
107
What is a Pelorus?
Portable instrument for relative bearings to ship’s head.
108
What types of compasses are used in navigation?
Magnetic compass & Gyro compass.
109
Why is a compass required on ships?
To steer and take bearings; required under SOLAS V/19.2.1.
110
Define variation.
Difference between True North and Magnetic North, east or west of True.
111
Define deviation.
Difference between Magnetic North and Compass North, caused by ship’s magnetism.
112
How is deviation corrected?
Using permanent magnets and soft-iron correctors (spheres, Flinders bar).
113
What is “swinging the ship”?
Turning ship through 360° to check and record compass deviation.
114
What info is on a deviation card?
Residual deviation on headings, date, place, adjuster details, Master’s signature, correctors.
115
When must a magnetic compass be adjusted?
On first installation, if unreliable, after repairs, after nearby equipment changes, every 2 years if not maintained.
116
Who can adjust a compass in the UK?
A certified Compass Adjuster with UK CoC.
117
Limitations of magnetic compass?
Errors near poles, affected by magnetism/electrical interference, sluggish in heavy weather.
118
What are the 2 key properties of a gyroscope?
Rigidity in space & Precession.
119
What are the main gyro errors?
Latitude error and speed error.
120
Where does a gyro fail?
Near the poles (>85° latitude).
121
What are advantages of gyro over magnetic?
Not affected by ship’s magnetism, gives direct True bearings, can be repeated to other systems.
122
How is gyro error checked onboard?
By azimuth/altitude of celestial bodies, transit bearings, amplitude of the sun, or radar ranges.
123
What records must be kept of gyro error?
A record in the compass error log (per STCW & Bridge Procedures Guide).
124
What routine checks are made on a magnetic compass?
Free movement, no bubbles, clear liquid, legible card, illumination working, azimuth mirror intact.
125
What routine maintenance for a gyro compass?
Regular checks of repeaters, stable power, calibration, lubrication, error recording.
126
Manufacturer’s servicing for gyro?
Annual inspection; 18-month gyrosphere maintenance; 5-year gyrosphere replacement.
127
What is a Pelorus used for?
Taking relative bearings to the ship’s head.
128
What is an Azimuth Mirror used for?
Taking terrestrial/celestial bearings with the compass.
129
What is a Transmitting Heading Device (THD)?
Device that transmits compass heading to radar, AIS, autopilot.
130
If your gyro fails, what do you rely on?
Magnetic compass (mandatory backup).
131
If compass shows sudden erratic deviation, what do you suspect?
Electrical interference, new equipment nearby, or strong local magnetism.
132
How often should compass performance be checked?
After large alterations of course, and at least once every watch if no major alteration.
133
Why do we record deviation regularly?
To monitor for repair/adjustment needs and confirm accuracy of deviation card.
134
What are the 3 main methods to check a compass?
1. Transit bearings. 2. Amplitude of the Sun (sunrise/sunset). 3. Azimuth of a heavenly body (anytime).
135
How is deviation found using transit?
Take compass bearing of two charted objects in transit. Compare with true bearing from chart. Apply variation → deviation. ## Footnote Example: True = 045°T, Compass = 048° → Error = 3°W. Variation = 2°E → Deviation = 5°W.
136
How do you check compass with amplitude of the sun?
Take bearing of sun at rising/setting. Use almanac declination + latitude → true azimuth. Compare with compass bearing. ## Footnote Note: Take bearing when sun’s upper limb (semi-diameter) touches horizon due to refraction.
137
Steps for compass check using azimuth of sun?
Take sun’s bearing & time. Get GHA & declination from almanac. Calculate LHA = GHA ± longitude. Enter sight reduction tables → extract true azimuth. Compare with compass/gyro bearing. ## Footnote Example: Observed 144°G, True 146°T → Gyro = 2° low.
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