Category: Bridge Equipment

Marine Sextant Explanation

Sextant is a precision instrument used for –

• Measuring altitudes of celestial bodies and horizontal angles between terrestrial objects vertical angles of terrestrial objects.

Principle of Sextant:

1. When a ray of light is reflected by a plane mirror, the angle of incidence is equal to the angle of reflection, while the incident ray, reflected ray and the normal lying in the same plane.
2. When a ray of light, suffers two successive reflections in the same plane, by two plane mirrors, the angle between the incident ray and the final ray is twice the angle between the mirrors.

Formulae for Sextant:-

Reading of Sextant:

• When the sextant reads zero, Index mirror and horizon glasses are parallel to each other.
• When the index bar is rotated through an angle, the angle between the incident ray and the final reflected ray.
• The arc of the sextant is only 60° in extent, Micrometer is provided to measure accurate reading upto 0.1°.

Errors of Sextant:

Two types:

• Adjustable errors:
  • Error of perpendicularity:- Caused when the index mirror is not perpendicular to the plane of the sextant.
  • Side error:- Caused when the horizon glass is not perpendicular to the plane of the sextant.
  • Index error:- When the index bar is set at zero, the plane of the index mirror and horizon glass are NOT parallel to each other.
  • Error of collimation:- When the axis of the telescope is not parallel to the plane of the sextant.
• Non-Adjustable errors:
  • Graduation error:- due to inaccurate graduation of the scale on the arc or of the micrometer/vernier.
  • Shade error:- due to the 2 surfaces of the coloured shades not being exactly parallel to each other.
  • Centering error:- pivot of the index bar not coincident with the centre of the circle of which the arc is a part.
  • Optical Error:- may be caused by the prismatic errors of the mirror or aberrations in the telescope lenses.
  • Back-lash:- Wear on the rack and worm, which forms the micrometer movement would cause a back-lash, leading to inconsistent errors.
• Index error, how to determine:
  • During day time, clamp the index bar at zero and holding the sextant vertically, view the horizon through the telescope.
  • If the true horizon and its reflection appear in the same line, Index error is not present.
  • If they appear displaced vertically, turn the micrometer drum till they are in the same line.
  • The micrometer reading then is the index error, which is on the arc if the micrometer reading is more than zero, off the arc if it is less than zero.

Corrections of Sextant Altitude:-

• Visible horizon: Is the small circle on the earth’s surface, bounding the observer’s field of vision at sea.
• Sensible horizon: Is a small circle on the celestial sphere, the plane of which passes through the observer’s eye, and is parallel to the observer’s rational horizon.
• Rational horizon: The observer’s rational horizon is a great circle on the celestial sphere every point on which is 90° away from his zenith.
• Observed altitude: Of a celestial body is the angle at the observer between the body and the direction to the observer’s visible or sea horizon. The observed altitude is therefore, the sextant altitude corrected
  for any index error.
• Dip: Is the angle at the observer between the plane of observer’s sensible horizon and the direction to his visible horizon. Dip occurs because the observer is not situated at the sea level. The value of dip increases
  as the observer’s height.
• Apparent altitude: Is the sextant altitude corrected for Index error and dip.

A freely suspended Magnet in a Magnetic Compass points towards the North:

• A magnetic compass works because the Earth is like a giant magnet, surrounded by a huge magnetic field. The Earth has two magnetic poles which lie near the North and South poles. The magnetic field of the Earth causes a magnetized ‘needle’ of iron or steel to swing into a north-south position if it is hung from a thread, or if it is stuck through a straw or piece of wood floating in a bowl of water.
• A compass works by utilizing the Earth’s magnetism in order to find directions. Its invention enabled people to perform navigation over long distances, opening up the sea for exploration
• A compass points north because all magnets have two poles, a north pole and a south pole, and the north pole of one magnet is attracted to the south pole of another magnet.
• The Earth is a magnet that can interact with other magnets in this way, so the north end of a compass magnet is drawn to align with the Earth’s magnetic field. Because the Earth’s magnetic North Pole attracts the “north” ends of other magnets, it is technically the “South Pole” of our planet’s magnetic field.

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Notes on Earth’s Magnetism:

• Earth’s magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth’s interior to where it meets the solar wind, a stream of charged particles emanating from the Sun.
• Its magnitude at the Earth’s surface ranges from 25 to 65 microtesla (0.25 to 0.65 gauss). Roughly speaking it is the field of a magnetic dipole currently tilted at an angle of about 10 degrees with respect to Earth’s rotational axis, as if there were a bar magnet placed at that angle at the center of the Earth.
• Unlike a bar magnet, however, Earth’s magnetic field changes over time because it is generated by a geodynamo (in Earth’s case, the motion of molten iron alloys in its outer core).
• The North and South magnetic poles wander widely, but sufficiently slowly for ordinary compasses to remain useful for navigation.
• However, at irregular intervals averaging several hundred thousand years, the Earth’s field reverses and the North and South Magnetic Poles relatively abruptly switch places.
• These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors in the process of plate tectonics.

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‘Variation’ and ‘Deviation’ of Magnetic Compass:

VARIATION:

• The true North Pole and the magnetic north pole are not located at the same spot. This variation causes a magnetic compass needle to point more or less away from true north.
  The amount the needle is offset is called variation because the amount varies at different points on Earth’s surface. Even in the same locality variation usually does not remain constant, but increases or decreases at a certain known rate annually.

The variation for any given locality, together with the amount of annual increase or decrease, is shown on the compass rose of the chart for that particular locality.

DEVIATION:

• The amount a magnetic compass needle is deflected by magnetic  material  in  the  ship  is  called  deviation.
• Although deviation remains a constant for any given compass heading, it is not the same on all headings.  Deviation  gradually  increases,  decreases, increases,  and  decreases  again  as  the  ship  goes  through an entire 360° of swing.
• The magnetic steering compass is located in the pilothouse, where it is affected considerably by deviation.  Usually the standard compass is topside, where the magnetic forces producing deviation are not as strong.
• Courses and bearings by these compasses must be carefully differentiated by the abbreviations PSC (per standard compass), PSTGC (per steering compass), and PGC (per gyrocompass).
• The standard compass provides a means for checking the steering compass and the gyrocompass.

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Notes on Ship’s Magnetism:

• On a ship built up of wood, a magnetic compass would point to magnetic north knowing the variation at that place, the magnetic direction corrected and the true direction obtained, the ships built up of steel structures is of two types, soft iron magnetism and the hard iron magnetism.
• Soft iron magnetism is the induced magnetism and hard iron magnetism is the permanent magnetism.

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Sketch & label a wet card Magnetic Compass:

• Necessity:- The dry card compass is too sensitive for steering purposes, especially in bad weather. Even small disturbances cause the dry card to oscillate. In the wet card compass oscillations are damped, without loss of accuracy, by immersing the card in a liquid. The card therefore has a ‘dead beat’ movement.
• The card:- The wet card is made of mica and is only about 15 cm in diameter. The card is attached to nickel- silver float chamber that has a sapphire cap. The cap rests on iridium tipped pivot. The sapphire has a polishing effect on the iridium tip. This arrangement is practically frictionless.
• The directive element:- In modern wet card compasses the directive element is a ring magnet fitted around the base of the float. The ring magnet offers less resistance to movement and causes less turbulence.
• The bowl:- The diameter of the bowl is about 23 cm in order to reduce disturbances caused by turbulence in the liquid during rotation of the card. The top of the bowl is of transparent glass. The bottom is of frosted glass.
• Allowance for expansion:- One method is to have a small accordion – like expansion chamber attached to the bowl. The chamber increases or decreases in volume, as necessary, as the liquid in the bowl expands or contracts due to changes in atmospheric temperature.
• Suspension:- The bowl of the wet card compass is suspended by gimbals. This bowl, being considerably heavier than that of the dry card compass, does not have a glass hemisphere of alcohol and water attached to its underside. Instead, a ballast weight consisting of a ring of lead, enclosed in brass, is attached along with circumference of the underside of the bowl to bring its centre of gravity below the gimbals.
• Care and Maintenance:- The care and maintenance required for a wet card compass and its binnacle is the same as that for a dry card compass. The only changes / differences are:-
  • The wet compass card, if found defective owing to stickiness of movement, has to be renewed by the manufacturer or his authorized agent. Hence, no spare wet card is carried. Instead, an entire bowl is carried as a spare.
  • In rare cases, a bubble may develop in the wet compass bowl. This has to be removed at the earliest opportunity.

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Correctors on a compass binnacle and why are they required, various corrections to be applied to magnetic compass

The Binnacle:- The binnacle is a cylindrical container made of teak wood and brass. No magnetic materials are used in its construction. Even the screws are of brass and the nails, copper. The compass bowl is slung inside the top portion of the binnacle. The middle potion is accessible by a door and contains an electric bulb. Light from this bulk passes upwards through a slot, through an orange coloured glass fitted over the slot, through the bottom of the compass bowl, to illuminate the compass card from below. The orange colour ensures that the night vision of the observer is not adversely affected.

• Corrector Magnets:- (See Figure) In the centre of the lower half of the binnacle, there are a number of horizontal holes, both fore & aft and athwartships, for ‘hard iron’ or ‘permanent’ corrector magnets which are meant to offset undesirable, disturbing, magnetic effects caused by the ship’s steel hull. The lower two-thirds of the binnacle has a vertical brass tube, at the centre, in which slides a ‘bucket’. This bucket has some magnets in it called ‘heeling error correctors’. The bucket is held in position by a brass chain.

• Quadrantal Correctors:-
  (See Figure) These are two ‘soft iron’ spheres which are fitted in brackets, one on either side of the binnacle. The brackets are slotted so that the distance between the spheres can be altered as desired during compass adjustment.
• Flinders Bar:- (See Figure)
  This is a soft iron corrector, (diameter about 7.5 to 10 cm) inserted in a 60 cm long brass case, fitted vertically on the forward or on the after part of the binnacle.  If the ship has more superstructure abaft the compass, the Flinders bar is fitted on the forward part of the binnacle and vice versa.

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Remove an air bubble from the compass bowl

Removal of bubble: A bubble may form in the bowl owing to the fact that some of the liquid has somehow escaped from the bowl. This is a rare occurrence and must be remedied by following the manufacturer’s instructions. In most compasses:

1. Tilt the bowl until the ‘filter hole’ comes uppermost. This hole is provided on the side of the bowl. Unscrew the stud/ screw provided.
2. Top up with ethyl alcohol. If this is not available, distilled water would do.
3. Screw the stud/ screw back into place.
4. Gently let the bowl return to upright.

In some modern compasses, small bubbles may be removed as follows:-

• Invert the bowl gently. This would cause the bubble to enter a bubble trap provided for this purposes. Gently return the bowl to upright. The bubble should have disappeared.

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Advantages of wet compass over Dry Compass Card

The dry card compass is generally used as a standard compass & the wet card compass as a steering compass. The dry card compass is very sensitive. Even a slight disturbance makes the dry card oscillate. In the wet card compass, the oscillation is damped in the liquid and hence more useful as a steering compass. In some ships, the wet compass is now used as a standard compass, mainly because of the availability of the gyro compass as the main direction indicating instrument.

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Why the vessel is required to be swung once in a year to verify Magnetic Compass Deviation Card?

Explanation:-

• Swinging the compass, or swinging the ship (as the operation is sometimes more accurately called as the ship swings around the compass card which, ideally, remains pointing north), involves taking the vessel to a suitable location in open water with plenty of room for maneuvering. With the vessel steady on each of the eight primary compass points, existing compass headings or bearings are compared with what we know the actual magnetic headings or bearings should be, the difference being the deviation.
• During the process, any magnetic fields, created by the ship’s structure, equipment, etc, which cause the compass to deviate are reduced or, if possible, eliminated, by creating equal but opposite magnetic fields using compensating correctors. These are placed inside the compass binnacle or adjacent to the compass:
  • Magnets are aligned fore and aft and athwartships to create horizontal magnetic fields to compensate for the permanent horizontal components of the ship’s magnetism.
  • Soft iron correcting spheres or plates and the Flinders bar compensate for the induced magnetism caused by the effect the earth’s magnetic field has on the ship’s magnetism.
  • Heeling error magnets compensate for the vertical component of the ship’s magnetism.
• The timing and logistics of this operation are often governed by the tide, the weather and other vessels in the vicinity. The time it takes to swing and adjust the compass is also influenced by the condition and accessibility of the compass and correctors, the manoeuvrability of the vessel, the skill of the helmsman and the complexity of, and reasons for, the deviating magnetic fields involved.
• On successful completion of compass swing, a table recording any remaining residual deviation and a statement as to the good working order of the compass will be issued. A current deviation card / certificate of adjustment is a legal requirement on all sea going commercial vessels.
• Deviation can be determined by a number of methods: the sun’s azimuth or known bearings of distant objects, such as a mountain peak or lighthouse are considered most accurate. In certain circumstances, such as poor visibilty, calibration is carried out by making comparisons with other navigation instruments, such as a gyro or GPS compass.
• Using other navigation instruments to find deviation is only satisfactory if the absolute accuracy of these instruments has first been verified, or any known error is factored into the calculations. Most professionals prefer something tangible, such as a fixed landmark, with a known position and bearing to work with.

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What is Dip? How compass is kept horizontal in varying latitudes?

Magnetic dip Error:-

• Magnetic dip is the tendency of the compass needles to point down as well as to the magnetic pole.
• Dip is greatest near the poles and least near the Magnetic Equator.
• The compass card is designed to operate in the horizontal, therefore, any movement from the horizontal plane introduces dip error.
• The needle of your magnetic compass will be parallel with Earth’s surface at the Magnetic Equator, but will point increasing downward as it is moved closer to the Magnetic Pole.
• Northerly turning error is due to the mounting of the compass. Since the card is balanced in fluid, when the vessel turns, the card is also banked as a result of centrifugal force.
• While the card is banked, the vertical component of the Earth’s magnetic field causes the north-seeking ends of the compass to dip to the low side of the turn. When making a turn from a northerly heading, the compass briefly gives an indication of a turn in the opposite direction.
• When making a turn from the south, it gives an indication of a turn in the correct direction but at a faster rate.

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Explanation of a Free Gyroscope:

Gyroscope having three degrees of freedom is called “FREE GYROSCOPE”

Properties of Free Gyroscope:-

1. Gyroscopic inertia or rigidity in space
2. Precession

1. Gyroscopic Inertia:- A freely spinning gyroscope will maintain its axis of spin in the same direction with respect to space irrespective of how its supporting base is turned. It resists any attempt to change its direction of spin. Thus a free gyroscope has high directional stability. This property is called GYROSCOPIC INERTIA or RIGIDITY IN SPACE.
2. Gyro Precession:- Precession is the angular displacement of the spin axis of the gyroscope when a torque is applied to gyroscope. Hence, when a torque is applied to the spin axis the resulting movement will be in the direction at right angle to the applied torque. Earth is also a free gyroscope pointing north axis toward Polaris. (rigidity in space). We all are also aware that earth also possesses force of gravity.

First property of free gyro scope is useful. However, due to the placing of this gyroscope on the surface of the earth it will be moved along the direction of rotation of the earth. As such the gyroscope will have an apparent motion. For example, at night if the gyroscope is made to point in the direction of a star, then the gyroscope will follow the star as the earth rotates and the star apparently moves in the sky.

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Tilt and Drift in a Gyro compass

• Tilt is elevation or depression of the spin axis above or below the horizon.
• Drift is the movement of the spin axis in the direction of azimuth.
• Rate of tilting in degrees per hour = 15^O sine Azimuth * cosine Latitude
• Rate of Drift in degrees per hour = 15^O sine Latitude

Tilt:-

• If a free gyroscope is situated on the equator and lies with its axis East West and horizontal, it can be assumed of as pointing to a star with zero declination and is about to rise.
• The East End of the gyroscope axis will follow the movement of this star and will tilt upwards as the star rises.
• After nearly six hours the axis will be vertical and after nearly twelve hours the gyroscope will have turned completely over with the axis again horizontal but now the original East end of the axis would be pointing to the star setting due West.
• After one sidereal day, the gyroscope would have tilted through 360^O and the star would again be rising.
• This rate of tilting of 360^O in a day is a rate of 15^O per hour.
• If the gyroscope had been situated on the equator with its axis lying in the North – South direction, then the North end would be pointing towards the Pole star and would then have no apparent movement relative to the Earth.
• The rate of tilting thus varies from zero when the axis is lying North – South to a maximum when it is lying East – West. That is the rate of tilting varies as the Sine of the Azimuth.
• A free gyroscope situated at a pole with its axis horizontal would have an apparent turntable motion due to the Earth’s rotation.
• That is it would follow a fixed star around the horizon but it would not rise or set.
• The rate of tilting thus varies from a maximum when the latitude is 0^O to zero when the latitude is 90^O. That is the rate of tilting varies as the Cosine of the Latitude.
• Rate of tilting in degrees per hour = 15^O sine Azimuth * cosine Latitude.
• The direction of tilting is such that the end of the gyroscope axis, which lies to the East of the meridian, tilts upwards and the end of the axis, which lies to the West of the meridian tilts downward.

Drift:-

• Drift is the apparent movement of a gyroscope in azimuth.
• A free gyroscope situated at the North Pole with its axis horizontal will have an apparent movement, which is entirely in the horizontal plane.
• Its axis will appear to move in a clockwise direction when viewed from above. This would be due to the real counter clockwise rotation of the earth beneath, this circular motion causes the gyroscope to drift through 360^O in one sidereal day, that is at a rate of 15^O per hour.
• A free gyroscope situated at the equator with its axis horizontal will not drift at all, irrespective of whether its axis is set in the North – South or East – West line.
• The rate of drift for a gyroscope with its axis horizontal thus varies from a maximum at the poles to zero at the equator.
• That is the rate of drift varies as the sine of the latitude. For a free gyroscope with its axis horizontal: Rate of Drift in degrees per hour = 15^O sin Latitude. The direction of drift depends upon hemisphere so that the North end of a horizontal gyroscopic axis drifts to the eastwards in the Northern hemisphere but to the Westwards in the southern hemisphere.

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Course, Latitude and Speed Error in a Gyro Compass:

• The gyro compass settles in the N/S direction by sensing Earth’s spinning motion. Same gyro compass when placed on a ship also senses the ship’s motion. And therefore, the axis of gyro compass settles in a direction which is perpendicular to the resultant of the Earth’s surface speed and the ship’s velocity.
• The direction, in which the compass settles, is therefore, different to the direction of the True North and depends on ship’s course, speed and latitude of the observer.
• This error also increases as the observer’s latitude increases. The error is westward on all Northerly courses and vice-versa. In exactly E-W courses, the error is nil. In exactly N-S courses, the error is maximum.
• To compensate for steaming error, a speed rider is provided, which in association with the latitude rider, shifts the lubber line equal to steaming error in the appropriate direction.

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How is the Gyro Compass System made North Seeking?

North Seeking Gyro:-

• In order to damp unwanted oscillation, we need to achieve damping in tilt.
• This is done by means of offset slightly to the east of vertical, resulting in component of the same force producing the required torque.
• The magnitude and direction of this force is pre-calculated to achieve the required damping oscillation.
• The amplitude of each oscillation is reduced to 1/3^rd of previous oscillation.
• The spin axis reaches equilibrium and settles in a position at which drifting is counteracted by control precession & the damping precession counteracts tilting.
• Finally, the gyro settles in the meridian & becomes north seeking.

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Latitude course & speed error with respect to the Gyro Compass Explanation

Course, Speed and Latitude Error (Speed Error):-

• The gyro compass settles in the N/S direction by sensing Earth’s spinning motion.
  Same gyro compass when placed on a ship also senses the ship’s motion and therefore, the axis of gyro compass settles in a direction which is perpendicular to the resultant of the Earth’s surface speed and the ship’s velocity.
• The direction, in which the compass settles, is therefore, different to the direction of the True North and depends on ship’s course, speed and latitude of the observer.
• This error also increases as the observer’s latitude increases. The error is westward on all Northerly courses and vice-versa.
• In exactly E-W courses, the error is nil. In exactly N-S courses, the error is maximum.
• To compensate for speed error, a speed rider is provided, which in association with the latitude rider, shifts the lubber line equal to speed error in the appropriate direction.
• This error can be corrected automatically by a mechanism which moves the lubber line by an amount equal to the error, or it can be found from correction tables or from a portable correction calculator and then applied as necessary.

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Three Degrees of Freedom:

As a mechanical device a gyroscope may be defined as a system containing a heavy metal wheel or rotor, universally mounted so that it has three degrees of freedom: spinning freedom, about an axis perpendicular through its center; tilting freedom, about a horizontal axis at right angles to the spin axis; and veering freedom, about a vertical axis perpendicular to both the other axes. The three degrees of freedom are obtained by mounting the rotor in two concentrically pivoted rings, called inner and outer rings. The whole assembly is known as the gimbal system of a free or space gyroscope. The gimbal system is mounted in a frame, so that in its normal operating position, all the axes are mutually at right angles to one another and intersect at the centre of gravity of the rotor.

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Gyro Compass ‘Tangent Error’ Explanation

• On a non-pendulous gyrocompass where damping is accomplished by offsetting the point of application of the force of mercury ballistic, the angle between the local meridian and the settling position or spin axis.
• Where the offset of the point of application of mercury ballistic is to the east of the vertical axis of the gyrocompass, the settling position is to the east of the meridian in north latitudes and to the west of the meridian in south latitudes.
• The error is so named because it is approximately proportional to the tangent of the latitude in which the gyrocompass is operating.
• The tangent latitude error varies from zero at the equator to a maximum at high northern and southern latitudes.

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Starting a Gyro Compass:

• A gyro needs time to settle on the meridian, the time taken will depend on the make, model & geographical location of the gyro.
• The settling time may be between one & several hours, manual provided by the manufacturer has to be consulted before switching on the gyro.
• If compass has been switched off, it will take longer time to bring compass into use.
• Following is the procedures for Sperry MK 37 digital.
• At power-up and prior entering the settling mode, system performs automatic procedure to determine if the equipment is operating within specified parameters.
• If gyro is stationary the system opts for cold start, if rotating a hot start if programmed.
• During a cold start, if no heading data is input to system when requested the gyro selects automatic. Once the power is switched on, two bleeps prompts for heading input, if the heading data is not entered within 5 minutes, the gyro switches to an auto level process. (In some older make, the slewing is done manually, a
  special key is provided for the same which is inserted into a slot).
• If heading data is fed the rotor is automatically slewed.
• The rotor is brought up to required speed within 14 minutes and the gyro will subsequently settle within an hour.
• If heading data is not fed, the gyro will settle within 5 hrs.

Some more points:-

• If entered heading is in error by more than 20 deg, gyro may take about 5 hours to settle.
• Once gyro is settled, synchronize the repeaters (radar & ECDIS also need synchronization.)
• If speed & latitude is fed manually, it should be done prior to starting the gyro.
• Once settled, compass error should be checked & compasses should be checked more frequently.

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Emergency Position Indicating Radio Beacon (EPIRB):

• EPIRB stands for Emergency Position Indicating Radio Beacon.
• An EPIRB is meant to help rescuers locate you in an emergency situation, and these radios have saved many lives since their creation in the 1970s.
• Boaters are the main users of EPIRBs.
• A modern EPIRB is a sophisticated device that contains:
  • A 5-watt radio transmitter operating at 406 MHz (see How the Radio Spectrum Works for details on frequencies).
  • A 0.25-watt radio transmitter operating at 121.5 MHz.
• A GPS receiver once activated, both of the radios start transmitting. Approximately 24,000 miles (39,000 km) up in space, a GOES weather satellite in a geosynchronous orbit can detect the 406-MHz signal. Embedded in the signal is a unique serial number, and, if the unit is equipped with a GPS receiver, the exact location of the radio is conveyed in the signal as well. If the EPIRB is properly registered, the serial number lets the Coast Guard know who owns the EPIRB. Rescuers in planes or boats can home in on the EPIRB using either the 406-MHz or 121.5-MHz signal.

How do VTS contribute to safety of life at sea?

VESSEL TRAFFIC SERVICE (VTS):- A vessel traffic service (VTS) is a marine traffic monitoring system established by harbour or port authorities, similar to air traffic control for aircraft. Typical VTS systems use radar, closed-circuit television (CCTV), VHF radiotelephony and automatic identification system to keep track of vessel movements and provide navigational safety in a limited geographical area

SOLAS CHAPTER V – REGULATION 12 – Vessel traffic services:-

1. Vessel traffic services (VTS) contribute to safety of life at sea, safety and efficiency of navigation and protection of the marine environment, adjacent shore areas, work sites and offshore installations from possible adverse effects of maritime traffic.
2. Contracting Governments undertake to arrange for the establishment of VTS where, in their opinion, the volume of traffic or the degree of risk justifies such services.
3. Contracting Governments planning and implementing VTS shall, wherever possible, follow the guidelines developed by the Organization*. The use of VTS may only be made mandatory in sea areas within the territorial seas of a coastal State.
4. Contracting Governments shall endeavor to secure the participation in, and compliance with, the provisions of vessel traffic services by ships entitled to fly their flag.
5. Nothing in this regulation or the guidelines adopted by the Organization shall prejudice the rights and duties of Governments under international law or the legal regimes of straits used for international navigation and archipelagic sea lanes.

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Benefits of implementing a VTS

The purpose of VTS is to improve the maritime safety and efficiency of navigation, safety of life at sea and the protection of the marine environment and/or the adjacent shore area, work sites and offshore installations from possible adverse effects of maritime traffic in a given area. VTS may also have a role to play in security.

The benefits of implementing a VTS:-

• It allows identification and monitoring of vessels, strategic planning of vessel movements and provision of navigational information and navigational assistance.
• It can assist in reducing the risk of pollution and, should it occur, coordinating the pollution response. Many authorities express difficulty in establishing justifiable criteria for identifying whether VTS is the most appropriate tool to improve the safety and efficiency of navigation, safety of life and the protection of the environment.
• A VTS is generally appropriate in areas that may include any, or a combination, of the following:
  • high traffic density;
  • traffic carrying hazardous cargoes;
  • conflicting and complex navigation patterns;
  • difficult hydrographical, hydrological and meteorological elements;
  • shifting shoals and other local hazards and environmental considerations;
  • interference by vessel traffic with other waterborne activities;
  • number of casualties in an area during a specified period;
  • existing or planned vessel traffic services on adjacent waterways and the need for cooperation between neighbouring states, if appropriate;
  • narrow channels, port configuration, bridges, locks, bends and similar areas where the progress of vessels may be restricted; and
  • existing or foreseeable changes in the traffic pattern in the area.

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Objectives of VTS:

1. The purpose of vessel traffic services is to improve the safety and efficiency of navigation, safety of life at sea and the protection of the marine environment and/or the adjacent shore area, worksites and offshore installations from possible adverse effects of maritime traffic.
2. A clear distinction may need to be made between a Port or Harbour VTS and a Coastal VTS. A Port VTS is mainly concerned with vessel traffic to and from a port or harbour or harbours, while a Coastal VTS is mainly concerned with vessel traffic passing through the area. A VTS could also be a combination of both types. The type and level of service or services rendered could differ between both types of VTS; in a Port or Harbour VTS a navigational assistance service and/or a traffic organization service is usually provided for, while in a Coastal VTS usually only an information service is rendered.
3. The benefits of implementing a VTS are that it allows identification and monitoring of vessels, strategic planning of vessel movements and provision of navigational information and assistance. It can also assist in prevention of pollution and co-ordination of pollution response. The efficiency of a VTS will depend on the reliability and continuity of communications and on the ability to provide good and unambiguous information. The quality of accident prevention measures will depend on the system’s capability of detecting a developing dangerous situation and on the ability to give timely warning of such dangers.
4. The precise objective of any vessel traffic service will depend upon the particular circumstances in the VTS area and the volume and character of maritime traffic as set forth in 3.2 of these Guidelines and Criteria.

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Use of VTS in navigation:

• Automatic Identification System (AIS) is a system that makes it possible to monitor and track ships from suitably equipped ships, and shore stations. AIS transmissions consist of bursts of digital data ‘packets’ from individual stations, according to a pre-determined time sequence.
• AIS makes navigation safer by enhancing situational awareness and increases the possibility of detecting other ships, even if they are behind a bend in a channel or river or behind an island in an archipelago.
• AIS can also solve the problem inherent with radars, by detecting smaller craft, fitted with AIS, in sea and rain clutter.

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Reporting procedures of VTS and SRS:

Reporting procedures of VTS and SRS:- Standard Reporting Procedures, IMO Resolution A.851 (20) – ‘General Principles for Ship Reporting Systems and Ship Reporting Requirements’.

Types of Communication Messages and Message Markers:-

• To facilitate shore-to-ship and ship-to-shore communication in a VTS environment, one of the following eight message markers should be used to increase the probability of the purpose of the message being properly understood.
• It is at the discretion of the shore personnel or the ship’s officer whether to use one of the message markers and, if so, which marker is applicable to the situation.
• If used, the message marker is to be spoken preceding the message or the corresponding part of the message.
• The contents of all messages directed to a vessel should be clear; IMO Standard Marine Communication Phrases should be used where practicable.

Elements of the Ship’s Routeing System:

The objective of ships’ routeing is to “improve the safety of navigation in converging areas and in areas where the density of traffic is great or where freedom of movement of shipping is inhibited by restricted sea room, the existence of obstructions to navigation, limited depths or unfavourable meteorological conditions”. Ships routeing systems can be established to improve safety of life at sea, safety and efficiency of navigation, and/or increase the protection of the marine environment.

Elements used in traffic routeing systems include:

• Traffic separation scheme: a routeing measure aimed at the separation of opposing streams of traffic by appropriate means and by the establishment of traffic lanes.
• Traffic lane: an areas within defined limits in which one-way traffic is established, natural obstacles, including those forming separation zones, may constitute a boundary.
• Separation zone or line: a zone or line separating traffic lanes in which ships are proceeding in opposite or nearly opposite directions; or separating a traffic lane from the adjacent sea area; or separating traffic lanes designated for particular classes of ship proceeding in the same direction.
• Roundabout: a separation point or circular separation zone and a circular traffic lane within defined limits.
• Inshore traffic zone: a designated area between the landward boundary of a traffic separation scheme and the adjacent coast.
• Recommended route: a route of undefined width, for the convenience of ships in transit, which is often marked by centreline buoys.
• Deep-water route: a route within defined limits which has been accurately surveyed for clearance of sea bottom and submerged articles.
• Precautionary area: an area within defined limits where ships must navigate with particular caution and within which the direction of flow of traffic may be recommended.
• Area to be avoided: an area within defined limits in which either navigation is particularly hazardous or it is exceptionally important to avoid casualties and which should be avoided by all ships, or by certain classes of ships.

Before Implementing or starting a TSS or Vessel routeing system the below mentioned information should be collected:

1. Data about the area and problem or threat thereof:
   • Resources within are
   • Potential navigation hazard.
   • Environmental factors
2. Data about the ship traffic (e.g., vol., traffic patterns)
3. Information regarding existing measures
4. Foreseeable changes in traffic patterns
5. Information regarding incident history
6. Existing aids to navigation
7. Charts (are they up to date?)
8. IMO documents (models)

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VTS Category – Information Service:

Defined by IMO as ‘a service to ensure that essential information becomes available in time for on-board navigational decision-making’. The information service comprises broadcasts of information at fixed times or when deemed necessary by the VTS Authority or at the request of a vessel, and may include for example :

1. Reports on the position, identity and intentions of other traffic;
2. Waterway conditions;
3. Weather;
4. Navigational hazards;
5. Any other factors that may influence the vessel’s transit.

Navigational Assistance Service: Defined by IMO as ‘a service to assist on-board navigational decision-making and to monitor its effects, especially in difficult navigational or meteorological circumstance or in case of defect or deficiencies.’ There may be occasions when an increased or new risk makes it appropriate to enhance the service through the additional provision of a Navigational Assistance Service. The IMO Resolution explains the key tenets of this service as:

1. A service that is intended to assist in the navigational decision making process on board and to monitor its effects.
2. Particularly relevant to:
   • Difficult navigational circumstances;
   • Difficult meteorological conditions;
   • Vessel defects or deficiencies.
3. A service that is rendered at the specific request of a vessel or by a VTS Authority when deemed necessary.
4. A service that is provided only on specified occasions and under clearly defined circumstances.
5. The beginning and end of navigational assistance should be clearly stated by the vessel or the VTS and acknowledged by the other party.

The IALA VTS Manual indicates that Navigational Assistance Service can fall into one of two categories, depending on whether navigational information or advice is given. Navigational Assistance Service consisting only of the giving of navigational information is referred to in this guidance as Contributory. Navigational Assistance Service consisting of the giving of navigational advice as well as navigational information is referred to as Participatory. The definitions, particularly of the Participatory service, are open to interpretation and for the avoidance of doubt their meaning is refined and expanded as follows.

1. Contributory Navigational Assistance Services:

A Contributory Navigational Assistance Service is solely the provision of factual navigational information to assist the on-board decision making process.

The information is provided either in response to a specific request from a vessel or when the VTS Authority perceives that the information would be of use to the vessel.

A Contributory Navigational Assistance Service may include information on :

1. Courses and speeds made good;
2. Positions relative to fairway axis and waypoints;
3. Positions, identities and intentions of surrounding traffic;
4. Warnings of dangers.

1. Participatory Navigational Assistance Service:

In a Participatory Navigational Assistance Service, the VTS can become involved in the on-board decision making process by providing navigational advice. Through the exchange of information between vessel and VTS, an agreed course of action may emerge. However, any recommendations from the VTS must be result orientated and must not include specific instructions on courses to steer and speed through the water. As with the Contributory service, it is provided on specific request or when perceived necessary by the VTS Authority, in the interests of safety.

Dependent on the complexity of the situation and the level of risk mitigation required, consideration should be given to the following :

(1) Authorisations of operators providing the service and recording of such authorisations;

(2) The need to reflect this category of service in the On the Job Training of VTS Operators;

(3) Operator work load during Participatory Navigational Assistance Service, including other responsibilities and activities, and the number of vessels being monitored or advised;

(4) Use of a discrete frequency;

(5) Increased traffic restrictions;

(6) The requirements of the Pilotage Act 1987.

Traffic Organisation Service: Defined by IMO as ‘a service to prevent the development of dangerous maritime traffic situations and to provide for the safe and efficient movement of vessel traffic within the VTS Area.’

The provision of a Traffic Organisation Service includes a comprehensive and dedicated service, throughout the declared service period, without which the long term planning of traffic movement and developing situation would not be possible. This service is, by its nature, more comprehensive than an Information Service, the capability of which it necessarily includes.

Where the risks identified through the formal risk assessment are such that the only appropriate mitigating measure is the provision of service that monitors vessel traffic movement and enforces adherence to governing rule and regulation, a Traffic Organisation Service should be considered appropriate.

A Traffic Organisation Service is concerned with, for example :

1. Forward planning of vessel movements;
2. Congestion and dangerous situations;
3. The movement of special transports;
4. Traffic clearance systems;
5. VTS sailing plans;
6. Routes to be followed;
7. Adherence to governing rules and regulations.

Instructions given as part of a Traffic Organisation Service shall be result orientated, leaving the details of the execution to the vessel.

Rate of Turn Indicator

Introduction:

• IMO Recommendations on passage planning lay stress on controlled navigation. The passages in narrow channels or harbors are either along straight courses or along arcs of circles.
• As per SOLAS 2000 Amendment Chapter V Regulation 19.2.9, it is mandatory for ships over 50,000 GRT to have a rate of turn indicator. IMO recommends that large alteration of courses have to be planned along circular tracks with wheel over point marked.
• The Rate of Turn Indicator (ROTI) is a device which indicates the instantaneous rate at which the ship is turning. It is fitted on ship as an independent fitment integrated with the steering gear/auto pilot.

• When the wheel is turned over, the ship actually traverses along a curved track rather than performing a sharp turn about a point. It is very useful knowing the nature of this traversed path the ship takes which can help in planning:
  • The desired turn with given radius
  • Desired speed of the vessel to execute the planned turn.
  • When to apply the turn (wheel over point).

RATE OF TURN FORMULAE:

ROT = v/R

Where,

v – Speed of the vessel .

R – Radius from a fixed point around which to turn the ship.

Note: ROT is directly proportional to the speed.

ROT is inversely proportional to radius.

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Use of ROTI (Rate Of Turn Indicator):-

1. The rate of turn indicator is equipment which indicates the instantaneous rate at which the ship is turning.
2. This indicator is fed 60 to 200 pulses per minute from the steering repeater and from this input it works out the instantaneous rate of turn.
3. The dial is marked usually 0^O to 60^O on either side. As per IMO performance standard the dial should be marked not less than 0^O to 30^O per minute on either side and graduated in intervals of 1^O per minute.
4. As we know that when ship turn she actually traverses some distance round the arc of a circle and cannot execute a sharp turns about a point.
5. When ship is making a turn it precise the ship track uncertain due to her characteristic, condition, weight and UKC.
6. Therefore navigator uses the touch of ship track during the turn that is uncertain of position until the ship is steadied on the new course.
7. IMO recommends for passage planning is not only monitor the position on straight course but also on curve section of passage. This can be achieved by the technique called radius turn by the help of roti and ship’s log.

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Ship Reporting System (SRS):

• A ship reporting system enables the SMC to quickly:
  • Identify vessels in the vicinity of a distress situation, along with their positions, courses, and speeds
  • Be aware of other information about the vessels, which may be valuable (whether a doctor is aboard, etc.)
  • Know how to contact the vessels
• Masters of vessels are urged to send regular reports to the authority operating a ship reporting system for SAR.

The Automated Mutual-Assistance Vessel Rescue (AMVER) System:-

• AMVER is a worldwide system operated exclusively to support SAR and make information available to all RCCS.
  • There is no charge for vessels to participate in, nor for RCCs to use AMVER
  • Many land-based providers of communications services world-wide relay ship reports to AMVER free of charge.
• Any merchant vessel of 1,000 gross tons or more on any voyage of greater than 24 hours is welcome to participate.
• Benefits of participation include:
  • Improved likelihood of rapid aid during emergencies
  • Reduced number of calls for assistance to vessels unfavorably located to respond
  • Reduced response time to provide assistance.

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Types of Reports does a ship need to send out:

Reports should be sent as follows:

• Sailing plan (SP) – Before or as near as possible to the time of departure from a port within a reporting system or when entering the area covered by a system.
• Position report (PR) – When necessary to ensure effective operation of the system.
• Deviation report (DR) – When the ship’s position varies significantly from the position that would have been predicted from previous reports, when changing the reported route, or as decided by the master.
• Final report (FR) – On arrival at destination and when leaving the area covered by a system.
• Dangerous goods report (DG) – When an incident takes place involving the loss or likely loss overboard of packaged dangerous goods, including those in freight containers, portable tanks, road and rail vehicles and shipborne barges, into the sea.
• Harmful substances report (HS) – When an incident takes place involving the discharge or probable discharge of oil (Annex I of MARPOL) or noxious liquid substances in bulk (Annex II of MARPOL).
• Marine pollutants report (MP) – In the case of loss or likely loss overboard of harmful substances in packaged form, including those in freight containers, portable tanks, road and rail vehicles and shipborne barges, identified in the International Maritime Dangerous Goods Code as marine pollutants (Annex III of MARPOL).
• Any other report – Any other report should be made in accordance with the system procedures as notified in accordance with paragraph 9 of the General Principles.

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Importance of Ship Reporting Systems for safe navigation:

1. Ship reporting systems contribute to safety of life at sea, safety and efficiency of navigation and/or protection of the marine environment. A ship reporting system, when adopted and implemented in accordance with the guidelines and criteria developed by the Organization pursuant to this regulation, shall be used by all ships, or certain categories of ships or ships carrying certain cargoes in accordance with the provisions of each system so adopted.
2. The Organization is recognized as the only international body for developing guidelines, criteria and regulations on an international level for ship reporting systems. Contracting Governments shall refer proposals for the adoption of ship reporting systems to the Organization. The Organization will collate and disseminate to Contracting Governments all relevant information with regard to any adopted ship reporting system.
3. The initiation of action for establishing a ship reporting system is the responsibility of the Government or Governments concerned. In developing such systems provision of the guidelines and criteria developed by the Organization shall be taken into account.
4. Ship reporting systems not submitted to the Organization for adoption do not necessarily need to comply with this regulation. However, Governments implementing such systems are encouraged to follow, wherever possible, the guidelines and criteria developed by the Organization. Contracting Governments may submit such systems to the Organization for recognition.
5. Where two or more Governments have a common interest in a particular area, they should formulate proposals for a co-ordinated ship reporting system on the basis of agreement between them. Before proceeding with a proposal for adoption of a ship reporting system, the Organization shall disseminate details of the proposal to those Governments which have a common interest in the area covered by the proposed system. Where a co-ordinated ship reporting system is adopted and established, it shall have uniform procedures and operations.
6. After adoption of a ship reporting system in accordance with this regulation, the Government or Governments concerned shall take all measures necessary for the promulgation of any information needed for the efficient and effective use of the system. Any adopted ship reporting system shall have the capability of interaction and the ability to assist ships with information when necessary. Such systems shall be operated in accordance with the guidelines and criteria developed by the Organization pursuant to this regulation.
7. The master of a ship shall comply with the requirements of adopted ship reporting systems and report to the appropriate authority all information required in accordance with the provisions of each such system.
8. All adopted ship reporting systems and actions taken to enforce compliance with those systems shall be consistent with international law, including the relevant provisions of the United Nations Convention on the Law of the Sea.
9. Nothing in this regulation or its associated guidelines and criteria shall prejudice the rights and duties of Governments under international law or the legal regimes of straits used for international navigation and archipelagic sea lanes.
10. The participation of ships in accordance with the provisions of adopted ship reporting systems shall be free of charge to the ships concerned.
11. The Organization shall ensure that adopted ship reporting systems are reviewed under the guidelines and criteria developed by the Organization.

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Explanation of how the ship reporting system provides the necessary information for search & rescue in case of distress:

Ship Reporting System:-

• A ship reporting system enables the SMC to quickly:
  • identify vessels in the vicinity of a distress situation, along with their positions, courses, and speeds
  • be aware of other information about the vessels, which may be valuable (whether a doctor is aboard, etc.)
  • know how to contact the vessels.
• Masters of vessels are urged to send regular reports to the authority operating a ship reporting system for SAR.

The Automated Mutual-Assistance Vessel Rescue (AMVER) System:-

• AMVER is a worldwide system operated exclusively to support SAR and make information available to all RCCS.
  • there is no charge for vessels to participate in, nor for RCCs to use AMVER
  • many land-based providers of communications services world-wide relay ship reports to AMVER free of charge.
• Any merchant vessel of 1,000 gross tons or more on any voyage of greater than 24 hours is welcome to participate.
• Benefits of participation include:
  • improved likelihood of rapid aid during emergencies
  • reduced number of calls for assistance to vessels unfavorably located to respond
  • reduced response time to provide assistance.

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Short notes on INSPIRES with respect to Ship Reporting System:

INDIAN Ship position and information reporting system (INSPIRES) :

Indian navy in co-ordination with DG of Shipping has established INSPIRES to exercise effective open ocean vessel management, to provide security to vessel, weather forecast to enhance safety of navigation and monitor incidence of pollution. An Indian Naval communication center (COMCENs) Mumbai and Vizag are functioning as the shore stations for receiving INSPIRES messages from vessels. All Indian vessels including coasting/ fishing vessels of tonnage 300 GRT and above shall participate in this reporting system. All vessels other than Indian ships of tonnage 100 GRT and above are encouraged to participate in this reporting system.

INDIAN SHIP REPORTING SYSTEM:

INDIAN SHIP POSITION AND INFORMATION REPORTING SYSTEM (INSPIRES) SHIP REPORTING SYSTEM FOR SAR (INDSAR):

The INSPIRES has been established to achieve the following objectives:

• To provide up to date information on shipping for search and rescue.
• For effective vessel traffic management service.
• For weather forecasting.
• For prevention and containment of marine pollution.

This reporting system has wider area of coverage in the Indian Ocean. An Indian Naval Communication Centre (COMCENs) Mumbai and Vishakhapatnam are functioning as the shore stations for receiving INSPIRES messages from all vessels.

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Explanation of Voyage Data Recorder (VDR):

• A VDR or voyage data recorder is an instrument installed on a ship to continuously record vital information related to the operation of a vessel.
• It contains a voice recording system for a period of at least last 12 hours.
• This recording is recovered and made use of for investigation in events of accidents.
• The data records covering the last 12 hours are continuously overwritten by the latest data.
• A VDR is capable of withstanding heavy weather, collisions, fires and pressure conditions even when a ship is at a depth of several meters in water.

Working of VDR:

• There are various sensors placed on bridge of the ship and on prominent location from which the required data is continuously collected.
• This data which comprises of voices, various parameters, ships location etc. are then fed to a storage unit where the whole input is recorded and saved for at least 12 hours.
• There is also a record button provided in the bridge unit so that after pushing button (say during starting of any incident like collision or grounding), the recorder will start recording new set of information from that period of time.
• The data collected by VDR is digitalised, compressed, and is stored in a protective storage unit which is mounted in a safe place.
• This tamper proof storage unit can be a retrievable fixed or floating unit connected with EPIRB for early location in the event of accident.

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Main Components of VDR:

• Data Management Unit: It acquires data from various sources using interfaces, processes and stores the data in a specified format.
• Audio Module:
  • It consists of an audio mixer for recording audio from microphones placed in the wheelhouse, bridge wings, ECR and various other locations.
  • VHF audio signals can also be interfaced with this unit.
• Final Recording Unit:
  • This is a fire resistant, pressure tight storage medium to store recorded data.
  • The capsule is resistant against shock, penetration, fire, deep sea pressure and immersion. Housed in a highly visible protective capsule which can withstand high temperatures (1100^OC) and deep sea pressure of 6000 m.
• Remote Alarm Module: This is a small panel connected to the Data Management Unit that will sound an alarm should any error or fault develop in the equipment.
• Replay Station:
  • This is an optional module for downloading and replaying the recorded data.
  • The data when played back can help in casualty investigations as well as for self analysis.
• Information Recorded:-
  • Date & Time from GPS every 1s
  • Position & Datum – Lat/Long and datum from GPS, Loran-C etc. The source of data is identified on playback.
  • Speed (water / ground) recorded every 1s to 0.1k resolution
  • Heading (gyro or magnetic) is recorded at intervals of 1s to a resolution of 0.1 deg
  • Depth under keel from echo sounder to a resolution of 0.1m.
  • Auto pilot settings for speed, latitude, rudder limit, off-course alarms etc.
  • Bridge audio in real time, both internal & external (150-6000Hz). The mic test beeps every 12 hrs & this is recorded.
  • Radar image recorded every 15s includes range rings, EBLs, VRMs, radar maps, parts of SENC & other essential navigational indications.
  • Wind speed/direction from the Anemometer is recorded & stored individually with time stamps.
  • VHF communication from 2 VHFs are recorded for both transmitted and received audio signals. Audio is compressed and labeled VHF 1 & VHF 2.
  • Hull openings & watertight doors status is received every 1s and stored with time stamps
  • Hull stresses are received and stored with time stamps.
  • Thruster status (bow/stern) can be recorded for their order and response
  • Rudder order and response angle is recorded to a resolution of 1 deg
  • Engine order and response from the telegraph or direct engine control with shaft revolution and ahead and astern indicators are recorded to a resolution of 1 rpm
  • AIS target data is recorded as a source of information regarding other ships.
  • Alarms are recorded with time stamps. All IMO mandatory alarms as well as other audible alarms are stored individually by the bridge audio microphones.

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Purpose of VDR:

• The main purpose of VDR is to record and store ship’s critical parameters to facilitate reconstruction of the incident for the purpose of analysis
• Additionally navigator can use this for self-analysis, as lessons-learning tool and thus improvement of procedures in the future.
• VDR can be used to identify cause of an accident and thus make major contribution to maritime safety.
  • The benefits are:
  • Promotion of safe practices
  • Accident investigation and enquiry
  • Response assessment and study
  • Training aid and support
  • Reduction in insurance costs
  • Statistics generation

VOYAGE DATA RECORDER – DATA ITEMS TO BE RECORDED:- IMO Performance Standard (Res. A.861(20)) and IEC Information format (IEC 61996).

DATA ITEM	SOURCE
Date & Time	Preferably external to ship (e.g.GNSS)
Ship’s position	Electronic Positioning system
Speed (through water or over ground)	Ship’s SDME
Heading	Ship’s compass
Bridge Audio	1 or more bridge microphones
Comms. Audio	VHF
Radar data- post display selection	Master radar display
Water depth	Echo Sounder
Main alarms	All mandatory alarms on bridge
Rudder order & response	Steering gear & autopilot
Engine order & response	Telegraphs, controls and thrusters
Hull openings status	All mandatory status information displayed on bridge
Watertight & fire door status	All mandatory status information displayed on bridge
Acceleration & hull stresses	Hull stress and response monitoring equipment where fitted
Wind speed & direction	Anemometer when fitted

Recovery of VDR: Recovery of the VDR is conditional on the accessibility of the VDR or the data contained therein.

• In the case of a non-catastrophic accident, recovery of the memory should be straightforward. For example, in some VDRs it can be accomplished by removal of a hard disc from the VDR unit. This action will have to be taken soon after the accident to best preserve the relevant evidence for use by both the investigator and the ship owner. As the investigator is very unlikely to be in a position to instigate this action soon enough after the accident, the owner must be responsible, through its on-board standing orders, for ensuring the timely preservation of this evidence in this circumstance.
• In the case of abandonment of a vessel during an emergency, masters should, where time and other responsibilities permit, recover the memory and remove it to a place of safety and preserve it until it can be passed to the investigator.
• In the case of a catastrophic accident, where the VDR is inaccessible and the data has not been retrieved prior to abandonment, a decision will need to be taken by the Flag State in co-operation with any other substantially interested States on the viability and cost of recovering the VDR balanced against the potential use of the information. If it is decided to recover the VDR the investigator should be responsible for co-ordinating its recovery. The possibility of the capsule having sustained damage must be considered and specialist expertise will be required to ensure the best chance of recovering and preserving the evidence. In addition the assistance and co-operation of the owners, insurers and the manufacturers of the VDR and those of the protective capsule may be required.

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Long Range Identification and Tracking (LRIT) system architecture Explanation:

Purpose of LRIT:-

• The Long Range Identification and Tracking (LRIT) system is a designated International Maritime Organization (IMO) system designed to collect and disseminate vessel position information received from IMO member States ships.
• The main purpose of the LRIT ship position reports is to enable a Contracting Government to obtain ship identity and location information in sufficient time to evaluate the security risk posed by a ship off its coast and to respond, if
  necessary, to reduce any risks.
• LRIT has also become an essential component of SAR operations and marine environment protection.
• It is a satellite-based, real-time reporting mechanism providing almost worldwide coverage (Inmarsat Coverage) that allows unique visibility to position reports of vessels that would otherwise be invisible and potentially a threat.

CARRIAGE REQUIREMENT of LRIT :- Ships in international voyages

• Passenger ships
• Cargo ships over 300 t
• Mobile platforms

Ships fitted with AIS and sailing in sea A1 areas do not need to transmit LRIT data.

INFORMATION TRANSMITTED in LRIT :-

• Identity (Ship’s LRIT Identifier)
• Position (Lat/Long)
• Date and time (UTC)

UPDATE INTERVAL in LRIT:-

• Default value 6 hourly
• Update interval remotely selectable
• Minimum interval 15 min
• May be switched off by the Master under certain conditions

THE LRIT SYSTEM CONSISTS OF:

1. The ship borne LRIT information transmitting equipment.
2. Communications Service Providers (CSPs).
3. Application Service Providers (ASPs).
4. LRIT Data Centres (DC), including any related Vessel Monitoring System(s) (VMSs).
5. The LRIT Data Distribution Plan (DDP).
6. The International LRIT Data Exchange (IDE),
7. LRIT coordinator

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How does LRIT differ from AIS Explanation:

• Some confuse the functions of LRIT with that of AIS (Automatic Identification System), a collision avoidance system also mandated by the IMO, which operates in the VHF radio band, with a range only slightly greater than line-of-sight.
• (See AIS) While AIS was originally designed for short-range operation as a collision avoidance and navigational aid, it has now been shown to be possible to receive AIS signals by satellite in many, but not all, parts of the world. This is becoming known as S-AIS and is completely different from LRIT.
• The only similarity is that AIS is also collected from space for determining location of vessels, but requires no action from the vessels themselves except they must have their AIS system turned on.
• LRIT requires the active, willing participation of the vessel involved, which is, in and of itself, a very useful indication as to whether the vessel in question is a lawful actor.
• Thus the information collected from the two systems, S-AIS and LRIT, are mutually complementary, and S-AIS clearly does not make LRIT superfluous in any manner.
• Indeed, because of co-channel interference near densely populated or congested sea areas satellites are having a difficult time in detecting AIS from space in those areas.

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Authorized receivers / users of LRIT

LRIT Data Centres:-

• The primary purposes of an LRIT Data Centre (DC) are to collect, store and make available to authorised entities the LRIT information transmitted by ships instructed by their administrations to utilise the services of that DC. In carrying out these core functions, the DC is required to ensure that LRIT data users are only provided with the LRIT information they are entitled to receive under the terms of SOLAS Regulation V/19.1.
• In addition, the LRIT DC acts as a “clearing house” by receiving requests for LRIT information lodged in other DCs from its associated Administration(s) and obtaining the data requested. Generally LRIT reports so requested will be exchanged through the International Data Exchange.
• LRIT Data Centers are required to archive their data so that the reports can be recovered, if required, at a later date and the activities of the DC can be audited by the LRIT Coordinator.
• LRIT DCs may make a charge for LRIT data they provide to other DCs.
• DCs may be either National (established to provide service to only one Contracting Government); Cooperative (established to provide services to a number of Contracting Governments) or Regional (established to provide services to a number of Contracting Governments acting through a regional entity of some kind).
  The IMO Performance Standard envisages also an International Data Centre (IDC), to provide LRIT services on an international basis to many countries that do not wish to establish their own DCs, but the IMO Maritime Safety Committee (MSC) has not yet decided to establish such an IDC.

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Functions of LRIT National Data Centre

• The International LRIT Data Exchange (IDE) exists to route LRIT information between LRIT DCs using the information provided in the LRIT Data Distribution Plan. It is therefore connected via the internet to all LRIT DCs and the LRIT Data
  Distribution Plan server.
• The IDE cannot access and does not archive the LRIT data itself, but it does maintain a journal of message header information – which can be understood as the “envelope” containing the LRIT information. This journal is used for invoicing functions and for audit purposes.
• The performance of the IDE is audited by the LRIT Coordinator.

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How does LRIT differ from AIS?

Explanation:-

• AIS is a broadcast system and data is available to all receiver in the receiving range whereas LRIT is available only to the authorized person.
• AIS works on the very high frequency, whereas LRIT is based on the satellite system.
• AIS range is limited to the VHF range but LRIT range is worldwide.
• AIS DATA is not stored by any organization whereas LRIT data is stored and available on demand.
• There is display for AIS ON BOARD but there is no display for LRIT on board the ship.

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Compare the AIS & LRIT:

AIS	LRIT
Satellite	VHF
Global	Only where AIS coverage is provided
Secure Data	Public Data
Position, IMO Number, Date Time	Position, IMO Number, Date Time, Vessel Type, Speed, Course
Unlimited range	Line of sight, up to 40NM
Flag State Owns Data	Anyone can see data
Maritime Security and Awareness	Navigation and Anti-collision Tool

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Electronic Chart Display and Information System (ECDIS) Explanation:-

• Electronic Chart Display and information Systems (ECIDS) means a navigation information system which with adequate back-up arrangements can be accepted as complying with the up-to-date chart required by regulation V/20 of the 1974 SOLAS Convention, by displaying selected information from a system electronic navigational chart (SENC) with positional information from navigation sensors to assist the mariner in route Monitoring, and if required display additional navigation related information.
• Generation of ECDIS:-
  • The electronic navigation chart is the data base standardized as to content, structure and format and is issued by the hydrographic office (HO) under the authority of the government, the ENC contains all the chart information necessary for safe navigation and may contain supplementary information in addition to that contained in the paper chart (e.g. list of lights and fog signals etc.) which may be considered necessary for safe navigation.
  • The system electronic navigation chart (SENC) is the data base resulting from transformation of the ENC by the ECDIS for appropriate use, updates to the ENC by appropriate means and other data added by the mariner. It is the data base that is actually accessed by the ECDIS for the display generations & other navigational functions and is equivalent to an up-to-date paper chart.

ECDIS is basically a CPU with a monitor to display electronic chart, SENC is an integral part and below figure can be referred for better understanding which shows that SENC is interfaced with various equipment as mentioned below results in an ECDIS.

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Advantages of Electronic Chart Display and Information System (ECDIS):

1. Availability: One of the great advantages of ECDIS over paper charts is the availability of electronic charts – especially when voyage orders are received at the last minute.
2. Speed and Accuracy: With ECDIS as the primary source of navigation, the Navigating Officer can plan and summarise the passage much faster than on Paper Charts. Daily reporting data such as Distance to Go, Distance Covered, Average Speed, etc. can be done quickly with hardly any effort.
3. Corrections: The Navigating Officer now receives weekly updates to the Electronic Charts via Email which he has to download onto a zip drive and upload them to the ECDIS. Even the dreaded T&P notices are now shown electronically on the ECDIS.
4. Continuous Monitoring of Vessel’s Position: The ECDIS is interfaced with both the vessel’s independent GPS transceivers, thereby making the system work even if one fails.
5. Anti-Grounding Alarms and Settings: The ability of the ECDIS to warn the user of approaching shallow waters make it one of the most useful equipment on the bridge.
6. User Determined Alarm Settings: While there are certain safety critical alarms that are ON by defaults and cannot be changed, there are a host of other alarms and warnings which may be switched on or off by the User depending on the situation.
7. Enhances Search and Rescue Capability onboard: Modern ECDIS units have the option of interfacing NAVTEX and EGC with the ECDIS display. Warnings and Alerts are automatically displayed on the ECDIS screen, whilst at the same time giving an audible and visual indication on the unit itself.
8. Cost Efficient: Although, Electronic charts are by no means cheap, they still have an edge over paper charts dollar for dollar.
9. Environmentally Friendly: The ECDIS does pack in a strong punch in reducing the carbon footprint of every vessel which goes paperless.

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Disadvantages of Electronic Chart Display and Information System (ECDIS):

1. Over-Reliance: A vessel could have switched off its AIS and hence might not be displayed on the ECDIS. If the Radar Overlay is not turned on, the vessel will just not be seen on the ECDIS display. Hence, it is very critical that Navigators continue to maintain an efficient lookout and a good radar watch.
2. Garbage In Garbage Out (GIGO): Erroneous position inputs from the GPS or loss of GPS signal can have grave consequences with the ECDIS going in DR mode. If the alarm is missed out, the result can be disastrous.
3. Wrong Settings: Feeding in wrong parameters for safety critical settings such as the Safety Depths, Safety Contours etc can give a false sense of safety.
4. Alarm Deafness: If alarms start going off too frequently, the navigator could end up in a dangerous situation called Alarm Deafness.
5. System Lag: Modern ECDIS software can have a lot of data to display and with various equipment interfaced with the ECDIS, the system can slow down very easily leading to system lag.
6. Different Types: Different vessels will have different types of ECDIS equipment.
7. Anomalies: Every navigator needs to be aware of the anomalies present in that particular equipment. It could be a simple use of the SCAMIN (Scale Minimum) function or something serious where certain depths or symbols might not be visible at a particular scale or appear differently.
8. Information Overload: It is very easy to over feed information on the ECDIS. A lot of data which was earlier marked on charts such as position for calling Master notices to Engine Room, Echo Sounder Switch on points, Port Control VHF channels etc now have to be fed on the ECDIS.

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Advantages of ECDIS over conventional Paper Charts:

• Position fixing can be done at required interval without manual interference.
• Continuous monitoring of the ship’s position.
• When interfaced with ARPA/RADAR, target can be monitored continuously.
• If two position fixing system are available, the discrepancy in two systems can be identified.
• Charts can be corrected with help of CD/Online.
• Passage planning can be done on ECDIS without referring to other publications.
• Various alarms can be set on ECDIS.
• Progress of the passage can be monitored in more disciplined manner, since other navigational data is available on ECDIS.
• Various alarms can be activated to draw the attention of OOW.
• More accurate ETA can be calculated.
• Anchoring can be planned more precisely.

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“Zones of Confidence” in ECDIS:-

• The information presented in a reliability diagram requires knowledge of past and present hydrographic surveying practices — something most mariners neither have nor should need. To address this, the Australian Hydrographic Service developed a system known as “zones of confidence” that has since been adopted internationally.
• On each nautical chart the accuracy and reliability of the information used to compile the chart is shown on a “zone of confidence” (ZOC) diagram. Within official electronic navigational charts (ENCs), the same information is shown as a layer that can be switched on and off by the mariner.
• ZOC categories warn mariners which parts of the chart are based on good or poor information and which areas should be navigated with caution. The ZOC system consists of five quality categories for assessed data, with a sixth category for data which has not been assessed.
• The table accompanying the ZOC diagram on each chart summarizes the meaning of the ZOC categories.

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Define ENC as applicable to ECDIS:

Electronic Navigational Chart (ENC) means the database, standardized as to content, structure and format,  issued for use with ECDIS on the authority of government authorized hydrographic offices. The ENC contains all the chart information necessary for safe navigation and may contain supplementary information in addition to that contained in the paper chart (e.g. sailing directions) which may be considered necessary for safe navigation. Vector charts are an example.

Define SENC as applicable to ECDIS:

System Electronic Navigational Chart (SENC) means a database resulting from the transformation of the ENC (a vector chart) by ECDIS for appropriate use, updates to the ENC by appropriate means and other data added by the mariner. It is the database that is actually accessed by ECDIS for the display generation and other navigational functions and is the equivalent to an up-to-date paper chart. The SENC may also contain information from other sources.

Define Standard Display as applicable to ECDIS:

Standard Display means the SENC information that should be shown when a chart is first displayed on ECDIS. Depending upon the needs of the mariner, the level of the information it provides for route planning or route monitoring may be modified by the mariner.

Define Display Base as applicable to ECDIS:

Display Base means the level of SENC information which cannot be removed from the display, consisting of information which is required at all times in all geographic areas and all circumstances. It is not intended to be sufficient for safe navigation.

Define Vector Chart as applicable to ECDIS:

A vector chart is a digital database of all the objects (points, lines, areas, etc.) represented on a chart. Vector charts store information, such as isolated dangers, depths, depth contours, coastline features, cables and pipelines etc in separate layers which can be displayed as per the user’s requirements. Vector charts are also referred to as intelligent charts as they can be interrogated for information not displayed but stored in it’s memory.

Define Raster Chart as applicable to ECDIS:

Raster Chart data is created by scanning the information on a paper chart and storing this information in the form of pixels. Many thousands of pixels together make a flat digital image. Each pixel contains all the data for a particular point: colour, brightness etc. They are also geographically referenced which makes the raster chart identical in every way to the paper chart on which it is based. Raster charts cannot be manipulated or queried. Also referred to as the Raster Chart Display System (RCDS), the information is contained in one single layer only. Information can only be added to this type of chart.

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