NAV INSTRUMENTS

 

What is a Gyro Compass?


It is used for finding the right direction. Unlike magnetic compass, gyro compass is not hampered by external magnetic field. It is used to find correct North Position, which is also the earth’s rotational axis. Its repeater system must be present in the steering platform for emergency steering. A Gyro compass is a form of gyroscope, used widely on ships employing an electrically powered, fast-spinning gyroscope wheel and frictional forces among other factors utilising the basic physical laws, influences of gravity and the Earth’s rotation to find the true north.




Explain the difference between a Master Compass and a Repeater Compass.


Master Compass: Discovers and maintains the true north reading with the help of gyroscope. Repeater Compasses: Receive and indicate the true direction transmitted electrically from the Master Compass. Gyro compasses are linked to the repeater compasses via one transmission system. The fast-spinning rotor attached weighs from 1.25 pounds to 55 pounds. It is driven thousands of revolutions per minute by another electric motor. However, the most essential part in a Gyro compass system is the spinning wheel, which is known as the Gyroscope.




What is a Voltage Regulator?


Voltage Regulator: Maintains constant supply of the ship to the motor-generator.




With the use of a diagram name the components of a Repeater Compass found on the Bridge Wing.


Repeater compass




What is the Motor Generator connected to the gyro compass used for.


Motor Generator: Converts the ship’s DC supply to AC and energizes the Compass equipment.




Explain how a Gyro Compass works.


External magnetic fields which deflect normal compasses cannot affect Gyro compasses. When a ship alters its course the independently driven framework called ‘Phantom’ moves with it, but the rotor system continues to point northward. This lack of alignment enables it to send signal to the driving motor, which moves the phantom step in with the rotor system again in a path where the phantom may have crossed only a fraction of a degree or several degrees of the compass circle. As soon as they are aligned, electrical impulses are sent by the phantom to the repeater compasses for each degree it traverses. The Gyroscope in the Gyrocompass is mounted in such a way so that it can move freely about three mutually perpendicular axes and is controlled as to enable its axis of spin settled parallel with the true meridian, influenced by the Earth’s rotation and gravity. The Gyro compass system applications are based upon two fundamental characteristics, which are: Gyroscopic Inertia: The tendency of any revolving body to uphold its plane of rotation. Precession: A property that causes the gyroscope to move, when a couple is applied. But instead of moving in the direction of the couple, it moves at right angles to the axis of the applied couple and also the spinning wheel. These two properties and the utilization of the Earth’s two natural forces, rotation and gravity, enacts the Gyrocompass seek true north. Once settled on the true meridian the rotor indefinitely will remain there as long as the electrical supply of the ship remains constant and unaltered and unaffected by external forces.




Explaining Steaming Errors on a gyro compass.


Gyro compasses are pre-eminently used in most ships in order to detect true north, steer, and find positions and record courses. But due to the ship’s course, speed and latitude, there could appear some steaming errors. It has been found that on Northerly courses the Gyro compass north is slightly deflected to the West of the true meridian whereas on Southerly courses it is deflected to the East. Modern ships use a GPS system or other navigational aids feed data to the Gyrocompass for correcting the error. An orthogonal triad of fibre optic design and also ring laser gyroscopes which apply the principles of optical path difference to determine rate of rotation, instead of depending upon mechanical parts, may help eliminate the flaws and detect true north.




Explain the basic function of a Radar.


It is used to determine the distance of the ship from land, other ships, or any floating object out at sea. The marine radar is equipment that is perhaps used the most on the ship’s bridge by the OOW in carrying out a safe navigational watch. A mandatory aid to navigation, the radar is used in identifying, tracking (with integrated ARPA) and positioning of vessels (including one’s own vessel) among other things in order to adhere to the COLREGs so as to safely navigate a ship from one point to another. The marine radar is classified under the x-band (10 GHz) or S-band (3GHz) frequencies. The x-band, being of higher frequency is used for a sharper image and better resolution whereas the S-band is used especially when in rain or fog as well as for identification and tracking.




Explain the operation of a Marine Radar.


The operation of the marine radars can be explained as follows: The parabolic radar antenna transmits and receives electromagnetic waves; as far as a target being displayed is concerned, that is basically the wave that bounced off a certain object that paints itself on the PPI (Plan Position Indicator) The frequency and the time taken by the flashes to return (reflections) to the radar receiver of the ship helps to find out whether the route of the boat can be continued with or not. The transmission and receiving of the pulse travels twice the distance in going and hitting the target and back; therefore, the target displayed on the PPI is basically halved with regard to its range On the PPI, the reflections can be seen so that identifying the actual distance of the objects can be even easier. The same paint on the PPI can be also be checked for determination of the bearing of the target




Explain the uses of a Marine Radar.


The uses of a Marine Radar are as follows; - To calculate range and bearing of a target and thereafter use the information to determine speed, course etc - Integration with other shipboard equipment (such as ECDIS) to derive precise data - Navigating own vessel and her course with regard to collision avoidance - Fixing the ship’s position using terrestrial objects such as lighthouses, buoys etc - Differentiating between targets in high traffic density areas - Determination of the weather, to an extent - Use by VTS in controlling coastal traffic - Usage of features such as parallel indexing to ensure safe navigation - Alleviating workload on the OOW on the bridge - Used extensively in pilotage that covers the above aspects




Explain how a Magnetic Compass works.


The magnetic compass work in conjunction with the magnetic field of the earth. It is used to get planned direction for the voyage.




Explain how an Auto Pilot works.


It is a combination of hydraulic, mechanical, and electrical system and is used to control the ship’s steering system from a remote location (Navigation bridge).




Explain ARPA.


Automatic Radar Plotting Aid displays the position of a ship and other vessels nearby. The radar displays the position of the ships in the vicinity and selects the course for the vessel by avoiding any kind of collision.




Explain the Tracking Aid found on a radar.


Automatic Tracking Aid: Just like ARPA, automatic tracking aid displays the information on tracked targets in graphic and numeric to generate a planned layout for a safer and collision free course.




Explain the Speed and Distance Log.


The device is used to measure the speed and the distance traveled by a ship from a set point. By calculating the same, ETA of the ship is adjusted or given to the port authority and agent.




Explain an Echo Sounder.


This instrument is used to measure the depth of the water below the ship’s bottom using sound waves.




Explain ECDIS.


ECDIS is a development in the navigational chart system used in naval vessels and ships. With the use of the electronic chart system, it has become easier for a ship’s navigating crew to pinpoint locations, and attaining directions are easier than before. The ECDIS utilises the feature of the Global Positioning System (GPS) to successfully pinpoint the navigational points. It also has to be noted that the ECDIS adheres to the stipulations set by the International Maritime Organisation, and thus it adds to the trustworthiness of the electronic chart system. ECDIS is basically a navigational information system, interfaced with other navigational equipments such as the GPS, Gyro, RADAR, ARPA, Echo Sounder etc. ECDIS also incorporates and displays information contained in other nautical publications such as Tide Tables and Sailing Directions and incorporates additional maritime information such as radar information, weather, ice conditions and automatic vessel identification.




Explain the advantages of ECDIS over paper charts.


Advantages of ECDIS over paper charts are as follows; - All information is processed and displayed in real time - It eases the process of passage planning - One can get all necessary navigational information at a glance - Alarms and indications are in place to indicate and highlight dangers - Chart correction is made easier in ECDIS as compared to paper charts - Charts can be tailored as per the requirement of the voyage - Other navigational equipments such as the AIS, ARPA etc can be overlayed and integrated - Charts can be oriented as per requirement - With the facility to zoom in and out, features can be examined as per necessity - One can obtain a more accurate ETA - Charts can be interrogated for detailed information - The system enhances the safety of navigation




Explain the types of ECDIS Charts.


Types of ECDIS charts; - Raster Chart (RNC): RNCs are direct copy or a scan of the paper charts. It looks identical to a paper chart as all the information shown is directly printed. The chart only grows larger or smaller as per the zooming and when rotated, everything rotates. - Vector Chart (ENC): ENCs are computer generated charts. The details on an ENC can be turned on and off depending on the requirement of the user. Objects on the ENC can be clicked for more details on the same. Depths can also be monitored to obtain a warning with regard to grounding. When zooming, the features grow large or small but the text remains the same.




Explain how ECDIS Charts are updated.


Chart Updating; - Updates to the ECDIS charts may reach the ship in various ways, depending upon the capabilities of the service provider and the onboard communication facilities. - On data distribution media (DVD) - As an email attachment (SATCOM) - As a broadcast message via SATCOM plus additional communication hardware - As an internet download




Explain the limitations of ECDIS.


Limitations of ECDIS; - The accuracy of the information received via AIS is only as good as the accuracy of the AIS information transmitted. The same is applicable for all other equipments interfaced with the ECDIS. - Position of ships received on ECDIS display might not be referenced to WGS 84 datum - Over reliance on ECDIS for navigational safety should be avoided until it is confirmed that all the data transmitted, received and displayed are accurate - Users must be aware that any erroneous information is detrimental to the safety of own as well as other vessels - Some sensors might lack the integrity with regard to accuracy and those that have not been tested - Not all ships are fitted with ECDIS and hence one cannot be sure of technical ability with regard to positioning as well as navigation; the kind that ECDIS provides - It is never prudent for the OOW to depend solely on the information on the ECDIS. IT is only an aid to navigation and never replaces the human quotient which brings in the skill and expertise with experience that an ECDIS can never provide.




Explain AIS.


Automatic Identification system; AIS is a system which helps to pinpoint the location and other navigational statistics of ships. AIS uses VHF radio channels as transmitters and receivers to send and receive messages between ships which endeavors to fulfill a lot of responsibilities.




What are the SOLAS requirements for AIS and explain the AIS Types.


SOLAS Requirements: The IMO Convention for the Safety Of Life At Sea (SOLAS) Regulation V/19.2.4 requires all vessels of 300 GT and above engaged on international voyages and all passenger ships irrespective of size to carry AIS onboard. AIS Types: - Class A: Mandated for all vessels 300 GT and above engaged on international voyages as well as all passenger ships - Class B: Provides limited functionality and intended for non SOLAS vessels. Primarily used for vessels such as pleasure crafts




What data can be transmitted by AIS.


Data Transmitted; 1. Static Information (Every 6 minutes and on request): - MMSI number - IMO number - Name and Call Sign - Length and Beam - Type of ship - Location of position fixing antenna 2. Dynamic Information (Depends on speed and course alteration) - Ship’s position with accuracy indication - Position time stamp (in UTC) - Course Over Ground (COG) 3. Voyage Related Information (Every 6 minutes, when data is amended, or on request) - Ship’s draught - Type of cargo - Destination and ETA - Route plan (Waypoints)




What are the Limitations of AIS?


Limitations of AIS; As with all navigational and/or electronic equipment, the AIS has limitations: - The accuracy of AIS information received is only as good as the accuracy of the AIS information transmitted - Position received on the AIS display might not be referenced to the WGS 84 datum - Over reliance on the AIS can cause complacency on the part of the OOW - Users must be aware that erroneous information might be transmitted by the AIS from another ship - Not all ships are fitted with AIS - The OOW must be aware that AIS, if fitted, might be switched off by a certain vessel thereby negating any information that might have been received from such ship - It would not be prudent for the OOW to assume that the information received from other ships might not be fully accurate and of precision that might be available on own vessel




What is tthe LRIT?


Long Range Tracking and Identification (LRIT) System; LRIT is an international tracking and identification system incorporated by the IMO under its SOLAS convention to ensure a thorough tracking system for ships across the world. It came into existence on the 19th May 2006 and was incorporated formally starting from January 2008. Based on these lines, those ships which were built on or following 31st December 2008 were required to have this system of vessel identification. There are many countries which have incorporated the vessel tracking system as a part of their oceanic operation. Starting with the earliest, some of the countries can be listed down as follows: - The most number of vessels that have adopted the LRIT system are from the Panama Flag Registry – around 8000 ships - The European Union adopted the ship tracking system in the year 2007 - Canada became the first SOLAS nation to incorporate the system to track ships in the year 2009, followed by the United States in the same year - Amongst the South American countries; Brazil, Venezuela, Chile and Ecuador were some of the front-runners to have adopted the system. Ecuador was the last among these four nations adopting the system in the year 2010 The most important advantage of having this system is that the information required to be shared is restricted only to those parties which are required to have it. This reduces unnecessary problems and increases the transparency and viability of the system on the whole. The main requirements to the system’s application are the following: - The transmitting device and gadget to send the information data - Specific providers for this type of communication service. One such service provider is the - Absolute Maritime Tracking Services, Inc. (AMTS) established by the Panama Flag Registry. This service provider is the sole service provider to those ships falling under the Panamanian registration - Centers of data for the system - Service providers for the overall application of the system - A thorough distribution plan for the data collected from the system - International data exchange for the LRIT application also forms an important part of the overall system requirements




What is the Rudder Angle Indicator


Rudder angle indicator, as the name indicates, provide the angle of the rudder. The display is provided on bridge to control the rate of turn and rudder angle of the ship.




What is Voyage Data Recorder?


Voyage Data Recorder; A VDR or voyage data recorder is an instrument safely 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.




What is a Rate of Turn Indicator?


Rate of turn indicator; It indicates how fast the ship is turning at steady rate, normally shown as number of degree turned.




What is a GPS Receiver?


GPS Receiver; A Global Positioning System (GPS) receiver is a display system used to show the ship’s location with the help of Global positioning satellite in the earth’s orbit.




Briefly explain the history of Navigational Lights.


Navigational Lights; All boats – whether big or small are required to have night lights as a part of the navigation systems. This system was introduced in the year 1838 by the United States and then was followed by the United Kingdom in 1849. In the year 1889, the International Maritime Conference was established by the United States to establish proper guidelines to prevent marine accidents. In the year 1897, these rules were officially adopted internationally.




Explain a Ship's Whistle.


Ship Whistle; A ship’s horn is known as whistle and it is generally provided in duplicate. One is driven by air and the other is electrically operated.




What is a Daylight Signallling Lamp?


Daylight Signalling Lamp; They are light signalling devices used for emergency signalling in the day time.




What is Pilot Card?


Pilot Card; It is an informative booklet provided to the ship’s pilot. It consists of the dimension, draught, turning circle, manoeuvring, propulsion equipment etc. of the vessel for safe manoeuvring.




What is a Voyage Plan?


Voyage Plan; A voyage Plan must be present onboard for referring past voyage plans or planning a future voyage.




What is Forecastle Bell?


Forecastle Bell; It is used to mark the presence of the ship in fog or bad weather and sound the alarm in case of any emergency.




What is a Manoeuvring Book?


Manoeuvring Booklet; In this booklet the performance of the propulsion plant and the ship during manoeuvring in different weathers and situations is recorded for quick reference.




Explain the use of a Black Ball Shape.


Black Ball Shape; It is a day time signalling shape used to determine the characteristics of vessel with different arrangement of ball shapes. For e.g. a vessel at anchor will show a blackball at foremost end of the forecastle.




Explain the Bridge Log Book.


Record of Navigation Activities; All the navigational activities must be recorded and kept on board for ready reference. This is a mandatory and the most important log book.




Explain what must be done after Maintenance of Navigational Equipment.


Record of Maintenance of Navigational Equipment; Hard copy of the record must be present onboard ships for ready reference of port and regulatory authorities and must be signed by master and duty officers of the ship.




Where would you find the Manouvering Characteristics of the ship?


Present in the Navigation bridge, it displays a detailed information of manoeuvring characteristics of the ship.




Explain what a Black Diamond Shape is used for.


Black Diamond Shape; When the ship is being towed or when a vessel is unable to maneuvers on itself, a black diamond shape is shown during the day time.




Where would you find the ship's Signal Flags.


Ship Flags are generally found on the Bridge or in the Chartroom of the ship. Various types of ship flags with different colors and signs are used to indicate a ship’s position. Signal flags are they are commonly known, have been used since the ancient times and are still used on all vessels.