Question and Answers

    Question
    marinetales September 6, 2021
    AIS type A is mandatory for vessels 300GT and above and Cargo ships 500GT and above engaged on International voyages and all Passenger Ships irrespective of ships. AIS type B has a limited functionality and is intended for Non-SOLAS vessels. It is non-mandated by IMO. Class B is nearly identical to Class A except Class B does not transmit the vessel's IMO number, ETA or destination, navigational status, rate of turn information, sending safety messages (only receive), maximum present static draft and it also has a reporting rate less than Class A.
    marinetales August 26, 2021
    Following correctors are used in Magnetic Compass - 1. Corrector Magnets: In the lower part of binnacle there are several horizontal holes, both F & A and athwart ships for 'hard iron' or 'permanent' corrector magnets which are meant to offset undesirable, disturbing, magnetic effects caused by ship's steel hull. 2. Heeling Error Bucket: At the centre in the vertical brass tube, this bucket slides. This is held in position by a brass chain. Error caused is due to ship heeling which causes the vertical magnetic force to have a horizontal component. 3. Quadrantal Correctors: Soft iron spheres which are fitted in brackets, one on other side of binnacles, intended to correct the compass deviation [quadrantal deviation] resulting from induced magnetism from ship's steel. 4. Flinders Bar: Soft iron corrector, diameter 7.5 - 10cms, inserted in a 60cm long brass case, fitted vertically on the forward or the after part of binnacle. If the ship has more superstructure abaft the compass, this is fitted on the forward part and vice versa. It is used to counteract the vertical component induced within the ship.
    marinetales August 26, 2021
    The correctors are basically used to correct the errors induced in the magnetic compass due to magnetism. These magnetism errors can be ship induced magnetism and / or permanent magnetism induced in the steel. These are corrected using the corrector magnets. For ship induced magnetism Quadrantal Spheres and Flinders bars are used. For permanent magnetism Fore and Aft and Athwartship magnets are used.
    marinetales August 26, 2021
    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 error caused by the speed and latitude experienced by the gyro compass varies with the latitude and speed of rotation of the earth. This is because the earth's rotational speed reduces as you go up in the higher latitudes. At you near the poles, the gyro attains its direction perpendicular to the motion of the earth and therefore, in higher latitudes the gyro compass readings become erratic.
    marinetales August 26, 2021
    Following types of antennas and aerials are used on ships - 1. VHF Aerial which is 1/2 dipole aerial 2. T-type and L-type wire aerial 3. Microwave parabolic antenna or directional gyro stabilized antenna 4. Whip aerial - 6 to 8 meters 5. YAGI Aerial - made up of aluminum element 6. Omnidirectional Conical mesh
    marinetales July 23, 2021
    Add the two readings together and divide by 4. The result should equal the sun’s semi-diameter of the day in question. This can subsequently be compared with the Nautical Almanac to see if correct.
    marinetales July 23, 2021
    When checking the errors of the sextant, the third adjustment for Index Error, using the sun is found by: • setting the arm of the sextant at approximately 32on the arc and bringing the true sun above the reflected sun. Adjust the two images until they are ‘limb upon limb’, then note the reading (say 28on the arc); • re-set the arm at approximately 32off the arc and bring the images again Limb upon Limb, and read the sextant again (say 37off the arc). Take the difference of the two readings and divide by ‘2’ to give the Index Error, and call it the higher of the two. Example - 37'-28' = 9' 9/2 = 4.5' off the arc (Index Error)
    marinetales July 23, 2021
    Non-adjustable (or non-correctable) errors of the sextant, include: (i) shade error, (ii) prismatic error, (iii) graduation error.
    marinetales July 23, 2021
    Collimation is an error on the sextant caused by the axis of the telescope not being parallel to the plane of the instrument. With modern sextants the collar holding the telescope is permanently fixed and no adjustment is possible.
    marinetales July 23, 2021
    It is common practice to display a diagram on a bulkhead, in close proximity to the radar, if its operation is hampered by Blind Sectors. Alternatively, the Radar Specification Manual could be consulted and any Blind Sectors would be indicated in the manual
    marinetales July 23, 2021
    Radar performance check can be carried out by using the "performance monitor" function on the radar (if fitted).
    marinetales July 16, 2021
    Invert the compass bowl in the gimbal arrangement to bring the expansion chamber uppermost. Undo the screw cap of the chamber and top up the fluid in the bowl with distilled water. This action will fill the bowl, forcing out the air bubble.
    marinetales July 16, 2021
    Compass card (in liquid magnetic compass) is usually made of mica or melamine.
    marinetales July 16, 2021
    The ship would normally be swung after any of the following circumstances: (a) Following a collision or a grounding incident where major repairs are required to be made to the ship, which could affect the vessels permanent and induced magnetism. (b) In the event of a major fire on board the ship. (c) If engaged on a long charter trading in high latitudes, i.e. ‘Hudson Bay’. (d) After leaving the builders yard as a new ship. (e) If loading a high capacity metallic cargo, e.g. railway lines on deck. (f) In the event that compass errors became excessively large for no apparent reason or the compass becomes unreliable. (g) If electrical or magnetic equipment is added or removed to/from the proximity of the magnetic compass. (h) In the event that a period of 2 years has elapsed and the ship is without a record of deviations, or when the compass shows a physical defect when first installed.
    marinetales July 16, 2021
    The inclusion of alcohol in the mix is to prevent the liquid freezing when navigating in high cold latitudes, while the purpose of the distilled water is to prevent the alcohol evaporating in the warm middle latitudes.
    marinetales July 5, 2021
    The receiving range of LRIT signal for a coastal state is upto 1000 nautical miles.
    seawizard June 5, 2021
    Any distress which is transmitted falsely, shall be cancelled immediately. If not, can initiate legal action against the vessel. Hence the Master and officers shall be well versed with the procedure for cancellation of distress alert and such instructions shall be conspicuously posted near to the equipment. Following shall be the procedure to cancel the distress alert on VHF, MF HF, INMARSAT C AND EPIRB- 1. VHF a. Switch off the transmitter immediately b. Switch to VHF Ch 16 and broadcast to all stations in a format below - ALL STATIONS ALL STATIONS ALL STATIONS This is in Cancel my DSC Alert of Name of Master, Call sign, MMSI, date and time 2. MF a. Switch off the transmitter immediately b. Switch to RT frequency 2182 kHz and broadcast to all stations in a format below - ALL STATIONS ALL STATIONS ALL STATIONS This is in Cancel my DSC Alert of Name of Master, Call sign, MMSI, date and time 3. HF a. Switch off the transmitter immediately b. Cancellation alert shall be sent to all the RT frequencies corresponding to DSC frequencies on which alert was sent ALL STATIONS ALL STATIONS ALL STATIONS This is in Cancel my DSC Alert of Name of Master, Call sign, MMSI, date and time 4. INMARSAT-C a. Stop the distress transmission b. Notify the RCC by sending the Distress Priority Message c. Format should be - cancel my distress alert of , 5. EPIRB a. Switch of the equipment to stop the transmission b. Master to contact the nearest Coast station or Land Earth Station (LES) / RCC and then cancel
    marinetales May 30, 2021
    Steering Gear testing is required by the SOLAS regulation 26 Chapter V. Within 12 hours prior departure, Steering gear to be checked by ship’s crew Following shall be tested- 1. The main steering gear. 2. The auxiliary steering gear. 3. Remote steering gear control stations. 4. Steering position located on Navigation Bridge. 5. Emergency power supply operation 6. Rudder angle indicator in relation to the actual position of the rudder. 7. Power failure alarms. 8. Automatic isolating arrangements and automatic equipments. 9. Full movement of rudder from hard over to hard over under required time 10. Visual inspection of steering gear. 11. Means of communication between bridge and ECR. 12. Block diagram for steering gear system to be displayed. 13. Officers/crew to be familiar with change over procedures. 14. Emergency drills to be carried out at least every 3 months 15. Date and time of tests/checks/drills to be recorded and logged down.
    marinetales May 9, 2021
    Following are the errors that can be encountered in Echo Sounder: 1. Stylus speed error: The stylus is rotating with a certain constant speed and the speed of the stylus that the time is taken for the stylus to travel from top to bottom is exactly equal to that for an acoustic pulse to travel twice the distance of the range selected. Due to the fluctuation in the voltage, the speed of the stylus motor changes hence the depth recorded Will be inaccurate. It should be checked periodically and adjusted as per the instruction is given in the manual. 2. Multipath Echoes: The echo may be reflected a number of times between the keel and the seabed, thereby giving multiple depth marks on the record, in such case the first echo is the correct depth. 3. Pythagoras error: This error is found when two transducers are used one for transmission and other for reception. 4. Thermal and Density layer. The density of the water varies with temperature and salinity, which will tend to form different layers. It is possible for echoes to return from the surface of these layers and a faint line appears between zero and actual depth. 5. Zero line adjustment error If the zero adjustment is not correct, the depth recorded will not be correct. 6. The velocity of acoustic wave changes if temperature, salinity or pressure changes and since velocity is not correct, the depth recorded will be inaccurate.
    marinetales October 29, 2020
    1.Master to ensure that the Designated officers are competent to operate the equipment 2. The required training shall be demonstrated by the officers during every drill 3. Ensure that the testing of GMDSS equipment shall always be undertaken by the designated officers 4. Ensure that details of INM-C, MF-HF equipment, Epirb etc are updated in case there is change in data of such vessel. 5. Ensure that EPIRB is properly stowed and not activated falsely 6. If false distress is transmitted such distress alert shall be cancelled using the appropriate procedures and all officers shall be aware of same
    marinetales May 24, 2021
    GDOP (geometric dilution of precision) or PDOP (position dilution of precision) describes the error caused by the relative position of the GPS satellites. In simple terms, the value of GDOP defines the accuracy of GPS position. If the satellites are CLOSER you will have a HIGHER GDOP and LESS ACCURATE POSITION if the satellites are FAR APART you will have LOWER GDOP and MORE ACCURATE POSITION HDOP (Horizontal Dilution of Precision) is a part of GDOP and concerns with the horizontal distance between the satellites
    marinetales May 19, 2021
    In Head-Up display, the 12 o'clock position on the PPI represents own ship's course and hence the heading shows zero on the graduated scale around the PPI. All bearings taken on this display will be relative to the heading. The right side of the heading marker on PPI is the Starboard side of the ship and the left side of the heading marker is the Port side of the ship. If Radar is used in Headup mode while altering the course the Heading marker remains at the same position and the targets start moving on the screen, due to this the picture gets smudged. Picture smudges in azimuth during alterations of course. Because of smudging, accurate bearings cannot be taken during large course alterations Plotting becomes highly inaccurate during yaw in bad weather, as ship's head keeps changing several degrees per second, resulting in severe smudging.
    marinetales May 9, 2021
    There are two stabilisation modes on Radar – ground and sea. Ground stabilisation means that the display is referenced to the seabed by GNSS or through a twin-axis Doppler log. For sea stabilisation the display is referenced to the sea current that own ship is experiencing, typically based on SDME measurements. It is generally accepted that the ground stabilised mode is more useful for normal navigation, especially when combined with setting tracked targets to show their True vectors. However, since set and drift affect heading and aspect, ground stabilised displays should be used with caution where target tracking is concerned. Sea stabilisation mode gives the navigator a better understanding about the aspect and therefore is used in collision avoidance.
    marinetales August 23, 2020
    The best way is to do a quick PM test (Performance Monitor) test. This along with the Magnetron Current value and Value of Attenuation of the Transceiver will give OOW an idea about whether the RADAR is working satisfactory or not.
    marinetales August 23, 2020
    One of the methods is to check the Admiralty Sailing Directions for the area the vessel is currently at. The surface pressure chart of that area will state the Value which is expected in that month and location. This method, unfortunately, is not always accurate and there can be variations in reading that might be encountered. The best way here is to compare your readings with vessels in the vicinity. Similar readings will suggest that the Barometer is showing correct readings. This is certainly the quickest way of determining the accuracy of your Barometer.