Question and Answers

T & P Notices also called as Temporary and Preliminary Notices, are provided in Weekly Notices to Mariners in Section II. These are shown with suffix (T) or (P) after each Notice Number. Temporary Notice may be issued to inform the mariner of any navigation affecting changes which are temporary in nature. Such eg may include - naval exercise, drilling activities, dredging etc. Preliminary Notices are issued to promulgate navigationally significant data to mariner when - 1. Action or work will shortly be taking place. 2. Information has been received but is too complex to be promulgated by chart updating notice 3. Further confirmation of details is needed. A chart updating Notice will be promulgated or New Edition issued when the details have been confirmed 4. For an ongoing and changeable situation such as a bridge under construction

Wheel-over point is a point where the rudder is put over while considering the distance to the new course and the ship's turning characteristics. For a safe turn, it is necessary for a vessel to determine her wheel-over position or point.

Great Circle Sailing : shortest distance measured along the earth's surface between two places is called the Great Circle Distance. The departure and arrival positions are marked on a Gnomonic Chart and joined by a straight line. Waypoints are transferred from Gnomonic to Mercator chart and it appears as a Curved line on Mercator chart. Mercator Sailing : Used to find the Rhumb Line course and distance between two positions. It uses the following formula - tan Course = dLong / DMP This holds good when the distance is more than 600 NM. For distances lesser than 600 NM, we use Parallel sailing. The formula is given by - Cos mLat = dep / dLong Rhumb Line: Rhumb Line is a line drawn on a Mercator Chart which cuts all meridian at same angles. Composite Sailing: Sometimes, it is not possible to execute a full great circle for a voyage. This could be due to presence of navigational dangers in between OR if the Master decides not to go beyond a certain latitude owing to weather conditions. In this case, a combination of rhumb line and great circle sailing. Together this type of sailing is called as Composite Sailing.

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.

The amplitude of any celestial body is taken, when the centre of the celestial body is at the rational horizon. In the case of moon, when it's centre is at the rational horizon, the moon is not visible on the horizon.

The best time to take amplitude is when the body is theoretically rising or setting. This means when the sun's lower limb is half the Semi Diameter above the visible horizon. At this time, the centre of the body is at the rational horizon, but the body is seen above the visible horizon because of refraction.

Tides are long-period waves that roll around the planet as the ocean is "pulled" back and forth by the gravitational pull of the moon and the sun as these bodies interact with the Earth in their monthly and yearly orbits. During full or new moons—which occur when the Earth, sun, and moon are nearly in alignment—average tidal ranges are slightly larger. This occurs twice each month. The moon appears new (dark) when it is directly between the Earth and the sun. The moon appears full when the Earth is between the moon and the sun. In both cases, the gravitational pull of the sun is "added" to the gravitational pull of the moon on Earth, causing the oceans to bulge a bit more than usual. This means that high tides are a little higher and low tides are a little lower than average. These are called spring tides, a common historical term that has nothing to do with the season of spring. Rather, the term is derived from the concept of the tide "springing forth." Spring tides occur twice each lunar month all year long, without regard to the season. Seven days after a spring tide, the sun and moon are at right angles to each other. When this happens, the bulge of the ocean caused by the sun partially cancels out the bulge of the ocean caused by the moon. This produces moderate tides known as neap tides, meaning that high tides are a little lower and low tides are a little higher than average. Neap tides occur during the first and third quarter moon, when the moon appears "half full." Whenever the change of tide occur from low tide to high tide at a given place , the tide is said to be flooding. During the period when the water level recedes from high tide to low tide, the tide is said to be ebbing.

Dead Reckoning position: After a fix is obtained, the next position of the vessel which is found by applying course steered, leeway and engine speed ONLY is called Dead Reckoning position. This is denoted by the symbol 'X'. Estimated Position: If the DR position (obtained above) is adjusted for prevailing set and expected drift then the position is said to be Estimated Position. This is denoted by the triangle symbol. Observed position or FIX: The actual position of the ship is called as the Observed Position or Fix. This is denoted by a Circle. The OP or Fix is the most accurate position of the ship.

Following factors affect the squat of the vessel - 1. Speed of the vessel 2. Block Coefficient 3. Blockage factor 4. UKC of the vessel 5. Trim of the vessel 6. Location of the vessel (open seas or canal / channel)

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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.

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.

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.

Sometimes it is not possible to obtain sextant altitude of the celestial body when it is on the meridian due to clouds, hazy horizon, rain or other reasons. The celestial body is then observed when it is near the meridian. The value of Ex-meridian limits are obtained from the nories tables OR as an estimate, if the Latitude and Declination are the same name then subtract the value and if different names than add the value, the value obtained will be the value of limits in minutes before and after meridian passage for taking sight. This is called Ex meridian limits. Within this window period one should obtained the sight of the celestial body when it is near the meridian.

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

There are two aspects to this question - Number 1: How to determine the cargo quantity which can be carried in a particular hold? Number 2: After the cargo has been loaded, how to determine the cargo quantity loaded in that hold? Number 1: The maximum cargo quantity which can be carried in a particular hold can be estimated by using a simple mathematical formula i.e. mass = volume x density or mass = volume / Stowage factor (as stowage factor is the reciprocal of density). This will give you the mass of the cargo which can be loaded in the hold. HOWEVER, this may not be correct as the total mass of cargo which can be loaded in a cargo hold is limited by the fact load density which depends upon the tank top strength in a cargo hold. In order to obtain the maximum cargo which can be loaded safely into a given hold, the vessel's trim and stability booklet (or capacity plan) shall be consulted. Number 2 : In order to determine the quantity of cargo in a particular hold after the cargo has been loaded in to the vessel is a very vague concept and unfortunately it cannot be obtained very accurately. The rough estimation could be first you determine the height of the cargo in the hold and using the length and breadth dimensions of that hold (given in the general arrangement plan) and determine the volume of the cargo. Thereafter, use the formula mentioned above to arrive at the mass of the cargo loaded. Please note above works only in the case of bulk cargo.

1. Shall be contained in Watertight casing 2. Have brief instructions about how to use them 3. Emit smoke of highly visible color at a uniform rate of not less than 3 minute when floating in calm water 4. Shall not emit any flame during entire smoke emission time 5. Not to be swamped in a seaway 6. Continue to emit smoke when submerged in a water for a period of 10 seconds under 100 mm of water

Following are the SOLAS requirements of Hand flares - 1. To be contained in a Water tight casing 2. Instructions shall be given regarding operation 3. Should have integral means of ignition 4. Burn with a bright red color 5. Burn uniformly with an average luminous intensity of not less than 15,000 cd 6. Have a burning period of not less than one minute 7. Continue to burn after having been immersed in 100 mm of water for a period of 10 seconds

Requirements of Rocket Parachute as per SOLAS - 1. Be contained in a Water tight casing 2. Supplied with brief instructions for activating 3. Have integrated means of ignition 4. When fired vertically shall atleast reach an altitude of 300 meters 5. Burn with bright red color 6. Burn uniformly with an average luminous intensity of not less than 30000 cd 7. Have a burning period of not less than 40 seconds 8. Have a rate of descent of not less than 5m/s 9. Should not damage its parachute or attachments while burning

Segregated ballast means the ballast water introduced into a tank which is completely separated from the cargo oil and oil fuel system and which is permanently allocated to the carriage of ballast or cargoes other than oil or noxious liquid substances as variously defined in the annexes of the present convention

Enroute means that the ship is underway at sea, on a course or courses including deviation from the shortest direct route which as far as practicable for the navigation purpose will cause any discharge to be spread over as great an area of the sea as is reasonable and practicable.

Clean ballast means the tank in which, since oil was last carried therein has been so cleaned that effluent there from if it were discharged from the ship which is stationary, into clean calm water on a clear day would not produce visible traces of oil on the surface of the water or on adjoining shore lines or cause a sludge or emulsion to be deposited beneath the surface of water or upon adjoining shorelines. If the ballast is discharged through an oil discharge monitoring system, approved by the administration, the oil content of the effluent did not exceed 15 ppm