LOGS

The log is an instrument for measuring the speed and distance traveled by a ship. It is important to note that the speed measured by log is affected by current and tidal streams.

There are 2 main types of log

  1. The towed or patent log – This type of log is usually towed astern of the ship through the water.
  2. The bottom log – This log is fitted on the bottom of the ship usually on the bottom plating. It is more reliable than towed log it can be withdrawn into the ship’s hull when not required(At the end of the voyage when navigating in shallow water)There are 3 main types of bottom log –
    1. Impeller Log – Impeller log as the name itself suggests – the impeller is fitted in a tube and is installed on the bottom plating of the ship. The whole tube can be retracted into the hull when not in use.
      • Working – Impeller rotates as the ship moves through the water. Converts the rotation of impeller into electrical signal. This is how we get distance and speed on bridge.
    2. Pressure tube or Pivot type log – It is also a tube fitted at the bottom and can be retracted back into the hull when not required. The tube has 2 pipes fitted to it, one facing forward called the DYNAMIC TUBE and the other tube facing downwards called the STATIC TUBE.
      • Working – When the ship is stopped and there is no current or tide the pressure in both tubes will be equal to the depth of tube below the waterline. When the ship moves the pressure in the dynamic tube will be higher than the static tube. This difference in pressure is converted into electrical signal and used for distance and speed information on bridge.
    3. The electromagnetic log – This log works on the principle that if any conductor passes through a magnetic field a small EMF will be induced within itself which is proportional to speed of the movement of the conductor. In case of electromagnetic log the conductor is the seawater, the magnetic field is created by a coil in the tube and the induced EMF is measured by two sensors on the side of the tube.
    4. The doppler log-A transducer fitted on the bottom of the ship emits a continuous beam of sound vibration in the water at an angle of about 60 degrees to the keel in the forward direction. The beam is bounced of the sea bed or a layer of water and received back at the transducer. Now the difference in the frequency between the transmitted and received signal is measured and is proportional to the speed of the vessel.
      • When vessel is in shallow water the signal is bounced back from the sea bed giving speed over ground but when in deep water transmitted signal is bouched back form layer of water giving a speed through water.
      • JANNUS CONFIGURATION – Most logs have transducers to measure both fore and aft speeds(ahead and stern) as well as athwarthship transducers to measure speed in the sideways direction (Useful when berthing). Such a transducer which measures both alongship as well as athwartship speed is called JANNUS CONFIGURATION.
Janus-configuration-Doppler-log
Janus configration, image credit myseatime

Doppler log is a important topic so we will go deep inside the topic –

Modes in Doppler log

Doppler logs will have the functionality to choose the tracking mode. The three tracking modes available are

  1. Water (Measure speed through water)
  2. Ground (Measures speed over ground)
  3. Auto (Selects water mode or ground mode automatically as per depth)

IMO Requirements for Doppler log

IMO resolution A.824 (19) as amended by MSC 96(72) gives the details of the performance standards for the Doppler logs fitted on ships.

The few of the main requirements as per this are

  1. The device measuring speed and distance through the water should meet the performance standard in water of depth greater than 3 m beneath the keel
  2. Error in the measured and indicated speed for a digital display should not exceed 2% of the speed of the ship, or 0.2 knots, which is greater. For analogue display the error should not exceed 2.5% of the speed of the ship or 0.25 knots whichever is greater.
  3. The performance of the equipment should be such that it will meet the requirements of performance standards when the ship is rolling up to 10 degrees and pitching up to 5 degrees.

Working principle of dopler log

Principle of Dopler log

Dopplerfrequency

Doppler log is based on the principle of Doppler shift in frequency measurement i.e. apparent change in frequency received when the distance between source and observer is changing due to the motion of either source or observer or both. In Doppler log an observer is moving with a source of sound towards a reflecting plane, then the received frequency. By measuring the received frequency and knowing the value of transmitted frequency and velocity of sound in seawater, the speed of the vessel can be determined.

Limitation of Dopler log

At least 3m depth is required below the keel to get speed through water. If the mode is not changed to ground (or auto) when the depth below keel is less than 3 meters, Doppler log will show errors in the speed.

But the option to change modes are not present in all makes and model of the Doppler log.

Some Doppler log only measures what it is supposed to measure, which is speed through water.

In depths less than 2~3 meters below keel, these Doppler logs displays the GPS speed for which a GPS connection to the Doppler log is required.

Errors of the Doppler log

  1. Error in transducer orientation: The transducers should make a perfect angle of 60° with respect to the keel or else the speed indicated will be inaccurate.
  2. Errors in oscillator frequency: The frequency generated by the oscillator must be accurate and constant, any deviation in the frequency will result in the speed indicated being in error.
  3. Error due to propagation of wave at different temperatures. The velocity of the acoustic wave at the temperature of 16°c and salinity of 3.4% is 1505m/sec, but generally, it is taken as 1500m/sec for calculation.
  4. Errors due to the ship’s motion: during the interval between transmission and reception, the ship may marginally roll or pitch.

SHORT NOTE ON MAGNETIC COMPASS

INTRODUCTION

  • The magnetic compass is fitted on the upper bridge(also called the monkey island). And it is placed exactly on the centerline of the ship.
  • It is referred to as the standard compass because it is considered the primary means of direction indication.
  • There are two types Dry card and Wet card.
    • The dry card was used in the olden days, But it was too sensitive for steering so now we have wet card. Now dry card is not found on any merchant ship.

WET CARD COMPASS

The wet card is made of mica and is only about 15 cm in diameter. Graduations are printed on it. In Modern wet card compasses, the directive element is a ring magnet fitted around the base of the float. Ring magnet is used as it provides less resistance and turbulence. By immersing the card in liquid, oscillation caused by vibration, Rolling and pitching are damped.

THE LIQUID

The bowl is filled with a mixture of distilled water and pure ethyl alcohol so that the mixture has following properties.

  • Low freezing point about -30’C
  • Small coefficient of expansion.
  • Low relative density about 0.93
  • Does not discolor the card.

THE BOWL

Wet card is about 15cm in diameter, The bowl is 23cm so that the card rotates comfortably. The top of bowl is transparent glass. The bottom is of frosted glass to diffuse the light coming from the bulb below.

The wet compass bowl -image credits cruising.coastalboating.net

What is the Lubber line in the above image?

On the inside part of the bowl, there is a small projection with a line marked on it. This line is called the Lubber line and it represents the direction of ship’s head.

THE BINNACLE

It is a cylindrical container made of non-ferrous metal. Olden days teak wood was used.

  • The Bowl is slung inside the top portion of the binnacle. The middle portion is accessible by a door and contains corrector magnets.
  • Corrector magnets – There are a number of horizontal holes, both fore and aft and athwart for hard iron or permanent corrector magnets which are used to adjust undesirable, disturbing magnetic effects caused by ships steel hull or other metal body onboard. This correction is done by qualified compass adjuster.
image credits – owaysonline.com

Quadrantal Corrector – There are two soft iron spheres that are fitted in brackets, one on either side of the binnacle. This can be adjusted by sliding it towards or away to get the desired compass adjustment.

The helmet is just a cover made up of non-ferrous metal to provide protection to the compass bowl from sunlight, rain, and spray. Generally, it is also covered with canvas in practical onboard vessels.

Care and maintenance of Magnetic compass

  1. The door to access the corrector magnets should always be closed and keys must be kept in safe custody.
  2. Soft iron sphere (Quadrantal Corrector ) and brackets should be painted to prevent rusting.
  3. The Brass part of binnacle should be polished regulary.
  4. Magnetic material, Electric machinery, Electric wires should be kept away from the compass.
  5. Helmet should be closed when not needed.
  6. In rare case, A bubble may develop in the wet comapss bowl. This has to be removed at earliest opportunity.

Explain importance of Taking & Recording Compass Error?

The compass error should be checked each watch and on every new course to measure the error of the gyrocompass, which is the angle the gyro north makes with the True north to establish trends in deviation on different courses at varying latitudes.

To ensure a compass is in good working condition, it is important to check performance of magnetic compasses particularly after: a vessel has been operating on short voyages for a long period of time then relocates, which results in a large change in magnetic latitude

SEP 2021 – PAPER: BRIDGE EQUIPMENT & WATCHKEEPING

GOVERNMENT OF INDIA
Date: - 06 September-2021
SECOND MATE OF A FOREIGN GOING SHIP
FUNCTION: NAVIGATION
PAPER: BRIDGE EQUIPMENT & WATCHKEEPING
TIME: 3 Hours PASS MARKS: 100 MAX. MARKS: 200

Attempt any Eight Questions.

All Questions carry equal marks i.e. 25 marks each.


Q.1 a) Describe the procedure for removing air bubble from Magnetic Compass. (Marks 10)
b) With respect to Auto-pilot, write short notes on:
i) Proportional control
ii) Off-course alarm (Marks 15)


Q.2 How Janus configuration of the Doppler Log minimizes various errors?


Q.3 a) Explain how the frequencies used by GPS satellites can also be used to determine the speed of the vessel? (Marks 15)


b) Explain the methods of updating Electronic Nautical Charts (ENCs). (Marks 10)


Q.4 a) List the authorized users of LRIT information and state the conditions under which LRIT information from ships can be released to the authorized users. (Marks 15) b) List the data recorded by VDR and SVDR. (Marks 10)


Q.5 a) List the exchange of information between the Master and Pilot when the pilot boards the vessel. (Marks 15)
b) What information in contained in the Wheel House Poster. (Marks 10)


Q.6 List the duties & responsibilities of the On-scene Co-coordinator in IAMSAR.


Q.7 As per STCW watchkeeping principles, list the factors to be taken into account when deciding the composition of the watch on the bridge.


Q.8) a) What does the STCW say regarding performing a deck watch in general and particularly on ships carrying hazardous cargo? (Marks 10)
b) State your actions on receiving a distress alert on VHF DSC channel 70. (Marks 15)


Q.9 Draw a turning circle for a vessel. Mark and explain Advance, Transfer, Tactical Diameter, and Drift Angle.

OCT 2021 – PAPER: BRIDGE EQUIPMENT & WATCHKEEPING

GOVERNMENT OF INDIA
Date: - 06 October-2021
SECOND MATE OF A FOREIGN GOING SHIP
FUNCTION: NAVIGATION
PAPER: BRIDGE EQUIPMENT & WATCHKEEPING
TIME: 3 Hours PASS MARKS: 100 MAX. MARKS: 200

Attempt any Eight Questions.

All Questions carry equal marks i.e. 25 marks each.


Q.1 Explain following terms with respect to Operation of Gyro Compass:
a) Gyroscopic Inertia b) Precession c) Tilt
d) Drift e) Three degree of Freedom


Q.2 a) What corrections are to be made to Echo Sounder before comparison with Chart?(Marks 10)
b) Explain the use of ‘Janus’ configuration in a Doppler log? (Marks 15)


Q.3 a) Write short notes on True North, Magnetic North, Variation, Deviation. (Marks 15)
b) Explain Purpose and Working of a Course Recorder? (Marks 10)


Q.4 Write short notes with on any two of the following:
i) LRIT ii) VDR iii) ECDIS iv) BNWAS v) AIS


Q.5 a) Explain Term “Responsibility” as per Rule 2 of Rule of the Road (RoR). (Marks 12)
b) Under what conditions and circumstances will you call a Master on the Bridge? (Marks 15)


Q.6 a) List content of IAMSAR Vol 3. (Marks 15)
b) Explain when & how the sector search is executed. (Marks 10)


Q.7 a) What are the dangers associated while navigating in a Heavy Weather Area? (Marks 12)
b) What do you understand by Effective Communication and Assertive Leadership? (Marks 13)


Q.8) a) List actions you will take while on watch and a MOB occurs? (Marks 15)
b) Prepare a checklist for maintaining a Safe Anchor Watch? (Marks 10)


Q.9 a) Define and Explain Terms SQUAT, PIVOT POINT, FOUL HAWSE, BOW CUSHION. (Marks 16)
b) List all the information that you will get from Pilot Card? (Marks 09)

NOV 2021 PAPER: BRIDGE EQUIPMENT & WATCHKEEPING

GOVERNMENT OF INDIA
Date: - 08 November-2021
SECOND MATE OF A FOREIGN GOING SHIP
FUNCTION: NAVIGATION
PAPER: BRIDGE EQUIPMENT & WATCHKEEPING
TIME: 3 Hours PASS MARKS: 100 MAX. MARKS: 200

Q.1 a) Write short notes on “Tilt” and “Drift” of a gyro and discuss their rates? (Marks 8)
b) Write short note on Magnetic Compass? (Marks 8)
c) Explain importance of Taking & Recording Compass Error? (Marks 9)


Q.2 a) Explain the advantages of ‘Janus’ Configuration of Doppler log. (Marks 15)
b) Enumerate steering gear tests & checks. (Marks 10)


Q.3 a) Explain the working of a GPS (Marks 15)
b) How does DGPS enhance position fixing of GPS data. (Marks 10)


Q.4 Write short notes with comparison on the following:
i) LRIT vs AIS
ii) VDR(Voyage Data Recorder) vs S-VDR
iii) ECS (Electronic Chart System) vs Paper Charts


Q.5 While keeping Bridge watch at sea, list actions would you take when following alarms are activated:
a) Fire Alarm b) Gyro Failure c) VHF DSC Distress Alert


Q.6 a) List the contents of IAMSAR Volume III. (Marks 15)
b) How does VTS enhance safety of navigation? (Marks 10)


Q.7 a) Explain Situational Awareness? (Marks 10)
b) Explain terms SAFE SPEED, LOOKOUT, STAND-ON VESSEL. (Marks 15)


Q.8) Prepare a checklist for taking over a navigational watch at sea
a) In Restricted Visibility. (Marks 12)
b) Approaching a Heavy Weather Area. (Marks 13)


Q.9 a) What are the dangers associated with and precautions to take while navigating in shallow waters? (Marks 10)
b) Draw a Turning Circle and Define below mentioned associated Terms

  • ADVANCE
  • TACTICALDIAMETER
  • TRANSFER, DRIFT ANGLE. (Marks 15)

DEC 2021 PAPER: BRIDGE EQUIPMENT & WATCHKEEPING

GOVERNMENT OF INDIA


Date: – 03rd December-2021


SECOND MATE OF A FOREIGN GOING SHIP
FUNCTION: NAVIGATION
PAPER: BRIDGE EQUIPMENT & WATCHKEEPING


TIME: 3 Hours PASS MARKS: 100 MAX. MARKS: 200
Notes:

  • Attempt any Eight Questions.
  • All Questions carry equal marks i.e. 25 marks each.


Q.1 a) Write short notes on “Tilt” and “Drift” of a gyro and discuss their rates? (Marks 8)
b) Write short note on Magnetic Compass? (Marks 8)
c) Explain importance of Taking & Recording Compass error? (Marks 9)


Q.2 a) Explain the advantages of ‘Janus’ Configuration in the Doppler log. (Marks 15)
b) Enumerate steering gear tests & checks. (Marks 10)


Q.3 a) Explain the working of a GPS (Marks 15)
b) How does DGPS enhance position fixing of GPS data. (Marks 10)


Q.4 Write short notes with comparisons on the following:
i) LRIT vs AIS
ii) VDR(Voyage Data Recorder) vs S-VDR
iii) ECS (Electronic Chart System) vs Paper Charts


Q.5 While keeping Bridge watch at sea, list actions would you take when following alarms are activated:

  • a) Fire Alarm
  • b) Gyro Failure
  • c) VHF DSC Distress Alert

Q.6 a) List the contents of IAMSAR Volume III. (Marks 15).

b) How does VTS enhance the safety of navigation? (Marks 10)


Q.7 a) Explain Situational Awareness? (Marks 10)
b) Explain terms SAFE SPEED, LOOKOUT, STAND-ON VESSEL. (Marks 15)


Q.8) Prepare a checklist for taking over a navigational watch at sea
a) In Restricted Visibility. (Marks 12)
b) Approaching a Heavy Weather Area. (Marks 13)


Q.9 a) What are the dangers associated with and precautions to take while navigating in shallow waters? (Marks 10)
b) Draw a Turning Circle and Define below mentioned associated Terms ADVANCE, TACTICAL, DIAMETER, TRANSFER, DRIFT ANGLE. (Marks 15)

PAPER FORMAT OF BRIDGE EQUIPMENT AND WATCH KEEPING – 2ND MATES


Duration: 3 hrs. SECOND MATE (F.G.) Maximum Marks: 200
Pass Marks: 100
BRIDGE EQUIPMENT AND WATCHKEEPING.
Note: 1. ATTEMPT ANY 8 OUT OF 9 QUESTIONS.

ALL QUESTIONS CARRY EQUAL MARKS

  1. GYRO COMPASS, MAGNETIC COMPASS, AUTOPILOT, COURSE RECORDER, ROTI
  2. DOPPLER LOG, ELECTROMAGNETIC LOG, ECHO SOUNDER, OTHERS
  3. ELECTRONIC POSITION FIXING SYSTEM
  4. AIS, LRIT, VOYAGE DATA RECORDER, SEXTANT
  5. BRIDGE PROCEDURES
  6. IAMSAR, VTS PROCEDURES, SHIP REPORTING SYSTEMS
  7. WATCHKEEPING, BRM
  8. SAFETY, WATCHKEEPING, EMERGENCIES
  9. MANOEUVRING


Please note that the above format is only an indicative of the examination paper.
The candidates are advised to refer to detailed teaching syllabus and the course outline.