What is Angle of Repose?

What is Angle of Repose? imunotes.in


The angle of repose, or critical angle of repose, of a granular material is the steepest angle of descent or dip relative to the horizontal plane to which a material can be piled without slumping.

Or it is the maximum horizontal angle at which granular particles can stack without using any other force or support.

Now, this might come to your mind that what is the maximum and what is the minimum angle of repose possible – So Theoretically speaking the angle will be between 0 and 90 degrees. Now let’s check which material has the largest and the least angle of repose –

Materials like Asphalt, Chalk, Coconut (Shredded), Coffee beans (Fresh), Earth, Gravel(Crushed stone) can have a maximum angle of repose up to 45 degrees. Whereas Looking to the least side we will have Urea, Wheat, Sand they can have as low as 27-30 degrees.

CARGO WORKS – ORAL QUESTIONS

Following are the oral questions asked to the candidate, Click on the question to get answer (We are working on the answers). What we provide is a sample answer we cannot claim that our answer will be the best answer.

  1. What is load density and where you can find it?
  2. What is a bay plan and where you can find it onboard?
  3. Where can we find the location of IMDG cargo?
  4. Contents of MSDS Sheet?
  5. Purpose of MSDS Sheet?
  6. Markings on a container?
  7. What is BAY, TIER, ROW?
  8. List vs Trim?
  9. What is COW (advantages and disadvantages)
  10. Crude oil washing action is taken before and after arriving at port.
  11. What is pounding?
  12. What is a too lean and too rich hydrocarbon mixture?
  13. Difference between through and surface ventilation?
  14. Where is SuezCanal?
  15. What is the transportable moisture limit?
  16. What is the proof load?
  17. What is broken stowage?
  18. How to find the safe working load of a crane?
  19. what is breaking stress?
  20. What is the Angle of repose?
  21. In what type of fire we can use foam?
  22. What is a foam system & Explain high and low expansion.
  23. What is a chain register?
  24. Where is the chain register kept and what are its contents?
  25. The hazard of tank cleaning?
  26. Explain IMDG casses and Contents?
  27. Precautions for heavy lift cargo?
  28. What is stability booklet and where is it kept ?
  29. Contents of stability booklet?
  30. What is the cargo Securng manual?
  31. contents of cargo securing manual?
  32. What is IG tank?
  33. What is mast riser?
  34. What is purging?
  35. Duties of OOW while at a container port?
  36. Duties of OOW while at a loading oil?
  37. Parts of IG plant?
  38. What is liquefaction?
  39. What is flow state?
  40. What is loadicator ?
  41. Diff methods of purging?
  42. Hazard of Iran ore while loading?
  43. What is stowage factoe? What is broken stowage?
  44. If lodicator fails can you still load the cargo?
  45. If loadicator fails how will you load cargo?
  46. What is BLU code?
  47. What action you will take if you see oil around your vessel?
  48. IMSBC code?
  49. Ventilation and its need.?
  50. What is GM? What is the minimum GM?
  51. What is PV valve and what is PV breaker Valve?
  52. What is annealing? Why we do annealing?
  53. What is Exposimeter?
  54. Function of Exposimeter?
  55. Explain Flammablity dagram ?
  56. Alarms on IG Pannel?
  57. IG Blower?
  58. Scrubber ?
  59. Content of IG?
  60. What is Volatile Cargo ?
  61. What s Non Volatile Cargo?
  62. Define LFL and UFL
  63. What s MFAG?
  64. what is keel reke?
  65. what is stem rake?
  66. What is angle of LOL?
  67. What is Stable and unstable equlibrium ?
  68. Corrective action for angle of lol?
  69. Stages and Procedure for COW?
  70. What is CSM code?
  71. What is Shell Expansion plan?
  72. Name Bridge euipments
  73. Life boat requirement?
  74. Life raft requirement?
  75. What is intact stablity?
  76. How is a container secured onboard?
  77. Lashing arrangement ?
  78. Which one is more important base lock or twist lock or Lashing?
  79. In RORO ship what is axil load?
  80. Disadvantage of crude oil washing?
  81. Advantages of crude oil washing ?
  82. Diffrent type of piping system on tanker?
  83. Stowage factor unit?
  84. Hazard of grain ?
  85. Hazard of coal ?
  86. Hazard of sulpher ?
  87. Hazard of timber cargo?
  88. What is Moisture content ?
  89. What is FMP and TML?
  90. What is Trimmed and untrimmed cargo?
  91. What is Noxious lquid substance?
  92. What is CSC plate?
  93. What is Hydrostatic draft?
  94. What is hogging and Sagging?
  95. What is SF factor ?
  96. Methods of ballast water management?

What is the difference between List and Trim.

LIST is defined as transverse inclination of vessel due to weight of cargo on ship( generally uneven distribution of cargo in ship’s cargo hold) either direction. This is transverse inclination of the vessel. Whereas TRIM is the transverse inclination of the vessel due to wind, Current and other natural factors.

Note- In interview sometime they can ask by showing a image if it is a trim or list, Be confident and tell them its not possible to tell without knowing if the cargo is loaded uneven or if the weather is the factor even if in a image you see a bad weather in the image you cannot assume that cargo is distributed evenly.

List of cargoes which generate heat, gases and moisture:

  1. Wood, paper pulp and agricultural products may result in rapid and severe oxygen depletion and formation of carbon dioxide.
  2. The IMSBC code lists the following cargoes as potentially oxygen depleting: coal, direct reduced iron, sponge iron, sulphide concentrates, ammonium nitrate based fertilisers, linted cotton seed. Various gaseous products are formed including carbon monoxide, carbon dioxide, hydrogen sulphide and hydro carbons.
  3. Some cargoes like coal and sulphur can cause severe damage due to corrosion.
  4. Common cargoes like coal, sulphur, cotton, and fishmeal are liable to spontaneous heating. Coal also emits methane which is a flammable gas. When mixed with air it can form an explosive mixture.
  5. Dust created by certain cargoes may constitute an explosion hazard. Sulphur dust can readily ignite causing an explosion.
  6. Friction between cotton bales can cause spontaneous combustion and produce heat.
  7. Ammonium nitrate-based fertilisers support combustion. If heated, contaminated or closely confined, they can explode or decompose to release toxic fumes and gases.
  8. Metal sulphide concentrates. Some sulphide concentrates are prone to oxidation and may have a tendency to self-heat, leading to oxygen depletion and emission of toxic fumes. Some metal sulphide concentrates may present corrosion problems.

What is a mast riser? What is the use of mast riser and Regulation as per ISGOTT.

In Crude oil tankers and vessels carrying homogeneous cargo, We can use just one line for venting purpose as all the cargo is homogeneous(same). From all the cargo tanks venting pipelines lead to the Mast riser. The mast riser is fitted with a valve (called mast riser valve). Use of mast riser – While loading the pressure inside the cargo tank is released through the mast riser by opening the mast riser valve and also the cargo tank pressure is monitored and if required the mast riser valve is throttled to maintain the cargo tank pressure at certain level. During discharging cargo to avoid negative pressure in the tank, the inert gas is continuously supplied to the cargo tanks.

The exhaust of mast riser must be at least 6m above the deck.

Whether to Ventilate or not to ventilate? For Cargo and ship sweat

The following information is necessary before deciding whether to ventilate or not:

  • Temperature and dewpoint of the outside air.
  • Temperature and dewpoint of the air inside the hold.
  • Temperature of the cargo surface.
  • Temperature of the steel structure (Ships) inside the cargo compartment and
  • The moisture content of hygroscopic cargoes if applicable.

Whether to Ventilate or not to ventilate?

The following basic Dew Point rule provides relevant guidance which is:

  • If the dew point of the air within the hold is higher than the dew point of the OUTSIDE atmosphere, then ventilate.
  • If the dew point of the air within the hold is lower than that of the OUTSIDE atmosphere, then do not ventilate.

ANOTHER WAY OF EXPRESSING THIS IS –

  • If the Dew point of the outside air is lower or equal to that of the hold atmosphere……continue ventilation.
  • If the Dew point of the outside air is higher than the hold atmosphere dew point ………do not ventilate with outside air.

A further extension of the basic rule must be examined depending upon the two basic types of cargo.

HYGROSCOPIC CARGO -Warm region to Cold region:

As the ship proceeds from a warm region to a cold region it will experience a gradual drop in the temperature and a drop in the dew point. The atmosphere within the hold will receive large quantities of moisture from the cargo.  Hence in a situation such as this, ventilate vigorously during the early stages but eventually the outside Dewpoint will be too low.

NON-HYGROSCOPIC CARGO –Warm region to Cold region: 

Ship sweat is inevitable but cargo unaffected unless, condensation drips back onto the cargo.

HYGROSCOPIC Cargo:Cold region to warm region:

Not critical, therefore ventilation not essential. In some cases on opening hatches at the discharge port immediate condensation may form on surface but will dry off as cargo is discharged.

Non-HYGROSCOPIC Cargo:Cold region to warm region:

No Ventilation. Cargo sweat would occur on the surface of the cargo if relatively warm moisture laden air was admitted.

If due to any reason it is not possible to take readings within the hold then ‘Three Degree Rule’ can be used;

  • During loading regular cargo temperatures should be recorded. Whilst on passage if the atmosphere dry bulb temperature is at least 3ºC cooler than the average temperature of the cargo when loaded, then ventilate the hold, if the temperature of the atmosphere is less than 3ºC cooler than the average temperature of the cargo when loaded, the do not ventilate the hold.

Reasons for Ventilation for cargo on board? Why is cargo and ship sweat caused? Cargo sweat and Ship sweat.

It is a very simple topic and as common as everyday event like WHY Water bottle from fridge gets water on the outer surface.

A large number of cargo claims are made for goods transported by ships which have been damaged in transit. Much of this damage is caused by either ‘ships sweat’ or ‘cargo sweat’ and could be effectively reduced by prudent ventilation of cargo spaces.

Cargo or goods carried at sea are exposed to the atmosphere which is high in moisture content. Due to the very nature of the trade, cargo damage due to moisture continues to be a cause for concern to all parties in the trade. Very heavy cargo claims due to damage to cargo caused by moisture continue to be made.

Between 1996 and the year 2000 claims accounted for in excess of 2 million US dollars in only one P&I club.

Cargo ventilation, as statistics indicate, appears to be the most neglected or least understood aspects of cargo care & cargo operations.  It is also one such activity that does not attract the attention it deserves and more often than not it is too late by the time the consequences are realised.

Why is sweat caused onboard?

Sweat is caused by the condensation of saturated air on a cooler surface. It is formed when water vapor in the air within the hold condenses out into water droplets once the air is cooled below its dew point. The water droplets may be deposited onto the ship’s structure or onto the cargo.

Some definitions are useful in understanding sweat.

Dew point:

Is defined as the temperature at which air cannot absorb any more water vapour; i.e. it is saturated. In simple language if the air parcel falls below its dew point temperature, then the moisture within the air parcel will condense.

Saturation:

Means that a parcel of air has absorbed its maximum amount of moisture for that temperature, however raising the temperature will allow for more moisture to be absorbed.

Relative Humidity:

Is the ratio between the actual moisture content and the maximum moisture content that the parcel of air can contain.

Hygroscopic cargo:

Is cargo, which can absorb or give off moisture. They are mainly of plant origin. Since they may retain or absorb water, excessive amounts of inherent moisture may lead to significant self-heating and moisture migration within the cargo. This will result in cargo getting caked or rotting.

Examples of Hygroscopic cargo: Rice, flour, grain, coffee, tea.

Non-hygroscopic cargo:

Is cargo, which does not absorb or give off moisture. Cargoes like steel are non-hygroscopic but are liable to damage if the atmosphere is moist.

Cargo Sweat:

This results when water droplets are deposited on parts of the cargo when the surrounding air comes in contact with a cool cargo. For this to happen, the temperature of the cargo must be lower than the dew point of the surrounding air.The condensation which forms directly on the cargo, when the temperature of the cargo is less than the dew point of the air in the hold.This is generally associated with incorrect ventilation. That is introducing warm moist air into the hold with cold cargo.It usually occurs when the voyage is from a cold region to a warmer place and the outside air has a dew point above the temperature of the cargo.Cold cargo cools the air in contact with it and condensation takes place.

Ships sweat:

Is the condensation which forms directly on the vessels structure when the temperature of the ship’s steel work is lower than the dew point of the air inside the hold. Condensation so formed on the structure will then trickle down to the cargo. This can occur when the ship moves to cooler climates (from a relatively warm area) and the ship’s sweat so formed can trickle onto the cargo or even accumulate at the bottom of the hold.

Related TOPICS

Whether to Ventilate or not to ventilate?

Hygroscopic and NON- Hygroscopic

List of cargoes which generate heat, gases and moisture:

IMO STANDARD MARINE COMMUNICATION PHRASES (SMCP)

Activity – You are transiting a strait and passing a VTS reporting point. Write down the phrases that you will use to communicate the required information to the VTS. Use the IMO Standard marine communication phrases (SMCP).

SMCP stand for – IMO STANDARD MARINE COMMUNICATION PHRASES

Why we need SMCP (IMO STANDARD MARINE COMMUNICATION PHRASES)?

The Standard Marine Communication Phrases (SMCP) has been compiled: –

  • To assist in the greater safety of navigation and of the conduct of the ship,
  • To standardize the language used in communication for navigation at sea, in port-approaches, in waterways, harbours and onboard vessels with multilingual crews, and – to assist maritime training institutions in meeting the objectives mentioned above.
  • Please note – These phrases are not intended to supplant or contradict the International Regulations for Preventing Collisions at Sea, 1972.

IMO STANDARD MARINE COMMUNICATION PHRASES

Step 1 – Initiation

When it is necessary to indicate that the SMCP is to be used, the following message may be sent:

  • “Please use Standard Marine Communication Phrases.”
  • “I will use Standard Marine Communication Phrases.”

Step 2 – Spelling

To give the correct spelling we use phonetics –


phonetics – SMCP

phonetics – SMCP

Step 3 – Message Notation / format / maker

  • (i) Instruction
  • (ii) Advice
  • (iii) Warning
  • (iv) Information
  • (v) Question
  • (vi) Answer
  • (vii) Request
  • (viii) Intention

Step 3B – Distress, urgency, and safety signals

  • MAYDAY to be used to announce a distress message
  • PAN – PAN to be used to announce an urgency message
  • SÈCURITÈ to be used to announce a safety message

Step 4 – Response is started with and then your message

  • Affirmative
  • negative
  • Stand by
  • No information.

Standard organizational phrases

“How do you read (me)?”

  • “I read you …
    • bad/one with signal strength one (i.e. barely perceptible)
    • poor/two with signal strength two (i.e. weak)
    • fair/three with signal strength three (i.e. fairly good)
    • good/four with signal strength four (i.e. good)
    • excellent/five with signal strength five (i.e. very good)
  • When it is advisable to remain on a VHF Channel/frequency say: “Stand by on VHF Channel … / frequency … ”
  • When it is accepted to remain on the VHF channel/frequency indicated, say: “Standing by on VHF Channel … / frequency … ”
  • When it is advisable to change to another VHF Channel/frequency, say: “Advise (you) change to VHF Channel … / frequency … .” “Advise(you) try VHF Channel .. / frequency… .”
  • When the changing of a VHF Channel/frequency is accepted, say: “Changing to VHF Channel … / frequency … .”
  • correction / readyness and Repetition
    • Example – “My present speed is 11 knots – mistake.
      • Correction, my present speed is 12, one-two, knots.”

Compass Error Calculation by Azimuth of Planets

Let’s learn how to calculate compass error by the Azimuth of any planet. We will understand this with the help of an easy example.

Sample calculation (Azimuth- Planets):


On 06 May 2006 at 22h20m 10s UTC, a vessel in position 48°00’N 050°00’E observed Mars bearing 327° by compass. Find the compass error. If variation was 4.0° East, calculate the deviation.


GHA Mars (06d 22h): = 089° 55.7′
Increment (20m 10s): = 005° 02.5
v (0.9)             =     00.3
GHA Mars: = 094°58.5′


Longitude (E):  (+) 050° 00.0′ (plus-since longitude is easterly)
LHA Mars:                 144° 58.5


Declination (06d 22h): = N 024° 18.6
d (0.2): = 00.1 (D correction)
Declination Mars: = N 024° 18.5

Now we will FIND – P and use ABC method for further calculations.
P= 1440 58.5 (If LHA 180° P=LHA)
A = Tan Latitude/ Tan P
A = Tan 48° 00′ / Tan 144° 58.5
A = 1.584646985 N (A is named opposite to latitude, except when hour angle is between 090° and 270°).
B = Tan Declination/Sin P
B= Tan 024° 18.5′ / Sin 144° 58.5′
B = 0.787011353 N (B is always named same as declination)
C = A+B = 2.371658338 N (C correction, A+/- B: If A and B have same name-add, If different name- subtract).


Tan Azimuth = 1/(CX Cos Latitude)
Tan Azimuth = 0.6301399
Azimuth = N 32.2° W (Azimuth takes the combined name of C correction and Hour Angle – If LHA is between 0°and 180°, it is named “west”, if LHA is between 180° and 360, it is named “east).


True Azimuth= 327.8°
Compass Azimuth= 327.0°
Compass Error = 0.8° East
Variation = 4.0° East (you can find this in ECDIS when finding compass error onboard)
Deviation = 3.2° West