MET152S Exercise-Eleven (1) (1) PDF

MET152 EXERCISE-11 Question 1 1.1. What is Sea ice? (6) https://www.youtube.com/watch?v=x5mrIqtuhy8 (Duration: 07 mins. 59 secs.) Sea ice is frozen seawater that floats on the ocean’s surface and i...

MET152 EXERCISE-11 Question 1 1.1. What is Sea ice? (6) https://www.youtube.com/watch?v=x5mrIqtuhy8 (Duration: 07 mins. 59 secs.) Sea ice is frozen seawater that floats on the ocean’s surface and is produced when saline ocean water is cooled below its freezing temperature of approximately -1.5°C. Sea ice is formed in all waters of the frigid zones in both hemispheres and in parts of the temperate zones in winter, particularly in the Antarctic. In springtime, it breaks up and spreads into more temperate waters. 1.2. Name 2 types of ice encountered at sea. (4) There are two kinds of floating ice encountered at sea: sea ice, is frozen seawater that floats on the ocean’s surface and is produced when saline ocean water is cooled below its freezing temperature of approximately -1.5°C. Icebergs, which break off the seaward end of glaciers and from shelf ice. 1.3. Wherefrom do icebergs originate? (3) Icebergs, in general, originate from the frigid zone in the North Atlantic area and in both the frigid and temperate zones in the Antarctic. In the Antarctic and western North Atlantic, they drift well into the temperate zone during springtime. The ice shelf normally possesses cracks and crevasses, along which fractures occur, causing a piece of the ice to break off, forming an iceberg. 1.4. Briefly describe the terms: growler and bergy bits. (4) Growler is a small berg, less than one metre in height above the waterline. Bergy bit is a larger berg with one to five metres above the waterline, with the term icebergs used for larger pieces of ice. 1.5. What is the importance of sea ice to the atmosphere? (6) Sea Ice interacts with the climate system. It helps with the heat exchange between the atmosphere and the polar regions as the white surface colour of the sea ice, which has a high reflective index. Page 1 of 9  The high reflective index causes most of the sun’s incoming solar radiation to be reflected back out to space, thus keeping the polar regions cool. Sea Ice also interacts with ocean currents and this interaction occurs when the cooling of surface water increases its density, and it sinks, and warmer, less dense surface water flows to replace sinking water. 1.6. Without the aid of diagrams, list the stages of the development of sea ice. (16) Frazil Ice The development of sea ice begins with the formation of needle-shaped crystals called frazil ice (below). These crystals tend to float with their long axis vertically, and they give the sea an oily appearance. The Frazil ice crystals then thicken and congeal to form a greasy or soupy layer on the sea surface known as grease ice (below). Page 2 of 9 Alternatively, falling snow crystals can produce slush (below). In the next stage, Shuga ice (below) develops, consisting of spongy lumps a few centimetres across. All the above are classified generally as new ice. Page 3 of 9 Nilas Nilas is a thin, elastic crust of ice, easily bending on waves or swells, or under pressure, thrusting in a pattern of interlocking fingers. It has a matt surface and is up to 10 cm in thickness. Nilas ice can be subdivided into dark nilas and light nilas; ice rinds. This is followed by pancake ice (below), consisting of flat pieces, roughly circular in shape, often with a rim around the edge due to rubbing against adjacent pieces. The pancakes gradually join to form a more or less continuous ice sheet, called young ice (below); this can also be broken up by wave action. Page 4 of 9 Young ice eventually thickens and becomes field ice or pack ice (below), which is a generic term for all fully developed sea ice floating on the ocean and not attached to the shore; it varies in thickness from a few inches to several feet. Individual pieces of pack ice more than 20 metres across are called floes and the pack is termed ‘open’, ‘very open’, ‘close’ or ‘very close’ depending on the distance between the floes. Very close pack leaves little or no water visible. Pack ice originating in Arctic or Antarctic waters may be several feet thick and very uneven due to hummocking (piling up) by the waves. Fast ice (above) is sea ice that is "fastened" to the coastline, to the sea floor along shoals or to grounded icebergs. Fast ice may either grow in place from the seawater or by freezing pieces of drifting ice to the shore or other anchor sites. Unlike drift (or pack) ice, fast ice does not move with currents and winds. Page 5 of 9 1.7. State how serious ice accretion can affect a vessel's operation and safety with regard to the stability of the ship, her strength, her equipment, and her closing/securing arrangements. (10) https://www.youtube.com/watch?v=eN1TRzCFknE (Duration: 01 minute 43 secs.) Stability Added weight can result in a significant loss of freeboard and buoyancy. Ice on masts, derricks, and the superstructure can raise the ship’s centre of gravity and introduce large heeling moments. Asymmetrical load distribution can cause a ship to trim or list. Strength Ships travelling at high speed and not changing direction can accumulate tons of ice on the foredeck area. In such an instance, in a hogging condition, higher tensile stress would be placed on deck structures. This could lead to fatigue cracking or brittle fracture associated with extremely low air temperatures. Equipment The icing on lifeboat davits, and lifeboats could seriously jeopardize the survivability of the ship and crew. The icing on communication equipment could seriously jeopardize the survivability of the ship and crew. Securing and closing arrangements The icing of containers and their securing arrangements could require deicing, which could delay offloading operations. Deicing of hatch covers takes time and could result in mechanical damage to them. Deicing should be followed by careful inspection. 1.8. What are the main preventative measures that should be taken to avoid this serious hazard? (4) Reduction in speed Change of heading Ships’ officers to be made aware of the potential dangers of ice accretion. Head into warmer waters. 1.90. List the precautions to be taken prior to sailing into a recognized ice region. (10) https://www.youtube.com/watch?v=J4VT30Wqil4&list=PLjZi6sSb2w5aAq9UsL bn8w3M2h2QdM2dy&index=6 (Duration: 07 mins. 03 secs.) All firefighting deck lines are properly drained Extinguishers indoors. Check the sprinkler system. Lifeboat freshwater tanks are down 4% to 96% full. Heating on lifeboat engines and tanks Page 6 of 9  All ship's fuel tanks and fresh tanks are to have heating. Ballast tanks: increase the density of SW by adding salt. Keep a good GM. Keep trimmed by the stern and have a heavy vessel for good momentum. If heavy ice accretion occurs, then head into warmer weather. The passage made through the ice should be 3x the breadth of the ship. Use maximum revs and minimum pitch on the propeller. Tuning radar for arctic conditions. Keep scanners rotating. OOW + 2 lookouts on the bridge. If going astern in ice, keep rudder amidships. 1.91. Name six indications of ice. (6) https://www.youtube.com/watch?v=ibBHYrFHdfo&list=PLjZi6sSb2w5aAq9UsL bn8w3M2h2QdM2dy&index=5 (Duration: 03 mins. 50 secs.) Iceblink by day or night. A yellowish-white light reflected from the ice onto the sky near the horizon. There is often a thick wall of fog at the ice's edge. A rapid fall in the sea temperature to below freezing. Herds of seals or flocks of birds far from land. The absence of sea or swell in a fresh breeze is an indication of ice or land to windward. The noise of the ice cracking or falling into the sea may be heard. The use of radar. On calm days echoes may be heard from higher ice. 1.92. State five (5) causes for shipboard ice accretion. (5) https://www.youtube.com/watch?v=jbHG3wtZD0k (Duration: 2 mins. 32 secs.) Sea spray hitting the vessel with the air temperature being at least minus 2 o C. Fog freezing on the structure of your vessel. Rain Freezing on the structure of your vessel. Seas entering your vessel and freezing up. Freshwater leaking or being discharged from a pipe on your vessel. 1.93. Formation of ice on the upper works of the vessel must be removed as quickly as possible by: (4) Cold water pressure. Hot water and steam. Break up ice with ice crows, axes, ice picks, metal ice scrapers, wooden sledgehammers, and metal shovels. Heating of upper structures similar in effect to radiators or central heating arrangements in a house. 1.94. Define the term full Icing allowance. (5) Page 7 of 9  A full icing allowance is defined as an additional pressure of 1 kN/m 2 (100 mm of ice) applied to all exposed horizontal or near horizontal surfaces and 0,25 kN/m 2 (25 mm of ice) applied to all exposed vertical surfaces. The volumetric centre of the ice is to be taken as that of an equivalent head of water. The density of the ice is assumed to be 1000 kg/m3. As a minimum, a full icing allowance is to be applied to vessels operating in areas listed in 1.97. and 1.98. 1.95. Define the term half Icing allowance. (5) A half icing allowance is defined as an additional pressure of 0,5 kN/m 2 (50 mm of ice) applied to all exposed horizontal or near horizontal surfaces and 0,18 kN/m 2 (18 mm of ice) applied to all exposed vertical surfaces. The volumetric centre of the ice is to be taken as that of an equivalent head of water. The density of the ice is assumed to be 1000 kg/m3. As a minimum, a half icing allowance is to be applied to vessels operating in the winter seasonal areas as defined in the International Load Line Convention. 1.96. State 3 (three) Icing Allowances that should be applied in the stability calculations applicable to vessels operating in areas where shipboard ice accretion is likely to occur. (6) For vessels operating in areas where ice accretion IS likely to occur, the following Icing allowance should be made in the stability calculations: 30 kg per square metre on exposed weather decks and gangways; 7.5 kg per square metre for projected lateral area of each side of the vessel above the water plane; The projected lateral area of discontinuous surfaces of rail, sundry booms, spars (except masts) and rigging of vessels having no sails and the projected lateral area of other small objects should be computed by increasing the total projected area of continuous surfaces by 5% and the static moments of this area by 10%. 1.97. In which regions does Full Icing Allowance apply? (10) 1. The area north of latitude 65° 30 ' N, between longitude 28° Wand the west coast of Iceland; north of the north coast of Iceland; north of the rhumb line running from latitude 66° N, longitude 15° W to latitude 73° 3~ ' N, longitude 15° E, north of latitude 73° 3~' N between longitude 15° E and 35° E, and east of longitude 35° E, as well as north of latitude 56° N in the Baltic Sea; 2. The area north of latitude 43° N is bounded in the west by the North American coast and the east by the Rhumb line running from latitude 43° N, longitude 48° W to latitude 63° N, longitude 28° Wand thence along longitude 28° W; 3. All sea areas north of the North American Continent, west of the areas defined in 6.3.2.1 and 6.3.2.2; 4. the Bering and Okhotsk Seas and the Tartary Strait during the icing season; and 5. south of latitude 60° S. 1.98. In which region(s) do other Icing Allowance apply? (3) For vessels operating in areas where ice accretion may be expected: Page 8 of 9  6. within the areas defined above in 1., 3., 4. and 5. known to have icing conditions significantly different from those described in 6.3.1, ice accretion requirements of one- half to twice the required allowance may be applied; and 7. Within the area defined in 2., where ice accretion in excess of twice the allowance required by 1. may be expected, more severe requirements than those given in 1 may be applied. 1.99. Name three ways in which the diminution of ice takes place. (3) 1. Calving is the breaking of ice from a glacier or iceberg, ice front, ice shelf, crevasse. 2. Melting: caused by warm air and or sunlight. Warm ocean currents, such as underwater melting will result in toppling and calving. 3. Erosion: caused by the erosive action of wind and waves. Total Marks: Page 9 of 9