In the centuries-old chronicle of navigation, it is possible to find a great deal of evidence of the struggle of Man against the terrible chaos of the Ocean in literature, paintings and sculpture. These are the impassioned lines of telegraph messages and gripping descriptions of storms and hurricanes, epic paintings by artists and stone monuments to seamen who have perished in the Ocean.
Man has gradually begun to fight back against violent Ocean chaos by strengthening vessels, finding better and more reliable means of navigation and communication and increasing the power of his engines.
The knowledge of dangerous phenomena in the Ocean helps seafarers to successfully to overcome these.
| ||Approach direction of tsunami waves (seismic sea-waves) |
From neighbouring coastal regions
Far from coast regions
| ||1. Bottom of the Ocean |
2. Displacement of the bottom
Tsunami damages Lisbon, November 1, 1755
At a 1929 archaeological excavation near the modern Syrian town of Ra’s-Shamrah, clay tablets from the 2nd Millennium BC were found. From translations of the inscriptions, archaeologists have learned about a wave of unprecedented height and magnitude that had crushed the formerly blossoming ancient city-state of Ugarit. The city was completely destroyed by this wave. Such events in the history of Mankind are only known for the moment, but their memory is saved for centuries.
When these waves originate as a result of seismic or volcanic events, they are given a name of Japanese origin: "tsunami" (harbour wave).
Tsunamis are sea waves generated by earthquakes, landslides and volcanic eruptions on the sea floor. Two thousands of years ago, the Greek geographer, Strabo, concluded that the probable reason for tsunamis was the displacement of the sea floor during earthquakes. Scientists now believe that, as a result of earthquakes or underwater volcanism, the sea floor ruptures. The separate segments of the sea floor instantly fail, and are removed above an epicentre. On the Ocean surface, a depression formed, into which the water pours downward. The cylinder of downward-rushing water falls onto the newly formed sea floor, exciting huge surface waves to form. Sharp, vertically-directed motions from the sea floor can also form a tsunami. For example, the Chilean tsunami (21 - 22 May, 1960) was formed along a strip of sea floor 800 miles long. It spread across the Pacific Ocean and caused a significant increase in sea level at a moment in time, that was observed along the Kurile - Kamchatka coasts of Russia, (at Severo-Kuril'sk up to 7 m).
The characteristics of tsunamis are different from wind waves. Tsunamis lengths are measured in hundreds of kilometres, and the speed at which they travel can reach 1,000 km/h; the time of distribution of a tsunami from its place of its origin up to a coast can take as long as several hours, and as short as tens of minutes, depending on the location of the source and the direction of movement.
An ocean-going vessel almost never notices a tsunami, since its amplitude in the deep ocean is no more than 2 metres. However, when approaching the shallow waters of island or continental coastlines, it sharply decreases its speed, and a deformed, large wall of water as high as 16-20 m and more, contacts the shore. Damage to buildings installations and especially, people can be enormous. In the last 1,000 years, Pacific Ocean tsunamis have been observed and recorded over 1,000 times. All of these were major catastrophic events, since smaller events often go unrecorded.
The people of the Pacific Ocean coasts live under a constant threat of violence generated by tsunamis. Taking into account the magnitude of this problem, the International Tsunami Information Centre in Honolulu maintains a tsunami early-warning system for 15 countries on the Pacific Rim. The centre transmits alarm signals by radio and teletype. It is the responsibility of each country to notify the population of a possible tsunami approach to the coastal regions. The most dangerous regions for tsunamis in the Russian Federation are on the west coasts of the Kamchatka peninsula and the Kurile Islands.
In Russia, there is a Tsunami Warning Service, with centres located in Yuzhno-Sakhalinsk, Petropavlovsk-Kamchatskiy and Kuril'sk.
A CHRONICLE OF SOME DISASTROUS TSUNAMIS
| || || || |
| || ||The city of Helix was totally washed away.|
| || ||Hundreds of settlements were destroyed. Thousands of people were affected.|
| || || ||The city centre of Callao is destroyed. Ships were thrown onto the shore and inland. Of the 5,000 inhabitants, only 200 survived.|
| || || ||10,000 buildings were destroyed. About 4,000 persons were affected|
| || || ||Two waves of a tsunami essentially destroyed the city of Severo-Kuril'sk and the town of Baykovo, located on the opposite side of the strait. The third wave had almost nothing left to destroy. The radio operator aboard a ship near a harbour broadcasted, "The island of Paramushir is under water."|
| || || ||A seismic sea-wave generated off the coast of Chile crossed the Pacific ocean, hitting the shores of New Zealand, Australia, Philippines, Hawaiian islands, Japan. The total number affected in Japan alone is 150,000 persons|
| || || ||The cities of Alberni and Port Alberni (Canada) and Crescent-City (California, USA) suffered minor damage. The wave hit the entire Pacific coasts of Canada and USA, and also hit the Hawaiian Islands and the shores of Japan.|
Coast of Alaska after a tsunami that was generated by the “Good Friday” earthquake on March 29, 1964.
One of the greatest natural phenomena is underwater volcanism, which at great depths is almost imperceptible, and in shallow regions has an explosive character. In the Philippine Sea, there are several cases on record where vessels have been lost as a result of submarine volcanic eruptions. However, the greatest danger from underwater volcanism is seen in the products of the eruption: pyroclastic ash flows and steam. Upon reaching the Ocean surface, they sharply worsen visibility and cause mats to form on the Ocean surface, which impedes surface transportation.
Birth of the island of Surtsey in the Ocean off the coast of Iceland, December, 1963.
Development of an underwater volcano as it reaches sea surface. Western Pacific Ocean, September, 1952.
Navigation in high and middle latitudes sometimes entails such dangers as collision with drifting icebergs and icing of vessels.
Icebergs are massive blocks of ice broken off from glaciers or ice-shelves and dropped into the Ocean. There are two types: tabular and pyramidal.
Tabular icebergs are formed as a result of separation from ice shelves having very large volumes of ice. They are characterised by having a rather flat, planar surface and an immense size. Some are giants, covering up to 175 km in the long direction. Their place of origin are on the icy shores of the Antarctic Continent. These table-shaped icebergs can rise to 90 or more metres above the surface of the Ocean. The highest recorded tabular iceberg was 201m, though there is some information about icebergs in the past being 450 - 510m tall. Taking into account that under the water ice occupies six to seven times the amount of ice that is seen above the surface, or 85% of its volume, it is possible to imagine the immensity of the size of icebergs.
Pyramidal icebergs are formed when large blocks of ice from a glacier, fall (calve) slowly into the water after migrating to the coast from adjacent coastal mountains. The separation occurs because of the effects of oscillations of sea level, current acting under the overhanging ice mass and under its own weight. Pyramidal icebergs with pointed tops descend from shores of Baffin Island, Greenland and the Franz Josef Land archipelago. These masses of ice contain many inclusions: debris of broken and transported rocks, sand and silt. When an iceberg calves, it is usually accompanied by a loud noise. Ocean currents transport them significant distances. Encounters of seafarers with icebergs in southern and northern latitudes are not unusual occurrences.
The greatest iceberg danger to navigation is found in the shipping lanes of the North Atlantic Ocean, especially in the region of the Grand Banks of Newfoundland. It has been calculated that in the North Atlantic Ocean, about 20 thousand of icebergs are sighted each year.
After the tragic loss of the passenger liner, "Titanic," after collision with a giant iceberg in April, 1912, with a loss of over 1,500 lives, the International Ice Patrol was created. Financed by 17 countries, the function of the International Ice Patrol is to observe the movement on the North Atlantic, collecting of statistical data and broadcasting notices to mariners warning of areas of iceberg accumulations, and tracking solitary, giant icebergs.
Broadcasts have greatly reduced, but not eliminated collisions of vessels with icebergs. These sometimes occur because the radar screen cannot always discern the small top of an old iceberg rising above the water in fog and/or other adverse weather conditions. However, the service of the International Ice Patrol most-often warns mariners with enough time to take collision avoidance measures and subsequently reduces vessel emergencies.
Distribution of icebergs
| ||Icebergs |
Scientific exploration ship, "Professor Kozhin," is in the foreground
Ratios of underwater and surface parts of iceberg
Icebergs in the Antarctic region
Another dangerous natural phenomenon in high latitudes is the icing of vessels. It arises in storm conditions, where high winds, prevalent in the high latitudes during the autumn and winter seasons. Development of an icing condition aboard occurs with a sharp downturn of air temperature combined with lots of rain, snow or heavy and prolonged mists.
At below-freezing temperatures, exposed metal parts of a vessel (hull, deckhouses, deck freight, boats, bridge, masts) take on the ambient temperature of the environment, and raindrops, snowfall and Ocean spray freezes immediately upon contact with these freezing surfaces. The number of sprays can reach 10 - 12 per minute. In such conditions, up to 50 tons of ice can cover even a small vessel within several hours. The vessel loses manoeuvrability, stability and buoyancy, loses radio communication and use of radio navigational devices because of ice on the antennae. The loss of stability results in sudden capsizing of the vessel, and most often the entire crew perishes. In the Norwegian Sea in January, 1968, three English fishing trawlers capsized due to icing and all aboard were lost; in the Bering Sea in January, 1965, four Soviet trawlers suffered the same fate. Between 1963 and 1967, in just the region of Kurile Ridge and Tatar Strait, 19 Japanese vessels with 296 fishermen have perished due to icing and subsequent overturning.
A statistical analysis of more than 3 thousand cases of vessel-icing shows that almost 90% of the cases arose due to spray and splashed sea water contacting the superstructure. Much less common events are where icing occurs because of super-cooled precipitation in the form of rain, drizzle and wet snow falling on a vessel.
The most common method of dealing with icing is the labour-intensive, mechanical method, that is, chopping of ice aboard the vessel, and withdrawal from the icing zone, going into a port, or to the edge of the ice, where the storms and heavy seas are diminished.
New ideas to combat icing are the use of various anti-icing covers and shields, using the heat from engine exhausts and operating vibrating devices to break up ice coatings. Heating methods are presently being tried.
Significant advances in anti-icing systems have been achieved. They work by creating a magnetic field opposite that of the vessel to create a barrier to icing and are placed in strategic places aboard the vessel.
Icing on a fishing trawler. The Sea of Okhotsk
Mechanical chopping of ice on the hull of a submarine
Ice on a ship’s rigging
Areas of possible icing of vessels
Periods of possible icing, by regions
|Northwest Atlantic Ocean|| |
|Norwegian and Greenland Seas|| |
|North Atlantic Ocean|| |
|Barents Sea|| |
|Baltic Sea|| |
|Baffin Bay, Hudson’s Bay|| |
|Bering Sea|| |
|Sea of Okhotsk|| |
|Sea of Japan|| |
|Northwestern Pacific Ocean|| |
|Arctic seas (Kara, Laptev, East-Siberian, Chukchi)|| |
|Antarctic region|| |
Tropical cyclones originate when a rapid heating of an Ocean surface combines with heavy evaporation. Strong, vertical air currents carry away masses of humid, warm air, and the rotation of the Earth gives them a more-or-less circular motion. Amplifying and expanding, the ascending air currents act as a strong centrifugal pump. At the moment of origin, a tropical cyclone moves at a low speed (10-12 m/s). As its development continues, the speed increases, the cloud cover is condensed, winds rage and rains begin to fall. Winds of storm force and the significant change of atmospheric pressure cause wind waves to form, some with heights of up to 14-16 m.
A formed cyclone produces a funnel-shaped storm that may reach 100 - 1,000 km in diameter. The quietest part of the tropical cyclone is its centre, called, "the eye of the storm", which has a cross-section on the average 15 - 30 km, and in strong cyclones, 60 - 70 km. Some tropical cyclones may have two and even three centres. The sky in the centre is frequently clear and cloudless, with weak or no winds, and wave directions are mixed, creating a huge fountain of water, with water spraying up to 20 m into the air. The zone of storm winds adjoins the centre of a cyclone. On the average, wind speeds of 40 - 60 m/s, and quite often and 80 m/s are created. The greatest wind-speed ever recorded was 113 m/s (407 km/h) during typhoon "Ida" (September, 1958). The passing of tropical cyclones over the Ocean is accompanied by great amounts of precipitation (200-400 mm/day). In the Philippines, a maximum rainfall of 1168 mm day was recorded in one day, which is 2-3 times the average annual rainfall for most places in middle latitudes.
When tropical cyclones strike low coastal zones, they cause great loss to life and property. Storm tides cause strong floods which destroy port facilities, businesses and homes, and in turn, kill and injure people. Ships in port suffer emergencies because of collisions, groundings, mooring breakage, etc.
It is impossible to prevent disasters from happening, but their prediction is possible by specialists. At this time, there is a great ability for detection, tracking and prediction of tropical cyclones by using meteorological observation satellites. In addition, weather ships and floating, automatic weather stations (buoys) constantly monitor certain areas, observing the origin and development of cyclones at sea. Finally, underway meteorological observations are carried out by merchant vessels and fishing fleets, and transmitted to data collection centres by radio.
The Consolidated Typhoon Warning Centre is located on the Pacific Island of Guam.
Coast of the island-nation of Sri Lanka after the passing of a tropical cyclone
Structure of a tropical cyclone
| ||1. Calm, still |
2. Weak winds, small disturbance
3. Storm winds, strong disturbance
4. "The eye of the storm": calm, swells, waves up to 20 m
In the summer of 1949, a message was broadcast describing an exotic natural phenomenon. On a coastal region of New Zealand, a rain shower was accompanied by the fall of thousands of small-sized fish. A similar occurrence was observed in 1933 by the inhabitants of village of Kavalerovo in Primor'ye Territory, but instead of fish, there was a rain of jellyfish.
In August, 1972, a giant waterspout appeared near the town of Khosta (Black Sea coast). Darkness covered the town. On the coast of Tikhaya Bay, a waterspout dropped a huge mass of water (about 150,000 tons).
In historical chronicles, there are many authentic stories about similar kinds of unusual rains. The cause of these rains is often waterspouts, the diameter of which range from several tens of meters up to 3 km, with an average height of 800 - 1,500 m, and on occasion, 2 - 3 km. The wind-speed inside a waterspout reaches 100 m/s. The vortices move with a speed of 5 - 10 m/s and sometimes, up to 30 m/s. The duration of the “life” of waterspouts is from several minutes to several hours. During this time, they can travel hundreds kilometres, destroying everything in their paths.
For a long time, the nature of waterspouts remained a riddle. It has now been found that waterspouts occur when air masses spin rapidly during thunder-storms in areas where the air-flow has a sharply distinguished speed of movement, temperature and water vapour content.
When a storm-cloud passes, there are sharp changes in the wind direction and speed and also differences in the air temperature in the most intense section. Unevenly heated air masses have different densities and collisions occur, causing a spinning motion. The rotation rate increases, and a waterspout is born. When air rotates in a vortex, centrifugal forces are generated. The air pressure inside the tube of a waterspout is sharply reduced, and the difference between this pressure and the outer edge may be as much as 200 mbar. Because of this air-pressure difference, there is almost no cooling taking place, resulting in condensation of the water vapour always present inside of the tube.
A waterspout has a cloudy tube descending to the sea-surface. The sharp decrease in air-pressure inside the tube of a waterspout also explains why suction occurs when one is present. For this reason, as soon as the tube of a waterspout breaks contact with the sea-surface, all of the water being carried is dumped, falling to earth. A waterspout is capable of lifting and carrying particles of sand, water, stones, live sea creatures, and sometimes, people, roofs of houses, etc. All of these can be carried long distances. Waterspouts often cause some destruction at coastal beaches, frequently killing people. If a vessel at sea encounters a waterspout, it is a dangerous situation.
Waterspout at the city of Nice. Mediterranean Sea, 1780.
Trunk of a tree pierced by a piece of wood during a waterspout, 1966.
Origin of clouds in the vortex - tube of a waterspout, 1961.
Waterspout in the Adriatic Sea, 1950
Waterspout next to the coast of Shanghai 1933
DEVELOPMENT OF A WATERSPOUT
Birth of the funnel
Beginning of the vortex motion
Derivation of the water tube
Water suction occurs
Beginning of destruction
Despite the high level of modern navigation, fogs represent significant hazards to navigation. They sometimes limit visibility only several meters. Therefore, navigators must reduce their vessel speeds, since the conditions are perfect for collisions at sea. In ports, dense fogs also impede docking and unloading of vessels.
In Nature, fog is an accumulation of smallest water droplets or ice crystals suspended in the air. An indispensable condition for fog formation is the availability of particles of dust or smoke around which water can condense when the relative humidity is near 100%.
One of the ways fogs form is when evaporation is minimal, and the water surface is covered by a very thin (mono-molecular) film. Evaporation is reduced by 50-60%, creating the right conditions for fogs to form.
Another method of fog formation is based on an artificial change of the status of a fog. Moisture from a liquid state turns into microscopic ice crystals, which fall out as a precipitate. This method is possible when most air is supercooled.
There is also a thermal method of fog formation, the essence of which consists of the heating of a low layer of air, resulting in the evaporation of water droplets in the air and their rise by the ascending air-flow.
THE WAYS FOGS FORM
| ||1.Warm humid air |
3.Cold surface of the Ocean
| ||1.Cold air from land |
2.Warm Ocean surface
| ||1.Cold front |
This dangerous natural phenomenon has been known to seamen for a long time. It is particularly common on the Black Sea, where sailors have named it tyagun (“ptyalin”). Similar occurrences in other places have been given such names as surf palpitations (beats), long-range action and seats. Ptyalin is now understood to be resonant wave oscillations of the sea in ports, bays and harbours, causing sharp horizontal movements of vessels. The period of oscillations of water in a ptyalin is from 0.5 to 5 minutes, with wave heights of up to 0.3 m. In times when a ptyalin is felt in port, there are small vertical disturbances of a water mass, rather large horizontal movements. Therefore, moored vessels, or those standing at anchor, make reciprocating movements and experience strong, chaotic pitching and rolling. The threat of collision, grounding on a bank, hull and pier damage exists from the action of a ptyalin.
Ptyalin have been observed in many ports of the world, in widely varied places such as Naples, Cape Town, La Havre, Bombay and Dakar. Cases where ptyalin have idled ships (for up to 28 days) as a result of damage have been recorded in the ports of Taupe and Batumi. Heavy damage by tyagun has also been reported by vessels visiting the ports of Korsakov, Kholmsk, Il'ichevsk, Poti, Sochi.
The reasons for the origin of ptyalin has attracted the attention of scientists for a long time. Using complied statistical data and observation reports, they came to the conclusion (based upon experimental and theoretical research and modelling), that ptyalin results from a resonance of oscillations of water masses in port when the port area experiences the effects of long period waves entering the harbour area and contacting ships at anchor and docked at piers.
The most effective defence against the effects of tyagun rests with a well-timed prediction of its origin, a prediction of its intensity and time of it will arrive. It permits the reduction of vessel idle times caused by accidents as a result of tyagun.
Since 1966, ports in the Russian Far East have successfully predicted ptyalin with probability up to 93 %, and with a twelve-hour advance notice.
Strong spray (breakers) called tyagun.
Sea wall in the city of Batumi
The storm approaches
Storms occur on the Ocean when there are continuous, strong winds, with speeds exceeding 16 m/s.
Storms on the high seas were serious tests for sailing vessels in the last century and have remained such for modern, large-tonnage vessels. The danger consists of a possible loss of stability. In a strong storm at sea, even modern vessels lose their the state of balance, and sometimes are unable to recover their stability, resulting in capsizing. This is sometimes caused by movement of freight during periods of strong pitching and rolling, heavy seas washing over the deck and also from “human error”, such as incorrect selections of speed and course with respect to the motion of the waves generated by the storm.
Meeting storm waves head-on has destroyed bridges and deckhouses, broken out windows and caused other significant damages to ships. Storms, combined with other coastal conditions, e.g., the shore configuration, bottom relief, wind, tides, etc., can result in great disasters.
In 1968 and 1969, cyclone activity on the Black Sea produced the formation of a series of whole gales, the outcome of which was the destruction of beaches, sea walls, jetties, and hydroelectric power plants in Yalta, Tuapse, Adler, Pitsunda and other places.Storm tides are dangerous natural phenomena that cause flooding in coastal regions. They are generated when a cyclone, moving over the sea, excites a long period wave. The strong air flow causes a water mass to conform to the shape of the coast, gradually flooding low, terrestrial coastal areas. The flow occurs coincident with an incoming tide, and as a result during ebb, the tide cannot completely recede. The water rises quickly, and can reach 7 m and more. Such an occurrence is called a storm tide.
Damages caused by storm tides in the Baltic Sea region are recorded in historical documents of the 14th century. During the span of the 17th to 19th centuries, the dwellers of these and other coastal areas became victims of same conditions, causing not only physical damage, but also economic distress.
Storm tides in Denmark in November, 1872 uprooted and carried away huge trees, covered fields with sand and killed many cattle. Similar occurrences have devastated the shores of England, France and Italy. In 1888, a storm tide breached a dike in the lower Elbe River in Germany.
During the 1900 flooding of Galveston, Texas (USA), hurricane winds of 60 m/s raised the sea level by 5 m. The waves inundated the city and 5,000 people were killed, along with a significant material loss to property and industry.
In February, 1953 a full gale raged on the North Sea, causing a rise of water along the shores of the Netherlands of 4 m. The defending dikes were broken, and sea water covered the reclaimed land. As a result, 25,000 hectares of land were flooded and 1783 persons perished. The material loss was placed at $250 million dollars.
In Japan in September 1956, about 5,000 people perished, and 1,600,000 were left homeless as a result of a flood caused by a storm tide.
In July and August 1989, the coastal territories of the Far East underwent a devastating rush of storm tides. Under the impact of the elements, 215,000 hectares of crops and pastures flooded, as well as 109 cities and settlements. Additional physical damages were logged as follows: 282 bridges destroyed, 1340 km of roads damaged, and in more than 3,000 homes, people lost their lives. Estimated capital loss was 400 millions of roubles.
St. Petersburg (Leningrad), situated on the edge of the Gulf of Finland at the mouth of the Neva River, has taken the brunt of the force of storm tides over a span of almost 300 years in recorded history. The most monumental flood was observed in November, 1824, when the water level crested at a mark of 410 cm above the norm. One hundred years later, in September 1924, the flood water level was less, but a great number of streets were nonetheless flooded. In 1979, flood protection for St. Petersburg from storm tides in the Gulf of Finland was initiated, by the construction of a flood-control system.
Floods cause huge damage all over the world and thus, the number people perishing from the effects continuously grows. Statistics shows that over the last 100 years, more than 9 million people have died as a result of storm tides.
SAINT-PETERSBURG FLOOD, 19 NOVEMBER 1824
View from Men'shikov Palace
View from Winter Palace
A.S Pushkin, in the poem, "Copper Horseman" describes this flood:
|But by the force of winds from the bay |
Flooded the Neva.
It entered, angry and boiling
And flooded islands,
And the weather more grew savage,
|The Neva exploded and foamed, |
As a boiler bubbling and swirling,
And suddenly, as a frenzied animal,
It was cast upon the city. Before it
All have run, all around.
|Suddenly it was empty - water suddenly |
poured into underground cellars,
To the railings, the channels have rushed,
And Petropol has emerged, as Triton,
Immersed in water up to his belt.
LENINGRAD FLOOD, SEPTEMBER 23, 1924.
Vasil'evskiy Island, harbour (afternoon)
Palace sea-wall (the next day)
The design of protective facilities to prevent flooding in St.-Petersburg
"Saint Elmo’s Fire" was the name given by mariners to silent discharges of lighting. These are observed before and sometimes during a thunder-storm, when the intensity of the electric field in atmosphere increases by hundreds and thousands times, reaching 500 V/m and more at the upper limits. This visible form of discharge is accompanied by a glow and a discharge, forming coronas. "Saint Elmo’s Fire" is observed in places where there is a concentration of large electrical charges. Very long ago, the appearance of these "fires" was seen by seamen as a sign announcing the ending of a storm.
Thunder discharges (“claps”) - cyclical, short-term impulses creating atmospheric radio interference are called “atmospherics.” They cause electromagnetic variations over a wide range of radio frequencies.
But a more dangerous enemy of seafarers is lightning. Wooden sailing vessels were particularly vulnerable to being struck. Upon the installation of lightning-rods (conductors to grounds/earths) on vessels, lightning strikes resulting in damage has become an unusual occurrence. Although the danger of damage from lightning strikes has considerably decreased, problems with atmospheric electricity have not been completely eliminated, and continue to be studied.
In some tropical regions, there is the danger of lighting strikes during storms up to 200 days per year. At sea, there may be as many as 25 discharges per square kilometre of sea surface. For oil tankers transiting these regions, there is a large danger of explosion of gasses in the storage tanks due to static electricity.
Saint Elmo’s Fire
Sailboat being hit by lightning
Lightning on the sea
The appearance of complex, anomalous conditions on the Ocean surface can be dangerous to seafarers. Some of these are: fountains,, pounding, slicks, whirlpools, the development of internal waves, strong currents., giant single waves and the appearance of “dead water".
In ancient times, Mediterranean seafarers noted strong whirlpools and the appearance of “boiling water” in the Strait of Messina. The ancient Greek mythical monsters, Scylla and Charybdis, were blamed for these occurrences. Similar phenomena have been observed in the fjords of the Scandinavian peninsula, in straits through the Kurile Ridge, in other straits (La Manche / English Channel, Kerch Strait, Singapore Strait, Pentland Firth (UK), and sometimes, in open regions of the Ocean in depths greater than 500 m.
Fountains are chaotic sprays of water on the sea surface, which occur when there is a sharp decrease of the speed of a current. These occur where currents flow from different directions, where a current flows through a narrow passage, or from strong winds blowing against the outflow of a river or channel.
Whirlpools Scylla and Charybdis on a marine chart, 1665
THE WAY A “FOUNTAIN” FORMS
At a meeting of two currents flowing from opposite directions
In shallow water
The water surface in a zone of developed sprays is reminiscent of the surface of boiling water. In these areas, chaotic waves are observed, with heights sometimes reaching 4 to 5m. Quite often, a fountain is accompanied by whirlpools and “dead” spots on the surface, with silt forming sharply defined edge boundaries. A smooth, circular area, from hundreds of meters to several kilometres in area, and surrounded by zones of increased turbulence and a quiet zone on the edges is sometimes encountered on the open sea.
Fountains can result in the loss of sailboats and small fishing vessels. Even large vessels passing through a fountain deviate from their paths, and mariners experience chaotic pitching and rolling.
Fountains in the Strait of Ekaterina
Spots of calm ( “dead” water) - slicks
Maelstrom (from an engraving of 1687)
The Maelstrom is a whirlpool which occurs at the meeting of tide-generated waves with the tidal stream between islands Mosken and Veroy (Lofoten islands of Norway).
Internal waves are spread in the deep waters of the open Ocean reaching a height of 150 m. As a comparison, an internal wave is so large, that St. Isaac’s Cathedral could easily be placed inside of one. The impact on deeper waters from the effects of the crashing of internal waves considerably exceeds the impact from the effects of surface waves.
Under the influence of internal waves, a sharp change in water density is possible, and that is dangerous for submarines which may be heavily affected, causing loss at greater depths. There is one theory that the loss of the American nuclear submarine, “Thresher,” in the early 1960s was a result of the effects of a collision with an internal wave.
Internal waves are not only dangerous to submarines, but also can have disastrous effects on drilling platforms, piers and viaducts.
Lowering of the salinity of surface waters of the Ocean near a river outflow or thawed glacier causes deceleration of a ship because internal waves may be generated above the interface between the low-salinity surface and steeper layers of salty waters. As demonstrated by experiments, the resistance to motion by a vessel in "dead water" can be up to 9 times greater, than under normal conditions. The appearance of “dead water” can have an influence on the manoeuvring of submarines. Sailboats and towed vessels are often thrown off course by this phenomenon.
To overcome a zone of "a dead water" a vessel should travel faster than 5 knots.
Fritjof Nansen observed and recorded this phenomenon during the drift of the vessel, ”Fram” in the Arctic Ocean between 1893-1896.
During calm weather in the Spring, the appearance of "dead water" has been observed in the Arctic seas and Norwegian fjords, close to the mouths of the Lena, Yenisey, Amazon, Orinoco, and Mississippi Rivers, in the Dardenelles Strait, the White Sea, and on the shores of Canada.
A large tonnage vessel break-up due to a giant single wave
Some areas of the Ocean are known for the unexpected appearance of, large, mountainous, single waves (killer waves) on the sea surface. Prediction of when and where these waves will form is impossible at the present time.
A preponderance of these waves occurs in the region near the south-east shores of Africa (between East London and Durban). The origin of killer waves has to do with the character of the sea floor relief near the coastline and the prevailing currents in the area. In this region, the continental shelf-edge comes very near the coastline. A strong south-westerly wind generates wind waves, which meet strong currents coming from the opposite direction off Cape Agulhas. The collision and interaction of waves from different directions create large disturbances on the sea surface, raising waves to heights of 20 metres and more, with unusual, steep forward slopes and slanting troughs on an otherwise quiet sea. At a speed of about 15 knots, a collision with such a wave often proves to be fatal for the ship.
Single, “killer” waves are very dangerous for modern, large-tonnage vessels. In 1968, the tanker, "World Glory", carrying 49,000 tons of crude oil, was broken in half, and both halves sunk within 4 hours. In 1973, the cargo vessel, “Neptune Sapphire,” on her maiden voyage, carrying about 15 thousand tons of various cargo. The impact of a single, large wave off the south eastern shores of Africa caused the bow and 61 m of the forward part of the ship to break away and sink. The remainder of the ship was towed to East London.
Giant waves form on the surface where strong counter-currents are formed and in other regions of the World Ocean (regions of the Gulfstream, Kuroshio). In the Antarctic region, during the first voyage of a diesel-electric vessel "Ob’,” a 25-meter high wave was reported, and in 1965, waves broke windows in cabins 24 meters above the water line on the Italian passenger liner "Michaelangelo".
The methods for prediction of these waves are not yet developed. It is only possible to recommend avoidance of these regions when there is the most probability of occurrence.
Region where counter currents meet
| ||1.Cape Agulhas current |
Break up of a vessel on a giant wave
Salty Ocean waters and sea air have a continual, destructive effect on the hulls and superstructures of ships and on structures built on and beneath the sea. The complex structure of sea water promotes intense and highly variable chemical and electrolytic processes at the boundary where water and metal meet. These processes are called “metal corrosion.” Corrosion considerably intensifies the effects of fouling. Fouling is defined as a large accumulation of various types of marine plants and animals that attach themselves to the submerged portion of the hull.
Accumulation of marine organisms and corrosion of the submerged part of the hull can significantly reduce the speed of a vessel, increasing fuel consumption. On the whole, the World merchant marine fleet loses hundreds of millions of dollars annually due to marine corrosion and fouling.
It is known from practical experience, that hull corrosion is especially great along the area near the water line, where the effects of the sea and air are most intense, and also on the stern part of the ship, above where the screws throw water into the air.
Over a long time, a hull that remains in sea water will become covered with a thick layer on the surface, consisting of rust and marine organisms (bacteria, fungi, algae, seaweed, barnacles, starfish, sponges, crabs, etc.). The amount of fouling on the underside of a ship’s hull can reach 100 kg / 1 m2 per year. If this happens, the plates can become so thin, that the hull can be easily pierced under minor impact. Heavy corrosion can also take place inside a ship’s, especially in places where an accumulation of fouled water is in contact with humid air.
The hulls of vessels carrying liquid cargoes are especially subjected to strong corrosion. The average depth penetration depth of corrosion reaches 0.38 mm per year.
Cases are known where, as a result of systematic, salt water washdowns of the insides of tanks, corrosion penetration reached 4.7 mm per year.
To fight corrosion of steel, it is necessary to create resistant alloys. A small component of copper (0.2 - 0.4%) noticeably increases resistance of steel to atmospheric corrosion. By introducing more than 12% of chromium to steel, its resistance to corrosion increases further.
Electrolytic protection for a vessel’s hull and ballast tanks from corrosion has been widely distributed. It involves the placing of cathodes (normally lead) on various parts of the hull, which is 2-3 times less expensive than electrochemical plating.
Distribution of fouling and corrosion
Fouling of facilities by marine organisms, observed at low tide
The first written information about Man’s fight against marine was noted by Aristotle (4th century BC.) and later, by Pliny (1st century AD.). However, the struggle with this problem began much earlier in time. Studies of the remains of ancient vessels have shown that during the 5th millennium BC, the fight against fouling was already underway. Later, wooden hulls were covered with copper sheets. Still later, a resin, (tar with sulphur, arsenic and lime added) was applied. In England alone, 300 inventions for anti-fouling coverings were granted patents between 1626 and 1865.
At this time, the best, nearly permanent asset against fouling is an anti-fouling paint or polymer with components that are toxic or repellent to marine organisms. Some of the components in these coatings are copper, mercury, arsenic etc.) are selected in water deluge about a body and destroy fouling organisms.
Metals and alloys less subject to fouling are sometimes used. Among them are copper, tombac (copper and zinc alloy), brass, tin and siliceous bronze.
Fouling of the submerged part of a vessel
Fouling of the plating
As a result of the accumulation of luminescent marine organisms in one area during the night, the sea attains a glowing characteristic. The width of a glowing layer of water can range from several tens centimetres to several meters, and sometimes, tens of meters. The brightness of glow of the sea depends on the abundance of bioluminescent organisms. The organisms flash at night, but during the day, they spread and absorb light. Therefore, in day time, they reduce the transparency of the water, masking the plankton located within it.
At night, a flashing track - the loop - is retained, even during the incoming tide, and can seen by vessels lying at anchor. On a bright night, the glow of the sea is most spectacular.
The glowing sea has a negative effect on a navigator, lessening his attention and lowering his visual acuity during night hours, especially when there is a sharp contrast between the glowing areas of the sea and the ambient darkness. When separate areas glow brighter at night, the navigator becomes disoriented, since the glow takes on the appearance of a bank, shoal or breaking water on a reef.
Night glow of the sea in a wake
Curly glow of the sea
Coastal banks and sand bars have long been known to be hazards to navigation. The unpredictable changes in the positions of some of these shallows creates an inaccuracy in marine navigational charts, creating possible groundings and / or shipwrecks. It is known that the shores of Gulf of Biscay, Norwegian fjords, reefs and banks in the Straits of Magellan and Bab-el-Mandeb, the rocky and foggy shores of Alaska, straits through the Kurile Islands and along the shores of Florida all have problems with moveable grounding hazards. Some banks are even called, “graveyards of ships". The sand on these banks constantly moves, and it is even possible for the Ocean create new passages, while filling in older ones.
A very dangerous area for navigation is near Sable Island on the coast of eastern Canada. Named “Holy Cross” on old Portuguese sailing charts of the 16th century, it is located at the junction of the warm Gulfstream with the cold Labrador Current. In this zone of decreased current speeds, large amounts of sand, rubble and mollusc shells are deposited, forming a large bank of indeterminate shape. Under the operation of the currents and waves, the island and associated bank constantly changes size, shape and position. As the western side is gradually washed away, the eastern side grows. As the new sand bank forms, the island migrates in an easterly direction.
Vessels sunk long ago periodically reappear on the Ocean surface when the sand shifts and uncovers them.
For at least the last 200 years, Sable Island "has walked" several miles across the Ocean. Uncountable banks, frequent storms, variable winds, hurricanes, long rolling seas, fogs, currents and Gulfstream "smoke" makes this region one of the most hazardous to navigation in the World. However, one of the main dangers of the banks is quicksand. Whether the vessel drifts off course because of currents, or touches bottom in a storm, she will forever remain there. After 2-3 months, the vessel completely disappears below the surface of the sea. Over a span of several centuries, hundreds and possibly thousands of vessels perished here. And now, under many meters of sand lies a natural museum of shipbuilding - from the vessels of the Vikings, karackes and galleons of the Spaniards up to modern, multi-tonnage vessels. Sometimes, currents and the waves wash away the sand, revealing again masts and yards of sailing ships or rusty, corroded, hulks and stacks of powered ships sunk into oblivion over the years.
Graveyard of ships near the islands of St. Pierre et Miquelon
No less notorious are the sand banks called, Goodwin Sands, located in 6 miles from the south eastern extremity of Great Britain at the southern end of Dover Strait. During the incoming tidal flow, they are hidden below a 4-meter depth of water. During the tidal ebb, however, for a stretch of 11 miles, a 2-meter high layer of dry hard sand uncovers. Under the influence of strong, variable currents, the banks sometimes change their shape daily. Goodwin Sands has been a place where ships have run aground and were destroyed over a span of many centuries. Modern, heavily loaded vessels hitting the banks have broken in half. This happens because the incoming tide washes near the middle of the hull, and the ebbing tide removes a fair amount of sand from under the bow and stern. After this process is repeated several times, the bow and stern hang, and having no support, the weight fore and aft arches the ship and it breaks in half.
A sandy, underwater channels of 2 to 4 m depth change position after each storm, revealing “snapshots” of the last ship-wrecks near Sable Island Bank
"SILVIA ONORATO" ON GOODWIN SANDS. 1948
Grounding on the bank
The last hours
Stranded on a bank, the vessel was abandoned by the crew
Among regions of ship-wrecks, the island of Tasmania also holds a primary place. For over 150 years, along its coast and adjacent islets, 603 vessels have perished. Here, huge ocean waves break with great fury over unapproachable rocks. For a full third of the year the "Bold Wests" - winds with a Beaufort force of 7-8, often accompanied by strong rainstorms dominate the weather. The winds lift the spray of the Ocean surf, and for weeks there is an impenetrable haze along the dangerous shores. Frequently, the fog covers both the sea and shore for many miles around. The straits abound with underwater reefs and rocky banks.
With the advent of the age of steam, marine “nomads” became a relative scarcity, since, in the case of a severe problem or collision, steam vessels quickly lost buoyancy and sunk. Modern, seaworthy vessels usually remain afloat after emergencies. These floating hulks represent a great danger to fast ships, especially when they appear in shipping lanes. Statistics show that up to 100 encounters with abandoned, floating wrecks occur on the North Atlantic Ocean each year.
The hydrographic vessels "Tropic" and "Meridian" were working on the Atlantic Ocean. There was dead calm, excellent visibility and the Ocean surface was smooth. Suddenly, for no apparent reason, "Meridian" experienced a strong impact at the stern, resulting in the loss of the propeller screw. After being towed back to port by “Tropic,” the ship entered a drydock. In the dock, the shipyard workers found pieces of wood and of cable in the propeller shaft area. Apparently, "Meridian" struck the buoyant, submerged remains of an old sailing vessel.
The large-tonnage, Dutch oil-ore ship, "Jacob Verholm," capsized but did not sink. Instead, she drifted on the waters of the Atlantic for more than a month. Sinking of the vessel appeared to be a ghostly, sinister matter. She resisted sinking even during a storm, and only her complete destruction resolved the incident.
Portrayal of a shipwreck
"The Flying Dutchman," as described by seamen of the last century.
Locations of encounters with abandoned, floating hulks on the North Atlantic Ocean between 1886 and 1893
Daily numbers of ships on the North Atlantic Ocean in summer
Debris of a sunken vessel in shallow waters
The British-based, maritime classification company, Lloyds Register of Ships, reports that for almost the last three centuries, an average of 271 ships have been lost at sea each year. Over the past 150 years (during peacetime), more than 40,000 merchant ships have been lost. Another 20 thousand were lost when the World was at war. The Lloyds Register compiles and stores information on merchant ships of 100 registered tons or more that have had emergencies at sea or have sunk. If smaller-tonnage vessels were also included in the data base, the annual number of shipwrecks would average about 500. The company has been publishing the data since 1961, divided by sea or Ocean. For the period 1961-1980, 19.3 million registered tons of seagoing vessels, numbering 6632 vessels, were sunk. Between 1961 and 1970, 2,868 vessels (about 6.6 million registered tons) were lost, and for the second decade (1971-1980), 3,764 vessels (12.7 million registered tons) went to the bottom.
In 1981 alone, as a result of every possible kind of emergency 359 vessels with a capacity of not less than 100 registered tons perished; if only larger vessels (500 registered tons or more) were counted, the loss was 250 ships.
THE REASONS FOR VESSEL-CATASTROPHES DURING 1981
| || || |
|Loss of buoyancy|| || |
|Fires and explosions|| || |
|Collision with other vessel or any other object|| || |
|Groundings on banks rocks, and reefs|| || |
|Disappeared without a trace|| || |
|Other reasons|| || |
Seasonally, autumn is the worst for sinkings, followed by spring, winter and summer.
The least number of losses occur on the open Ocean.
The most dangerous water areas are the coastal zones, narrows and fjords. A vivid illustration of this fact is that of the loss of the passenger liner, "Mikhail Lermontov," which cruised in the regions of Australia and New Zealand. Near the Jackson Head lighthouse in Queen Charlotte Bay, the vessel hit a submerged rock, receiving a significant rupture in the hull. All attempts to rescue the vessel and to tow it to a shallow bank proved futile. Unable to be towed a distance of one-half mile, the "Mikhail Lermontov" sank in depth of 33 m.
Marine emergencies also cause a loss of life measured in hundreds of people annually. For example, the passenger ship, "Admiral Nakhimov," collided with the cargo ship "Petr Vasev", costing the lives of numerous people.
The economic costs from the loss of such large ships as the tankers, "Torrey Canyon", "Amoco Cadiz" and "Exxon Valdez", are calculated in the hundreds of millions of dollars. The damage to the environment caused by these catastrophes does not have a dollar figure attached.
In 1987, the UN General Assembly adopted a resolution for the establishment of a committee to try to predict and prevent dangers to navigation and subsequent losses.
Reefs of the Seychelles islands (Indian Ocean): a place for shipwrecks
A gaping hole and damage to the bow was received by the cargo ship "Britta" upon colliding with the tanker, "Mirella de Amoco," in heavy fog.
Having a gross capacity of greater than 500 registered tons in 1982-1991 (thousands of registered tons).
FROM NWS CHICAGO
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