How can a boat sail into the wind?



The wind is the only thing that propels the sailing boat, so how can a boat sail against it? Amazingly, the most important force that drives a boat into the wind is suction.



The boat’s sail is like an aircraft’s wing on its side. On the outwardly curved, leeward side the wind has to flow around the sail, creating a powerful suction effect pulling the sail towards it. The same principle applies to an aircraft, which gets lift from the suction on the top of its wings.



The suction effect is produced by the laws of aerodynamics. The air that is diverted around a curved sail becomes compressed so that it can squeeze past. When a moving stream of air is compressed its speed increases - a draught under a door can be surprisingly strong for this reason. And when the wind’s speed increases, a lot of pressure occurs. This is because the faster the air is moving, the fewer molecules there are in any given space.



The area of low pressure on the leeward side of sucks that sail towards it with the twice the force that the same strength of wind can push into it on the windward side.



So the wind forces the boat sideways. However, the keel - or centreboard - of the boat resists the sideways movement. The wind’s force is then converted partly into a forward movement of the boat and partly into a tilt to leeward which the yachtsman has to counteract by leaning out from the other side of the boat. The boat sailing close to the wind is bound to move substantially sideways - an effect called leeway. But the helmsman can compensate when plotting his course.



Boat can sail directly into the wind, but at 12 m yacht can sail only 12-15 degrees off the wind. To go in the direction of wind is coming from, the boat has to zigzag, or make a series of tacks. The closer a boat sails to the wind, the slower its speed will be. The helmsman can go faster by making wider zigzags at a bigger angle to the wind, but then he has to travel farther.



 



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What is echo sounding?



The sinking of them British liner Titanic in 1912, after it collided with an iceberg, spurred scientists to find a means of detecting underwater obstacles. And early form of sound detection was used by British and American forces for submarine detection during the First World War. Modern sonar (sound detection and ranging), which uses the echoes from emitted sounds, was developed by the French scientist Paul Langevin.



Today, echo sounding is used in ship navigation to determine water depth and by fishing vessels to spot shoals of fish, as well as for Marine research and mapping the seabed. Sound pulses, generated electronically, are beamed through the water and echoed back to the ship by any obstacle up to about 6 miles (10 km) away. The returning signals are displayed on a video screen.



Sound travels through water at about 1600yds (1500m) a second - around four times faster than in air. As with radar, the distance to the obstacle is calculated from the time the echo takes to return, and the Doppler shift of the sound waves shows if the object is moving.



 



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How are undersea telephone cables repaired?



Most of the world’s international telephone conversations are carried by cables laid along the seabed, linking the continents. Communications satellites have not yet removed the need for submarine cables – even the ‘hotline’ between Washington and Moscow uses them. But what happens when a cable fails?



The first transatlantic telegraph cable, laid in 1858, failed within a few weeks. Today the risk of failure has been much reduced by using polythene insulation, and by choosing safer routes that avoid volcanic activity, strong currents and fishing grounds where trawlers may snag their nets on the cables. In shallow sea, cables are often buried.



Despite these precautions, failures still happen. Large telecommunication companies, such as Cable and Wireless, have maintenance ships standing by round-the-clock to carry out repairs.



The job is done by remote-controlled submersibles, as big as a medium-sized van, which are lowered into the water from the maintenance ship, dive to the seabed, locate the fault and attach lines to the surface and repaired on board the ship.



CIRRUS (Cable Installation, Recovery and Repair Underwater Submersible) and it’s even more sophisticated successor ROV128 are controlled through an ‘umbilical’ cable from the ship and powered by hydraulic thrusters.



A submersible’s first job is to find the fault. It follows the line of the cable on the seabed, picking up faint low-frequency signals sent along the cable from the terminal station ashore. If a cable is broken, the water will form a short circuit that will link the individual wires together. When the signal disappears, the submersible settles on the ocean floor and exposes the damaged cable with a powerful jet of water which blows away the layer of sand and silt.



CIRRUS is equipped with powerful lights and television cameras, both colour and black and white, which enable operators on board the ship to see every detail of the seabed. Using the pictures as guidance, the operators extend powerful manipulator arms and grip the cable. CIRRUS uses a special blade to cut the damaged cable, and leaves an acoustic ‘pinger’ on the seabed to mark the spot.



It then rises to the surface, picks up a strong steel line, takes it down to the seabed and clamps it to one end of the cable. The cable is then winched up to the surface. The same process is used to receive the other end of the cable.



Once the cable has been repaired and joined together on board the ship, it is lowered carefully back to the seabed.



 



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How does an aqualung work?



Ever since the 19th century, scientists had tried to invent an effective self-contained breathing device for divers. But if their inventions worked at all, they involved cumbersome diving suits or restricting safety lines. Then in 1943 a French naval captain, Jacques-Yues Cousteau, and his colleague Emile Gagnan, invented the aqualung. Cousteau used the invention to dive to depths of 200ft (60m).



A person’s lungs are not powerful enough to expand against the pressure of water below about 18in (450mm). Water pressure increases rapidly with depth, and at 33ft (10m) it exerts a pressure equal to 2 atmospheres – nearly 30lb per square inch (2 kilos per square centimetre).



To breathe underwater, a diver has to receive air at the same pressure as the surrounding water. This is what the aqualung – or scuba (self-contained underwater breathing apparatus) – provides. Air is stored at high pressure – up to 3000lb per square inch (200 atmospheres) – in cylinders on the diver’s back with a tube to a mouthpiece.



At reaches the diver through a two-stage regulator. The first stage reduces the pressure to about 150lb per square inch (10 atmospheres) above the surrounding water.



The second stage, in the mouthpiece, supplies the diver with air at the same pressure as the surrounding water. A flexible diaphragm in the mouthpiece is open to the water on one side and to an air chamber on the other side. As the diver inhales, the diaphragm is drawn inwards and presses against a lever in the chamber. This opens a valve to let in air from the tube, which drops in pressure as it enters.



When the diver finishes inhaling, the air coming into the chamber pushes against the diaphragm, shutting the valve and cutting off the airflow.



Even when the diver is not inhaling, an increase in water pressure as he dives pushes the diaphragm forward to open the valve and let in air from the tube. So the air in the mouthpiece chamber is always at the same pressure as the surrounding water.



 



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What are the sea sunken secrets?



On the bed of the Atlantic, 2½ miles (4km) down, Dr Robert Ballard saw the bulk of the liner Titanic looming in front of him. He and the crew of the miniature submarine Alvin were the first men to set eyes on the ocean giant since she was sunk by an iceberg nearly 75 years earlier. ‘Directly in front of us was an apparently endless slab of black steel rising out of the bottom – the massive hull of the Titanic,’ he wrote.



Of a second dive – one of nine he made in the Alvin during July 1986 – Dr Ballard recalled: ‘Here I was on the bottom of the ocean, peering at recognizable, man-made artefacts designed and built for another world. I was on the bottom of the ocean, peering at recognizable, man-made artefacts designed and built for another world. I was looking through windows out of which people had once looked, [at] decks along which they had walked, rooms where they had slept, joked, made love. It was like landing on the surface of Mars only to find the remains of an ancient civilization similar to our own.’



The Titanic sank about 450 miles (720km) south of Newfoundland, in the early hours of Monday, April 15, 1912. Of the 2200 people on board, only 705 were saved. It was the liner’s maiden voyage.



But it was not until September 1, 1985 – thanks to modern technological aids – that the wreck was located by a joint French-American expedition, headed by Dr Ballard.



The first step in finding a lost wreck – if it is not found by accident – involves meticulous research in historical archives which should establish as accurately as possible where the vessel went down. Sometimes, this can be quite straightforward.



The Mary Rose, King Henry VIII’s flagship, sank in 1545 in relatively calm waters in the Solent – within sight and hearing of hundreds of people ashore, including the king.



As she sail with a fleet of 60 other warships to confront a French invasion fleet, she heeled in the wind and water poured through her starboard gunports. Her cannons broke their moorings and rolled across the decks, adding their weight to the starboard side. The Mary Rose capsized, drowning 650 men. Her position was known, then lost or forgotten. And it was more than 400 years before she could be raised.



The location of ships that went down in sight of land is usually well documented. The Scilly Isles and Britain’s western approaches harbor at least 400 recorded wrecks and hundreds of unrecorded ones. And an estimated $1 billion worth of gold, silver, jewellery and porcelain lie around the coasts of Florida, the West Indies and Central America.



One of the richest finds was a flotilla of ten Spanish treasure ships off Florida. They set sail for home Havana, Cuba, in July 1715, laden with gold, emeralds, pearls and 2300 chests of newly minted coins from Mexico City – treasure worth at least $50 million in modern currency. The ships were caught in a hurricane and went down south of Cape Canaveral.



During the 1950s, local hotelier Kip Wagner, an avid beachcomber, found a few blackened silver coins in Sebastian Inlet, 40 miles (64km) south of Cape Canaveral. Researching their origin, he read about the fleet – and became convinced he had found some of its treasure. He sent a coin to the Smithsonian Institution in Washington, which told him that it could not be from the fleet, because it had sunk 150 miles (240km) farther south.



Undeterred, Wagner and a friend, Dr Kip Kelso, continued their own research and found that Bernard Romans, an English mapmaker, in 1775 had described the place where the fleet went down and had even drawn a map. Armed with a secondhand mine detector, Wagner searched the beaches near the area described – and found a huge hoard of valuables, including a gold chain and pendant, auctioned for $50,000, and a diamond ring worth $20,000.



Wagner put to sea and began to dive up find the wrecks. The treasure he ultimately recovered was worth more than $5 million.



Wagner’s use of a mine detector triggered the use of modern technology in the search for wrecks. In 1970, Rex Cowan, a London solicitor, decided to search for a Dutch East Indiaman, the Hollandia, lost off the Scilly Isles in 1743. He knew from contemporary accounts roughly where the wreck might be, but divers could find no trace. Cowan used a magnetometer – an instrument towed behind a ship which detects anomalies in the magnetic field caused by iron objects such as cannons.



After months of crisscrossing the likely area in a grid pattern, Cowan and his team finally got a reading only a few days before the end of the diving season in September, after which weather conditions tend to be unfavorable. They went below, found nothing, but returned the next day – and discovered cannons bearing the monograph of the Amsterdam chapter of the Dutch East India Company. Next they discovered a silver spoon bearing the crest of a Dutch family, the Imhoff-Bentincks, one of whose members was known to have been aboard the Hollandia, confirming the source. Ultimately, more than 35,000 silver coins, worth around £1 million, were found.



Magnetometers proved unsuccessful, however, in rediscovering the Mary Rose. Although she had sunk only a few hundred yards from the shore, she was covered by mud and sand when the search for the wreck began. A magnetometer found a buried cable not recorded on Admiralty charts – but no wreck.



The breakthrough came from another modern invention – sonar. Developed for underwater warfare, sonar sends out sound signals and records the echoes as they are reflected off solid objects.



A type of sonar called a sub-bottom profiler, which can detect objects embedded in mud or sand, produced signals suggesting the presence of a mound on the seabed – and something solid beneath. Three years later, tides had removed some of the silt from the port side of the wreck and timbers could be seen. Then began the historic recovery and the painstaking recording of its contents – a unique time capsule of life aboard a medieval man-of-war.



But the rediscovery of the Titanic must rank as the most remarkable deep-sea find. It lies too deep for divers and finding it in the immensity of the North Atlantic with only a rough idea of where it lay called for special skill. The joint French-US team used a deep-sea sonar device to search the ocean floor and find the wreck – then a remote-control underwater camera to take the first pictures. A year later, Dr Ballard, a marine geologist from the Woods Hole Oceanographic Institute, Massachusetts, saw the wreck for himself, from the three-man submarine Alvin.



The submarine landed on the bow and the bridge. A remote-control underwater robot camera. Jason Junior, described the Grand Staircase, photographing still-hanging chandeliers, clocks, silverware, and the interiors of staterooms.



With such techniques, few wrecks anywhere beneath the Earth’s oceans are beyond man’s reach. If they are worth investigating mankind now possesses the technology.



 



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How do pufferfish inflates?



Scientists believe it to be the second-most poisonous vertebrate in the world after the golden arrow poison frog of South America. A poison called tetrodotoxin is present in pufferfish liver and sometimes skin. Pufferfish are also known as bubblefish, blowfish, balloonfish and toadfish. They have thin spines that are visible only when they are completely puffed up. The fish inflates its yellow underbelly by filling it with water when attached, making it too big for the predator to bite or swallow.



When the puffer is threatened, the stomach expands into the peritoneal space and the stomach unfolds to fill gaps beneath the head, dorsal, anal fin and caudal peduncle. The fish balloons and the spines that lie on the surface of its skin stick out, making it a highly unattractive meal!



Although puffers have evolved to suck in water, if lifted out they can sometimes suck in air. They sometimes have difficulties expelling this from their stomach, so take extra care when catching them.



 



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What are the facts about jellyfish?



Here are the twelve incredible facts about jellyfish:




  1. Jellyfish are invertebrates, that is, they have no spinal cord (the backbone that helps us sit up).

  2. Jellyfish have no brains – they have no hearts or eyes. Yet, they have been around in the seas for over 500 million years since history began to be recorded. In all these years, the shape of the jellyfish has hardly changed. They still strongly resemble their ancestors from 500 million years ago. Remarkable!

  3. The box jellyfish is considered the most vermous marine animal in the world. It has a cube-shaped body. Its tentacles are covered in poison-filled darts. Some of these box jellyfish have venom that can kill humans. Anyone stung by one of them can go into cardiac arrest or die within minutes.

  4. Jellyfish are mostly water. About 5% of jellyfish bodies are made of structural proteins, muscles and nerve cells, while the remaining 95% is water. Human bodies, by comparison, are up to 60% water.

  5. Groups of animals are usually given a collective noun as a name. A group of cows is a herd, for example, while many fish swimming together form a “school.” Jellyfish groups can go by three different names. A collection of jellyfish is called a “bloom,” “smack,” or “swarm.” Which other group is called a “swarm”?

  6. Jellyfish are not classified as a variety of fish. Fish are vertebrates that live in water and breathe through their gills. Jellyfish, on the other hand, are invertebrates, meaning they have no backbone and they absorb oxygen from water through membranes.

  7. In 1991, over 2,000 jellyfish polyps were blasted into space to test how they reacted to the lack of gravity. Those jellyfish reproduced in space, creating over 60,000 jellies, but the space-bred jellies weren’t able to function.

  8. While some are poisonous, jellyfish can be a delicacy. There are some 25 edible types of jellyfish. They’re typically added to salads or are pickled. As raw fish, they have a salty taste and the consistency of noodles.

  9. One type of jellyfish is described as immortal. The Turritopis dohrnii jellyfish is thought to be immortal, since it can turn into a colony of polyps (individual organisms). As the jellyfish grows old, it settles on the sea floor and becomes polyps. The polyps then give birth to new, genetically identical jellyfish.

  10. Jelyfish tend to follow the currents of the ocean as they move. So they can be found around the world in every type of ocean water. They can thrive in warm tropical water or cold Arctic water. They’ve been found at the bottom of the ocean and near the surface.

  11. Since jellyfish don’t have any bones, it is difficult to find fossils of ancient jellies. But in 2007, a preserved jellyfish fossil was discovered in Utah that’s thought to be over 505 million years old. Dinosaurs lived from about 245 million to 66 million years ago, meaning jellyfish pre-date them by at least 250 million years.

  12. Bioluminescence is the term for  creature’s ability to produce its own light. Some jellyfish have this and produce an internal glow.



 



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Which is the largest and smallest jellyfish?



In July, 2019, two divers were swimming off the south-western tip of England. They hoped to see some rare fish, but what they came across blew their mind away. Crossing their water-path was a huge hulk of a barrel-jellyfish (Rhizostoma pulmo). The giant jellyfish was the size of a human being. It is a rarely seen species. Luckily, the divers – biologist Lizzie Daly and underwater cinematographer Dan Abbott – managed to film the mammoth creature.



The divers then shared the encounter in a Facebook video they posted on July 13. This was the time when Britain was running the Wild Ocean Week campaign to raise funds for the United Kingdom’s Marine Conservation Society. People has been invited to present pictures of any strange creatures underwater.



The divers actually saw the giant jellyfish emerge from the murky water. The fish is also called the dustbin-lid jellyfish. It is characterized by eight thick arms ending in tentacles. Its head is large and rounded. Put together, these features make it look like the lid of a garbage bin. Barrel jellyfish sometimes wash up on the shore.



The largest



Is the barrel jellyfish the largest of the species? No. That award goes to the lion’s mane jellyfish (Cyanea capillata), the largest known species in the world. This coldwater jellyfish has 1,200 long, trailing tentacles. If you measure the length of the tentacle, an individual lion’s mane jellyfish can be as long as 120 feet (36.5 metres). The tentacles of a lion’s mane can sting 50 to 100 people in just a few minutes if it is let loose among a crowd. Most encounters cause temporary pain and localized redness.



On a July day in 2010, around 150 beach-goers at Wallis Sands State beach in New Hampshire in the U.S. were study by the remains of a lion’s mane jellyfish that had broken up into countless pieces. Thankfully it caused temporary pain and redness around the area of the sting.



The smallest



The smallest of the species is called Irukandji (Malo maxima). It is 1 mm long and 5 mm across the part that looks like a lid. Box Jellyfish (Chironex fleckeri) is the most venomous. It is found in the Australian coasts and is considered the most poisonous, deadliest and meanest of all the jellyfish. The variety of box jellyfish known as the sea-wasp or marine-stinger has been declared one of the most deadly creatures on Earth.



Their food



What do they eat normally? Jellyfish typically eat small plants, shrimp, or fish. They use their tentacles to stun prey before eating it. According to the Mayo Clinic, if you find yourself stung by a jellyfish, your best course of action is to remove any tentacles carefully with tweezers and soak the area in hot water. If a person gets a severe reaction or becomes unconscious after a sting, seek medical attention immediately.



 



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