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Tides are not just an ocean event. The solid crust under your feet rises and falls by up to about half a meter each day, stretching as much as 55 centimeters at the equator, because the Moon and Sun squeeze the whole planet. The Sun's gravity on Earth is 179 times stronger than the Moon's, but tidal force falls off with the cube of distance, so the Moon supplies about 69 percent of the effect and the Sun about 31 percent. The real driver is the horizontal, or tractive, component of that pull, which sweeps water sideways into two bulges, one facing the Moon and one opposite. Because the Moon orbits as Earth spins, a tidal cycle runs about 12 hours and 25 minutes. Alignment at new and full moon, called syzygy, brings spring tides, while quarter moons at quadrature bring weak neap tides.

Understanding took centuries. Pytheas linked tides to the Moon around 325 BC, Seleucus of Seleucia blamed the Moon around 150 BC, and the Venerable Bede in 730 AD tracked tides running about four fifths of an hour later each day. Kepler credited lunar gravity, Galileo mocked the idea and blamed Earth's motion, and Newton's Principia settled it in 1687. Real coastlines scramble the math into amphidromic points where the water barely rises, 16 to 17 meter tides in the Bay of Fundy, opposite tides on either side of Cook Strait, and a double high tide at Southampton. Lord Kelvin built gear driven machines to predict local tides. All that friction dissipates about 3.75 terawatts, has lengthened the day by about two hours over 600 million years, and pushes the Moon away by roughly 3.8 centimeters a year.

• Sailors use the rule of twelfths to estimate how fast water rises each hour after low tide.
• The atmosphere has its own tides in air pressure and wind.
• Galactic tides from the Milky Way can knock comets out of the Oort cloud.
• GPS networks and observatories must correct for the ground's daily rise and fall.
• Laser reflectors left by Apollo astronauts measure the Moon's drift.

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The SS Andrea Doria, laid down in 1950 and on her maiden voyage in 1953, was Italy's postwar statement of recovery after losing half its merchant fleet and the liner Rex. Built for luxury rather than size or speed, she carried about 1,200 passengers and 500 crew on the Genoa to New York run, held over a million dollars in original art and a bronze statue of Admiral Andrea Doria, and gave each of three classes its own pool. She advertised a double hull, 11 watertight compartments, and radar, but model tests showed she was top heavy, and a rogue wave on her maiden voyage rolled her 28 degrees. Her manual required pumping seawater into emptied fuel tanks as ballast, yet crews skipped it to avoid costly tank cleaning in New York.

On July 25, 1956, in fog south of Nantucket, Captain Piero Calamai was steaming at about 21.8 knots when the eastbound Swedish liner Stockholm, running 20 miles north of the recommended lane with an ice reinforced bow, approached at 18 knots. Neither ship radioed. The Stockholm's officer likely misread an unlit radar range dial, the Doria turned to port while the Stockholm turned to starboard, and at 11:10 p.m. the Stockholm's bow drove 40 feet into the Doria's starboard side. With empty tanks and no ballast, she listed past 20 degrees, leaving half her lifeboats useless. The French liner Ile de France under Captain Raoul de Beaudean turned back, lit every exterior light, and took 753 people aboard, while the damaged Stockholm rescued more than 500. The Doria stayed afloat 11 hours and sank at 10:09 the next morning.

• Fifty one people died: 46 on the Doria and five Stockholm crewmen in the bow.
• Maria Sergio and her four children, bound for Indiana, were lost in their cabin in the impact zone.
• Fourteen year old Linda Morgan was carried from her cabin onto the Stockholm's bow and survived.
• Hearings ended in a confidential settlement, and the Swedish line was then building a ship at the same Italian yard.
• The wreck lies at 240 feet, is called the Mount Everest of diving, and has killed at least 22 divers.

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Robert Fulton was born in 1765 on a farm in Little Britain, Pennsylvania, and first made his living as a portrait painter in Philadelphia, earning enough by 1785 to buy a farm near Pittsburgh for his mother. Tuberculosis in 1786 sent him to England for the sea air, where he studied under Benjamin West and then caught canal mania. He patented a dredging machine, promoted inclined planes to replace locks, and found a backer in Manchester cotton manufacturer Robert Owen. Between 1796 and 1799 he built a steam tug named Bonaparte in the Duke of Bridgewater's timber yard, but its wake eroded the canal's clay lining. Moving to Paris in 1797, he funded himself with the city's first panorama painting and designed the Nautilus, a hand cranked submarine built at Rouen that stayed down 17 minutes at 25 feet in the Seine. With US ambassador Robert R. Livingston he built a 66 foot steamboat in 1803 that broke and sank, then rebuilt it to run upstream at about three knots.

In 1804 he switched sides, building floating contact mines for William Pitt's Royal Navy, used in the raid on Boulogne, until Trafalgar in 1805 ended the invasion threat and his funding. Back in America in 1806, he and Livingston launched the North River Steamboat, later called the Clermont, mocked as Fulton's Folly. The 136 foot, 160 ton boat with 15 foot open paddle wheels and backup sails carried passengers 150 nautical miles from New York to Albany in 32 hours in 1807. In 1811 and 1812 he, Livingston, and Nicholas Roosevelt built the New Orleans at Pittsburgh, proving steam could push upstream on the Mississippi. In 1815, at 49, he rescued his friend Thomas Addis Emmet from the broken ice of the Hudson and died of pneumonia soon after.

• Fulton admired Napoleon enough to name his English steam tug Bonaparte.
• Before steam, Ohio Valley farmers broke up their flatboats in New Orleans and walked home.
• He served as an Erie Canal commissioner and designed Demologos, the first steam warship.
• He is buried at Trinity Church in New York, near Alexander Hamilton.
• He appears with Samuel Morse on the 1896 two dollar silver certificate, and five ships were named USS Fulton.

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The Mayflower was an aging cargo ship that had hauled wine between England and France and reeked of it. Its passengers included English separatists who had fled to Leiden in Holland, where farmers were forced into grueling textile work washing wool. With the 12 year truce between the Dutch and Spain ending and King James I courting Dutch alliances, they chose North America despite Jamestown's death toll. The plan used two ships, but the Speedwell had been refitted with oversized masts whose torque pulled its seams apart. After repeated turnbacks it was abandoned, eating up rations and money and pushing departure into September storm season. The Mayflower sailed with 102 passengers and about 30 crew in a hull roughly 100 feet long and 25 feet wide, with passengers confined to a gun deck of about 1,600 square feet and a five foot ceiling above a hold of dogs, pigs, goats, and poultry.

Its tall castles caught the westerly gales like fixed sails, and in one storm the main beam cracked. A passenger's iron jack screw, packed for raising house beams, cranked it back into place. Only one passenger, a young servant, died at sea, a baby named Oceanus was born, and John Howland survived being swept overboard by grabbing a trailing halyard. Storms landed them at Cape Cod, far north of their Virginia Company patent near the Hudson River, and when hired strangers declared the contract void, the leaders drafted the Mayflower Compact before anyone went ashore. Wintering aboard, half the passengers and about half the crew died. The Wampanoag showed survivors how to grow crops. Captain Christopher Jones sailed home in about a month in spring 1621 and died roughly a year later.

• Crossing took about two months against the prevailing westerlies.
• The crew struck all sails in the worst gales to save the masts.
• By 1624 the idle ship was appraised at 128 pounds and sold to a ship breaker.
• A lingering rumor says its timbers built a barn in Buckinghamshire.
• An estimated 35 million living people descend from its passengers.

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Robert FitzRoy was born in 1805, a descendant of King Charles II, joined the Royal Navy at 12, and became the first officer to score full marks on the lieutenant's exam. In 1828, in his early 20s, he took temporary command of HMS Beagle off Tierra del Fuego after Captain Pringle Stokes died by suicide, a loss that left him with a lifelong fear of breaking down under the isolation of command. When local people took one of his boats, he seized hostages and carried four Fuegians to England, renaming them Fuegia Basket and Jemmy Button among others, and presented them to King William IV and Queen Adelaide. Returning them meant sailing again, so he sought a gentleman companion and chose Charles Darwin. The pair clashed most bitterly over slavery in Brazil, and FitzRoy's temper earned him the nickname Hot Coffee.

The mission in Tierra del Fuego failed, and FitzRoy briefly resigned his command after the Admiralty refused to repay a surveying ship he bought with his own money. After the voyage ended in 1836 he embraced biblical literalism, defending Noah's flood in his narrative. As governor of New Zealand from 1843 he sided with the law after the Wairau Affray, issued unbacked promissory notes, watched Hone Heke cut down the flagpole at Kororareka four times, and was recalled. In 1854 he took charge of a three person weather office, the forerunner of the Met Office. After the 1859 Royal Charter Storm he used the telegraph to gather barometer readings from 15 coastal stations, coined the term weather forecast, and hoisted storm cones at ports. At the 1860 Oxford meeting he raised a Bible and begged the audience to believe God rather than man.

• Fishing fleet owners resented his warnings because ships held in port earned nothing.
• Queen Victoria sent messengers for his forecasts before crossing to the Isle of Wight.
• He spent his own fortune on the weather service and died on April 30, 1865.
• Darwin contributed to a fund for his widow and daughter, and the Queen granted them an apartment at Hampton Court Palace.
• In 2002 the shipping forecast area Finisterre was renamed FitzRoy.

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Eddie Aikau was born in May 1946 in Kahului, Maui, the third of six children of Solomon and Henrietta Aikau, and a descendant of Hewahewa, high priest to Kamehameha I and Kamehameha II. In 1959 the family moved to Oahu and lived rent free on a nine acre Chinese cemetery in exchange for keeping the grounds. At 16 Eddie left school and worked at a Dole pineapple cannery to buy his first surfboard. His middle name, Makuahanai, means a nurturing or feeding parent. In 1968 the City and County of Honolulu hired him as the first lifeguard on the North Shore, alone on the stretch between Sunset Beach and Haleiwa, where winter swells break at 30 feet over shallow reef. Working with a buoy, fins, and a surfboard, he saved more than 500 people at Waimea Bay, and no one died there on his watch. He was named Lifeguard of the Year in 1971 and won the Duke Kahanamoku Invitational in 1977.

Personal loss hit hard. He married Linda in 1971, and in 1973 his brother Gerald, a Vietnam veteran, was killed in a car crash, a grief that strained the marriage. In 1978 he joined the Polynesian Voyaging Society's Hokulea for a 2,500 mile voyage to Tahiti using traditional wayfinding. Departing March 16, 1978, the canoe capsized about 12 miles south of Molokai. Eddie took off his bulky life jacket so he could paddle faster and set out for Lanai. The crew was later rescued, but despite the largest air and sea search in Hawaiian history, he was never found. The Eddie Aikau Big Wave Invitational at Waimea runs only when open ocean swells reach 20 feet and has been held just 11 times since 1985, most recently in December 2024.

• Eddie and his youngest brother Clyde are the only Native Hawaiians to win the Duke Kahanamoku Invitational.
• A notable early 1978 rescue pulled television producer John Orland from the surf.
• Surfer Mark Foo coined the phrase Eddie would go while organizers debated canceling the first contest.
• Purists adopted Eddie wouldn't tow to reject jet ski assisted big wave surfing.
• Sam George's Emmy winning 2013 documentary concluded that Eddie's heroism rested on a deep sense of fairness.

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The standard diving dress, the classic copper hat rig, could weigh up to 190 pounds of canvas, rubber, lead, and spun copper, and it began as firefighting gear. In 1820s England, John Deane watched horses trapped in a burning stable and in 1823 patented a smoke helmet fed by a hose and a double bellows. Lacking capital, the Deane brothers sold the patent to their employer Edward Barnard, who brought in engineer Augustus Siebe. By 1828 the helmet had gone underwater, but the suit was open at the bottom like an upturned glass, so a diver who tripped or leaned too far could flood and drown. Konrad Kyeser had sketched a leather diving jacket and helmet in 1405, but only 19th century materials such as Charles Macintosh's waterproof canvas and vulcanized rubber made a working suit possible. In the 1830s Siebe sealed the helmet to a watertight suit with an exhaust valve, and in 1834 Charles Deane walked the wreck of HMS Royal George and recovered 28 bronze cannons.

The episode breaks down the gear: the bonnet and corselet locked by a one eighth turn interrupted thread, shoes of up to 34 pounds, lead weights, and the US Navy Mark V belt of over 80 pounds. Surface crews hand cranked air pumps and read depth from the delivery pressure gauge, since every 33 feet adds an atmosphere. If a hose parted with no safety valve, the suit instantly lost pressure and the sea forced the diver's body up into the rigid helmet, a fatal helmet squeeze prevented only by the non-return valve. The opposite danger was the blow-up, when air trapped in the legs flipped a diver and rocketed him upward, risking the bends, torn lungs, and a burst suit that sent him sinking again.

• In 1874 Auguste Denayrouze built a speaking tube with a diaphragm at each end, later replaced by electrical diver telephones.
• Tenders used soapy water or metal cuff expanders to force a diver's hands through tight rubber wrist seals.
• Divers pressed a valve button with their chin to dump air and control buoyancy.
• A spitcock let a diver sip seawater and spit it onto the viewports to clear fog.
• Communication once relied entirely on tugs on the lifeline.

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The blue-ringed octopuses of the genus Hapalochlaena are only about five to eight inches long, yet one carries enough venom to kill more than 20 adults. Found from Japan to Australia across the Pacific and Indian Oceans, they live two to three years, hide shyly in shells and rock crevices, and camouflage with pigment cells called chromatophores. When threatened, one turns bright yellow and flashes 50 to 60 iridescent blue rings in about a third of a second. The rings have no pigment cells covering them. Instead, tiny muscles pull skin over the reflective iridophores at rest and relax to expose them as a warning. The venom is not made by the octopus at all: symbiotic bacteria in its posterior salivary gland produce it. In 1978 researchers found that the toxin once called maculotoxin was tetrodotoxin, the pufferfish poison, and this was the first known case of tetrodotoxin used as an injected venom.

Tetrodotoxin jams the sodium channels that carry nerve signals, but the octopus's own channels have mutated so the toxin cannot bind. For humans the bite is often painless. Within five to ten minutes come numbness, nausea, paralysis, and respiratory arrest, while the victim stays fully conscious. No antivenom exists, but the body clears the toxin, so artificial respiration and a ventilator through the first 24 hours usually bring a full recovery. Only around 11 human deaths are documented. The life cycle is short and harsh: a female lays a single clutch of about 50 eggs, broods them under her arms for roughly six months without eating, passes tetrodotoxin into the eggs, and dies after they hatch.

• The blue-lined octopus, Hapalochlaena fasciata, can release tetrodotoxin into the surrounding water without biting.
• Males mate using a modified arm called a hectocotylus and will attempt to mate with males and females alike.
• The IUCN lists the octopuses as least concern, and some species help control the invasive Asian date mussel.
• The octopus appears as a symbol in the 1983 Bond film Octopussy and as a murder weapon in Michael Crichton's State of Fear.
• British zoologist Guy Coburn Robson formally described the genus in 1929.

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For roughly 2,000 years, the ama, or sea women, of Japan have freedived into cold coastal water on a single breath. Hard records place them in the Heian period, when they gathered seaweed, shellfish, sea urchins, and above all abalone, which was presented as a sacred offering to emperors and major shrines. They worked without goggles until the late 19th or early 20th century, finding their catch by touch, and they lost weight every season to the cold. Surfacing, each diver released her breath in a long whistle called the isobue, a controlled exhale that protected her lungs and became the sound of the Japanese coast. Japanese tradition held that women made better divers because of a thicker layer of body fat that delayed hypothermia. They dove in loincloths in some regions until the 1960s, later in white uniforms linked to purity and believed to ward off sharks, and they embroidered their head scarves with a star drawn in one continuous line, the seiman, and a lattice charm, the doman.

Everything changed in 1893, when Mikimoto Kokichi produced a cultured pearl. Pearl farming needed divers who could move and clean oyster baskets on the seafloor, so Mikimoto hired the ama at Mikimoto Pearl Island in Toba, where tourists watched them from observation decks. Fame followed: the 1958 documentary Ama Girls, the sensational 1963 film Violated Paradise, the Bond character Kissy Suzuki in You Only Live Twice, and later the NHK drama Amachan and the series Amanchu. The pearl trade kept the practice alive but put it on display. Around 6,000 ama worked in the 1940s. Today perhaps 60 or 70 remain, with no young women taking up the training that once began at age 12 or 13.

• The isobue whistle prevents a sudden gasp that could cause hyperventilation or uneven pressure equalization.
• The seiman star returns to its starting point, a charm for coming back safely from every dive.
• Hokusai's 1814 woodblock print The Dream of the Fisherman's Wife depicts a young ama with two octopuses.
• Divers visited small coastal shrines after each day's work to give thanks for a safe return.
• Some active ama are still diving in their 70s and even their 90s.

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The name Jolly Roger first appears firmly in Captain Charles Johnson's 1724 A General History of the Pirates, where Bartholomew Roberts and Francis Spriggs both call their quite different flags by it, and neither featured a skull and crossbones. Theories trace it to Old Roger, slang for the devil, to the French jolie rouge for the red flags of privateers, or to roger meaning rogue. Black with a white skull became standard only around 1730. A French log from 1687 describes a red skull and crossbones flag used on land, and Barbary corsairs flew green flags with skulls. Pirates approached under false national colors, then raised the black flag to offer quarter if the target struck its colors, and a red flag, the bloody flag, if it resisted.

Famous designs are later myths: contemporaries describe Blackbeard flying only a simple death's head, and Calico Jack Rackham was flying a white pennant when captured, not crossed cutlasses. A 1959 book by German author Hans Leip helped spread such fictional attributions. In 1914 First Sea Lord Arthur Wilson called submarines damned un-English and wanted their crews hanged as pirates, so Max Horton flew a Jolly Roger from HMS E9 after sinking a German cruiser, starting a tradition of stitching patrol tallies onto the flag.

• Pirates feared no legal limits, while privateers with letters of marque had to accept surrender and take prisoners of war.
• Submarine flags used red bars for warships, white bars for merchant ships, and a dagger for cloak and dagger missions.
• HMS Proteus added a can opener after its diving planes ripped open an Italian destroyer that tried to ram it.
• HMS Conqueror flew a Jolly Roger in the Falklands War, and USS Jimmy Carter has returned to port flying one.
• In 2025 Indonesian truck drivers flew the straw hat flag from One Piece instead of the national flag, and officials called it treason.