Iron men and wooden ships was the mantra of the age of sail.
(Over Christmas and New Year’s weeks, it seems appropriate to shift gears and review how ships’ propulsion systems have evolved historically, using differing forms of energy.)
Conditions on sailing ships were unimaginable for those living today.
It was not uncommon for crewmen to climb ratlines to 100 feet or more above the deck of a ship rolling 10 or 15 degrees, then, swaying back and forth above the deck and ocean, with sleet hurled relentlessly into their faces, using bare and freezing hands to haul in sails to slow a ship struggling in gale force winds.
Even on calmer days, there was always danger lurking with every step. Certainly there was constant backbreaking work. Sea shanties were sung by the crew so they could work in unison as they bent over, with feet braced against the deck, to haul in lines.
The advent of steam, using coal was a godsend to the average crewman.
Sail slowly disappeared from commercial traffic.
The last grain race, where a sailing ship carried grain between Europe and Australia, was in 19381.
Early steam ships used fire-tube boilers and triple expansion reciprocating steam engines. Coal was shoveled into the boiler’s fire box, and the heat from the burning coal traversed through the boiler’s tubes, bringing the water surrounding the tubes to a boil, generating steam that was fed to a triple expansion steam engine.
This was hot, back-breaking work, but far safer than climbing the rigging of sailing ships.
Coal also required establishing coaling stations around the world, where ships could replenish their supplies of coal. The coaling operation, which lasted for two or three days, often required crew members to carry the coal onto the ship where it could be loaded into coal bins.
The Royal Navy, the predominant navy leading to WW I, was limited in its ability to move quickly to counter threats from China to the Falklands, and to the North Sea2. The American navy was also encumbered in like manner.
Churchill forced the Royal Navy to convert to oil, a far more flexible fuel, where replenishing could be done far more expeditiously. The fleet could be supplied with oil in port or while at sea, using underway replenishment.
Converting to oil was a risky undertaking as all of the UK’s oil came from British oil companies working in Iran and Iraq.
Around the same time, water tube boilers were introduced. Oil could be atomized and blown into the firebox, with the heat from the burning oil rising to very high temperatures, causing the water circulating in tubes around and over the firebox to be converted to steam, with the steam then heated again to become super heated.
Steam turbines were introduced to replace the triple expansion reciprocated engines.
While the reciprocating engines rotated at around 80 revolutions per minute (rpm), the steam turbines rotated at 3,600 rpm which required adding huge reduction gears, referred to as Bull Gears, to reduce the rotation to around 100 rpm. The slower rpm was required to allow propellers to operate efficiently. Propellers that rotated too quickly caused cavitation, where the spinning propeller created vacuum bubbles that reduced the propeller’s efficiency, and which, when they collapsed, would eat into the propeller.
Steam turbines with water tube boilers were fairly standard by the outbreak of WWII, but shortages of turbines and the ability to produce large reduction gears necessitated using triple expansion reciprocating engines once again, so that nearly all the Liberty Ships built during the war used triple expansion engines.
Some alternative methods of propulsion were also used.
The T-2 tanker used electric propulsion, where the steam from water tube boilers drove turbine generators that produced electricity for powering motors that, in turn, drove the propellers.
Electric propulsion was also used to power submarines during WWII, with batteries which could be recharged using diesel generators.
Several innovations in ship’s propulsion emerged after WW II.
Continued in Part 2
- The book, Grain Race, by Alan Villiers tells the story of one of the last sailing ships to carry grain between Europe and Australia.
- Castles of Steel, by Massie, describes the British navy during WWI, its battles and, initially, its dependence on coal.
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