Steamship

• 1. Introduction

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  A steamship has been described as a "major driver of the first wave of trade globalization (1870-1913)" and a contributor to "an increase in international trade that was unprecedented in human history". That is a large claim for a vessel that began as a clumsy contraption thrashing a paddle through the water. A steamship, often called a steamer, is an ocean-faring vessel driven by one or more steam engines, turning either propellers or paddlewheels. The first ones came into practical use during the early 19th century, though a few exceptions came before. How did a machine tied to a boiler and a heap of coal break the grip of the wind on the sea? Why does the prefix "SS" mislead so many people about what it means? And what allowed a ship to finally carry both enough coal and enough cargo to reach the Far East? The answers run from a French inventor to a British engineer obsessed with the geometry of hulls.

• 2. Paddle To Screw

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  Paddlewheels became the standard motive source on early steam vessels, and they worked well only under ideal conditions. The paddle-wheel performed best at a certain depth. When added weight pushed the ship lower, the wheel submerged further and performance dropped sharply. The change from paddle-wheel to screw-propeller was the key innovation that made ocean-going steamers viable. A propeller's efficiency stayed consistent no matter how deep it sat, and being smaller, fully submerged, and lighter, it was far less prone to damage. James Watt of Scotland is widely credited with applying the first screw propeller to an engine at his Birmingham works, beginning the use of a hydrodynamic screw for propulsion. Built in Britain in 1839 by Francis Pettit Smith, the first screw propeller-driven steamship for open-water seagoing pushed ship development forward. It encouraged the Royal Navy to adopt screw propulsion and shaped commercial vessels too. In America, the first screw-driven propeller steamship arrived on a ship built by Thomas Clyde in 1844, and many more ships and routes followed.

• 3. Engineering The Shaft

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  Screw propulsion delivered power along a shaft, and that single fact forced a chain of inventions before it could work at sea. Steam engines had to be redesigned so power was delivered at the bottom of the machinery, giving direct drive to the propeller shaft. A paddle steamer's engine drove a shaft above the waterline, with the cylinders below. One late design change to propeller propulsion even used chain drive to transmit power from a paddler's engine to the propeller shaft. An effective stern tube and its bearings were the next hurdle. The stern tube carries the propeller shaft where it passes through the hull, and it must deliver power without flexing that would bend the shaft or wear it unevenly. Its inboard end has a stuffing box to keep water out. Early stern tubes were sometimes made of brass acting as a water-lubricated bearing, or fitted with a long bush of soft metal. One ship suffered very large amounts of uneven wear on its first transatlantic voyage. The fix was a lignum vitae water-lubricated bearing, patented in 1858, which became standard practice and is still in use today. A thrust bearing was also needed to transfer the shaft's load to the hull without excessive friction. One arrangement used a 2 ft diameter gunmetal plate bearing against a steel plate on the engine beds, with water at 200 psi injected to lubricate and separate them. That was not enough for higher powers. Oil-lubricated "collar" thrust bearings became standard from the early 1850s, then gave way at the start of the 20th century to floating pad bearings that built up wedges of oil able to withstand 500 psi or more.

• 4. Crossing The Atlantic

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  The first steamship credited with crossing the Atlantic between North America and Europe was an American ship, though she was a hybrid of steamer and sailing ship, using her engine only for the first half of the voyage. Savannah left the port of Savannah, Georgia, on the 22nd of May 1819 and arrived in Liverpool, England, on the 20th of June 1819, her steam engine running on parts of 18 days, with estimates of total use ranging from 8 to 80 hours. A rival claimant to the first crossing made substantially under steam is the British-built, Dutch-owned Curacao, a wooden 438-ton vessel built in Dover and powered by two 50 hp engines. She crossed from Hellevoetsluis, near Rotterdam, on the 26th of April 1827 to Paramaribo, Surinam, on the 24th of May, spending 11 days under steam on the way out and more on the return. Another claimant is a Canadian ship in 1833. Before any of these Atlantic crossings, the first sea-going steamboat was Richard Wright's Experiment, an ex-French lugger that steamed from Leeds to Yarmouth in July 1813. The first iron steamship to go to sea was the 116-ton Aaron Manby, built in 1821 by Aaron Manby at the Horseley Ironworks. She crossed the English Channel in 1822, arriving in Paris on the 22nd of June, carrying passengers and freight at an average speed of 8 kn.

• 5. Brunel's Giants

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  Isambard Kingdom Brunel understood a principle his critics missed: the carrying capacity of a hull increases as the cube of its dimensions, while water resistance increases only as the square. Larger ships were therefore more fuel efficient, which mattered enormously across the Atlantic. In 1836 Brunel and a group of Bristol investors formed the Great Western Steamship Company to build steamers for the Bristol-New York route. The first steamship purpose-built for regularly scheduled trans-Atlantic crossings was his British side-wheel paddle steamer, starting in 1838, inaugurating the era of the trans-Atlantic ocean liner. Great Western was an iron-strapped, wooden, side-wheel paddle steamer with four masts for auxiliary sails. Those sails also kept the ship on an even keel in rough seas so both paddle wheels stayed in the water. Built at the shipyard of Patterson & Mercer in Bristol, she was launched on the 19th of July 1837, then fitted in London with two side-lever engines from Maudslay, Sons & Field producing 750 indicated horsepower. She was the largest steamship for one year, until the British and American's British Queen entered service. In 1845 came another Brunel vessel, the first iron-hulled screw-driven ship to cross the Atlantic, and the first to combine those two innovations. Brunel had inspected John Laird's 213 ft iron-hulled channel packet Rainbow in 1838 and was soon converted to iron. He scrapped his wooden-ship plans, persuaded by iron's lower cost, immunity to dry rot and woodworm, and far greater structural strength. A wooden hull's practical limit is about 300 feet before hogging, the flexing of the hull as waves pass beneath it, becomes too great. In spring 1840 he inspected the first screw-propelled steamship, completed only months earlier by F. P. Smith's Propeller Steamship Company. Smith lent Archimedes to Brunel for extended tests, and over several months they tried many propellers, settling on a four-bladed model submitted by Smith. When launched in 1843, SS Great Britain was by far the largest vessel afloat. Brunel's last major project, built in 1854-1857, was meant to link Great Britain with India via the Cape of Good Hope without any coaling stops. She had a double hull with watertight compartments, was the first liner with four funnels, and remained the biggest liner for the rest of the 19th century at almost 20,000 gross tons, with capacity for thousands of passengers. She never served her intended purpose.

• 6. Reaching The Far East

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  The most testing route for steam ran from Britain or the U.S. East Coast to the Far East, a distance of roughly 14000 to 15000 nmi down the Atlantic, around the southern tip of Africa, and across the Indian Ocean. Before 1866, no steamship could carry enough coal for this voyage and still leave room for commercial cargo. The Peninsular and Oriental Steam Navigation Company adopted a partial solution, using an overland section between Alexandria and Suez with steamship routes along the Mediterranean and through the Red Sea. For most China-to-Europe trade, especially tea carried in clippers, sail remained the only option. The Steam Auxiliary Ship was another partial answer, a steam vessel also rigged for sail, using its engine only in light or contrary winds. Some, such as Erl King, had propellers that could be lifted clear of the water to cut drag under sail. These ships struggled toward China, where standing rigging became a handicap when steaming into a head wind, most notably against the southwest monsoon when returning with new tea. It was Erl King that carried the first cargo of tea through the Suez Canal. What was really needed was a leap in fuel efficiency. The Board of Trade, under the Merchant Shipping Act 1854, would not allow ships to exceed 20 or 25 psi, which kept the efficient compound engine off the sea. Carnatic, a P&O ship of 1863, ran a compound engine at 26 psi with heavy superheat and beat other ships of its time. Alfred Holt, who came to marine engineering after a railway apprenticeship, experimented with 60 psi boilers in Cleator. He persuaded the Board of Trade to permit such pressures and, with his brother Phillip, launched Agamemnon in 1865. Holt's compact compound engine and carefully designed light, strong hull let her steam at 10 knots on 20 long tons of coal a day, a saving of between 23 and 14 long tons a day over rivals. Fewer firemen and less coal cut crew costs and accommodation space. Agamemnon reached China from London with a single coaling stop at Mauritius each way, faster than competing sailing vessels. By the time she returned from her first China trip in 1866, Holt had already ordered two sister ships for his new Blue Funnel Line, and competitors quickly copied him. The opening of the Suez Canal in 1869 cut about 3250 nmi off the China-to-London route. The canal was impractical for sailing vessels, since towing was difficult and expensive, so the saving belonged to steamers. They were in high demand for the 1870 tea season, commanding higher freight rates and lower insurance premiums. So successful were they that in 1871-45 ships were built in Clyde shipyards alone for Far Eastern trade.

• 7. Triple Expansion Triumph

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  John Elder established the theory of the triple expansion engine in the 1850s, but it demanded steam at very high pressures that boilers of the day could not safely deliver. In this engine, steam expanded successively through a high pressure, an intermediate pressure, and a low pressure cylinder, wringing out the inefficiencies that still dogged the two-cylinder compound. Wrought iron lacked the strength for higher pressures. Steel became available in larger quantities in the 1870s, but its quality was variable. The first ship fitted with triple expansion engines was Propontis, launched in 1874, with boilers meant to run at 150 psi. Technical problems forced their replacement with boilers running at 90 psi, badly degrading performance. The breakthrough came when Aberdeen entered service on the route from Britain to Australia. Her triple expansion engine was designed by Dr A C Kirk, the same engineer behind Propontis, but this time paired with two double-ended Scotch-type steel boilers running at 125 psi. Their patent corrugated furnaces balanced heat transfer against the strength needed for the pressure. In trials at 1,800 indicated horsepower, Aberdeen burned 1.28 lb of coal per indicated horsepower, a cut of about 60% compared with a typical steamer of ten years earlier. In service she used less than 40 tons of coal a day at 13 kn, and her maiden voyage to Melbourne took 42 days with one coaling stop, carrying 4,000 tons of cargo. By 1885 the usual boiler pressure was 150 psi, and nearly every ocean-going steamship was ordered with triple expansion engines, with new installations soon running at 200 psi. Tramp steamers at the end of the 1880s could make 9 kn on 0.5 oz of coal per ton mile. In 1890, steamers made up 57% of the world's tonnage, and by World War I their share rose to 93%.

• 8. Turbines And Decline

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  Charles Parsons demonstrated his steam turbine-driven yacht Turbinia in 1897, and the use of steam turbines for propulsion spread quickly afterward. The Cunard RMS Mauretania, built in 1906, was among the first ocean liners to use the steam turbine, adopted through a late design change shortly before her keel was laid, and all subsequent liners followed. The era of the ocean liner had already taken shape. By 1870 the White Star Line set a new standard by placing first-class cabins amidships with large portholes, electricity, and running water, and liner sizes grew from 1880 to carry migrants to the United States and Australia. Launched in 1938, the largest passenger steamship ever built marked the height of the form. Queen Elizabeth 2, launched in 1969, was the last passenger steamship to cross the Atlantic on a scheduled liner voyage before her conversion to diesels in 1986. The last major passenger ship built with steam turbines was Fairsky, launched in 1984 and later renamed Atlantic Star, reportedly sold to Turkish shipbreakers in 2013. The decline set in after the early 1950s, when steamers still held about 73% of world tonnage. Many had been lost in the war, and the marine diesel engine had matured into a cheaper, more space-efficient rival with far better thermal efficiency and far less need for supervision, boilers, or a water supply. The Liberty Ships were the last major steamship class with reciprocating engines, while the later Victory ships already carried marine diesels. No commercial ocean-going steamers with reciprocating engines have been built since the 1960s. Steam did not vanish entirely. Most steamships today are powered by steam turbines, and nuclear-powered ships are essentially steam turbine vessels whose boilers are heated by a reactor rather than combustion. LNG carriers kept turbines alive by burning boil-off gas from the cargo tanks, though dual-fuel engines pushed turbines to about a 10% share of newbuildings in 2013. The newest class of steam turbine ships, the Seri Camellia-class LNG carriers, were built by Hyundai Heavy Industries starting in 2016 and comprise five units.