steam propulsion

steam propulsion. The aphorism ‘steam gives way to sail’ came out of the marine steam revolution of the 19th century, for steam-powered vessels had a range of speeds and manoeuvrability denied to sailing ships. The International Regulations for Preventing Collisions at Sea, ratified in the 1890s, recognized this new technology and steamships were nearly always required to keep clear of sailing ships. But in all other respects sail gave way to steam, in terms of economies of scale, reliability, speed, and profitability. Coastal and riverine traffic adapted to steam propulsion, but on the high seas the transition was an extended one, with, ironically, sailing ships hastening their demise by carrying coal, and later fuel oil, to bunkering stations throughout the world.

Coal Burners.

Early steamships fuelled by coal were all paddle steamers and they had to carry large amounts of coal, which meant less space for cargo or passengers. The engines were unreliable and had a short steaming range, and this, combined with the innate conservatism of shipowners and navy boards, resulted in ocean-going ships being also rigged for sailing for many decades after they became powered by steam. It was an unsatisfactory combination, and even when steam engines became reliable, ships continued to be built with masts, though, eventually, not the rigging and sails that went with them.

Steam is vaporized water. Its production requires high temperatures and pressures in efficient boilers using fossil or nuclear fuel. Before the last quarter of the 18th century steam machinery had no practical uses afloat, but in the 1780s James Watt did make it more efficient by means of the separate condenser and other improvements. However, it was in France in 1776 that the practical application of steam technology on water was initiated by the French engineer the Marquis de Jouffroy d'Abbans (1751–1832). The American John Fitch (1743–98) was another pioneer and their experiments were followed in the early 1800s with the Clermont and the Charlotte Dundas.

The first transatlantic voyage by a steamship, the Savannah, took place in 1819, but she had to sail most of the way with her collapsible paddle wheels stowed on deck. The voyage was not commercially successful, nor was the one undertaken to India by the Enterprize in 1825, and it was not until 1838 that the Sirius proved a steamship could cross the Atlantic under power. Even so, the inefficiency of the double-acting single cylinder engine was not overcome, by John Elder on the Clyde, until the 1850s. He patented a system of compounding where high-pressure steam at high temperature was expanded in two stages—this was the compound engine. Initially a two-stage expansion, it developed into the ubiquitous triple and quadruple expansion reciprocating engines which dominated the world's fleets for the rest of the 19th century. Compounding, combined with better, higher-pressure boilers, such as the cylindrical Scotch and Yarrow water tube boilers, reduced fuel consumption by at least 60%, allowing profitable passages to be made as far afield as the Far East and Australasia.

With the introduction of the screw propeller, and iron and steel into shipbuilding—large wooden ships were too flexible in a seaway and had difficulty coping with the increased stresses in power transmission—steam propulsion slowly gained the upper hand over sail. However, despite the success of Brunel's Great Britain, both iron construction and propellers were initially treated with some scepticism. To see if the propeller was superior to the paddle wheel, the British Admiralty even arranged a tug-of-war between two same-sized frigates, HMS Rattler (screw) and HMS Alecto (paddle). It took place in 1845 and the former won. Although the relative power of their engines is debatable, it did show the inherent caution with which shipbuilders treated anything new. It was not until the late 1880s, when ocean liners adapted the twin screw, that they ‘at last dared to rely on their engines alone’ ( C. Gibbs , Passenger Liners of the Western World (1952), 101
), and began to discard the heavy masts and spars that were needed to raise sails in an emergency.

Steam-turbine Engine.

Coal was the main fuel for steamships for many years. It was easily available but, besides taking up valuable space, the disposal of the residue of ashes was a perennial problem, and coal stocks had to be maintained at bunkering stations throughout the world. Nevertheless, by the last decade of the 19th century sail had finally given way to coal-burning ships, but it was the appearance of the steam-turbine engine that really heralded a revolution in marine steam propulsion. This is a marine rotary propulsion engine in which a jet of steam is directed onto blades set at an angle in a drum connected either direct or through gearing to the propeller shaft. The action of the steam on the blades revolves the drum and by this means the drive is transmitted to the propellers. In the late 1880s turbine-driven electric generators were fitted in some ocean liners, and a number of designers, such as Curtis in the USA and De Laval in Sweden, were active in this field. However, it is generally acknowledged that the marine turbine engine as we know it today was developed by the British marine engineer the Hon. Charles Parsons (1854–1931). The youngest son of the third Earl of Rosse, he founded the firm of C. A. Parsons at Heaton which produced the first turbo-dynamo machinery for a power station. In 1897 he designed the Turbinia, the first vessel in the world to be powered by steam turbines. She was built specifically to demonstrate this new invention and made her first appearance at the British Naval Review held at Spithead in that year to celebrate the diamond jubilee of Queen Victoria, an international gathering of ships where she was bound to attract the maximum attention and publicity. She had three shafts, each carrying three propellers, and each driven by a turbine, which produced a speed of 31 knots, quite unheard of those days.

The high power to weight–size ratio of the steam turbine compared with the steam reciprocating engine made it popular with the owners of fast ocean liners and ferries, but for cargo ships the tried and trusted steam reciprocating engine remained popular and some triple expansion engined merchant ships were still being built in the 1950s. For warships, the steam turbine was ideal as its low height allowed the machinery to be placed very low in the ship. The major disadvantage of the early steam turbine was its high rotational speed, and not until the development of the geared turbine about fifteen years after Turbinia's run did the turbine find greater popularity. An efficient propeller operates at a speed between about 100 r.p.m. and 150 r.p.m., and only with gearing was the steam-turbine plant able to achieve such low speeds. Although the geared steam turbine was adopted by cargo ship operators as well as passenger ship owners, development of the marine diesel engine at about the same time reduced the impact it might otherwise have had on the marine propulsion field.

Oil Burning.

At about the same time as early steam-turbine engines appeared oil was just beginning to replace coal in steam propulsion. In 1866, Spakowski, in Russia, where the Baku oilfields promised a reliable oil supply, had developed a commercial oil burner for marine use, but the ready availability of coal supplies and the relative lack of oil stifled its adoption. However, as oil production increased, Britain and America began to use it instead of coal. In 1905 Royal Navy trials showed a distinct advantage in oil-fired warship boilers and in 1913 the Royal Navy started to convert all its warships to oil firing. After the First World War (1914–18) oil fuel was available at many bunker stations worldwide and the conversion of merchant ships, particularly the large ocean liners, became an economic proposition. Not only was oil cleaner than coal, it could be stored in double bottoms, and so save space within the ship. It also required fewer people. The liner Mauretania was converted to oil burning in 1922. This reduced the engine-room staff from 366 men to 79 and the fuel consumption fell from 1,000 tons of coal per day to 620 tons of oil. In 1914 coal burners comprised 89% of steamships, but by the 1920s oil-fired boilers had taken over as the main method of steam propulsion and of the new tonnage being built approximately 75% was oil fired and 25% coal burning.

Like modern diesel engines, oil-fired boilers burn residual fuel oil which must be heated before it can be pumped. But the fact that it can be pumped makes transportation between the storage tanks and the boilers much simpler than the movement of coal. At a boiler burner the heated fuel oil is sprayed into the furnace in fine droplets which will burn easily; the air supply is regulated by dampers in order to obtain good combustion of the oil. It is possible to vary the amount of oil sprayed into the furnace at any time in order to control the rate of steam generation; this is referred to as the ‘turn down ratio’ of the burner. An oil burner has a minimum flow below which it will not spray effectively and if a lower firing rate is required the burner has to be shut down. When firing is again required the fireman needs to ignite the burner manually. Automatically controlled boiler systems appeared in the 1960s and these allowed for the firing and ignition systems to be operated automatically, thus resulting in fewer firemen having to operate the boiler.

Nuclear Power.

The most modern form of ship propulsion by steam is that produced by a nuclear reactor. The first reactor-powered submarine, the USS Nautilus, was launched in 1955, and nuclear-powered surface vessels such as cruisers, ice-breakers, and aircraft carriers are now also in service. However, the commercial use of nuclear fuel in merchant ships has not been successful. The American Savannah, the German Otto Hahn, the Japanese Mutsu, and the Russian Sevmorput were all dogged by technical, political, and economic problems and have either been withdrawn or converted to diesel propulsion.

Steam machinery was behind the Industrial Revolution; marine applications over the past 200 years have powered a revolution in efficient transportation. Today, the largest man-made moving object, the tanker Jahre Viking, 564,650 deadweight tonnage, is powered by four Stal-Laval geared steam turbines producing 265,000 shaft horsepower.

See also gas turbine engine; ‘up funnel, down screw’.

Bibliography

Craig, R. , The Ship: Steam Tramps and Cargo Liners 1850–1950 (1986).
Gardiner, R. (ed.), The Advent of Steam (1995).
Jane's Fighting Ships (2002).
Padfield, P. , The Battleship Era (1975).

Martin Lee/ and Denis Griffiths