Post by director on Sept 3, 2018 2:34:12 GMT -6
Ships designed and constructed in the period from 1900 to 1950 can be classified by their propulsion systems. Broadly, there are five:
1) Reciprocating engines, culminating in triple-expansion piston engines. These were efficient at low speeds but unable to sustain high speeds for long periods due to vibration and wear of many moving parts. Many ships reported heavy vibration at high speed causing issues rising to the level of metal fatigue.
2) Early 'direct' steam turbines, as were fitted on 'Turbinia', 'Dreadnought' and many other ships. Here the turbine shaft was directly coupled to the propellers, with resulting low efficiency and high cavitation but high speed. On common method was to put multiple propellors on a shaft. Vibration did not disappear with turbine drive: a number of large, fast turbine-powered liners had their sterns reconstructed because of heavy vibration at high speeds, but this seems to have not been caused by the turbines themselves.
3) Geared turbines. A later refinement of the steam turbine plant, the turbine drive shaft is coupled to the propellers through a gearbox that transfers the high turbine speed to a slower propeller speed, reducing cavitation and improving efficiency. The drawback is that the gears must be precisely machined and this adds to the expense and weight of the plant.
4) Electric drive. Usually configured as a turbine driving generators to produce direct current which is then fed to DC motors, but can be driven by diesel engines as in later submarines. The advantages are many: the elimination of long propeller shafts, the ability to better divide the boiler and turbo-generator and engine spaces, the ability to almost instantly slow, stop or reverse an engine, and good fuel efficiency, as the turbines or diesels can run steadily at their most efficient speed, independent of propeller speed. The chief drawback is weight and space - electric drive is somewhat heavier and larger than a geared turbine plant, but in a submarine application the diesel-electric drive can charge the batteries and drive the boat at the same time.
5) Combustion engines, chiefly diesel. This propulsion plant is heavy and smoky, and it is difficult to achieve high horsepower, large size or rapid acceleration but it does offer very good fuel economy at cruising speeds. This type of propulsion was slow to come into service because of the difficulty of designing and manufacturing really large diesel engines. Broadly speaking only Germany mastered the techniques; for example, the successful diesel engines used in US submarines in WW2 were licensed from German designs. Proposed diesel full or partial propulsion for large German battleships (Bismarck and later) failed because building the extremely large diesels requested was not feasible and too much room and space would have had to be provided if many small engines were used.
This development was neither smooth nor straightforward: RMS Titanic used both reciprocating and a turbine engine. The USS Nevada was equipped with geared turbines while her sister Oklahoma was given reciprocating engines in order to test out the merits of each; the Oklahoma's triple-expansion engines did produce slightly less horsepower and speed. US warships were alone in adopting turbo-electric drive, although I believe design studies were done in other navies for turbo-electric or diesel-electric drive systems.
The second area of propulsion engineering worthy of study is the production of steam, via coal or oil-firing, during the increase in working pressure from less than 100psi to WW2-standard pressures of 600psi and higher.
1)Coal firing was a mature technology by 1900, coal was readily available in Great Britain, Germany and the US, and its working was well understood. The disadvantages, however were many: large crew size needed for stoking and moving coal, the certainty of smouldering coal-fires in bunkers, the problem of ash removal, the heavy production of smoke. Compared to oil, burning coal gives off relatively little energy and so enormous quantities are consumed - three tons an hour at cruising speed was not uncommon for a pre-dreadnought. Thus, for a coal-fired ship, cruising ranges were short and the all-hands work of coaling ship is almost constant.
For HMS Queen, pre-dreadnought of 1901, according to Jane's: coal 900 tons, working pressure 300psi, heating surface 38,400 sq feet, coal consumption 9 tons per hour at 15 knots, 12-14 tons per hour at 18 knots. That's 100 hours of steaming at 15 knots, with no reserve.
2) Oil firing began to be introduced before WW1 but it had its own set of problems. Where coal was relatively abundant, oil was initially scarce. Methods had to be worked out for keeping the bunkers heated so that the thick sludgy bunker-grade oil could flow, and issues arose from fumes, which had to be safely vented. (At least one US battleship had a serious fire or explosion from this but I've lost the reference as to which - I think it was a USNI article). Despite this, oil was immediately seen as the fuel of the future: its use required fewer crew, permitted continuous use of high speed and enabled ships to steam much farther on the same tonnage of fuel and so was adopted for all new construction after WW1, with older ships being retrofitted for oil fuel.
Article on moving from coal to oil: www.dtic.mil/dtic/tr/fulltext/u2/a524799.pdf
3) Working pressures steadily increased, since more work could be extracted from higher-pressure steam; from 1900 to 1939 the working pressure doubled, tripled or quadrupled from 300 to as much as 1200 psi. This did not go smoothly; German warships in WW2 (for one example) were constantly working out issues with their steam plants and other navies had similar teething problems. This of course required better design, better and more consistent metallurgy and made repair hazardous - superheated steam of 450 degrees and 600+ PSI is extremely dangerous.
I've rambled on a good bit - mostly wanted to raise some points for discussion and to point out that propulsion engineering was not a smooth, straightforward series of gradual improvements.
1) Reciprocating engines, culminating in triple-expansion piston engines. These were efficient at low speeds but unable to sustain high speeds for long periods due to vibration and wear of many moving parts. Many ships reported heavy vibration at high speed causing issues rising to the level of metal fatigue.
2) Early 'direct' steam turbines, as were fitted on 'Turbinia', 'Dreadnought' and many other ships. Here the turbine shaft was directly coupled to the propellers, with resulting low efficiency and high cavitation but high speed. On common method was to put multiple propellors on a shaft. Vibration did not disappear with turbine drive: a number of large, fast turbine-powered liners had their sterns reconstructed because of heavy vibration at high speeds, but this seems to have not been caused by the turbines themselves.
3) Geared turbines. A later refinement of the steam turbine plant, the turbine drive shaft is coupled to the propellers through a gearbox that transfers the high turbine speed to a slower propeller speed, reducing cavitation and improving efficiency. The drawback is that the gears must be precisely machined and this adds to the expense and weight of the plant.
4) Electric drive. Usually configured as a turbine driving generators to produce direct current which is then fed to DC motors, but can be driven by diesel engines as in later submarines. The advantages are many: the elimination of long propeller shafts, the ability to better divide the boiler and turbo-generator and engine spaces, the ability to almost instantly slow, stop or reverse an engine, and good fuel efficiency, as the turbines or diesels can run steadily at their most efficient speed, independent of propeller speed. The chief drawback is weight and space - electric drive is somewhat heavier and larger than a geared turbine plant, but in a submarine application the diesel-electric drive can charge the batteries and drive the boat at the same time.
5) Combustion engines, chiefly diesel. This propulsion plant is heavy and smoky, and it is difficult to achieve high horsepower, large size or rapid acceleration but it does offer very good fuel economy at cruising speeds. This type of propulsion was slow to come into service because of the difficulty of designing and manufacturing really large diesel engines. Broadly speaking only Germany mastered the techniques; for example, the successful diesel engines used in US submarines in WW2 were licensed from German designs. Proposed diesel full or partial propulsion for large German battleships (Bismarck and later) failed because building the extremely large diesels requested was not feasible and too much room and space would have had to be provided if many small engines were used.
This development was neither smooth nor straightforward: RMS Titanic used both reciprocating and a turbine engine. The USS Nevada was equipped with geared turbines while her sister Oklahoma was given reciprocating engines in order to test out the merits of each; the Oklahoma's triple-expansion engines did produce slightly less horsepower and speed. US warships were alone in adopting turbo-electric drive, although I believe design studies were done in other navies for turbo-electric or diesel-electric drive systems.
The second area of propulsion engineering worthy of study is the production of steam, via coal or oil-firing, during the increase in working pressure from less than 100psi to WW2-standard pressures of 600psi and higher.
1)Coal firing was a mature technology by 1900, coal was readily available in Great Britain, Germany and the US, and its working was well understood. The disadvantages, however were many: large crew size needed for stoking and moving coal, the certainty of smouldering coal-fires in bunkers, the problem of ash removal, the heavy production of smoke. Compared to oil, burning coal gives off relatively little energy and so enormous quantities are consumed - three tons an hour at cruising speed was not uncommon for a pre-dreadnought. Thus, for a coal-fired ship, cruising ranges were short and the all-hands work of coaling ship is almost constant.
For HMS Queen, pre-dreadnought of 1901, according to Jane's: coal 900 tons, working pressure 300psi, heating surface 38,400 sq feet, coal consumption 9 tons per hour at 15 knots, 12-14 tons per hour at 18 knots. That's 100 hours of steaming at 15 knots, with no reserve.
2) Oil firing began to be introduced before WW1 but it had its own set of problems. Where coal was relatively abundant, oil was initially scarce. Methods had to be worked out for keeping the bunkers heated so that the thick sludgy bunker-grade oil could flow, and issues arose from fumes, which had to be safely vented. (At least one US battleship had a serious fire or explosion from this but I've lost the reference as to which - I think it was a USNI article). Despite this, oil was immediately seen as the fuel of the future: its use required fewer crew, permitted continuous use of high speed and enabled ships to steam much farther on the same tonnage of fuel and so was adopted for all new construction after WW1, with older ships being retrofitted for oil fuel.
Article on moving from coal to oil: www.dtic.mil/dtic/tr/fulltext/u2/a524799.pdf
3) Working pressures steadily increased, since more work could be extracted from higher-pressure steam; from 1900 to 1939 the working pressure doubled, tripled or quadrupled from 300 to as much as 1200 psi. This did not go smoothly; German warships in WW2 (for one example) were constantly working out issues with their steam plants and other navies had similar teething problems. This of course required better design, better and more consistent metallurgy and made repair hazardous - superheated steam of 450 degrees and 600+ PSI is extremely dangerous.
I've rambled on a good bit - mostly wanted to raise some points for discussion and to point out that propulsion engineering was not a smooth, straightforward series of gradual improvements.
