With appreciation to Reese Library for carrying this copy,
and the Internet Archive and Microsoft for making this version available.
I. History and Progress or Marine Engineering ... 1
including:II. Work and Efficiency ... 19
Defects of paddle-wheels
Adoption of the screw propeller
Return connecting-rod engines.
Compound or double expansion engines.
Vertical (compound) engines.
Three-cylinder compound engines
Triple expansion engines.
Quadruple expansion engines.
III. Heat and Its Effect on Water ... 22
IV. Combustion and Economy of Fuel - Boiler Efficiency ... 32
V. Methods of Accelerating the Rate of Combustion of Fuel ... 45
VI. Petroleum as Fuel ... 53
VII. Arrangement and Efficiency of Boilers Water Tank Boilers (excerpts) ... 57
Marine locomotive boilers.
VIII. Water-Tube or Tubulous Boilers (excerpts) ... 74
Babcock & Wilcox
IX. Boiler Mountings and Boiler-Room Fittings ... 100
X. Corrosion and Preservation of Boilers ... 127
XI. Efficiency of the Steam ... 184
XII. Expansion of Steam ... 139
XIII. Methods of Increasing the Expansive Efficiency of Steam ... 155
XIV. Compound Or Stage Expansion Engines ... 162
XV. Regulating and Expansion Valves and Gear ... 166
XVI. Slide-Valves and Fittings ... 172
XVII. Starting and Reversing Arrangements ... 197
XVIII. Arrangement of the Cylinders of Compound, Triple, and Quadruple Expansion Engines ... 212
XIX. Details of Cylinders and Engine-Room Fittings in Connection ... 225
XX. Condensers, Feed-Water Fittings, and Under- Water Valves ... 244
XXI. Rotary Motion (steam turbine addition only) ... 268
including Parsons' marine steam turbine.
XXII. Propulsion ... 287
XXIII. Co-efficients and Curves of Performance ... 301
XXIV. Paddle-Wheels ... 309
XXV. Screw-Propellers ... 315
XXVI. The Indicator and Indicator Diagrams ... 334
XXVII. Pumping, Watertight, and Fire Arrangements ... 362
XXVIII. Auxiliary Machinery and Fittings ... 372 XXIX. Raising Steam and Getting Under Way ... 416
XXX. Management of Engines Under Way - Engine and Boiler Defects ... 428
XXXI. Engines Done With - Examinations, Adjustments, and General Information ... 444
XXXII. Materials Used in Construction ... 450
XXXIII. Theoretical Indicator Diagrams of Stage Expansion Engines ... 459
(A) Application of the Indicator Diagram to Determine the Stresses on Crank- Shafts. Curves of Twisting Moments ... 483
(B) Effect of the Inertia of the Reciprocating Parts of the Engines ... 485
(C) Extracts from the Board of Trade Rules relating to Machinery and Boilers ... 491
(D) Lloyd's Rules for Boilers and Machinery ... 502
To the many who knew the late Richard Bennett, my old friend and predecessor in office, and appreciated his work and worth, and regretted the all too early closing of his brilliant career, it will be a source of gratification that the revision of this book has been undertaken by so capable a marine engineer as Inspector of Machinery H. J. Oram, R.N.
Mr. Oram has acquired a vast amount of special knowledge and experience of marine machinery of the latest types, and it is believed this has been incorporated in the present edition in a manner that will make it of great value to students, young engineers, and officers of the Royal and Mercantile Navies in carrying on their studies and duties.
A. J. Durston,
Engineer-in-Chief of H.M. Navy.
This work, originally written by the late Mr. Richard Sennett, was never revised, owing at first to the pressure of his official duties, and subsequently by reason of his death, so that it had become obsolete, on account of the very great changes which have taken place in marine engineering, more especially in the naval machinery with which it originally dealt.
When considering the preparation either of an independent new work or the thorough revision and modernisation of the old one, the latter course was chosen, as there appeared to be features in the work and its arrangement which offered advantages over others of its kind, although this course has involved practically rewriting it.
The style and arrangement have, however, been preserved, and the result appears in the present volume as a practically new book, which it is hoped will be of service to students of engineering, and enjoy a measure of popularity equal to that received and so well deserved by the original work.
The amount of printed matter and also the number of illustrations have been considerably increased, as in the writer's opinion ample illustration is essential to the proper understanding of written descriptions of engineering details. The illustrations have generally been specially prepared for the work, and alteration of type and size of page have been made to keep the book within convenient size, owing to the increased contents.
These illustrations and the subject matter have also been made more general in character, and been drawn from the practice of the most successful makers of mercantile marine, as well as naval, machinery. The fact may be noted that during recent years there has been, as regards the engines of large vessels, a much nearer approximation to identity in mercantile and naval practice than was usual previously, showing that valuable features have been mutually borrowed.
The growing importance of water-tube boilers has caused this subject to be dealt with at considerable length, and this part of the book exemplifies the great changes that have taken place since the work was first published. It may be observed in passing, as indicating the national importance of this section, that in the Royal Navy there are now about 1,000,000 I.H.P. of water-tube boilers, either built, building, or about to be commenced.
A new feature is the detailed description of the care and management of, and the treatment of defects in, marine engines and boilers, which it is expected will be found of value to students of engineering and young engineers. It is not pretended, however, that this part of the duties of engineers can be adequately learnt from books, for actual experience in the engine rooms will alone completely supply the requisite instruction. What is given will, however, prepare young engineers for such experience, and give information on points which they are at first more or less unacquainted with.
In the preparation of a work of this kind, one becomes indebted to many friends for assistance of various kinds, and to these I tender my best thanks, especially to Mr. P. Marrack, R.N., Engineer Inspector, Admiralty, who has kindly read over most of the proof sheets.
H. J. Oram.
THE MARINE STEAM-ENGINE.
HISTORY AND PROGRESS.
THE earliest steam engines were simply reciprocating engines, and for many purposes such engines are still used even at the present day. Until, however, a suitable method of turning reciprocating into rotative motion had been discovered and utilised not any progress was made in adapting the steam-engine to the propulsion of vessels. The adoption of the crank effected this desirable object, enabled the power of the engine to be transmitted to the propeller smoothly and without shock, and was an indispensable step in the progress of steam navigation.
The marine steam-engine may justly be considered as a production of the present century. In the latter part of the eighteenth century several attempts were made to adapt the steam-engine for the propulsion of boats, but none of them were quite successful.
The first practical steamboat was built on the Clyde, in 1801, by William Symington, for Lord Dundas. She was called the "Charlotte Dundas," and was worked for some time with success as a tug on the Forth and Clyde Canal, but was withdrawn from this service in consequence of an apprehension that the banks of the canal would suffer from the wash of the propeller. This boat was fitted with a single paddle-wheel placed near the stern, driven by a horizontal direct-acting engine, with connecting-rod and crank, and the general arrangement of her machinery would be considered creditable even at the present day.
The first recorded instance of steam navigation proving commercially successful was in America, where, in 1807, Robert Fulton built a steam vessel called the 'Clermont,' propelled by paddles driven by a Boulton & Watt engine. In 1812 Henry Bell built a vessel called the 'Comet,' (built for Henry Bell by John Wood & Co (Wikipedia)) which was successfully worked on the Clyde as a passenger steamer between Glasgow and Greenock. The 'Comet' was propelled by two pairs of paddles, each paddle having four floats or blades, somewhat resembling a pair of canoe paddles, crossed at right angles. The paddles were driven by an engine of somewhat peculiar design, which, however, approximated to the side-lever engine of a later day. This small boat was the first passenger steamer in Europe.
From this date the success of steam navigation may be said to have been secured, and the advancement that has been made since has not consisted so much in the discovery of new principles as in the extension of old ones, and the introduction and development of improved mechanism and workmanship, with consequent economy of fuel. The result has been a progressive increase in the size, power, and speed of steamships and in the extent of their voyages; so that at the present day we have ships displacing 19,500 tons, and capable of being driven at a speed of 22 knots by engines developing more than 30,000 indicated horse-power, while even larger vessels are under construction.
The propeller used in the earlier steamships was invariably the paddle-wheel, and the type of engine existing and giving satisfaction on land was naturally adapted at first to rotate these paddle-wheels. Almost all these early engines were, therefore, of the beam type. In America the beam was generally placed over the crank, while in this country it was placed below the crank. The latter type of engine was known as the side-lever engine.
The general arrangement of the side-lever engine is shown in outline in Fig. 1, and it represents the type usually fitted not only in the first steam vessels, but also for some years after.
Figure 1 - Side-lever Engine (example - machinery weight, 13.75 cwts. per I.H.P.)
On the top of the piston-rod is fixed a crosshead with side-rods, S, attached at each end, which, passing down on either side of the cylinder, are connected to the ends, A, of a beam or side-lever, A B, oscillating on a fulcrum or gudgeon at its centre, C.
The opposite ends, B, of these side-levers are fitted with journals carrying the crosstail, to the centre of which, one end of the connecting-rod B D is attached, the other end working on the crankpin D.
The air-pump E is worked by side-rods from intermediate points in the side-levers, the upper ends of the air-pump side-rods being jointed to the opposite ends of the air-pump crosshead, to the centre of which the air-pump rod is secured.
The piston-rod crosshead works in vertical guides to insure parallelism, and the parallel-motion rods used in land beam engines are dispensed with.
The arrangement of the side-levers was sometimes varied by making them levers of the third order, the gudgeon or fulcrum being at one end and the steam cylinder placed between the gudgeon and connecting-rod. These engines were commonly known as grasshopper engines.
The side-lever type of engine, though very heavy and occupying a large space for the power developed, was safe and reliable, securing a sufficient length of connecting-rod, and having its moving parts practically in equillbrium. It consequently continued in general use for a great number of years, but was at length superseded by the direct-acting type, which was lighter and more compact.
Introduction of steam war vessels.
Steam vessels were introduced into the Royal Navy in the year 1820, when the 'Monkey,' a vessel of 210 tons, was built at Rotherhithe and fitted by Messrs. Boulton & Watt with engines of 80 nominal horse-power. There were two cylinders, about 35 1/2 in. diameter and 3 ft. 6 in. stroke, working at 26 1/2 revolutions per minute, giving a mean piston speed of 185 ft. per minute.
She was followed in 1822 by the 'Active,' of 80 nominal horse-power, by the same firm, and in 1823 by the 'Lightning,' of 100 horse-power, by Messrs. Maudslay, and some others whose names appeared for the first time in the Official Navy List for March 1828.
These early steam vessels were mainly used for towing and general purposes, and could scarcely be classed as war vessels. Between this date and 1840 seventy other steam vessels were added to the Navy, the majority being fitted with flue boilers and slow-moving side-lever engines worked with steam at a pressure of 4 lbs. per square inch above the atmosphere. The 'Rhadamanthus,' (mythological Greek king) one of these ships, was fitted with side-lever engines and flue boilers by Messrs. Maudslay, Sons, & Field in 1832.
The nominal horse-power was 220, but the engines were capable of being worked up to 400 I.H.P., or 1.8 times the nominal power. The load on the safety valves was 4 lbs. per square inch, and the number of revolutions per minute when working at full power 17 1/2, giving a mean piston speed of 175 ft. per minute. The total weight of the machinery was 275 tons, or 13.75 cwts. per I.H.P. developed.
Between 1840 and 1850 tubular boilers were introduced. In these boilers a group of small tubes was substituted for the long winding flue, to convey the heated gases from the furnaces to the chimney. The boilers were thus made lighter and more compact, and the working pressures of steam generally were increased to from 10 to 15 lbs. per square inch above the atmosphere.
Abandonment of side-lever engines.
Attempts were soon made to reduce the space required by the machinery, and the side-levers were abandoned and direct-acting engines fitted for rotating the paddle-wheels. Several arrangements of this kind were fitted, the two best known being the double-cylinder engine by Messrs. Maudslay and the oscillating engine adopted by Messrs. Penn. Fig. 2 shows the double-cylinder engine, which consisted of two equal cylinders side by side, the piston-rods from the two cylinders being connected to a single cross-head. In order to get sufficient length of connecting-rod, the cross-head was of peculiar form and passed down between the cylinders, having a journal at its lower end, on which one end of the connecting-rod worked, the other end being attached to the crankpin.
Figure 2 - Double Cylinder Engine
Figure 3 - Oscillating Engine (example - machinery weight, 4.23 cwts. per I.H.P.)
Fig. 3 shows the general arrangement of the oscillating engine, which is the simplest and most compact type for driving paddle-wheels. This type of engine, although first fitted for marine purposes by Messrs. Maudslay, Sons, & Field, who in 1828 fitted a pair of oscillating engines into the steamship 'Endeavour,' and subsequently in several other ships, was adopted and perfected by the late eminent engineer, Mr. John Penn, with whose name it is now generally associated.
In these engines the connecting-rod is altogether dispensed with, the upper end of the piston-rod being fitted with brasses to work directly on the crankpin, and the cylinder itself is carried on trunnion bearings, to allow the necessary oscillation to suit the motion of the crank. The trunnions are hollow, and the steam is admitted to and exhausted from the cylinders through them. In this type of engine, space and weight have been economised as far as is posslble for paddle-wheel engines, and the majority of engines now made for paddle-wheel vessels are on this plan.
The 'Magicienne' was one of the best specimens of the steam war-vessels of that period. She was fitted with oscillating engines by Messrs. Penn in 1850. The pressure of steam in the boilers was 14 lbs. per square inch, number of revolutions per minute at full power 20 1/2, giving a mean piston speed of 287 ft. per minute, with a maximum I.H.P. of 1,300. The total weight of the machinery was 275 tons, or 4.23 cwts. per I.H.P.
HMS Magicienne, 16 gun paddle frigate (Photo Ships)
Defects of paddle-wheels
The paddle-wheel possessed many practical disadvantages which interfered with progress beyond a certain point. Its performance was much affected by the variation of draught of the ship during a voyage, as the coal and stores were consumed, and the paddle-boxes offered resistance to the progress of the vessel. For fighting ships paddle-wheels were particularly unsuitable. The wheels themselves were exposed to danger from shot and shell, and the paddle-boxes interfered seriously with the training and working of the guns, while the shafting and many parts of the engines had to be considerably above the water-line, much of it above the upper deck. The paddle-wheel also is not a form of propeller well adapted for the application of high powers.
Adoption of the screw propeller
The adoption of the screw propeller in lieu of the paddle-wheel was the most important step taken in the progress of marine engineering, for this rendered many subsequent advances posslble. Its principal advantages, as compared with the paddle-wheel, are, that it is comparatively little affected by the rolling, or by the variation of the draught of the ship during a voyage, and it is equally capable of application to either great or small powers. It is not exposed to damage by projectiles, and also permits of the engines being kept below the water-line, which is very important in unarmoured warships.
Screw engines, whether horizontal or vertical, can be further protected, if necessary, by being kept below the steel armour deck, with armour gratings in the necessary engine-room hatchways and other openings, while in the larger class of war vessels, such as the battleships and large cruisers, their height is so moderate that efficient protection can be given them by armour, even when the engines are vertical and the cylinders above the water-line. With screw engines the decks are also kept clear for the guns.
The substitution of the screw propeller for the paddle-wheel began to grow general about the period 1845-50. The screw propeller had been invented long before, but its practical utility had not been generally recognised, and it was still regarded as being in the experimental stage. The first notable experiments as to the comparative efficiencies of paddle-wheels and screw propellers were made in 1840, when the 'Archimedes,' with a screw propeller, beat the paddle-wheel boat 'Ariel' between Dover and Calais by five to six minutes under steam and sail. The 'Archimedes' afterwards beat the paddle-wheel steamers 'Beaver' and 'Swallow,' but was beaten slightly by the 'Widgeon.'
The Admiralty, in 1843, caused some important experiments to be carried out with the screw ship 'Rattler ' and the paddle-wheel ship 'Alecto,' and, in 1849, with the screw ship 'Niger' and paddle-wheel vessel 'Basilisk.' The results in each case were in favour of the screw propeller, and many valuable conclusions were deduced from the trials.
Screw sloop HMS Rattler and paddle sloop HMS Alecto (Photo Ships, no enlargement)
From that time the use of the screw propeller gradually became more general, till at the present day it is almost solely employed for marine propulsion, the paddle-wheel only being applied in special cases. It is not too much to say that ships of the class now traversing the ocean in all directions, both in the royal and mercantile navies, would not have been possible had not the screw superseded the paddle.
Gearing for screw engines and its abandonment.
In order to attain the same speed of ship the screw propeller had to be driven at a much greater speed than the paddle-wheel, and as it was not posslble in the then condition of mechanical engineering to drive the pistons at a sufficiently high speed to enable the engine shaft to be connected directly to the propeller shafting, the earlier engines used for working screw propellers were geared, so that the screw shaft was caused to revolve at a much higher rate of speed than the engine shaft.
A large spur wheel, keyed on the crank-shaft of the engine, worked into a pinion on the screw propeller shafting, so that the speed of the engine shaft could be multiplied on the screw shaft as might be necessary. Before long, however, such improvements in workmanship and mechanical details were effected, that the speeds both of piston and of revolution could be sufficiently increased to allow direct engines to be fitted.
In these the gearing is left out, and the crank-shaft connected direct to the screw shafting. In many marine engines at the present day, even of the largest size, the mean piston speeds are as high as from 800 to 950 ft. per minute at the maximum power, while in the fast-running engines supplied for torpedo boats and destroyers it rises as high as 1,200 ft. per minute, and in extreme cases to 1,400 ft. It is probable that in the future of marine engineering the speeds may be increased even beyond this, in order to attain increased economy.
The paddle-wheel engines were either vertical or inclined; but when the screw propeller was introduced, and it became posslble to place the whole of the propelling apparatus below the water-line, the engine was placed horizontally, and from that time, for about thirty years, the engines of warships were almost always of the horizontal type. One of the great obstacles that had then to be overcome in connecting the crank-shaft of the horizontal engine direct to the screw shafting was the close proximity in which the cylinder was necessarily placed to the centre-line of the ship, owing to the limitation of the beam of the ship, which made it difficult to get a connecting-rod of suitable length to work between the cylinder and the crank.
Mr. John Penn solved this difficulty by his invention of the trunk engine. In this engine a large hollow trunk, cast on or bolted to the piston, and working through a steam-tight stuffing-box on the end of the cylinder, was substituted for the piston-rod, and the connecting-rod was attached directly to a journal or gudgeon in the centre of the piston itself, as shown in Fig. 4.
Figure 4 - Trunk Engine (click to enlarge)
Though the use of a large trunk of this description does not at first sight appear desirable, yet the engines of this type have generally worked in a satisfactory manner, and they were amongst the most smooth-working and efficient marine engines employed. With the introduction of high-pressure steam, however, they became obsolete, owing to the difficulty of keeping the trunks in a steam-tight condition.
Return connecting-rod engines.
This kind of engine was adopted by the majority of marine engineering firms to enable the horizontal cylinders to be brought close to the crank-shaft, and, as usually fitted, is shown in Fig. 5.
Figure 5 - Return Connecting-rod Engines (click to enlarge).There were two rods to each piston, one passing above, the other below the crank-shaft, to the opposite side of the ship, while the further ends of the piston-rods were fixed to a cross-head, having a journal at its centre, from which the connecting-rod worked back to the crank.
In some later examples, in order to obviate the disadvantage of having more than one stuffing-box for each cylinder, and simplify the design of the piston, a single piston-rod was fitted, attached to a cross-head between the cylinder and the crankshaft, from which two rods were carried, one above, the other below, the shaft, to a similar cross-head on the opposite side, as in the ordinary return connecting-rod arrangement.
The direct-acting engine shown in Fig. 6, having the connecting-rod between the cylinder and the crank, was often employed, especially by Messrs. Humphrys, in the later horizontal examples, the parts being stowed as compactly as posslble in the limited space available, and a short connecting-rod fitted. It is the simplest type, and the most suitable for general work, and, whenever sufficient room can be obtained, it is usually adopted. For vertical engines, with the cylinders at the top working down to the crank-shaft, which are now generally fitted for marine purposes, this type is universally adopted.
Figure 6 - Direct-acting Engines (example - machinery weight, 3 to 3.75 cwts. per I.H.P.) (click to enlarge).
Early screw engines.
The majority of steamers, both war and mercantile, built during the years 1850-60, were fitted with horizontal screw propeller engines worked with steam of from 20 to 25 lbs. pressure per square inch. The engines had jet injection condensers, and were not remarkable for economy of fuel, but they were much lighter, and occupied considerably less space, than the paddle-wheel engines that preceded them. The mean piston speed in this type of engine was generally about 400 ft. per minute, and the weight of machinery about 3 3/4 cwts. per I.H.P.
The adoption of surface condensation, which became general about 1860, formed a most important step in marine engineering. Its value consisted not so much in the economy effected by the avoidance of loss from the brining of boilers, as in the fact that by its eliminating the element of danger resulting from deposit of solid non-conducting matter on the heating surfaces, it rendered posslble the use of higher steam pressures in marine boilers, and led eventually to the introduction of cylindrical boilers (see Chapter VII) and compound engines.
When surface condensation was first introduced, the old flat-sided boilers, made to fit the section of the ship, were still retained, but were strengthened by fitting additional stays to enable them to carry steam pressures of 30 to 35 lbs. per square inch, and the majority of warships built during the years 1860-70 were fitted with surface-condensing engines worked with steam of this pressure. The piston speeds were also considerably increased, especially in the larger ships in which a long stroke could be obtained. With this type of engine the mean piston speeds varied from 500 to 665 ft. per minute.
To promote economy of fuel the cylinders were usually steam-jacketed, and made large enough to allow for considerable expansion at full power, and the boilers were fitted with superheaters. The average weight of the machinery of this type, including the water in boilers and condensers, was about 3 cwts. per I.H.P.
Compound or double expansion engines.
After the introduction of the surface condenser, attention was directed to the use of higher steam pressures and greater expansion of steam, as theoretical considerations showed that considerable gain could thus be effected. The result was that the steam pressure was increased from 30 or 35 lbs. to 60 lbs., while cylindrical boilers were fitted to safely carry the increased pressure, and the engine was changed to the compound type. Compound engines were fitted to nearly all warships from 1870 to 1885.
In this type of engine the expansion is conducted in stages; the steam, after being admitted to a small cylinder and expanding therein, is led to a larger cylinder, where it expands still further prior to exhaust, so that the stresses on the framing and journals are decreased and the loss from liquefaction of steam in the cylinders reduced to a minimum.
The following summary of its advantages is confirmed by experience :
1. Reduction of the maximum stresses on the framing, shafting, and bearings, and consequent reduction of weight and cost.
2. Increased regularity of turning moment, and consequent increased efficiency of the propeller in the water.
3. More economical use of the steam in the cylinders and consequent increase of power from a given expenditure of heat.
The working steam pressure in the Royal Navy with this type of engine was originally 60 lbs. per square inch. This has been gradually increased from time to time, till in about the year 1880 it was 90 lbs., while in the last of this type fitted the pressure was increased to 120 lbs. From the adoption of compound engines and higher steam pressures a considerable economy of fuel at once resulted. The gain in economy by the use even of the 60-lb. compound engines over the ordinary surface-condensing engines worked with steam of 30 lbs. pressure may be taken to be at least 30 per cent. This gain was well authenticated, and the average amounts claimed by the principal Engineers and Steamship Companies, in reply to questions by an Admiralty Committee in 1872, was 30 to 35 per cent.
Vertical (compound) engines.
The vertical type of engine, with cylinders at the top and crank-shaft below, was adopted for merchant ships long before it was introduced into the Royal Navy, because it was a necessity in most warships that all the machinery should be kept below the water-line, and horizontal engines alone satisfied this condition. Figs. 7 and 8 show a vertical engine of the type fitted in the mercantile marine.
Vertical engines possess many practical advantages over horizontal engines, especially in connection with the working of the cylinders and pistons, and general accessibility of the engine. When, therefore, the twin-screw system was adopted for armour-clad ships, vertical compound engines were fitted, with a middle line water-tight bulkhead separating the two sets. By dividing the power into two parts, each set of engines, even in a ship of great power, would be of moderate dimensions, and although the whole of the machinery might not in all cases be entirely below the water-line, the parts above would be protected, not only by armour plating, but by a body of coal in addition, the coal-bunkers being continued on each side of the engine room.
This extension of the use of vertical engines has continued and been applied to all classes of vessel, and special means for protecting the cylinders have often been fitted. At the present time new engines for the Navy are being made vertical for all classes of vessel.
Three-cylinder compound engines
As the power of compound engines increased, the dimensions of the low-pressure cylinders became so great that it was found desirable to fit two low-pressure cylinders instead of one, in consequence of the difficulties experienced in obtaining sound castings of large size, and to keep the size of the reciprocating parts as small as possible. This led to what is known as the three-cylinder compound engine, which is simply a modification of the ordinary two-cylinder compound engine. Figs. 9 and 10 show a vertical compound engine of the three-cylinder type.
Figures 9 and 10 - Three-cylinder compound engines (click to enlarge)
Triple expansion engines.
With initial steam pressures above 100 lbs. per square inch, the variation of temperature in each cylinder of an ordinary compound engine again becomes great, so that the full economy due to the high pressure cannot be attained in consequence of the loss from liquefaction. It was therefore soon found desirable to extend the compound system, and divide the expansion into three stages, carried out in separate cylinders, so as to reduce the range of temperature in each.
Engines on this system are usually known as triple expansion or triple compound engines. They were first introduced by the late Dr., then Mr., A. C. Kirk, of Messrs. R. Napier & Sons, Glasgow, who, in 1874, fitted them on board the s.s. 'Propontis,' to utilise steam of 150 lbs. pressure, supplied by Rowan & Horton's water-tube boilers. These engines gave good economical results, but the boilers unfortunately gave trouble, and were ultimately taken out. Very little further was done in this direction, until, in 1881, Mr. Kirk fitted a set of triple expansion engines on board the s.s. 'Aberdeen,' for the trade to Australia and China. The results in this instance were so satisfactory that other engines of the same type followed, and the system was soon largely adopted in the mercantile marine.
Since 1885 the new ships for the Royal Navy have been fitted with triple expansion engines, which type is now the most general for marine purposes. The steam pressure first used with them in the Navy was 130 lbs., which was gradually increased to 155 lbs. in the year 1887. From this date to 1895 large numbers of triple expansion engines were added to the Navy, all with 155 lbs steam pressure. In the mercantile marine, however, 180 lbs. steam pressure is now largely used, and in many cases 200 lbs.
In the two large cruisers 'Powerful ' and 'Terrible,' commenced in 1893, and tried in 1896-97, a boiler pressure of 260 lbs. is adopted, reduced to 210 lbs. at the engines, while in cruisers of 1895, and subsequently, these pressures have been increased to 300 and 250 lbs. respectively. Triple expansion engines are fitted, the low-pressure cylinders being divided into two parts.
Quadruple expansion engines.
In many cases in the mercantile marine the stage expansion principle is carried still further, and quadruple expansion engines fitted, dividing the expansion into four stages, the boiler pressures being generally 200 lbs. per square inch, and in some cases 250 lbs. per square inch.
These engines are more suitable for the mercantile marine, where the range of powers required from the engines is limited, than for the Navy, where this range is large; also as regards the Navy generally, evidence does not show that the additional complication thus introduced, and the extra length of engine room required, together with the additional engine friction, is compensated for by a sufficient gain in economy. They are gradually being introduced into the mercantile marine, but in the Navy only one torpedo boat and some smaller craft have been so fitted.
Improvements in economy.
In consequence of the improvements effected, the consumption of coal with the most recent engines is less than one-third that required for the engines generally used before 1860, and the effect on warships of this great reduction of coal expenditure has been twofold :
a. The increased distance ships are able to steam without exhausting their coal supply has rendered seagoing mastless armour-clad ships posslble.
b. The reduced quantity of coal necessary to be carried for the same radius of action has enabled space and weight which would formerly have been required for coals to be devoted to other objects in order to increase their offensive or defensive powers.
Corresponding benefits have also been derived by the mercantile marine.
The conditions of service of ships in the Royal Navy render it necessary to provide for the development of high power and speed on special occasions, such as the events of action, chasing, etc., although the greater portion of the work of the ship has to be performed at comparatively low powers. It is therefore desirable in warships to provide special means of forcing the boilers when the full speed is required. Formerly a steam jet in the chimney was used for this purpose, but this wastes a lot of fresh water. In 1882 the system of forming the stokeholds into closed compartments, and keeping them under air-pressure by means of blowing fans was adopted and continued to the present day, with results that are satisfactory, provided only a moderate pressure of air be used, and by this means the steam generating powers of the boilers have been largely increased.
Details of the fittings required for this purpose are given in Chapter V. The introduction of forced draught has enabled the weight of machinery to be considerably reduced, and the average weight of machinery for the latest modern warships fitted with circular boilers is about 1 3/4 cwt. per I.H.P. developed with moderate forced draught. A lesser weight than this, viz., 1 1/2 cwt., was at one period allowed, but this is not now recommended. (by comparison, for the side-lever engine, the figure was 13.75 cwts. per I.H.P.)
From this brief sketch a general idea may be formed of the progress that has been made in marine engineering. The machinery of the 'Salamander,' built in 1832, weighed 275 tons, developed 400 I.H.P., and consumed 7 to 8 lbs. of coal per horse power.
In modern warships, machinery of the same weight would, under moderate forced draught, be capable of developing satisfactorily at least 3,000 I.H.P., with about one-fourth the consumption of coal per horse-power, and the space occupied would be considerably less. Another important feature is the great increase in the total power now available for the propulsion of vessels at high speeds.
For example, in H.M.S. 'Terrlble,' which in 1845 represented the finest type of steam warship of the day, the I.H.P. was less than 2,000, and her speed about 10 knots, while in the present H.M.S. 'Terrlble,' a first-class cruiser, the horse-power is 25,600, and the speed 22.8 knots.
In a later series of cruisers, the 'Drake' class, the power is still greater, viz. 30,000 I.H.P.
Quite recently water-tube boilers, of various types, have been adopted in the Navy with steam pressure in boilers of 300 lbs. and engines working at 250 lbs. per square inch. A great impetus will probably be given to the use of higher steam pressures by the more extended use of this type of boiler, since there is then, within moderate limits, but little increase of boiler weights involved by higher pressures, the only increase of importance being in the engine. Probably the near future will see a general advance of steam pressure coupled with the use of the water- tube boiler, and, especially in the mercantile marine, the development of quadruple expansion engines.
Considerable progress is still posslble as regards the boiler in the reduction of the great waste of heat which now takes place, due either to incomplete combustion, or the inability of the heat-absorbing surfaces, as now arranged, to prevent a serious loss of heat in the escaping gases. Further reductions in coal expenditure may be expected in the future under each of these heads.
More attention seems necessary also as regards the mechanical efficiency of the engines used in large vessels. Careful tests in this direction would probably point out many ways in which improvement would result.
(Note: there is no reference here to the forthcoming rotary marine steam turbine engine, which was "introduced and perfected by the Hon. C. A. Parsons, of Newcastle", but see the late addition to Chapter XXI)
Parson's steam turbine-driven Turbinia racing through the Fleet during
Queen Victoria's 1897 Jubilee Review (Chevalier de Martino)
ARRANGEMENT AND EFFICIENCY OF BOILERS - WATER TANK BOILERS.
"The boilers described in this chapter have the water outside the tubes and contained in an outer shell or so-called tank - technically 'water-tank' boilers. This distinguishes them from the class known as 'water-tube' boilers described in the next chapter."
IN this chapter and the succeeding, we will consider the different types of marine boilers in general use, and their efficiencies. ..........
The first boilers fitted to work marine engines were of the rectangular, or 'box' form; an example of this type is shown in Figs. 27 and 28, which represent the most general type of marine boiler for steam pressures not exceeding from 30 to 40 lbs. per square inch above the atmosphere.
Figures 27 and 28 - Low pressure boilers (click to enlarge)
This form is now entirely obsolete for new vessels, not being suitable for high pressures, as in these boilers the stresses are resisted principally by the action of straight iron stay-rods. For pressures above 30 or 40 lbs. per square inch, these would have to be so numerous and closely spaced, that the boilers would be excessively heavy, and the internal parts inaccesslble. The furnaces were made with flat sides, and arrangements could be made to keep their crowns sufficiently high above the bars to allow the gases to mingle freely with the air, whilst the bottoms of the ashpits could be kept low enough to permit an ample supply of air to pass through the fires for combustion.
Good results were obtained from these boilers, and this was due to a great extent to the very roomy furnaces and combustion chambers with which they were fitted. The furnaces were usually arranged in pairs, each pair having a common combustion chamber, as shown in the diagrams. .......... From the combustion chamber the smoke and gases pass through tubes, arranged over the furnaces, to an uptake in the front of the boiler, in which they all unite, and are conveyed to the funnel. .........
These may be divided into two classes, high or 'return- tube' boilers, and low or 'through-tube' boilers. High boilers are generally used where they can be conveniently arranged for, but the low boilers are fitted in war vessels of small depth of hold to keep them below the steel deck or water line for protection from shot, &c. These boilers are rather inferior to the low-pressure boiler in economy of generation of steam and in the amount of coal capable of being burnt per square foot of grate with the same draught. Figs. 29 and 30 show the general arrangement of a large example of the high type of cylindrical marine boiler used for pressures of 150 lbs. to 180 lbs. per square inch. In the diagram, which represents a four-furnace boiler of about sixteen feet diameter, each pair of furnaces has a separate combustion chamber, which is the most general arrangement in these boilers.
Figures 29 and 30 - High pressure boilers (click to enlarge)
The end plates above the tubes and combustion chamber and below the furnaces are supported by long bar stays passing through the plates with nuts inside, and nuts and stiffening washers outside. The large stiffening washers are riveted to the plate as shown in Fig. 29. The front plate and tube plate between furnaces and tubes are similarly stayed. The sketch indicates the construction of all the parts in detail. ..........
Low type of high-pressure boiler.
The low type of cylindrical boiler, shown in Figs. 32 to (33) 34, is fitted on board ships of the smaller classes, such as sloops, gun-vessels, &c., and also where, in larger vessels, there is not sufficient room below the vessel's protective deck to enable the high type of boiler to be fitted. Boilers of this type in the Navy have generally given higher evaporative powers than those just described.
The sketches show a low boiler with two furnaces, but in many vessels three furnace boilers of this type have been fitted, and in a few cases four and even five furnaces.
In the large majority of such boilers the furnaces discharge into a common combustion chamber, and such boilers have generally given very good results. The more recent examples supplied for the Navy have been fitted with a divided combustion chamber as recommended by the Admiralty Committee of 1892, so that each furnace has a separate combustion chamber. Fig. 32 shows such a boiler.
In this type it will be seen that the combustion chamber is wide, and that the tubes, instead of returning above the furnaces to the uptake at the front of the boiler as in the high type, are continued along the boiler at about the same level as the furnaces, to the uptake which is situated at the other end of the boiler. The path of the gases to the funnel is thus more direct than with the high type. This type is sometimes known as the 'through-tube type.' ..........
Figs. 37 and 38 show a double- ended boiler. This is a common type for mercantile steamers, and is also fitted in a considerable number of ships of the Royal Navy. It is practically equivalent to two single-ended boilers placed back to back, but lighter for equal power, because the weight of the end plates and of much water in the spaces at the backs of the combustion chambers, is saved. ..........
Marine locomotive boilers.
Figs. 44 and 45 illustrate the locomotive type of boiler which has been used for marine purposes in torpedo boats, etc., in which the working pressures of steam have been from 120 lbs. to 180 lbs. per square inch. In this type of boiler there is a broad and practically rectangular fire-box at one end, the crown of which is strengthened by means of stays to the roof of the boiler, as shown. The example illustrated is by Yarrow & Co.
The air for the combustion of the coal is supplied from underneath, and there is considerable space and height above the fires to allow for the combustion of the gases. The barrel of the boiler beyond the furnace is cylindrical, and contains the tubes which lead to a smoke- box at the opposite end of the boiler. ..........
In both torpedo boats and torpedo gunboats, however, the locomotive boiler has now been abandoned in favour of the water-tube boiler descrlbed in the next chapter.
74 THE MARINE STEAM-ENGINE
WATER-TUBE OR TUBULOUS BOILERS.
THE previously described boilers, having the water outside the tubes and contained in an outer shell or so-called tank, are technically called 'water-tank' boilers, to distinguish them from the class known as 'water-tube' boilers descrlbed below.
'Water-tube' boilers are those in which the flame and water in the older form of boiler are interchanged, so that the water being evaporated is contained inside the tubes, and the hot gases outside them. The hot gases outside the tubes are confined and led to the funnel by a casing fitted for the purpose.
The desire to obtain boilers having the capacity of safely generating steam of higher pressures than had been previously used, combined with lightness of construction, and having the tube ends favourably situated for resisting leakage, has led engineers for many years to seek for a satisfactory water-tube boiler.
History of water-tube boilers.
The earlier examples of the water-tube boiler fitted in the mercantile marine, commencing on the Clyde about 1857, were not successful; they generally failed owing to rapid corrosion of the tubes, combined in some cases with incrustation due to saline deposits on the water side of the tubes, from the salt water which either leaked through condensers or was admitted to supply the waste of feed-water. This incrustation was usually not readily accessible for removal.
Most of these early water-tube boilers were eventually removed and replaced by the cylindrical multitubular boilers previously descrlbed, the pressure of steam being correspondingly reduced. Later on, about 1870-75, with higher pressures, renewed attempts were made in Great Britain to obtain such boilers, but they were again unsuccessful, and for some years after this, the attempt in this country was practically abandoned. Mr. Loftus Perkins was perhaps the most successful, and the Perkins boiler and engine, with pressures of 300 to 500 lbs. per square inch, attracted considerable attention. Other of these early boilers were the Rowan, Howard, and Root types.
In France an important application of such a boiler was made in 1879, by the fitting of Belleville boilers to a despatch vessel which was employed on actual sea service to a considerable extent, and her boilers were reported to have given satisfaction, so that from this time there was a gradual extension of the use of this type in the French Navy. A cruiser launched in 1885 was the next vessel fitted with these boilers, followed in 1889 by the cruiser 'Alger,' of 8,000 I.H.P., and two torpedo gunboats.
Soon after this two steamers of the Messageries Maritimes Company were fitted with Belleville boilers, and as the result of the experience this company has fitted similar boilers to all their new vessels, including their largest and fastest mail steamers.
A considerable number of vessels of the French Navy have also been fitted with water-tube boilers of the Niclausse, and also of the Lagrafel and D'Allest types, and some of these have also been supplied to the French mercantile marine.
In England, in 1882. a mission steamer, and in 1885, No. 100 second-class torpedo boat, were fitted with Thornycroft water-tube boilers; and the same type was fitted in three first-class torpedo boats for the Indian Government in 1888; in the torpedo gunboat 'Speedy,' of 4,500 I.H.P., tried in 1893; and in several foreign vessels.
In 1893, Belleville boilers were ordered to replace the defective locomotive boilers of 'Sharpshooter.' It being recognised that these boilers had passed out of the experimental stage, it was subsequently decided to fit the 'Powerful' and 'Terrlble.' large cruisers each of 25,000 I.H.P., with them, and subsequently all large new vessels for the British Navy have similar boilers, including (up to 1899) 27 cruisers of 10,000 to 30,000 I.H.P., and 16 battleships of 13,500 to 21,000 I.H.P., besides gunboats and other vessels.
In England the Babcock and Wilcox water-tube boiler, previously fitted in some small vessels, was fitted and tried in 1893 in the s.s. 'Nero,' and some other mercantile vessels have since been fitted with this type. They have also been fitted to H.M.S. 'Sheldrake,' (see sister-ship HMS Skipjack below) which vessel passed through all her contract trials satisfactorily, and also in several vessels of the U.S. Navy, the performance of which during the war with Spain was very satisfactory.
Comparison with locomotive type.
As regards the use of those varieties of water-tube boilers which give the greatest power for their weight and the space occupied, a very considerable extension took place in Great Britain in 1893 by the demand for the class of small vessels of great speed known as 'torpedo-boat destroyers.' Many varieties have since that date been fitted and tried in such vessels with satisfactory results, and they have now entirely superseded the locomotive type, which had previously been mostly used for such purposes.
An example of the results obtained in sister vessels with locomotive and water-tube boilers may be given in the trials of 'Havock' and 'Hornet,' both built and engined by Messrs. Yarrow & Co., the ' Havock ' with locomotive boilers having copper fire-boxes similar to that illustrated in Fig. 44, and the 'Hornet' with water-tube boilers similar to Figs. 65 and 66.
Having now briefly descrlbed the history of the revival of water-tube boilers in recent years, we will proceed to the detailed consideration of these boilers, their advantages lying in their lightness for the power generated, the capacity of raising steam quickly owing to the small quantity of water carried, and their comparative freedom from leaky tubes, the joints being more protected from the direct impact of flame.
The Belleville boiler.
This type of water-tube boiler is shown in Figs. 49 and 50, and is of more extensive use on board large ships than any other. It consists essentially of a top steam cylinder and a lower water chamber, with a series of straight zigzagged tubes of comparatively large diameter connecting them. There is an external return water pipe on each side, connecting the ends of the top steam chamber with the lower water chamber. The zigzag generating tubes are inclosed in a sheet-iron or steel casing, which confines the flame and gases generated from the combustion of the coal on the fire-bars. ..........
Figure 49 and 50 - The Belleville boiler (click to enlarge)
The Thornycroft boiler
The Thornycroft boiler ('Speedy' type) Fig. 58, consists essentially of a central upper steam cylinder A, and two smaller lower water cylinders B, these latter being fitted about the level of the fire-bars.
Figure 58 A series of steam generating tubes of small diameter are fitted between the upper cylinder and each of the lower water cylinders. They are secured at each end by being simply rolled into the cylinder plating by means of the roller expander, the parts of the cylinders into which they are rolled being made thick enough for this purpose. These tubes form practically the whole of the heating surface of the boiler, and the inner row on each side is curved in such a manner that they are close together at the top and form the roof of the furnace or combustion chamber. ........
Thornycroft (Daring) type.
The length of the 'Speedy's' boilers to allow for return tubes is considerable, the tubes are not very accesslble, and the height of the furnace is not great, so that when the demand for torpedo-boat destroyers came, in order to meet their special requirements as regards lightness, also to give an improved furnace and greater means of access to the tubes, a modified type of boiler was designed, known as the Thornycroft (Daring) type (Figs. 59 and 60). This type obtains two furnaces' in each boiler and a greater amount of fire-grate in the available space.
It consists of an upper cylinder A similar to that of the preceding type, into which the upper ends of the generating tubes are rolled.
Vertically below this is the principal lower cylinder B, to which the lower ends of the majority of the tubes are attached.
Two smaller water cylinders, D, are arranged on each side of the principal lower cylinder, and the furnaces are situated between them.
Three rows of generating tubes connect the upper cylinder to each of the small water cylinders D and form the outside boundaries of the furnaces, the inner boundaries being made by the tubes connecting the upper cylinder A with the principal lower one.
Of the three rows connected to the small water cylinder, the outside two touch each other, and so form a water wall which confines the flames and gases. The main body of the tubes are so curved as to leave a considerable space, C, between the two groups on each side; the gases are discharged into this space, which forms the uptake of the boiler.
The inner and outer rows of tubes of each centre group are formed as walls of tubes, except at the lower part of the furnace side and upper part of the uptake side, where spaces are left for the entry and exit of gases.
The gases, after leaving the fire, enter through the spaces E, at the bottom of the outer row, pass up between the walls among the tubes, and emerge through the spaces F at the top of the inner rows to the uptake space C, between the two centre groups of tubes. They proceed along this space to the end of the boiler and thence to the funnel. ..........
The next most extensive experience has been obtained in the British Navy with the Normand type, with more or less modification fitted in a considerable number of torpedo-boat destroyers by Messrs. Laird Bros, and the Clydebank Engineering Company, and this type of boiler has given satisfaction in all cases where the boiler tubes have been made of steel. In the Normand type, a drawing of which is shown in Figs. 61 and 62, there is the usual top cylinder with two lower water chambers. ..........
We come now to the Yarrow boiler (Figs. 65 and 66), which has been fitted in several British torpedo-boat destroyers, and many foreign ones.
This boiler consists of a steam drum at the top, in the centre, with flat tube-plates at the lower end on each side, between which and the steam drum are a series of straight tubes which form the heating surface of the boiler. The tubes all deliver their steam to the steam drum below the water line. A small water chamber is bolted to these lower tube-plates. The original boiler of this type fitted in No. 77 torpedo boat had external return water-tubes. In the torpedo-boat destroyer 'Hornet,' however, which was the next vessel fitted with these boilers in our Navy, these external return water tubes were omitted.
Babcock & Wilcox boiler.
One of the best known water-tube boilers on land in England and America is the Babcock & Wilcox, one of which was fitted and tried in the s.s. 'Nero' in 1893. In this boiler (Figs. 72 and 73) the generating tubes are fitted between a number of headers, or narrow sinuous vertical water chambers of square section, each pair of which (one at the front and one at the back) is united by tubes inclined at an angle of about 1 in 4. The gases from the fire pass around the tubes and thence to the funnel ..........
This is illustrated in Figs. 74 and 75, and has been fitted in a considerable number of vessels in foreign navies, and consists of a series of slightly inclined double tubes, one inside the other, attached at the front end in such a manner that the colder water flows down the inside tube, and returns to the front between the two tubes when heated by the action of the fire and hot gases on the larger outside tube.
Note: Other boilers described in the text include the Blechynden, Du Temple, Reed, the "Mosher" and Wards.
There are many other water-tube boilers, but space will not permit of further descriptions. In this country the Fleming & Ferguson, Weir, White, Mumford, and other boilers are used, and in America the 'Towne.' In Germany the 'Durr ' boiler is used, which consists of the same arrangement of tubes as in the Niclausse, except that the connections at the front, instead of being in the form of separate headers, consist of continuous vertical sheets or walls.
268 THE MARINE STEAM-ENGINE
(a late addition to the chapter on the steam turbine)
Having now descrlbed the usual arrangements for producing the rotary motion of a shaft, which motion is essential for marine propulsion (using reciprocating engines), we will consider an example of the 'rotary engine' which is being used to a small extent for this purpose, viz. the marine steam turbine introduced and perfected by the Hon. C. A. Parsons, of Newcastle. 'Rotary engines' are those in which the steam causes a rotating motion by direct action on the shaft, without the intervention of any mechanism such as a crank and connecting rod. (This book was published in 1899, just two years after Parsons sped in the turbine-driven Turbinia through the ranks of the British fleet at Queen Victoria's Jubilee Review in 1897)
Parsons' marine steam turbine.
This machine consists of a hollow cylinder which rotates on its axis, and is provided with a large number of inclined blades arranged in a ring, and well secured in grooves in the revolving cylinder or drum. There are a series of such rings of blades along the length of the cylinder, and between each ring of revolving blades there is a corresponding ring of similar blades fixed in the outer casing containing the revolving drum, but inclined at a different angle to that of the revolving blades, the moving and fixed blades being practically similar, but with angles reversed.
Fig. 277a shows the relative arrangement of fixed and revolving blades and the direction of motion of the revolving blades and steam. The angles and curvature of blades are so arranged that the velocity of the revolving blades and steam causes the latter to enter the moving blades with a velocity parallel to their surfaces; and similarly, on leaving the moving blades the combination of the velocity of these blades with the velocity of the steam along the inclined surface of the blade causes the final velocity of steam on exit from these blades to be parallel to the axis of the turbine. The steam then proceeds through the next series of fixed blades, and so on till the condenser is reached. The impulse of the steam as it leaves the fixed blades and impinges on the revolving blades causes the turning effort on the shaft. The arrows in Fig. 277a indicate generally the direction of flow of the steam in its passage through the blades.
Figure 277b - Parson's marine steam engine (click to enlarge)
Fig. 277c shows a vertical section through the high-pressure turbine cylinder of H.M.S. ' Viper,' with the revolving drum shown in elevation. The boiler steam, after passing through a strainer, enters the steam orifice A, and thence to the hollow belt B, and then enters the turbine through orifices which are formed all around the cylinder. It now proceeds through the fixed and revolving blades along the narrow passage between the cylinder and revolving drum.
At C (next to steam inlet A) an enlargement of diameter occurs, the steam therefore expands and becomes of lower pressure. It then passes through the second series of fixed and revolving blades along the larger space between cylinder and drum until the point D is reached, where a further enlargement of cylinder diameter takes place with consequent further expansion of steam, still further expansions taking place at E and F till the exhaust orifice G (lower left) is reached.
In H.M.S. 'Viper' this orifice G leads the exhaust steam to the low-pressure turbine fitted on a separate propeller shaft, there being two shafts on each side the ship. The construction of this turbine is similar to the one illustrated, further considerable enlargements of cylinder and expansion of steam taking place, till exhaust to the condenser occurs at a low pressure. A large relief valve, discharging on deck, is fitted on the branch H, in case any undue pressure occurs which would be in excess of the safe pressure for the low-pressure turbine.
(continued in original book)