Steamships and their story

by E. Keble Chatterton

Furthermore, when the weight G is raised while the wheels Da, D and Db are moving backwards, the rope Fa gives way and the power of the weight G brings the wheel Ha forward and the paddles with it: so that the latter always keep going forward, notwithstanding that the three wheels Da, D, and Db move backwards and forwards as the piston moves up and down in the cylinder. LL—scarcely recognisable owing to the reduction of the sketch—indicate the teeth for a catch to drop in from the axis, and are so contrived that they catch in an alternate manner to cause the paddles to move always forward, for the wheel Ha, by the power of the weight G, is performing its work while the other wheel Hb goes back in order to fetch another stroke. Hulls explains that the weight G must contain but half the weight of the pillar of air pressure on the piston, because the weight G is raised at the same time as the wheel Hb is doing its duty, so that in effect there are really two machines acting alternately by the weight of one pillar of air of such a diameter as is the diameter of the cylinder.

Hulls expressed another crude idea for when the ship was navigating “up in-land Rivers” and the bottom could be reached. The paddles were then to be removed and “cranks placed at the hindmost Axis to strike a Shaft to the bottom of the River, which will drive the Vessel forward with greater Force.”

Daniel Bernoulli, in the year 1753, proved on paper that it was mathematically possible to use a steam engine for propelling ships, the medium being also wheels with vanes attached. There were not wanting other theories and experiments also in the eighteenth century which attained little or no success, their defects arising sometimes through lack of sufficient power to go against a stream, or through some erroneous principle. Of these we might mention especially the experiment made in France by Périer, who, after devoting careful consideration to the problem of the amount of power required, and, after reckoning the necessary force likely to be essential, by the number of horses which were required for drawing along a boat from the towing-path, set to work in his own manner. It happened that in the year 1775, to which we are now referring, there was on view in Paris a unique engine which the now famous and ever memorable James Watt had made. This aroused so much interest that it was decided to hire a boat on the Seine and place therein a Watt machine of one horse-power. Périer carried out his experiment, though owing to the force of the current of the Seine, and the too limited horse-power which the engine was capable of producing, the result was a failure. But one of Périer’s associates, the Marquis de Jouffroy, had also been excited by the advent of this English engine which was an improvement on anything that the world had yet seen, and he resolved to try for himself to find some means of making a ship to go against swift-running rivers independent of horse-towage. In spite of the prejudice which was likely to be aroused in case he should prove successful (for the owners of the monopoly of the more primitive form of inland water transport would not quietly consent to see their living taken away from them), he set forth with considerable courage and an heroic determination. Since it is doubtful whether these interesting experiments would ever have been made had it not been for the happy coincidence of Watt’s engine becoming known when it did, it is only right that we should first see something of the circumstances which combined to bring the Englishman’s work into such prominence, and then return to follow de Jouffroy in his efforts.

To James Watt, notwithstanding that his work and ingenuity were expended for the purpose of land engines, belongs the honour of having removed the most harassing obstacles which were delaying the full and entire possibility of the marine steam engine. In the chain of discoveries which leads back into early times, without whose cumulative effect he himself would not have done what he did, James Watt comes immediately next to Thomas Newcomen. Despised in his weak, delicate boyhood by his companions, his is another instance of the stone which the builders rejected becoming the head corner-stone. Or, to put the proposition in another way, Watt absorbed all the existing good that there was in the latest engineering knowledge, and advanced that several steps further until it reached the goal of practicability.

In the Newcomen engine there were several notable defects which marred its usefulness, and it was not until these could be improved upon that there could possibly be a future for the steamboat. This type of “machine” was not closely enough related to the work which it was called upon to perform. Its pre-eminent fault lay in the fact that the condensation took place in the cylinder. This meant a considerable waste, for after the latter had been made cool by the admission of the cold water for condensing the steam, the cylinder had to be heated again before every upward stroke. Heat, in fact, was literally thrown away. It was in the year 1764 that Watt, while endeavouring to repair a model of one of these Newcomen engines and to remedy its poor performance, was struck by the inadequacy of its mechanism and realised that some means should be found to ensure a greater economy of steam. From his ingenious brain, therefore, came an improvement. He provided for the condensation to take place not in the cylinder but in a separate condenser, in which a jet of water was to spray, and finally the condensed steam, the injected water, and the air which had also found its way in, were to be drawn off by means of an air-pump. After a delay of several years Watt was introduced to Matthew Boulton, founder of the Soho Engineering Works, near Birmingham, and in 1769 Watt’s invention, embodying the principle of the separate condenser, was patented. Although he had worked out his idea as far back as the year 1765, it was not till four years after that he had the means to secure its protection. In the specification for his patent Watt enunciated what is appreciated as an essential doctrine to-day, that the walls of the cylinder should be maintained at the same heat as the steam which was about to enter into the cylinder. And he proposed to bring about this improvement by adding an external casing to the cylinder, leaving a space between the casing and the outside of the cylinder itself and keeping always in this space steam so as to preserve a high temperature.

But, as was mentioned on a previous page, the steam engine at this date was not developed with a view to transport, but for the convenience of pumping up water from mines. As a result of Watt’s success a considerable demand arose among Cornish mine-owners for these engines made by Boulton and Watt, who were now working in partnership together. For the work of pumping, these machines continued to serve admirably, so long as a vertical up-and-down motion was required. At length Watt turned his mind to some method of obtaining rotary movement from his engine, but in a manner different from that in which Hulls had attempted to attain his end. Watt had covered in the top of his cylinder to keep out the cooling effect of the air, and his well-known beam pumping engine was an improvement on Newcomen’s, owing to the simple fact that in economising steam it halved the cost of fuel, and not even to-day are these old-fashioned engines in disuse. As we shall see later on, the beam engine is very much in evidence in some of the river steamships of the United States, apart altogether from those beam engines which are still worked for pumping in some parts of our own country.

With such satisfactory results to encourage him it was inevitable that sooner or later so brilliant a schemer would think out some means for rotary movement, and Watt’s first intention was to cause the beam (which was pushed up by the rod joining the piston) to drive a fly-wheel by introducing a crank in something of the same manner in which nowadays the crank of a bicycle drives round the cog-wheel, the cyclist’s leg being, so to speak, the connecting rod which joins the beam. But before Watt had a chance of getting legal protection for this method his secret was stolen by one of his workmen, named Pickard, who revealed it to a Bristol man of the name of Wasbrough, who was also in search of some method of obtaining rotary motion. The latter, therefore, having in 1780 obtained his patent by stealth, Watt was compelled to cast about for some other means of attaining the same end: but his fertile mind soon gave forth what was required, and in the following year he patented what is known as the “sun-and-planet” gear, which converted the vertical movement into a rotary. Put in a few words, the working of the engine was as follows: At the top was the straight beam of wood; from one side of this there hung vertically a rod which connected with the piston in the cylinder, and was thus made to go up and down as in the Newcomen engine. It will be remembered that in Newcomen’s machine, at the opposite end of the beam was the other rod for pumping the water. Now in Watt’s rotary engine the piston-rod was moved up and down as before, but the opposite rod, at the other end of the beam, was connected with a spur-wheel having cogs in it. There was also a large fly-wheel which had a similar cog-wheel on its shaft, and thus, as the piston rod pushed up its end of the beam the opposite end of the beam was lowered and its rod also. But through the arrangement of the two cog-wheels the connecting rod caused the fly-wheel to revolve, and at twice the rate at which it would have gone round had Watt’s original rod and crank idea been employed, for the “planet” cog-wheel goes round in a circle but does not revolve on its own axis. Some of his engines of this type were so arranged that the speed of the fly-wheel shaft was not so much greater than in the case where a crank was employed.

Thus, in this important adaptation of the vertical to the rotary movement, we get the nucleus of the future steamboat engine, which was to turn the paddle-wheels round. But Watt did not stop there. We have seen that whilst it was the steam which pushed the piston and its rod upwards, it was yet the pressure of the air and the weight of the parts which caused the piston and rod to descend. Now, as we have seen, Watt had already resolved to cover in the top of the cylinder in order to keep out the air from cooling the latter. It was, then, but a natural transition to utilise the steam not merely for pushing the piston upwards, but also for sending the same down after its ascent had been made. We thus get what is the well-known double-action of the modern reciprocating engine, in which steam is employed from either side of the piston alternatively, so that each stroke becomes a working stroke and the power of the engine is doubled. It was Watt who, as early as the year 1782, discovered the advantages which were possessed by the expanditure of steam, but as this does not enter into practical application just yet, we can postpone the subject to a later chapter. We need only emphasise the fact that the fly-wheel which is so familiar to all of us was the invention of Watt, and it is perhaps scarcely necessary to explain that the reason for the existence of this wheel is in order that it may, at the beginning of the stroke, when the engine is at its strongest, store up the surplus energy and give it back towards the end of the stroke. It thus maintains an equal motion throughout the whole stroke given forth by the piston and its rod.

The earliest marine steam engines were very much on these lines, then, and were really a slightly modified form of land engine. But, as we shall soon come to refer to the more complicated type of engine, and to make use of other terms, it may not be out of place here to deal at once with the expression “horse-power,” which is used for the purpose of indicating the force which an engine is capable of developing. The origin of this expression is not without interest, and Sir Frederick Bramwell, Bart., F.R.S., D.C.L., in his entertaining article on the life of Watt in the “Dictionary of National Biography,” points out that Savery, to whom we have referred, was accustomed to calculate that where any machinery had to be driven by means of a single horse, it would entail a stock of three of these animals being kept, so that one should be able always to be at work. Thus supposing that the power exerted by six horses was necessary to drive a pump, and Savery made an engine capable of doing the same work by mechanical means, he would call it not a six horse-power engine, but an eighteen horse-power. Watt, however, did not credit his engine with the idle horses. He satisfied himself that an average horse could continue working for several hours when exerting himself so as to raise one hundredweight to a height of 196 feet in one minute, which is about equal to lifting 22,000 pounds one foot high in the same time, as the reader will find by simple arithmetic. But in order that no purchaser of his engines should have any ground for complaint, Watt went one step better, and determined that each horse-power of his engine should be capable of raising to a height of one foot, in one minute, not 22,000 pounds, but 33,000 pounds, or half as much again. And so to-day when we speak of an engine possessing such and such horse-power we still mean that it is equivalent to such a power as would raise 33,000 foot-pounds per minute. I make no apology for dwelling to such an extent on this point, but since at least one writer on steamships has seen fit to refer to this assessment of horse-power as being entirely arbitrary, and to admit in the same paragraph that he was altogether ignorant as to what power a horse was actually capable of producing, I have thought it not inappropriate to make the point clear in the mind of the reader.