CHAPTER II. PADDLE WHEELS. 112. As the effective value of the marine steam engine is intimately connected with the form and dimensions of the paddle wheel, we purpose, in this part of the work, to say a few words on the subject. 113. Notwithstanding the fact that the common paddle wheel was decidedly the first adaptation of any kind attached to vessels for the purpose of propelling them through the water (and from the close affinity existing between the old undershot water wheel and its performances, and the desired effect required in propelling vessels, it appears obvious that such should have been the case); nevertheless, engineers and speculators not only doubted the possibility of the common paddle being effective, but actually laid it aside as altogether useless, because the steam engine itself was so inefficient as to be unable to cause the vessel to advance at all, except at such speeds as rendered the application of steam power to navigation altogether of no value. 114. For such reasons, the paddle wheel was condemned as useless; and the ingenuity of the curious was busily engaged in attempting to find out or adopt some other means for attaining the same end. 115. An intelligent Frenchman copied the very beautiful action of the duck's foot,' collapsing when drawn forward, and expanding when pushed back. Another individual applied paddles vertically to the sides of the vessel, acting similarly to those used by the Indian in propelling his canoe. Another had a series of float-boards attached to a beam, which were drawn through the water, raised, carried forward, depressed, and again drawn back. Again, the idea of driving water in at the bow of the vessel, and forcing it violently out at the stern, by means of a pump or pumps, occupied the public attention for some time; this scheme was also soon abandoned. Many other plans were successively tried, which it would be useless here to enumerate; it must be acknowledged, however, to the credit of the inventors, that all these various contrivances performed their duty, but at a speed so slow as to be discarded and thrown aside nearly as soon as they were completed. 116. There have been, however, one or two adaptations introduced within the last few years, which have attracted more attention than any of the former ones; namely, the screw propeller, and the chain and drum. The former consists of a screw, similar to that ascribed to Archimedes, placed horizontally in a chamber in the bottom of the boat or vessel, which is caused to revolve by means of gearing worked by a steam engine, and so worms the water through it; thus causing the vessel to advance without creating the back-water and undulations produced by the paddle wheel. The latter plan is to have a continuous chain laid along the bottom of the canal, which is passed round a drum on board the vessel, and again let down through a hawse pipe at the stern; thus, upon the drum being caused to revolve, the vessel is drawn forward. These two plans, however, are more adapted for canal navigation, where the undulation of the water which would be caused by the use of paddle wheels is so very injurious to the banks, than for any other kind of navigation, in which the paddle wheel is most certainly more efficacious than any other combination yet in operation. 117. The revival of the paddle wheel, and consequently almost the actual existence of the steamboat, at least at so early a date as it did come into use, was owing to the unprejudiced and energetic mind of the elder Stevens; who, when trying his experiments, was requested by one of his men, to make use of a wheel similar to the common water wheel, which he, amongst the rest, imagined much too simple an apparatus to effect such a purpose. He did, however, try the plan, and as it certainly answered his views better than any other contrivance, it was forthwith applied to boats by himself and others. 118. The credit of this, however, still remains with the family; and Mr. R. L. Stevens, one of the sons, has, within the last few years, considerably improved the paddle wheels; which improvement is now in general use throughout the United States and elsewhere. It should here be remarked, that the steam engine has been considerably improved in the meantime. 119. The first wheel used was a simple wheel with buckets or float-boards, radiating from the centre, and extending across the whole width of the wheel, in a direction parallel to the shaft or axle. 120. In the next, the floats were so arranged as to enter the water rather more at a right angle; this plan was soon condemned, as the wheel had a natural tendency to raise the water. The floats were again altered, and they were placed diagonally, instead of directly, across the width of the wheel. All these changes were for the purpose of obviating or removing, if possible, the bad effects of the back water and wave caused by the common float, which materially retarded the speed of the vessel; still the object was only partially gained. At this time, as before stated, Mr. R. L. Stevens applied his mind to remedy this evil, and he consequently introduced the split bucket, now so much used; how far he succeeded in accomplishing his object may be readily seen, by observing the great difference between the action of his wheels and others on the old plan, upon the water. 121. The paddle wheels of the new North America' are on this construction, (of which plate 27 represents one,) with the method of attaching the buckets or float-board. 122. The subject of paddle wheels, and the desire to overcome the above mentioned objections to the use thereof, at least in their original form, has occupied no little of the time of Eu ropean engineers during the last few years. Many patents have consequently been taken out, for combinations tending to this desired end; but, generally, the great expense attending their outfit, and very great liability to derangement, have confined their use to experimental vessels not adapted to ocean navigation. Morgan's patent paddle wheel, which is one of the best, has been successfully applied to some of the British steam vessels of war; their expense, however, and their complication has deterred most materially their introduction into general use. 123. It had now become obviously a great desideratum to arrange such a wheel as should obviate the original objection to paddle wheels, without incurring the objections to Morgan's wheel. Mr. Joshua Field, the celebrated English engineer, undertook, in consequence, a series of experiments on the comparative value of different arrangements, into which he entered with great accuracy and care, and the result he has embodied in what he terms the "Cycloidal Paddle Wheel." Such is the wheel which he applied to the 'Great Western' steam ship, now trading between this port and Bristol, and which is also applied to the steam ship 'British Queen,' between London and this port. This wheel, for ocean navigation, bears superiority over all others; as from its form it takes the water gradually, and, from the narrowness of each float-board, it lifts little or none; making, in consequence, a very small wave when compared to the old bucket wheel. |