Screw propellers

It has been contended for a considerable time by engineers, that the submerged propeller, as a mode of propulsion, was not the best adapted to the higher rates of speed in navigation, and that whatever might be the form, whether that of the regular, that of the irregular, or no screw at all, it could not supercede the paddle-wheel, in its adaptation to all the purposes of navigation ; and, indeed, so strongly impressed were some in favor of paddle-wheels, as being the very best application of power for propulsory purposes, that they have refused to entertain any proposition for propulsion which had no paddle in it. The slip of the wheel was acknowledged, and the proper modes of reducing the same to a mere moiety, were also referred to ; and, indeed, it was supposed that the mind must indeed be set at a most obtuse angle if it could not grasp, and at the same time coincide with, the proposition. On the other hand, the adherents of the screw have had so much confidence in it, on both sides of the Atlantic, that they have applied that great engine, the press, to their different modes of submerged application, and the result has been that we have had newspaper articles, pamphlets, and bound volumes in abundance upon the subject. Finding that the Empire City had taken such rank hold of side-wheels, the people of Philadelphia claimed, as their share in the distribution [p. 408] of knowledge, all that pertained to the application of the screw in submerged propelling power. And thus, at the date at which we propose to begin, the two modes of propulsion each had its adherents, without the least prospect of a compromise. We have not the space, had we the desire, to go back and examine all the sensible and senseless propositions which have been inducted into this department of the mechanical world, nor do we believe the readers of the Nautical Magazine would be interested by so doing ; and shall therefore carry out our review of the past few years, seeing that it would be injudicious to continue an article beyond the close of the volume. Steam navigation on this side of the Atlantic has been fairly divided into two kinds: the side-wheel, and the screw. The prejudices against the screw, in New- York, were very great ; a circumstance our neighbors did not fail to notice and turn to good account, and having the experience of our trans-Atlantic friends, they found no difficulty in following in their wake. The rivalry in steamboat travel on the Hudson River, Long Island Sound, and about New York, rendered it quite apparent that the fastest boats must be had, and that New York would be able, in her favorite mode of propulsory application, to secure the fastest river boats in the United States, if not in the world. Their complete success on this kind of vessel induced capitalists to suppose that they must be equally successful in submerged propulsion ; and, as a consequence, several large vessels for sea-going purposes were built, which, for want of adaptation in power and its application to resistance, proved to be little better than total failures. This encouraged the adherents to side-wheels in New- York, and was equally advantageous to the friends of screw propulsion in our sister city, encouraging the belief that they would be able to enjoy the exclusive benefit of what they were pleased to call their favorite mode of propulsion. Things moved on quietly, for a time ; the metropolitans of com- merce built side-wheel ocean steamers which were the admiration of the world, unequalled in beauty and speed ; and if New York required any propellers, they must be built in Philadelphia, as a matter of course. Still, there were some radicals in the Empire City, who obstinately persisted in maintaining that [p. 409] whatever had been done in Philadelphia could be done in New- York, and they perversely adhered to this opinion with such tenacity, that they actually made some of the merchants believe it, and the consequence was that several vessels were built, and the submerged application of propulsory power adopted ; when it was fairly yielded that it was in the men, more than in the locality, that success depended. But what is most remarkable in the history of screw propulsion is, that so completely had the manner of its adoption in England been followed by the engineers of the sea-board in the United States, that, in many instances, the success of the one seemed to be but little better than a duplicate of the other. On the other hand, in side-wheel propulsion the mechanics took independent ground, and thought for themselves, both in their engines and in the proportions of their paddle-wheel; and so far did they carry their improvements in the engines that, in many instances, they laid aside all other kinds of engine but those of the vertical beam, such as is used in the river boats -- purely American. The mechanics and engineers bordering on the fresh water inland seas were still more independent and self-confident -- too much so to be led by either the English engineers, or those of the city of brotherly love. Their navigation demanded a moderate draught of water and all the speed that could be obtained ; but, in addition to this, the season, at best, was not of greater length than was required for the work to be done, and a more reliable mode of transit than wind was desirable. They had obtained some experience both in paddle-wheel and screw propulsion : this, to them, had been of more value than an equal amount had proved to be on the sea-board. They had found some significance in the fact that their screw vessels ran about as fast loaded as they did light, and that the unimmersed section of the propeller, when the vessel was light, did not bear the same ratio to the diameter of the screw that the resistance of the emerged part of the vessel did to that which was immersed. Hence it was clear that a complete immersion was the most effective ; but to obtain this at all times would be to increase the draught of water, and inasmuch as this would not secure ingress into all the harbors, the conclusion was deemed a safe one to increase the diameter [p. 410] of the screw, though, as a consequence, it should never be submerged. The philosophy was sound, that inasmuch as the outer edge of the blade was most effective, by keeping it the same distance below the surface, and at the same time increasing the diameter, would secure the most efficient service, all things else being equal. Upon this hypothesis large screws were introduced with the most flattering success. Not content with the advantages gained, its advocates sought every opportunity to compare its power with the side-wheel, and they were not long in deciding that its powers for towing were decidedly the best. But as one innovation only paves the way for another, some daring spirits were of the opinion that if one propeller was so good on the stern of the vessel, that certainly one on each side would be still better; and we accordingly find that the side-wheel steamer Baltic, of Buffalo, was dismantled of her wheels to make way for a pair of side-propellers, on the plan of, and under the direction of, Capt. H. Whittaker, a man well known in the history of steam navigation on our inland lakes, whose observation and experience furnished a fund of knowledge well-adapted to a progressive mind. The Baltic, having been completed as a freight-boat with side-propellers, supported and protected by a guard, as in the paddle-wheel, has run one season, establishing the feasibility of the application of screws on the sides of the vessel. Capt. Whittaker proposes to apply three times the motive power on boats of the same size, or of equal tonnage with the lake propellers, of light build, and fine running model, causing an increase of revolutions with a greater pitch to the screw, which he thinks would travel from 30 to 40 miles per hour when making from 100 to 125 revolutions per minute, and to increase the number of engines and screws in proportion to the size of the boat. The engines to be oscillating high pressure, with direct action, and placed on the gunwale of the boat, two to each screw ; the two cranks attached to each shaft to be at right-angles with each other. On large boats he proposes to apply from two to six pair of engines on each side of the boat, with a propeller to each pair of engines ; the object of which is to save the large amount of power on each screw, which is lost by the present application to the wheel, and this increase he [p. 411] thinks may be obtained with very little increase of weight or expense. Capt. Whittaker is now in New- York with several models of his proposed improvements on exhibition, and, as we learn, he has had the good fortune to find parties to undertake the construction of a steam vessel, for towing, which shall fully test the merits of his invention. It is highly desirable that every innovation in marine engineering should have a fair trial. We shall revert to this subject at another time.