A GREAT SCREW. [From Dickens's Household Words.]

New Zealand Spectator and Cook's Strait Guardian, Volume IX, Issue 895, 1 March 1854, Page 4

A GREAT SCREW. [From Dickens's Household Words.]

When Mr. Hargreaves rode to Sydney with a small piece of gold and quartz-rock in his pocket, be could scarcely have understood that he carried with him that which would not only change the destinies of the great Australian continent, but likewise effect to a large extent a revolution in the commercial relations of the whole civilised world. And when, on the first of May, eighteen hundred and fifty-one — the very day on which our Great Exhibition in Hyde Park was opened — the Governor of New South Wales penned his official sanction to the gold explorer's further labours, neither of them can have pictured a tithe of the mighty results which were destined to originate from that one epistle — What great events from trifling causes spring! Few things of moment have bad more insignificant beginning than the screw propeller for steam-ships^ and few inventions are destined to produce more important benefits, more especially in connection with the great gold results which have sprung from Mr. Hargreaves's trifling nugget. The Australians can no more get on without the potent aid of the screw than they do without cradles, dampers, wide-awakes, Guernsey shirts, and patent revolvers. The screw will bring them within a fifty-five days' run of home. The screw will drive their gold to the marketsof Europe more safely and expeditiously than any other propeller. The screw will enable their " made men " to reach the mother country without a oale or a fit of sea-sickness by cheating both the much dreaded Capes. The screw is in fact, the Australians' " coming machine." Many of the most valuable scientific improvements have been brought to light by unexpected agencies. Amongst the hundred and fifty patents which have been taken out for various applications of the screw propeller, may be found, in addition to the names of engineers, machinists, sl)ip-build°rs, and other professional men, those ot ropemakers, farmers, printers, wharfingers, merchants, soldiers, and noblemen ; snd ii is an undoubted fact thai the most valuable additions made to our stores of screw knowledge have come from men uneducated for, Bnd unconnected with any branch of practical engineering. Whilst machinists and civil engineers iiad for fifty years failed to contrive any really practical adaptation of the screw for propulsion, the laurels of screw science were won, first, in seveuteen hundred and ninety-four l>y a merchant, and sine?, in eighteen hundred ami thirty-six, jointly by an English farmer, and a Swedish military officer. The first attempt at screw propelling, which in any degree realised its object, was that of Mr. Lyttleton, a merchant of Goodman's Fields. It was, however, too rude and inefficient for practical purposes, and was laid aside with scores of other useless projects which saw the light between that period and the year eighteen hundred and thirty-six. One single exception to this array of failures is to be found in the improvement of a Mr. Cummerow, also .a merchant of London ; who, in eighteen hundred and twenty- nine, placed tbe screw between the stern of the ship and the rudder-post, a principie which has been since adhered to. Early in the spring of eighteen hundred and thirty-six, Mr. J. P. Smith, a farmer of Hendon, obtained a patent for a new screw propeller; and so well did be succeed in working his first little model exhibited at the Adelaide Gallery, that he obtained assistance which enabled him to build and fit up a small vessel of six tons. During the month of November of the following year, the screw-propelling farmer ventured out to sea in his toy-ship ; and proceeded boldly down Cbanuel, making excellent progress through a stormy sea, and dead against the wind. So complete was the triumph of the screw, that all tbe scientific world were convinced ; and even the Admiralty found ears to listen. A large vessel was consequently built, in which many of the, naval authorities made experimental trips to sea and round the English coast, with such success that eventually Government formally adopted the new propeller, and laid down the Rattler of eight hundred and eighty-eight tons, to be fitted with engines and a j powerful and improved screw. By this time an j accident which happened to the first wooden model, demonstrated that a short screw, with narrow fans, was better than a long screw with broad fans ; and the iron screw made /or the Rattler was of a double thread, but of only onesixth of a convolution. A year or two later tbe principle was so completely established in the royal dockyards, that twenty ship of war were fitted with auxiliary screw-power. i While Smith had been thus active, Ericsson, a Swedish officer, had also laid before tbe authorities a screw cf a novel construction ; but however well this may have worked experimentally, tbe Government were not at that time disposed to think favourably of tlie new propeller, and Ericsson carried his patent to tbe United Slates, where be also improved oa Stirling's hotair engine, but only with partial success. The latest and most valuable advance in the construe-

tion of screw propellers is that made by Mr. Griffiths in which — by a modification of the breadth of each section of tbe curved thread, by altering the size and shape of tbe screw's centre, and not less by an ingenious contrivance for " feathering" the blades, and diminishing or increasing their pitch or slope at will— has greatly added to the value of screw machinery. The merchant service and public companies have equally availed themselves of the invention ; and, at the present time, some of the largest ships afloat are screw-propelled. Indeed, so marked are the advantages of the screw over tbe paddle, that there is little doubt but that the former will eventually be superseded, except in navigating shallow water ; and a paddle steamer across the ocean will, twenty years hence, be as rare an object as a stage-coach on the high roads of Britain. Having thus sketched the progress of Screw Steam Navigation, a short space will suffice for an explanation of what this screw consists, bow ! placed, and in what its great advantages reside. The reader will, no doubt, gladly be spared a treatise on the resistance of fluid bodies, on the true pitch and disc of screw propellers, on positive and negative slip, or centrifugal action. It may be enough to say, that screw propellers now most commonly in -use rre what are termed double-threaded, of about one-sixteenth of a convolution ; in plainer language, they consist of two twisted iron blades fixed upon a shaft revolving beneath the water, at tbe stern. Tnis shaft is surrounded by a stuffing box.with hemp-pack-ing, to keep the aperture in the ship's stern watertight ; its extremity is set in a socket attached to the rudder-post. The screw itself revolves in that part of the stern of the ship called the deadwood, in which a suitably sized bole is cut to admit of its working. It is the thrust, or forward pressure of the blades, or sections of the screw-threads, which is effective in propelling tbe ship. Numerous trials as to the relative qualities of the paddle and the screw have resulted in a most complete demonstration of the superiority of tbe latter as an auxiliary power to vessels under canvas. For long sea voyages, in which calms, light airs, or fair breezes are looked for, a screw ship of fifteen hundred tons and three hundred horse power, would be preferable in point of speed and economical working to a paddlo steamer of tbe same size and of three times the horse power. It has been clearly shown that a screw steamer makes as much way under canvas and with balf-steam on, as without sails and with her whole steam power applied. Indeed, wbereever sails can be used at all, the advantages of tbe screw appear most clearly : even in sailing close-hauled to the wind, a vessel by the aid of tbe screw may be propelled four knots, when previously only making one knot an hour. Experiment has demonstrated that an auxiliary screw-power sufficient to propel not more than a mile and a half an hour, when brought to the aid of the sails, has in reality added three or four miles an hours to her speed. This is accounted for in tbe following manner : — when the vessel is propelled by canvas alone, and at a low rate of sailing, the wind quickly rebounds from the sails, and forms a sort of eJdy or dead air in their rear, which adds to an extent adversely ; for the sails do not receive nearly the whole advantage of the breeze ; but, the moment more speed is imparted by auxiliary power, the sails retain the wind longer, having more of it, and there is not the s»me drgree of rebound. In like manner the sails assist tbe action of the screw, by enabling it to work upon a larger surface of water, and so extend its power It is evident, therefore, that except in running against a head gale, the screw-propelled ship must have the advantage. In regard to tbe original cost and working the two kinds of steamers, there is an enormous difference. Calculations show that the relative expense of the three classes of ships is as nine for paddle-steamers, to four for sailing-vessels and three for auxiliary screwships. Looking to these advantages, it is highly interesting to examine in what direction screw steamers fitted on the auxiliary principle are most likely to prove of the greatest utility. It was a happy circumstance that, coeval with the extension of the British possessions iv that most remote part of the earth, the great south land of Australia, tbe screw principle should have been brought forward as a means of economising the use of fuel. By any of the routes to the colonies of Australia, the voyage out and home, of a sailing vessel, has been to the present time a most tedious and unpleasant affair. It is is true there are Marco Polos, Flying Dragons, and Sovereigns of the Sea, which have made rapid passages with sails alone ; but we all know what tbe old adage tells us about one swallow not making a summer. An average taken from the voyages of six hundred vessels out and home, in 'thirty-nine and 'forty-nine, gives one hundred and thirty-four days as the outward run in the former year, and one hundred and nineteen days for the latter ; whilst, for the homeward voyage, I they were one hundred and fifty-one and one hundred and twenty-eight days. In 'forty-nine, the longest passage made to Port Phillip was one hundred and eighty-six days ; the shortest, one hundred and one days. This is tedious work; knocking about in calms, gales of wind, and adverse breezes, during those one hundred and eighty-six days, with the biscuit green and wormy, and tbe water looking like bad pea-soup, smelling of stale rum casks, and tasting of log-wood and rusty nails. Still it did not much signify when emigrants were few ; when the homeward-bound with fortunes were still fewer ; and when tbe great bulk of the cargoes from those countries consisted of wool, tallow, and copper ore. The golden dream of Hargreaves in eighteen hundred and fifty-one has become a splendid reality in eighteen hundred aod fifiy-tbree ; and a cornmuni.y, suddenly convened from shepherd*, storekeepers, and convicts, to capitalists, landholders, and bankers, demands some more rapid means of communicating with Europe than the collier craft hitherto employed in the trade to Australia. Two years ago a Committee of the House of Commons made r.n inquiry and published a report upon the subject of communication with the Australian colonies. Three routes were proposed to the committee and evidence adduced on behalf of them all. These consisted of — first, tbe present overland route to India, with a branch line of steamers to ply between Singapore and Sydney ; secondly, direct communication with the colonies

by way of the Cape of Good Hope ; and thirdly, f a line proposed by a new steam-packet company, to run more directly than either of the other ' routes, across the isthmus of Panama, across the Pacific ocean by way of New Zealand to Sydney and Melbourne. The two former were adopted by the Government authorities, for the mail ser-» vice ; nevertheless, so convinced were the projectors of the Australian Pacific Mail Steampacket Company of the superiority of the Panama line, that a fleet of six iron steam-ships of two * thousand tons, and fitted with powerful screw engines, were at once laid down. Two of them are already launched. The Cape and India lines have been working i for some time, and the result of their operations furnishes toe best answer to any speculations on the subject as far as speed is concerned. By way of Singapore the rxail contract to Sydney bas bten performed in eighty-three days, and homewards it has been accomplished in eightynine and eighty-six days. The Cape contract 4 bas been still more unfortunate, the ships in that service having occupied between ninety-four and one hundred and twenty days outwards; and, on the homeward run, something more. The above 1 work has been performed by paddle steamers, ami certainly offers no advantages over some of the r improved sailingvessels which now make the runin eighty to ninety days. , Although it is thus shown that the Peninsular and Oriental Company's vessels have failed in opening a rapid communication with the southern and eastern poits of Australia, they have unques- > tianably achieved great success on the Indian line ; what they have performed on the Suez routs to Calcuttt, the Australian Pacific Company will in a few more months accomplish by means of the isthmus of Panama and the Pacific, for Melbourne and Sydney. * By no means the least important feature in this new route is the existence of extensive coal-fields in New South Wales and New Zealand; existing as if expressly to further the great scheme which is now being matured of encircling the world with a chain of iron and steam. Looking at the relative positions of Australia, Panama, and England, it cannot fail to be evident that no difficulty will be experienced in keeping up a regular monthly and even fortnightly communication, in about forty-five days. Time is the one great consideration in all business transactions, and it is difficult to over-estimate the effects of thus bringing our friends in the golden colonies so near home as to enable us to receive replies to our letters in something over a hundred days, or in less time than it now requires to convey a letter out- < wards by some of the steamers of the Cape. The accomplishment of this roust constitute the Pacific route the great post-road to Australia — the highway for passengers, as well as the main gold channel thence to this country. The Australian merchants will economise a large sum annually by the saving of interest on the value of the goM sent home by this line — the result of bringing it hoaje in fifty-five days instead of eighty or ninety days as at present. This saving upon only half the yield of the Australian gold-fields would amouiu to a very considerable sum; thus verifying the axiom, that "Time is money." From Southampton to the Atlantic side of t lie Panama isthmus, the service will be performed by the Royal Mail Steam-packet Company, which is now building five new vessels, of great speed and accommodation. They are intended to ply in connexion with the ships already running to the West Indies. Arrived at Panama, ihe outwardbound tra\eller will find a railway ready, with nil its appliances, to whisk htm across the narrow band of earth (forty-nine miles in breadth) which separates the two great waters of the world. This line will be opened for traffic early in the ensuing year, twenty miles of it being already in operation, and steam will thus sink the distance mio utter insignificance. The shortness of this route is, however, not its only recommendation. The fair winds, the placid sea, the beautiful climate, all point to it as one that will be traversed in far more comfort and bodily enjoyment than any other. From January to December an unceasing monsoon wind blows across the South Pacific, always available, and, for auxiliary screw steamers, the finest breeze that could prevail. This would indeed appear to be the best field in which the many advantages of Screw Steam Navigation could be, shown. With an eight knot breeze, and all canvas spread, the Black Swan or the Emu iron steamers, aided by half steam power, may bound across that unruffled ocean, with a speed realizing the flight of their living namesakes across the great Australian prairies, It was this delightful region which enchanted the earliest English and French navigators ; it was here th'e adventurous Cook spent many weeks of his ocean life ; and it was from (his part of the Pacific that the author of Typee and Oraoo drew the materials for his interesting tales. For the return voyage, winds, nearly is favorable, are to be found by steering well to the southward for a short time after leaving the Australian continent. In these latitudes westerly breezes blow for a great part of the year, which will not fail to carry a vessel to the South American coast in fair weather. A screw vessel need not make the American coast; but, by steering towards the north, when within a certain distance of the land, the isthmus of Panama will be easily made. It should be borne in mind that, during the whole voyage, there is one continuous summer breeze and summer sky ; not a clcud dims the bright blue of the tropical sky ; the unruly wave seldom troubles the face of the well-named Pacific. By this route the passengers need fear no storms ; no heavy squalls of wind or rain; no unpleasant motion of the ship. The terrors of the much dreaded "Cape of Storms" are escaped equally with the piercing cold of Cape Horn in a voyage which the most delicate and nervous may uudertake without fear or inconvenience. Whether the great ship-canal which is promised to connect the Atlantic and Pacific oceans will be realized, or whether railways continue to be the means of transit across the Isthmus, will not affect the certain and speedy success of the "great screw" question in a region which, of all others, appears to be the best adapted to a mode of propelling ships, which is at once economical, rapid, and agreeable.