SYDNEY. TRIAL OF THE AUSTRALIAN BOMARENG PROPELLER. [From the Sydney Morning Herald.]

New Zealand Spectator and Cook's Strait Guardian, Volume VIII, Issue 728, 24 July 1852, Page 3

SYDNEY. TRIAL OF THE AUSTRALIAN BOMARENG PROPELLER. [From the Sydney Morning Herald.]

In accordance with the arrangements which formed the theme of some interesting discussion in this journal during the last few days, the steamer £Ceera, which had been fitted with Sir Thomas Mitchell's "Australian Bomareng Propeller," made her trial trip on. Saturday afternoon. A large party had assembled to meet Sir Thomas, amongst whom were Lord Audley, Mr. Justice Dickinson, the Solicitor- General, and many of the leading gentlemen of this city who are interested in maritime and mercantile affairs. At 22 minutes past two p.m., the Keera was put in motion by the Bomareng Propeller (an anxious moment, no doubt, to the inventor) ; and gradually she acquired speed, obeying her rudder from the first, so. as to describe a fine curve on the water from her position- off the patent" slip into her direct course. From the neighbouring wharves the warm cheers of the various parties assembled greeted this first public exhibition of the action of Australia's native weapon in a new element ; and highly gratified are we to be enabled to record the sue-

cessful result. It must be especially borne in mind, that the .rules of construction" upon which Sir Thomas Mitchell had founded the proportions of his propeller had, of necessity, been infringed in preparing the Boraareng Propeller for the Keera. This important point was pointed out by Sir

Thomas in a letter which we published in Saturday^ Herald. Sir Thomas derived his rules of construction from a pitch equal to the dia- ( meter ; whereas, he was obliged, in conformity ■ with the proportions of the Keera, to adapt his propeller to a pitch of eight feet, and to a diameter of only five feet eight inches. Under obviously unfavourable circumstances therefore was the trial made ; nev ertheless the main principle, asserted. by the inventor waa fully established. So soon as the Keera got into her direct course, it was found that her speed surpassed any whioli she hadihitherto attained on this coast. In her course along the first and best authenticated distance, viz., 2177 yards between Blue's Point and Pinchgut Island, the calculations were interrupted by a stop to receive on board some additional visitors, Mr. Robert Campbell, one of the members for the city and his party. But between Pinchgut and Bradley's Head (the flag-staff on the latter being the point of measurement) the distance, 2099 yards, was performed in 6m. 10s. We may here observe, that on the Keera s trial trip on the 10th of February last, she performed this distance in Bm. 20s. Her strokes of the piston,then were 42 per minute ; on Saturday they, between these points, were 55. Greater speed however, was soon afterwards attained ; and a scientific gentleman, who has recently arrived from England, drew our attention to the appearance of the water near the propeller; which, instead of flowing in towards the stern, to be disturbed there as in other screws, allowed the propeller to work through it very quietly. About this time the strokes of the piston were 62 per minute ; and we must particularly direct attention to the fact that, with the English screw in, the engines of the Keera have very seldom indeed been got to work up to 50. This serves to prove the freedom of the Bomareng Propeller from lateral resistance; whilst the greater speed attained •with a surface some 76 inches less than the English one proves, we submit, beyond dou"bt, the efficiency of the Bomareng form as an instrument of propulsion. We must further observe, that the pressure on the boiler never exceeded 10 pounds on the square inch. The hospitable owners cast anchor in North Harbour, where the health of Sir Thomas Mitchell, and prosperity to the spirited owners of the Keera, who had so liberally permitted this trial to be made, were the toasts which were drunk with enthusiasm. Sir Thomas, in returning thanks, paid a warm tribute to Mr. Henry Gilbert; Smith, who first brought steamers into the waters of Australia ; and he also referred to the valuable services of the late Mr. Bailey, Vice President of the Royal Society; Mr. Brunei ; and professor Co wper, of King's College ; each of whom had afforded many brilliant thoughts to guide and encourage the progress of discovery. Sir Thomas observed with reference to the Bomareng, that this weapon had been used in ancient Egypt for the same purpose for which the aborigines of Australia use it, namely, to kill, ducks. He said that this was plainly shown in some of the paintings in the tombs of Thebes ; especially in one engraved in Wilkinson's Egypt ; and also that Egyptian Bomarengs made of hardwood, about 1|- or 2 inches broad, curved, and about two feet long, are still to be seen in museums in Europe, having been found by explorers among the tombs of Thebes. Sir Thomas also observed that the " throwing stick" of the ancient Irish was a missile of the same nature as the Bomareng. It may not be out of place to observe here, that when Mr. Smith, the original inventor of the screw propeller, first applied it to water, he applied. a whole turn of the screw. He then tried two half turns, and, subsequently, other engineers adopted quarter turns of the screw or spiral. Latterly, forms of the windmill blades have been used, and other modifications made, of which the Keera' s screw brought from Eng-land-is one. It was incidentally remarked on Saturday, as a remarkable fact, that whilst such powerful and costly machinery is now applied to large vessels called screw steamers, the form of the instrument by which all this steam power is to be employed against the resisting power of water, is still allowed to depend upon mere fancy. The screw which the Keera brought from England is three-bladed, somewhat resembling trefoil or clover ; and it was stated by a gentleman during the trip, that lately, when a screw of this sort, employed in a steamer in the Mediterranean, lost one blade, she returned to England with her two remaining blades, at far "greater speed than she had ever attained with the three. " This day's excursion satisfies me," says Sir Thomas Mitchell, " that the weapon of the earliest of our kind in Australia has led to the determination mathematically, of the true form according to which alone it will be found possible on the screw principle, to attain high speed on water by the power of steam." Thus extremities meet even on the opposite sides of the globe. , In returning to Sydney, great care was taken to observe the time by stop-watches along the distance between Pinchgut Island and Blue's Pcint. By one gentleman the time was stated to be sm. ss. by another sra. This distance, as already stated, is 2177 yards, or rather more than a nautical mile, which, according to Roe's chart, is 2024 yards. The Keera 's speed, therefore, whilst performing this distance, was fully equal to twelve knots an hour, and this against a rather strong head- wind and tide. The slip was only 2| per cent, supposing the strokes of the j piston to have averaged 60 per minute. - Upon arriving off the Phoenix Wharf, three hearty cheers for Sir Thomas Mitchell were given, and amidst the warm congratulations of his friends the gallant officer left the vessel. It is strange to contemplate the slow progress of a discovery which* is to determine the law of the true form for an instrument of propulsion. We must observe, that Sir Thomas Mitchell's propeller combines the parabolic and cycloidai curves, equilibrium, gravitation, the laws of hydrostatics relating to the pressure on oblique surfaces under water ; and, more particularly, that particular law by which the area must be governed, and which the result of Saturday's trial fully establishes, namely, " that the area of working surface should never exceed the supplement- of the spiral surface over the section taken at right angles to the shaft." Every inch more than this only retards the ves- ' sel, and prevents her from attaining gradually

increasing speed. Few persons seem to remember that- the water will not perform the part of a solid female screw ; that repeated turnings or strokes are necessarj, and they seldom inquire why an oar 'is made of such little breadth ?