New Steamship Propeller.
Recently a number of scientific gentlemen, including Rear-Admiral George Brooker, C. 8.. Capt. W. G. N. Burner, and others connected with the Royal Navy and Mercantile Marine, attended at Gravesend for the purpose of taking a trial trip on boitrd the steam yacht Jolair with the object of testing the advantages of a newly-invented propeller.called “ De Bays’ Patent Direct Acting Propeller,” with which it has been fitted. Its construction is of a very peculiar character, and consists of two screws of the same pitch, one, the larger, with four, and the other with five blades ; portions of the blades of each are cut out. The screws are fixed on two shafts, one tubular, the other solid and rotating within it, each screw being made to revolve in opposite directions, the solid portions of each blade of one screw passing through the gaps cut in the other, and vice versa. The effect of this, in the first place, is to prevent the tremendous rush of water flying at a tangent in all directions from the ordinary screw, and drives the greatest weight of water astern in a line with the keel °f the ship, thus entirely obviating that waste of power which is the consequence of the effects of the ordinary screw. The influence of onescrew tending to deflect the water moving astern to the right is counteracted by the other screw, which .tends to send it to the left. The result is that the water can only be diiven direct astern by the screws, and moves very steadily in a right parallel with the keel, thus concentrating all the force of the water on the stern of the vessel. The company were met on board the Jolair by M. de Bays, ami having had the construction explained to them, the trial of the tests was made. In time the mile was run with the tide by the old propeller in 6min. 325 C.; whilst the time occupied by the new propeller was smm. 30 sec. ; against tide, old propeller, pmin. 57sec.; new propeller, pmin. 32sec. The whole of the experiments took place passing down the river in.the direction of the Nore, and in making a complete Circle the time occupied was 2min. 3fisec. In order to test the powers of the new propeller, and its efficacy in reversing and going astern, some reed covers of wine bottles were thrown from the stern at a moment when the yacht was going at the rate of eleven kn ts an hour, with tide. The order was given to reverse the engines, and the result was that the time occupied in 'reaching the floating covers was but 52sec., and that straight astern, without any divergence of the head of the vessel. This is considered a most important feature in the avoidance of collisions on rocks or other impediments ahead. It was suggested by Admiral Brooker that the complex machinery of the screw might cause it to be damaged by ropes or other substances getting into it, and the test was applied by throwing out ropes, which for a long while were regulated by the screw, till at last one of the men called out that the rope had caught, but there was no jerk, and in an instant it was loose, when it was discovered that the rope was completely cut by the flanges of the screw, a result consideied most saiisntctory. Another important feature connected with the test was to show that even in the smallest rivers and canals there was no side wash to destroy banks, &c.
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