SCREW PROPULSION.

Kumara Times, Issue 896, 14 August 1879, Page 4

SCREW PROPULSION.

The Times, of April 18, says that a new feature in connection with the working of the screw-propeller has recently been determined by Mr if. Griffiths, whose name has long[been known in connection with tbemethod of propulsion. Hitherto screw-propellers have been placed as close as possible to the stempost of the vessel, but this position Mr Griffiths has proved to be the wrong one. From a long course ef careful experiments he has been led to conclude that the propeller should be placed some little distance from the sterii-post and close to the rudder-post to get the best effect as regards speed. To demonstrate this some trials were recently made with a model boat sft in length, fitted with an ordinary screw driven by clockwork. The screw was four bladed, 3Jin in diameter, and 3.9 m pitch, and was, in fact, a copy of the screw - with which the Peninsular and Oriental Company’s new steamship Kaisar-i-Bind is fitted. By fixing the screw fiveeighths of an inch from the stern a speed of 100 ft per minute was obtained. By increasing the distance to three-fourths of an inch the speed was increased to 104 ft per minute. Placed at 1 Jin from the stern-post a speed of 110 ft per minute was attained. The screw was then shifted to what Mr Griffiths considers to be the best position, namely, 2Jih from the stern-post, and this resulted in a speed of 114 ft per minute. This shows an ultimate increase of 14ft per minute' upon the first arrangement. The ordinary screw was then removed, and in its place was fitted a Griffiths’ four-bladed screw of similar dimensions to the one it replaced, but having the forward edge of each blade cut. off. This screw was first fixed IJin from the stern-post, and a speed of 116 ft per minute was made. At 2Jin—the best position -the speed was 122 ft per minute, a part of the deadwooo, 1 Jin long, was-then removed from the stern and the screw was placed 2in from the end of the ship thus exposed, when the speed attained was 110 ft per minute. The screw was then removed 1 Jin forward, or Jin from the end of the wood, and the speed was only 48ft per minute. It will be seen that in both cases the highest speed was attained with the screw in what Mr Griffiths considers the best'position, but that the Oriffiths’screw gave a higher speed than that of ordinary construction under similar conditions. So far a,s these experiments go Mr Griffiths has Certainly made out a good case, and if the results of practice only correspond with those we have given, an important advance will have been made in screw propulsion.