SPEED OF OCEAN STEAMERS.

New Zealand Times, Volume XXXII, Issue 4939, 20 January 1877, Page 2 (Supplement)

SPEED OF OCEAN STEAMERS.

Mr. John Giles writing to l\\e Sydney Momht.rj Ilmdd on the speed of ocean steamers, advances the theory, which lie lias tested by experiment, that by altering the position of the screw a greater rate of speed could be obtained with a smaller expenditure of force. Ho asks the questions—“ 1. Can a given force bo applied continuously to a body in motion without that force being affected in the rate of its expenditure by the velocity with which the body moves ? 2. By what means, and by wbat expenditure of power ? ” He answers the first question in the affirmative, stating that it could be done by deflecting the line of propelling force from the line of the ship's motion, lie goes on to say “ The deflection of the line “f propulsion from the line of motion can bo most effectually and completely aecornnlislied by projecting the shaft of tin* screw upward-', through the keel of the vessel, at a pohit near tho vessel’s longitudinal centre or oravitv, so that tho plane of the screw is at an Hindu of 45deg. with the water level, Cert in modifications of naval structure ere ncecsBitry for the safe adoption of this method ; hut, finch modifications are all steps in the direction of increased speed, economy, and safety, ami are exhibited in the model mid ilrawj. gi. Tiio experiments made by the writer i the subject were male with the aid of a'small bout. so constructed that the same Hcrew could be worked both vertically mid_ obliquely, under precisely tho same conditions o' depth of immersion and propelling force, and the result invariably was that tho oblique screw propelled tho Vessel over a given space in a given time with less limn half tho number of revolutions in -do by the vortical screw in p-noiming the same wink in tho same time, and, thcre'ore. with less than half tho consumption of mechanical power. 1 only quote tin- as a practical verification of tho truth of the principle, because! it is quite possible to ar ivn at an approximate estimate of the value of oblique propulsion in comparison with the method new in use by analysing the im-chani-c; 1 rorco us d under tho two methods” Mr. Giie- explains that “the aciew (nr paddlev.lnel) operates by the process of recoil ; it p-opi-ls the riiip one v ay and the water the other 'I ho measure of ils ■ fleet upon the ship depends upon the stain l .ty of tho water ; ilm otner hand, it- effect on the water depends upon the stability of the ship. If the ship is secured - stationary, the effective force

of the screw i; all spent upon the water ; and, on the other hand, the more stable-the water, tin* greater will bo the impelling force upon tin- v sscl. It is of the utmost importance, therefore, to apply the propelling force so that it may be free of the current created by the hip’s motion.” According to Mr. Gim» a plan, the propelling force is so applied, and m-er-ased speed thereby obtained. Mr. Gj lo ’ lias exhibited a model and drawings _ot ft steamer fitted with the oblique screw in the Sydney Exchange.