TRANSACTIONS OF SECTION G. 779 



of steam in tbe steam-eDgine cylinder will thus be 1 lb. + i. - when the evaporation 



Li 



takes place under constant pressure, although it is only 1 when evaporation takes 

 place under constant volume. The heat required for evaporation under the author's 



assumption for the one pound of steam in the steam-engine will be L + =. — (T-<o), 



Ij 



T being temperature of evaporation and to the temperature of the feed water. (In 

 the elementary case T = to.) This, it must be noted, is the heat that will be required 

 for each pound of steam accounted for by the indicator. 



4. On a new System of Screw Propulsion tvith non-reversible Engines.^ 

 By W. WoRBY Beaumont, M.Inst.G.E. 



At the present time all screw propellers are driven by engines, which must be 

 so designed that they may be fitted with all the paraphernalia necessary for 

 reversing. 



A considerable part of this reversing gear must be at work during the whole 

 of the time the engines are running. Thus, although it may not be necessary to 

 reverse the propeller or the direction of motion of a ship during a long run, the 

 quickly moving parts of this gear must nevertheless be kept at work all the time. 

 In order to avoid the practical objections to this, and the stresses which are 

 brought to bear on the propeller and screw shaft by reversing the direction of their 

 rotation, it is now proposed to effect the reversal of the direction of motion of the 

 ship by means of tbe propeller, and the object of this paper is to bring before the 

 Mechanical Science Section of the Association a description of tlie apparatus 

 designed for this purpose by Mr. Robert McGlasson. 



For several years tlie feathering screw propeller has been in use on a consider- 

 able number of vessels. By means of this, known as Bevis' propeller, tbe angle 

 of the blades may be shifted by gear in the screw shaft tunnel, so that they may 

 be placed fore and aft, and thus offer no impediment to the motion of the ship 

 when it is desired to employ sails instead of engines. 



By means of the same propeller the angle of the blades may be set so as to alter 

 the pitch to that which may be found best for the ship, or to suit it for very low 

 power when only slow steaming is wanted. As employed for these purposes 

 this form of propeller has been long enough in use to show its practical sufBciencj-. 



By an extension of the application of the principle of this propeller, it is now 

 seen to be possible to achieve several ends which are considered to be of great 

 importance. Some of these may be enumerated as follows : — 



1. The propulsion of ships by means of screws, which rotate always in the same 

 direction, and may be actuated by non-reversible engines and screw-shafts. 



2. The simplification of marine engines, by dispensing with all the parts at 

 present used for making the engines reversible. 



3. The complete and quick reversal of the direction of propulsion of the ship, 

 without any of that heavy stress which often amounts to strain and rupture of the 

 screw-shaft, or couplings, or crank-shaft. 



4. The facile adjustment of the pitch of the screw blades while the engines are 

 running, so that the pitch may at all times be set to suit the form, trim, and con- 

 dition of the ship, the requirements of navigation, or any sudden emergency 

 requiring prompt action. 



The extension of the application of the principle of the feathering screw consists 

 in the employment of apparatus by means of which the pitch or angle of the blades 

 is always under control, and may be changed from moment to moment with the 

 same facility as is the rudder by means of steam or hydraulic steering gear. 



Either form of the apparatus thus employed operates by moving in one or other 

 direction a sliding collar on the tail shaft. This collar is connected to the rod of 

 levers which gives angular motion to the screw blades. 



' The discussion on this paper was given in Engineermg, September 4, 1891, 

 p. 2G9 ; and the paper with illustrations was published in Industries in September 

 1891 ; and in the Marine Evgineer, October 1891. ' 



