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August, 1914 & ¢C c o--2 2 ° oO 2° ° oO Qo jo 0 FT]! le HinF of 8 B o 0 a THE MARINE REVIEW 31/7 CSN ciency. In some instances in reciprocating engine vessels, a lower speed propeller than desirable has been fitted to suit the engine speed, but with the reduc- . tion gear, the propeller speed can al- ways be made to meet the require- ments of maximum propeller efficiency. While in most cases the revolutions per minute of a reciprocating engine can be made high enough to give a propeller of maximum efficiency, it is, of course, well known that quite a considerable increase in propeller speed is permissible without decreas- ing the efficiency of the propeller. There are a number of important advantages resulting from the use of the fastest running propeller, which will give maximum efficiency, and these may all be secured by the use of reduction gears. The higher propeller speed and con- sequent reduction in diameter permits deeper submersion of the screws and less | liability to racing in weather, thus allowing a high speed to be maintained. The deeper sub- mersion also reduces the danger of the propeller striking floating objects which might cause the loss of blades. With the reduction in the diameter, Net only is the original cost of the Propeller materially reduced, but like- Wise the cost of renewals and repairs mM case blades are lost, and further- Ore the reduction in weight may be Sufficient to warrant the use of bronze Where otherwise cast iron propellers would be fitted. -- use of the highest propeller ate aa with maximum effi- die also materially reduces the ia a of the tunnel and tail. shaft- Stern tube, and reduces the heavy -- size of plummer and thrust blocks, resulting in a very substantial saving Also the tunnel shafting in weight. of small diameter is not subjected to such high bending stress due to any slight misalignment or bending caused by "hogging" and "sagging" of the vessel, and consequently the plummer blocks are not so heavily loaded and the wear and danger of heating of the latter is minimized. A further desirable feature of the hydraulic floating frame is that the oil and a certain amount of air which is always entrained with it, serves to act as a dampener, and reduces the noise to a negligible amount. In fact, the noise made by gears fitted with the floating frame, is certainly not in excess of that produced by a recipro- cating engine developing the same power, and such noise as is produced, is of a very low pitch and is not of a disagreeable character. Two of the most essential require- ments in passenger service, are absence of noise and freedom from vibration. Fortunately, high speed _ turbines with short blades do not produce any appreciable noise, whereas, the slow speed turbines with long blades, which are necessary in direct connected in- stallations, produce a_ singing noise far in excess of that made by a re- duction gear fitted with an hydraulic- ally floated pinion. In regard to vibration, the geared turbine has all the advantages of the direct connected turbine in the ab- sence of reciprocating parts, and has the advantage that, owing to the slow speed of the propeller, the latter works FIG; 5