702 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 73.24 



side of the vessel. Each scoop was fitted with a 

 flap so that one could act as a discharge while the 

 other was acting as an inlet. By thromng over 

 both flaps, the water direction was reversed and 

 any foreign matter choking the tubes was drawn 

 overboard. At a later stage in the life of the vessel 

 an overboard discharge was fitted in the crossover 

 between the after ends of the condensers so that 

 both scoops could take in water simultaneously 

 and pass it through the condensers in parallel 

 [INA, 1897, p. 233; ASNE, May 1897, p. 376]. 



In the flush-lip inlets of the Schmidt type, in 

 which there is no scoop or external projection as 

 such, it is no small matter to guard against the 

 entrance of large fish and foreign objects into the 

 heat exchangers. Longitudinal bars must be 

 fitted across the scoop entrance, spaced perhaps 

 0.3 ft apart. They need rigidity to serve as guards 

 and to prevent lateral vibration. They must have 

 bolted end connections for ready removal. The 

 flow must be maintained around them in the 

 desired quantity. The bars and their end connec- 

 tions must make so Uttle disturbance that air is 

 not pulled out of solution in the water and passed 

 along to the heat exchanger. For all types of 

 inlet it seems best to mount the guard bars or 

 guide vanes in a single, integral streamlined 

 assembly which can be held in place by recessed 

 bolts and removed as a unit. 



There is great merit in a type of inlet and 

 discharge, hydrodynamically efficient, which can 

 lead into and out of the machinery spaces in a 

 transverse plane, making a rather sharp angle 

 with the shell, up to 90 deg. Such a design, devel- 

 oped in Italy, employs a generally rectangular 



opening with a moderately projecting Hp. A set 

 of sharply curved guide vanes, as used ui aU 

 modern water tunnels and channels, changes the 

 direction of the water. The guide vanes serve 

 also as strainer bars to prevent the entry of large 

 fish, blocks of ice, and other foreign objects. 



Besides having an efficiency and a resistance 

 apparently comparable to scoops of the Schmidt 

 design, the Italian arrangement of Lattanzi and 

 Bellante [Italian patent 404,551 of 18 Jun 1943; 

 Bureau of Ships, Navy Dept., Transl. 529. Also 

 Orlando, M., Ann. Rep Rome Model Basin, 1940, 

 Vol. X] has the advantage of superior flow, 

 especially the absence of vortexes within the 

 inlet diffuser. Although it has not, so far as known, 

 been tested as a discharge outlet there is no reason 

 why it should not work equally well in either 

 direction, as did the similar scoops and discharges 

 in destroyers and other vessels of the World 

 War I period. 



Despite the known workability of flush inlet 

 scoops there is also much to be said for a scoop — 

 and a discharge — which project sufficiently from 

 the ship's side to take advantage of the greater 

 velocity m the boundary layer at a small distance 

 from the shell. The right-hand upper diagram of 

 Fig. 73.R is an attempt to sketch a device which 

 may produce the desired result. In an orthodox 

 form of flush scoop the slowly moving water 

 entering on the forward side, combined with the 

 faster moving water entering on the after side, 

 often creates an eddy with backflow just abaft 

 the forward surface of the diffuser. The guide-vane 

 arrangement should be such as to pick up an 

 appreciable "belt" of water at the inside of the 



Partial Afterbody; Plan of Tronsom- Stern ABC Ship, from Fig. 66. P 



The Purpose of the Unequal Guide-Vane SpQcint] 

 is to Obtain the Moximum Uniform Velocity 

 in the Diffuser 



^-'^^j I Outlet is on Starboard Side 



Fig. 73.11 Main-Injection and Discharge Layout for Transom-Stern ABC Ship 



