Water- Jet Propulsion for High-Speed Surface Ships 



DISCUSSION 



William B. Morgan 



Naval Ship Research and Development Center 

 Bethesda 3 Maryland^ U.S.A. 



The propulsion device discussed by the authors would more 

 appropriately be called a ducted propeller. The term water-jet is 

 usually reserved for a propulsion device where a pump is located in 

 a long pipe and the pump does not induce a drag around the duct. The 

 device shown in Figure 4 is a ducted propeller of the decelerating - 

 flow type. Since the authors do not give any references it is not clear 

 whether they are familiar with the vast amount of literature which is 

 available. I thought that it has been conclusively shown that it is pos- 

 sible to consider the duct separately from the impeller and to perform 

 tests on the inlet, Figure 3, and the interior flow, Figure 6, separa- 

 tely. In the duct shown in Figure 4, the impeller would induce a cir- 

 culation about the duct which, in case of the decelerating -flow, would 

 cause a drag increase. I do not believe it is possible to separate the 

 internal and external flow as you have done. 



In Figure 1, you have purportedly shown a comparison bet- 

 ween the efficiencies of various propulsion devices. This figure was 

 not valid when it was published nor is it valid today. Also one should 

 consider the partially-submerged propeller. This propeller is not 

 applicable to hydrofoil craft but can be a very efficient means of pro- 

 pulsion where there is a flat bottom at the stern. 



REPLY TO DISCUSSION 



Jacques Duport 



SQGREAH 

 Grenoble 3 France 



Thank you, Dr. Morgan for your comments. About the dis- 

 cussion on denominations, I think we have also to find names in 



29 



