van Manen, Oosterveld and Witte 



The above figures have also been verified by several later installations. 



An important matter which has not been treated by the authors is the stop- 

 ping characteristics of these very large vessels. With a conventional stern ar- 

 rangement and a free fixed-pitch propeller, the stopping time for tankers be- 

 tween 50 and 100,000 TDW is normally between 8 and 10 minutes corresponding 

 to a stopping distance of 7 to 9000 feet. One may expect these figures to be even 

 higher when using a nozzle propeller as proposed by the authors. A consider- 

 able reduction in stopping time and distance may be achieved by using a control- 

 lable pitch propeller. I would like to finish with a few figures obtained with 

 some of our own propellers. 



For a 50,000-TDW twin-screw tanker with an output of 8900 HP each shaft 

 at 115 RPM and equipped with two 4-bladed 17-1/2-foot controllable -pitch pro- 

 pellers, a stopping time of 4.5 minutes from full speed, 15.75 knots, was re- 

 ceived. For a 72,000-TDW single-screw ore carrier with an output 17,600 HP 

 at 115 RPM, fitted with a 4-bladed 21-1/2-foot CP propeller, a stopping time of 

 5 minutes was obtained from full speed, 16.75 knots. 



Compared with similar ships with normal fixed-pitch propellers, this im- 

 plies a reduction in the order of 50 percent. 



REPLY TO DISCUSSION 



J. D. van Manen, M. W. C. Oosterveld, and J. H. Witte 



We wish to thank Messrs. Lackenby, Stron-Tejsen, Bindel, and Bjorheden 

 for their interesting comnients. 



In regard to Mr. Lackenby's question about the improvement in SHP with 

 the Hogner-type stern and nozzle and the improvement in SHP with an extreme 

 bulbous bow, it must be remarked that our experiments were performed with 

 ships without bulbous bows. It was found that the Hogner stern with nozzle 



274 



