Lindgren, Johnsson and Dyne 



Further self-propulsion tests may show if it is possible to improve the hull 

 efficiency of a ducted propeller arrangement by introducing some kind of Hogner 

 stern, as proposed by van Manen (5). 



6.3. Container-Vessel Project 



The results of the self -propulsion tests, carried out with the container- 

 vessel model, are given in Table 8 and in Fig. 20. 



Table 8 

 Container -Vessel Project. Propulsive Coefficients. 



Five-bladed aft propeller 



The diagram in Fig. 20 shows that the gain, when using contrarotating pro- 

 pellers, is in this case about 12%, compared to the single propeller, intended to 

 be used for the project. Compared to a stock propeller, having too-short outer 

 blade sections from the point of view of cavitation, the gain is about 10%. In 

 contrast to what was the case for the tanker model, the scale factor is in this 

 case not very large and the advance velocity of the propellers not particularly 

 low. Thus, the accuracy of the measurements can be expected to be better and 

 the results more reliable. The reasons for the gain in efficiency, obtained in 

 the present case, are somewhat different from those mentioned in connection 

 with the case of the tanker. In the present case, the diameter of the propeller 

 was limited to 6 m. Thus, the comparison with the single propeller is one, 

 based on constant Kj./j'^. Figure 13 shows that under such circumstances a gain 



1292 



