van Manen, Oosterveld and Witte 



Figure 6 shows clearly the reasons why ducted propellers are used at heavy 

 propeller-loadings occurring in tugs, trawlers, and large tankers. As tanker 

 sizes continue to grow, the advantage of ducted propellers, higher efficiency, 

 and reduced optimum diameter, will become greater. 



Analysis of the reduction in SHP due to the use of a nozzle has been made 

 for tankers with an installed power of 30,000 SHP and different deadweight. The 

 rotative speed of the impeller has been fixed at 100 RPM. The result is given 

 in Fig. 7 which clearly shows the great reduction in SHP which can be obtained. 

 For a tanker of 100,000 tons deadweight, a reduction of 8 percent in SHP is 

 attainable. 



50000 TDW 100000 



150000 



200000 



3a3 lAU 



nu 



83^ 



Fig. 7 - Reduction in SHP, due to the 

 application of a nozzle for large tankers 



Applications of Hogner-type Afterbody with Ducted Propeller 



From the results of the investigations discussed so far it can be concluded 

 that for large tankers, the Hogner-type afterbody provided with a complete ring 

 nozzle propeller system offers favourable prospects with respect to minimizing 

 vibration and cavitation problems in addition to a high propulsive efficiency. In 

 order to obtain data on the differences in resistance and propulsive efficiency of 

 tankers with a conventional stern arrangement and a Hogner-type stern with 

 nozzle fitted, tests were carried out at the N.S.M.B. with models representing 

 32,500-TDW and 48,500-TDW tankers. Both tankers had a conventionally shaped 

 bow. The various stern arrangements considered were as follows: 



32,500-TDW tanker: conventional stern (moderately U-shaped sections and 

 rudder shoe) 



Hogner-type Clearwater stern fitted with a nozzle 



246 



