Manoeuvrability and Propulsion of Very Large Tankers 



ship speeds between zero and v, jet steering will produce larger turning mo- 

 ments than the rudder system. This will result in better manoeuvring capabil- 

 ities. 



From the preceding discussion we conclude that for an evaluation of the jet 

 steering system it is necessary to compare (//^^^ at maximum rudder deflection 

 of 35° with the same 0^3^ generated by a certain nozzle with nozzle exit velocity 

 u. Table 8 shows the results which are obtained from Figs. 17, 18, 19, and 20. 



Table 8 

 Points where ^^^^ for Rudder Steering with a Rudder 

 Deflection S = 35° is Equal to i'^^^ for Jet Steering 



Considering the data given in Table 8, we observe that only the large nozzle, 

 D^ = 1.10 m, is competitive with rudder steering in the 0-5 knots range. Here 

 the power to drive the jets in order to be competitive with the rudder for rudder 

 angles between 0° and 35° is too large. The same holds good for the small noz- 

 zle D^ = 0.357 m at 5 knots as well as at 9 knots. However it can be seen in 

 Fig. 19 that the small nozzle needs about 1500 hp to be competitive with the 

 rudder at rudder angles between 0° and 16° at V = 9 knots. 



If we summarize the results, it can be said that the large nozzle can com- 

 pletely take over steering action from the rudder in the 0-5 knots range. For 

 ship speeds ranging from 5 to 9 knots, jet steering with the small nozzle can be 

 made only to assist and not to eliminate rudder action. Above 9 knots, rudder 

 steering is definitely superior; the power needed to drive the jets becoming 

 prohibitive. This is clear after considering the results in Tables 9 and 10 for 

 V = 13 knots. 



263 



