van Manen, Oosterveld and Witte 



Recently the idea of using the main cargo pumps of tankers for steering 

 purposes has been put forward. It is intended to deliver sea water with these 

 pumps to nozzles situated at stern and bow, the efflux of these nozzles creating 

 a lateral force and a turning moment on the ship. The economic incentives for 

 using this system are that expensive machinery which is otherwise idle is put to 

 work for manoeuvring the ship without any additional rotating machinery. The 

 possible elimination of tugboat assistance is also an important consideration. 



A typical simple thrust generating system is illustrated in Fig. 21. The 

 main cargo pumps deliver a certain volume flow rate with a certain head. The 

 pressure increase across the pumps is needed to cancel the pressure drop in 

 the system caused by friction in the pipelines and appendages, the height differ- 

 ence between sea chest and nozzle exhaust, and the pressure drop in the nozzle. 

 Generally the last pressure decrease is the largest, the friction losses in the 

 pipeline can become prohibitive only when the pipe diameter is chosen too small. 

 The thrusters can be modulated with a throttle -valve in the pipeline. The pres- 

 sure drop in the various pipes, valves, bends, etc., can be computed from data 

 given in engineering textbooks. In a smoothly rounded exhaust nozzle (Fig. 22), 

 the friction losses are very low compared with the friction losses in the pipeline 

 system; these losses can be neglected when designing these systems. In that 

 case Bernoulli's law results in 



12 12 



nozzle ~ 2 '^nozzle ^ ''^ pipe ' 



or using the law of continuity, 



AP, 



8pQ2 / 1 



no z z 1 e 2 



77^ VD" , D". 



* no zzle pipe 



Fig. 21 - Arrangement of simple nozzle system 



266 



