Water-Jet Propulsion for High-Speed Surface Ships 



level may also be varied between 0, 05 and 1, 4 atmospheres. 

 Water head between the two tanks is measured accurately by a dif- 

 ferential manometer (mercury weighing). Air pressure in the upper 

 tank is weighed in the same manner. 



Model rotation is ensured by an asynchronous motor, between 

 300 and 1 750 rpm whose speed is varied through a frequency 

 converter. Resultant stability is to within 1/1000 of rotation speed. 



The whole body of the jet propeller (i. e. intake bell-mouth, 

 pump and nozzle) is rigidly connected to a main stator structure 

 which is vertically guided in two self-centering guide -bearings fed 

 with water under pressure. The vertical resultant of weight and 

 hydraulic thrust acting on this structure is measured through a 

 weighing -balance to which it is connected through a oil pressure 

 frictionless thrust bearing. Since the total weight of the balanced 

 body, and pressures on both sides of each guide -bearings are known, 

 it is possible to derive from the balance measurement the net thrust 

 due to the jet effect. Because of the absence of friction in the guide 

 and thrust bearings, it is also possible to measure the stator torque 

 (which corresponds to the jet rotational momentum). 



The stator of the driving motor is mounted in the above - 

 mentionned stator body with help of self-centering guide and thrust 

 bearings fed with oil under pressure, thus allowing for accurate 

 driving torque measurement, then accurate shaft-power determina - 

 tion. The friction torque of the shaft guide bearings situated in the 

 propeller body is not directly measured but is taken into account 

 through a precalibration procedure. A pressure sensor in the oil 

 floating shaft thrust bearing is used to measure rotor thrust after 

 calibration. 



The 360 mm diameter water floating bearing, mounted bet- 

 ween the two tanks serves as a water seal. Its leakage rate is ca- 

 librated and is approximately 0, 15 l/s. The 160 mm diameter 

 upper floating bearing serves as an air seal. Its leakage is also 

 taken into account. 



This rig is equipped with centralised remote control and mea- 

 surement equipment. 



The flow, head and pressure characteristics of the rig are 

 such that it proves very useful for perfecting propeller pumps for 

 SFJP type drive, covering the forward speed range from (fixed 

 point propellers) up to approximately 100 knots. 



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