23 August 2008

[4S/yim227] Research on Ducted Propeller NSMB

Open water tests and cavitation tests were carried out in order to investigate the influence of the propeller load at the tip and the clearance between blade tip and nozzle on efficiency, cavitation and noise.
The screw models 2978 through 2981 were tested in nozzle no. 19.

The diameters of the screw models were reduced step by step in order to obtain different tip clearances. The inner diameter of the nozzle model remained unaltered.
Clearances of 1, 1.5, 2.01 2.5 and 3.0 mm were realized.

The characteristics of these models are given :

#Diameter (mm) 240.00
#Number of blades 4
#Pitch at 0.7 R (mm) 240.00
#B.A.R. 0.55
Variation screw propeller :

  • Screw no. 2978 - Pitch at root (mm) 253.10 and Pitch at blade tip (mm) 219.84
  • Screw no. 2979 - Pitch at root (mm) 240.00 and Pitch at blade tip (mm) 240.00
  • Screw no. 2980 - Pitch at root (mm) 213.70 and Pitch at blade tip (mm) 280.32
  • Screw no. 2981 - Pitch at root (mm) 200.00 and Pitch at blade tip (mm) 300.48
The pitch of screw 2979 is taken uniform. The pitch increase from 0.7 R to the blade tip of screw 2981 is 1.5 that of screw 2980.
The decrease in pitch from 0.7 R to the blade tip of screw 2978 is taken half the pitch increase of screw 2980.

#Wageningen, January 1963
#Author :Prof.Ir. J.D. van Manen (Principal Investigator)

further reading

The design of screw-propellers in nozzles - by J.D. van Manen and A. Superina - Publication no. 137 of the N.S.M.B. - Int. Shipb. Progress Vol. 6 nod 55, 1959.

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