HOW HIGHLY SKEWED PROPELLERS REDUCE NOISE AND VIBRATION

With controllable-pitch propellers in mind, the Author first explains how a highly-skewed propeller can lengthen the duration of suction-side cavitation as compared with a conventional propeller and so reduce the rate of variation of cavitation with time, resulting in a reduction of vibration. The dynamic forces absorbed through the propeller shaft will also be reduced. Although the Author's firm (Hjelset Motorfabrikk A/S, Norway) has not carried out full-scale meaurements, it was found that, where a comparison between a conventional and a highly-skewed propeller has been possible, a reduction of about 50% in propeller-induced vibration has been obtained with the highly-skewed blades. The article includes some comparisons (for a conventional four-bladed c.p. propeller) of pressure impulses, at blade frequency and twice blade frequency, between the values calculated by a statistical method developed from full-scale measurements, the values calculated by lifting-surface theory, and the values measured in sea trials. While it is not possible to recommend a general maximum for pressure impulses, it can be stated that 600 to 700 kp/m square (single amplitude at blade frequency) should not be exceeded in a single-screw ship. Spindle torque in a highly-skewed propeller can be kept at the same level as that of a conventional propeller through a balanced blade design. The primary application of the highly-skewed propeller is for passenger ships, where comfort requirements are high; it is also useful for favourable pressure-impulse and dynamic bearing-force characteristics can be utilised to save fuel. Where maximum vibration level is specified, the highly-skewed propeller can fulfil this requirement with a larger diameter and a low shaft- speed and so give improved propulsive efficiency.

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  • Corporate Authors:

    Institute of Marine Engineers

    Memorial Building, 76 Mark Lane
    London EC3R 7JN,   England 
  • Authors:
    • Berg, A
  • Publication Date: 1980-8

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Filing Info

  • Accession Number: 00329894
  • Record Type: Publication
  • Source Agency: British Ship Research Association
  • Files: TRIS
  • Created Date: Mar 12 1981 12:00AM