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.

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/issn/00475955
• Corporate Authors:

  Institute of Marine Engineers

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

Media Info

• Features: References;
• Pagination: p. 19
• Serial:
  • Marine Engineers Review
  • ISSN: 0047-5955

Subject/Index Terms

• TRT Terms: Blades (Machinery); Controllable pitch propellers; Damping (Physics); Energy absorption; Noise control; Propellers; Vibration
• Uncontrolled Terms: Noise reduction
• Old TRIS Terms: Blade frequency vibration; Propeller induced vibration; Propeller vibration; Skewed propellers; Vibration absorption
• Subject Areas: Marine Transportation; Vehicles and Equipment;

Filing Info

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