Continuing their description of examples of investigations on problems in superstructure vibration, the authors consider the case of an 87,000-dwt bulk carrier in which the longitudinal vibration was particularly bad when the ship was in ballast. This ship, propelled by a low-speed (122 rpm) Diesel engine, needed a six-bladed propeller to replace its five bladed one; this case is in contrast with that of a 160-m long containership investigated. In the latter ship, propelled by medium-speed Diesels driving a four-bladed propeller at 135 rpm, there was no risk of propeller-excited longitudinal vibration of the superstructure, whether the propeller had four, five, or six blades. Whatever steps are taken to cure such vibration problems, or to prevent them at the design stage, the superstructure block remains an "elastic system" with a natural frequency of longitudinal vibration liable to be excited by a major excitation source in the propulsion installation. Methods that can be used by the designer in approaching this problem are described, with examples, under the headings:--Approximate Methods Evaluating the Natural Frequencies of Superstructure Vibrations; Evaluation of Natural Frequencies of Superstructure Vibrations; Evaluation of Natural Frequencies taking Experimental Results into Account; Superstructure Vibration Calculations by the Finite Element Method. In the concluding section of the article, the authors mention the difficulties inherent in the prevention of excessive superstructure vibration and in mitigating it in existing ships. A Bureau Veritas Information Note on limiting shipboard vibrations should be of practical value to the designer interested in superstructure vibration; some information from the Note is included in the article. More knowledge is needed on damping, hydrodynamic excitations, and added mass, and the Society is continuing studies on these matters. Order from BSRA as No. 50,005.

  • Corporate Authors:

    Bureau Veritas

    One Western Union International Plaza
    New York, NY  United States  10004
  • Authors:
    • Voley, G C
    • Morel, P
  • Publication Date: 1978-9


  • French

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00194225
  • Record Type: Publication
  • Source Agency: British Ship Research Association
  • Files: TRIS
  • Created Date: May 26 1979 12:00AM