The VLCC (Very Large Crude Carriers) class of tankers is formed by vessels above 175,000 tdw and accounts for about 90 percent of the tonnage of ships above 50,000 tdw delivered during recent years. Some 90 percent of these ships are steam turbine driven. Growing ship size brings higher transport capacity per ship, with consequent increased requirement for propulsion plant reliability and efficiency related to initial costs and overall economy. The main objective of the study is to indicate the techno-economic potential of the various propulsion systems with special reference to the steam turbine and consider a techno-economic feasibility study which will include optimisation of propeller speeds for conventional single screw, propeller in nozzle, conventional twin-screw, propeller in nozzle, conventional twin-screw, overlapping and contra rotating propellers, such factors as turbines and gearing designs which are already available for torque output up to 6.7 MNm corresponding to power requirements of a 700,000 tdw tanker with a speed of 15.5 knots; large and heavy propellers resulting from high torque and low propeller speeds of 70 rev/min or less, which will call for improvements in shaft techniques and bearings; a break even point in average annual cost at about 400,000 tdw of the nozzle propeller compared with the conventional single screw; the implications of the development towards twin screw arrangements for VLCCs; and steam cycles with various degrees of complexity and steam conditions, as well as steam plants for separate, mechanically and thermo-dynamically coupled twin screws, are discussed in detail.

  • Supplemental Notes:
    • 45 Conference Papers presented at IMAS 73, London, 4-8 June 1973, organized by the Institute of Marine Engineers. This paper is available only in a set of 6 papers in Subject Group 2: "Ship Operation and Management: Ship and Propulsion Systems" at $10.00.
  • Corporate Authors:

    Institute of Marine Engineers

    Memorial Building, 76 Mark Lane
    London EC3R 7JN,   England 
  • Authors:
    • Larsen, G A
  • Publication Date: 1973

Subject/Index Terms

Filing Info

  • Accession Number: 00048457
  • Record Type: Publication
  • Source Agency: Institute of Marine Engineers
  • Files: TRIS
  • Created Date: Nov 14 1973 12:00AM