AN APPROACH TO THE RATIONAL SELECTION OF THE POWER SERVICE MARGIN

This study proposes a more rational method for the selection of the horsepower to be installed. In this approach, explicit attention is given to the random nature of the ship's speed in servcie. A more complete decision model recognizes the stochastic nature of the deteriorative effects and the environmental influences to which the ship is subjected. From this model, the "expected" speed of the ship in service is calculated, and a more realistic evaluation of the economic measure of merit is obtained. With this approach, the installed horsepower becomes the independent variable and the speed of the ship in service is now a dependent variable. The historical background to service margin requirements is presented along with notes on the quantitative values for power margins recommended by the Maritime Administration. Deteriorative effects are examined and a mathematical model for hull fouling and corrosion effects is assumed. A method is presented for the analysis of seaway statistics for the major shipping routes of the world. Seakeeping performance modelling is discussed, together with methods of calculating the added resistance and the motions of a ship travelling in a seaway. Two examples, a Persian Gulf tanker service and a North Atlantic container ship, are used to illustrate both the conventional and the proposed approach to early-stage ship design. These examples show that the conventional 25% power margin is excessive in both cases, resulting in significant economic penalties. An "effective power service margin" is defined, which may now be used more realistically by a designer employing the conventional approach to ship design. For the tanker service a value of 11% is proposed, and for the container ship a value of 18% is found best. Finally, a set of possible refinements to the decision model of the ship in service is recommended.

  • Corporate Authors:

    University of Michigan, Ann Arbor

    Department of Naval Architects and Marine Engineers
    Ann Arbor, MI  United States  48109
  • Authors:
    • Swift, P M
  • Publication Date: 1975-7

Media Info

  • Features: References;
  • Pagination: 136 p.
  • Serial:
    • Issue Number: 174

Subject/Index Terms

Filing Info

  • Accession Number: 00184788
  • Record Type: Publication
  • Source Agency: University of Michigan, Ann Arbor
  • Files: TRIS
  • Created Date: Jan 13 1979 12:00AM