The diameter of a ship's turn depends on several factors in addition to rudder angle, and one of the most important of these is water depth. For manoeuvring, deep water can be assumed to have a depth of more than five times the ship's draught; at three times the draught, the shallow-water effects become significant, and as depth decreases from twice the draught these effects increase rapidly. Water depth thus influences manoeuvring at time when misinterpreting its effects can be disastrous. Although, in shallow water, resistance to ahead motion is increased, it cannot be assumed that the ship can be stopped more quickly; the drag increase can be more than offset by an increase in the ship's virtual mass. The Author discusses these matters and explains the phenomena that occur when a ship is turning, in shallow water in particular. The drift angle (relative to the direction of advance) during the turn will vary with water depth. The rate of turn depends on the ship's directional stability, and, though the rate increases at first on leaving deep water, it decreases as shallower water is reached. These changes in rate of turn are comparatively small and could suggest to the ship handler that his ship is not significantly affected by the shallow water, but their combination with a smaller speed-loss in the turn as underkeel clearance decreases results in an increase in the ship's turning-circle diameter. Some numerical examples of these phenomena are shown diagrammatically and discussed. Although manoeuvrability in shallow water is inferior to that in deep water, trials carried out by Decca (with a ship-handling simulator)have suggested that operators were having more difficulty in deep water. Reasons for this are suggested.

  • Availability:
  • Corporate Authors:

    Fuel and Metallurgical Journals Limited

    Queensway House, 2 Queensway, Redhill
    Surrey RH1 1QS,   England 
  • Authors:
    • Reynolds, J
  • Publication Date: 1976-9

Media Info

  • Features: References;
  • Pagination: 2 p.
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00152511
  • Record Type: Publication
  • Source Agency: British Ship Research Association
  • Files: TRIS
  • Created Date: Apr 27 1977 12:00AM