The allowable deviation of a ship from a sea-bed reference is usually prescribed as a fixed distance at low operating depths and is taken as proportional to depth at higher depths. This restriction on lateral displacement is to limit the stress level in the drill string and riser system. A further restriction on drilling is imposed by vertical motion of the ship and drilling bit. The introduction of heave compensators has reduced the movement of the bit in a given sea state and extended the sea state range in which drilling can continue. However, when the sea conditions reach a certain level or other hazards arise it is necessary to disengage from the site and return and reenter later. The force and turning moment that can be applied to a dynamically positioned ship by the onboard thrusters must match the mean steady loads imposed by the environment and an aim of this paper is to describe means of estimating these quantities. In addition the paper describes some interaction effects that have been observed to occur between operating thrusters and the hull. With such a complex ship it is prudent, before completing the design to simulate mathematically the response of the ship to the environmental and thruster forces and a description of the equations of motion that were derived for this purpose are included.

  • Corporate Authors:

    North East Coast Inst of Engineers & Shipbuilders

    Bolbec Hall, Westgate Road
    Newcastle upon Tyne,   England 
  • Authors:
    • English, J W
    • Wise, D A
  • Publication Date: 1976-2

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00138494
  • Record Type: Publication
  • Source Agency: Engineering Index
  • Files: TRIS
  • Created Date: Sep 4 1976 12:00AM