Method for positioning a watercraft, in particular a drilling ship as well as relevant devices

A method of positioning a drilling ship in drilling position above a deep-sea well, comprising the steps of:

• coupling the ship to a plurality of anchors secured to the sea floor for confining movement of the ship generally to a first generally circular area on the surface of the sea, the perimeter of said first circular area being defined by the outer limit of movement of the ship when acted upon by external forces no greater than a first predetermined maximum;
• monitoring the position of the ship and the external forces tending to change its position, and securing values for said external forces;
• introducing the values for said external forces into a computer which controls operating status of a plurality of adjustable propellers on the ship, and
• activating propellers on the ship essentially only when the external forces acting on the ship tend to move the ship beyond the first generally circular area for confining movement of the ship generally to a second generally circular area having a greater area than said first generally circular area,
• such that when the external forces acting on the ship tend to change the ship's position to no greater an extent than the perimeter of the first generally circular area, the ship is confined to movement generally within said first area essentially only by the confining action of the anchors, but when the external forces tend to move the ship beyond the perimeter of the first generally circular area, the propellers are activated to cooperate with the anchors to confine movement of the ship generally within the perimeter of the second generally circular area.