System for providing stability to a floating offshore structure

Abstract

A system for improving the static and dynamic stability of an offshore floating structure in which outriggers having a unit with an inertial mass are supported from the structure to hold each unit at a radial distance from a centre of rotation of the offshore floating structure and be entirely submerged. Water may enter and exit a tank in a unit to statically adjust and dynamically control stability and dampen roll and pitch of the structure. The outriggers can be raised for tow. The outriggers ballast can be adjusted during tow, installation and in operation. The units can transport mooring lines. An embodiment of a hydrocarbon production or support facility is described with the dynamic flexible risers connected to a support structure of the system.

1 . A system for improving the static and dynamic stability of an offshore floating structure comprising:
 a plurality of outriggers, each outrigger having a unit, the unit having an inertial mass; and   a support structure, the support structure locatable to the offshore floating structure and holding the units at a radial distance from a centre of rotation of the offshore floating structure;   characterised in that:   the plurality of units are entirely submerged in use.   
     
     
         2 . A system according to  claim 1  wherein the inertial mass includes a fixed mass. 
     
     
         3 . A system according to  claim 2  wherein the unit includes a weight to provide the fixed mass. 
     
     
         4 . A system according to  claim 3  wherein the weight is one or more materials selected from a group comprising: steel, concrete, sand, gravel and water. 
     
     
         5 . A system according to  claim 1  wherein the inertial mass includes a variable mass. 
     
     
         6 . A system according to  claim 5  wherein the unit includes a filler tank and the variable mass is provided by water entering and exiting the filler tank. 
     
     
         7 . (canceled) 
     
     
         8 . A system according to  claim 1  wherein there is a ballast tank in a unit. 
     
     
         9 . (canceled) 
     
     
         10 . (canceled) 
     
     
         11 . A system according to  claim 1  wherein the units are identical. 
     
     
         12 . (canceled) 
     
     
         13 . A system according to  claim 1  wherein there are an even number of outriggers. 
     
     
         14 . A system according to  claim 1  wherein there are an odd number of outriggers. 
     
     
         15 . A system according to  claim 1  wherein the outriggers are arranged to provide an evenly distributed mass lying on a circumference around the offshore floating structure. 
     
     
         16 . (canceled) 
     
     
         17 . A system according to  claim 1  wherein the support structure comprises a plurality of support arms, each arm having a first end for connection to the offshore floating structure and a second end for connection to a unit. 
     
     
         18 . A system according to  claim 1  wherein the support structure comprises a plurality of support struts wherein the support struts connect between units and to the offshore floating structure. 
     
     
         19 . A system according to  claim 1  wherein the support structure is horizontal with the units. 
     
     
         20 . A system according to  claim 1  wherein the support structure is adapted to raise and lower the outriggers. 
     
     
         21 . (canceled) 
     
     
         22 . (canceled) 
     
     
         23 . A system according to  claim 1  wherein the offshore floating structure is an offshore hydrocarbon production or supporting facility. 
     
     
         24 . A system according to  claim 23  wherein the support structure includes connection means for one or more dynamic flexible risers. 
     
     
         25 . A system according to  claim 24  wherein there is a dropped object protection system arranged over the connection means. 
     
     
         26 . A system according to  claim 1  wherein one or more units include a compartment, the compartment having one or more elements of a mooring line and an end of the mooring line is connected to the offshore floating structure. 
     
     
         27 . A system according to  claim 1  wherein the system includes a vertical tether mooring system and the outriggers are anchoring points for the vertical tether mooring system.