water 12 having a bottom 14 a riser 16 extends from a subsea well 26 up through moon pool 18 to a point below the rotary table 20 moon pool 18 is merely a vertical opening through barge 10 riser pipe 16 is attached by a connector 17 to casing 19 which extends into the upper portion of well 26 and is rigidly attached thereto such as by cementing drill pipe 24 is supported within riser pipe 16 from derrick 22 in a known manner barge 10 is also provided with mooring lines 28 however during a storm they cannot keep riser pipe 16 centered within moon pool 18 by themselves thus it is necessary to provide additional means for centering the riser pipe 16 so that drilling operations can be continued during a mild storm cables 30 and 32 are shown in fig1 as being connected to the upper end of riser pipe 16 to aid in maintaining it in a centered position attention is now directed to fig2 which illustrates the positions in which cables 30 and 32 are connected as shown in fig2 cables 30 and 32 are connected 180 u00b0 apart on riser pipe 16 spaced 90 u00b0 from cables 30.