Fairing for a riser

Abstract

A fairing is disclosed for mounting upon a cylindrical member which is deployed underwater. The fairing has a generally wedge shaped body 4 which tapers from front to rear. The body 4 is mounted upon the cylindrical member 8 through a collar 6, 6 1 in which the member is received. The fairing is thus mounted with its front face adjacent the cylindrical member so that the assembly of the fairing body and the member can together form a teardrop shape. The collar permits the fairing to weathervane, rotating about the cylindrical member, to align itself with a current.

1 . A fairing for mounting upon a cylindrical member for underwater deployment, the fairing comprising a fairing body which, viewed along its length, is substantially wedge-shaped, having a relatively broad front tapering to a relatively narrow trailing edge, and at least two collars which are both secured to the fairing body and are separated from each other along the length of the fairing body, the collars being positioned and aligned to receive the cylindrical member with the fairing body's front lying adjacent the cylindrical member and the axis of the cylindrical member lying along the length of the fairing body, thereby to pivotally mount the fairing body upon the cylindrical member such that it is able to rotate about the axis of the cylindrical member and so align itself with a water current, the fairing body and the cylindrical member together defining, when viewed along the length of the fairing, a teardrop shape having a leading edge formed, between the collars, by the cylindrical member.  
   
   
       2 . A fairing as claimed in  claim 1  wherein a portion of each collar is interposed between the fairing body and the cylindrical member in use, providing clearance therebetween.  
   
   
       3 . A fairing as claimed in  claim 1 , wherein each collar forms a respective bearing ring for receiving the cylindrical member.  
   
   
       4 . A fairing as claimed in  claim 3  wherein each bearing ring has a substantially circular interior bearing surface.  
   
   
       5 . A fairing as claimed in  claim 3  wherein the bearing ring is split such that it can be opened out to allow the cylindrical member to be inserted into it laterally.  
   
   
       6 . A fairing as claimed in  claim 5  wherein at least an end portion of the collar is initially free to allow the bearing ring to be opened out and means are provided to subsequently secure the free end of the collar to the fairing body to retain the fairing upon the cylindrical member.  
   
   
       7 . A fairing as claimed in  claim 6  wherein means to secure the free end of the collar comprise a mechanical fastener.  
   
   
       8 . A fairing as claimed in  claim 1  wherein the collar comprises two bifurcated portions, one limb of each extending between the cylindrical member and the fairing body to provide clearance therebetween and the other limb of each being secured in use to the fairing body.  
   
   
       9 . A fairing as claimed in  claim 1  wherein the front of the fairing body is shaped to complement the cylindrical member, its surface(s) lying upon a notional cylinder.  
   
   
       10 . A fairing as claimed in  claim 1  wherein a bearing surface of the collar, which faces toward the cylindrical member and upon which the collar rides, comprises low friction material.  
   
   
       11 . A fairing as claimed in  claim 10  wherein the bearing surface comprises self lubricating material.  
   
   
       12 . A fairing as claimed in  claim 11  wherein the collar comprises a plastics material with an admixture of a friction reducing agent.  
   
   
       13 . A fairing as claimed in  claim 1  wherein the collar comprises an anti-fouling agent.  
   
   
       14 . A fairing as claimed in  claim 1  wherein the collar comprises a plastics material with an admixture of an anti-fouling agent.  
   
   
       15 . A fairing as claimed in  claim 1  wherein the fairing body and the collar are formed by separate plastics mouldings.  
   
   
       16 . A fairing as claimed in  claim 1  wherein the fairing body is a hollow plastics moulding whose interior communicates with the exterior to permit equalisation of pressure.  
   
   
       17 . A fairing as claimed in  claim 1  which is substantially neutrally buoyant.