Drawdown apparatus and installation method for a floating platform

Abstract

A floating platform includes a hull and a deck mounted thereon. The platform is anchored to the seabed by tendons connected to the hull at the upper ends thereof and secured to the seabed at the lower ends thereof. The platform includes a removable drawdown system for lowering the platform to the lock-off draft without utilizing an installation vessel.

1 . A method for mooring a floating platform to a plurality of tendons, the method comprising the steps of: 
 a) anchoring lower ends of said tendons to the seabed;    b) coupling drawdown tension members mounted on said platform to upper ends of said tendons; and    c) tensioning said drawdown tension members to lower said platform to said tendons.    
   
   
       2 . The method of  claim 1  including the step of drawing down said platform without ballasting said platform.  
   
   
       3 . The method of  claim 1  including the step of concurrently ballasting said platform.  
   
   
       4 . The method of  claim 1  including the step of passing said drawdown tension members through tendon porches and connecting said drawdown tension members to said upper ends of said tendons.  
   
   
       5 . The method of  claim 4  including the step of continuing to tension said drawdown tension members to submerge said platform to a lock-off draft and locking off said tendons.  
   
   
       6 . The method of  claim 5  including the step of removing said drawdown tension members from said platform.  
   
   
       7 . The method of  claim 6  including the step of deballasting said platform to increase the tension in said tendons to an installation tension.  
   
   
       8 . The method of  claim 1  wherein said platform includes guide sleeves vertically aligned above tendon porches located on said platform and further including the step of passing said drawdown tension members through said guide sleeves and said tendon porches and connecting said drawdown tension members to said upper ends of said tendons.  
   
   
       9 . The method of  claim 8  including the step of deballasting said platform to increase the tension in said tendons to an installation tension.  
   
   
       10 . A floating platform, comprising: 
 a) a hull having an upper end and a lower end;    b) a deck supported on said upper end of said hull;    c) pontoons secured to said lower end of said hull;    d) drawdown tension members mounted on said pontoons; and    e) tendons anchoring said floating platform to the seabed.    
   
   
       11 . The platform of  claim 10  wherein said drawdown tension members are adapted for removal from said platform upon lowering said platform to the installation draft.  
   
   
       12 . The platform of  claim 10  wherein said drawdown tension members comprise strand jacks adapted for connection to upper ends of said tendons.  
   
   
       13 . The platform of  claim 10  wherein said drawdown tension members comprise hydraulic cylinder assemblies adapted for connection to upper ends of said tendons.  
   
   
       14 . The platform of  claim 13  wherein said drawdown tension members includes guide sleeves vertically aligned above tendon porches located on said pontoons.  
   
   
       15 . The platform of  claim 10  including temporary stability columns supporting said drawdown tension members on said pontoons.  
   
   
       16 . The platform of  claim 15  including heave compensation devices operatively connected to said drawdown tension members.  
   
   
       17 . The platform of  claim 10  including heave compensation devices operatively connected to said drawdown tension members.  
   
   
       18 . A method for mooring a floating platform to a plurality of tendons, the method comprising the steps of: 
 a) anchoring lower ends of said tendons to the seabed;    b) coupling drawdown tension members mounted on said platform to upper ends of said tendons;    c) tensioning said drawdown tension members to submerge said platform to a lock-off draft;    d) locking off said platform at the lock-off draft; and    e) dismantling and removing said drawdown tension members from said platform.    
   
   
       19 . The method of  claim 18  including the step of heave compensation for preventing overloading of said drawdown tension members.