Installation and levelling of subsea templates

Apparatus for positioning and levelling a subsea template structure or the like on a seabed, said apparatus comprising:

• a floating vessel including hoisting apparatus for raising and lowering suspension means including an elongated riser string, said hoisting apparatus including a motion compensator operable to maintain a substantially predetermined tension on said suspension means, said motion compensator including means for releasably connecting said motion compensator to said suspension means;
• means at the lower end of said suspension means for lifting said template with respect to said seabed in such a way that said template will tend to assume a predetermined attitude with respect to said seabed;
• tensioning means including a winch having a rotatable drum driven by a fluid motor and a single tension cable connected at one end to said drum and adapted to be connected at its other end to a point fixed with respect to said seabed, the tension on said cable being controlled by controlling the delivery of pressure fluid with respect to said motor;
• and to reduce movement of said template with respect to said seabed during said positioning of said template, and
• said winch includes a support frame including means for supporting said frame by said suspension means whereby said cable may be secured at said other end to means fixed to said seabed and at said one end to said suspension means.

A method of installing, levelling and securing a subsea template on a seabed comprising the steps of:

• providing a floating vessel including hoisting apparatus for raising and lowering a template with respect to said seabed, said hoisting apparatus including a motion compensator and elongated suspension means extending from said motion compensator toward said seabed and adapted at a point on said suspension means to be connected to a template structure;
• and winch means supported by said hoisting apparatus between said motion compensator and said point on said suspension means, said winch means including cable means for connection at a free end of said cable means to means fixed to said seabed;
• providing a template structure comprising a frame having a plurality of spaced apart pile receiving sleeves, formed thereon, said template structure including gripping means associated with said sleeves for releasably gripping piles disposed in respective ones of said sleeves for securing said template structure to said piles;
• positioning said template structure with said vessel over a predetermined point on said seabed and lowering said template structure to said seabed;
• installing a selected number of piles in respective ones of said sleeves and extending adjacent to said gripping means, respectively;
• lifting said template structure with said hoisting apparatus to level said template with respect to a predetermined reference level condition;
• tightening said cable means with said winch means to damp motion of said suspension means and said template structure;
• actuating said gripping means to connect said template to said piles, respectively;
• and
• lowering said template with said hoisting apparatus to transfer the weight of said template to said piles through said gripping means.

A method of positioning a template or the like on the seabed comprising the steps of:

• providing a floating vessel having a hoisting apparatus including a motion compensator suspended from said hoisting apparatus, and suspension means connected at one end of said suspension means to said motion compensator and at the other end of said suspension means to said template for lifting said template in response to operation of said hoisting apparatus;
• providing support means fixed to the seabed and adapted to be connected to said template for securing said template in a predetermined position on the seabed;
• providing adjustable tension means including an elongated cable adapted to be interconnected between said hoisting apparatus and a point of connection fixed to the seabed;
• connecting said suspension means to said hoisting apparatus and said template;
• interconnecting said cable with said hoisting apparatus between said motion compensator and said template and with said point of connection fixed to the seabed;
• operating said hoisting apparatus to position said template in a predetermined position while allowing said motion compensator to compensate for movement of said vessel with respect to said seabed,
• adjusting the tension in said cable to damp motion between said template and said support means;
• and
• securing said template to said support means.