Offshore material handling system and material handling method

1. An offshore material handling system comprising:

a service or supply vessel having a conventional heave compensated crane;

an installation structure fixed to the seabed and projecting above sea level, said installation structure having an open trusswork that supports offshore drilling operations, said installation structure further comprising a lifting appliance on board; and

a platform structure having at least two hooks that are sized to be temporarily hung onto the open trusswork of said installation structure, and at least one horizontal truss bar connected to said platform structure by truss beams;

wherein said truss bar rests against said installation structure below said platform structure, and in combination with said hooks, supports said platform structure on said installation structure;

wherein said platform structure is placed by the conventional heave compensated crane at a level on said installation structure within reach of both the conventional heave compensated crane and the lifting appliance;

wherein said platform structure acts as a temporary, independent, load station supported on said installation structure; and

wherein said independent platform structure further comprises means for attachment to a crane hook on board said service or supply vessel so that said platform structure is lifted as a single unit onto said installation structure by the conventional heave compensated crane.

2. The offshore material handling system according to claim 1 , wherein said lifting appliance on board the installation structure is either a gantry crane, slewing crane, winches, or other lifting appliances able to elevate or lower a load from or to different levels internally on the installation structure.

3. The offshore material handling system according to claim 1 , wherein said installation structure is either an unmanned wellhead platform (UWP), or any offshore installation fixed to the seabed.

4. The offshore material handling system according to claim 1 , wherein said platform structure is a corner platform structure.

5. The offshore material handling system according to claim 1 , wherein said platform structure is attached to the installation structure a distance above the sea level.

6. The offshore material handling system according to claim 1 , wherein said platform structure includes a ladder or gangway to enable forming a walkway from said platform structure onto said installation structure.

7. The offshore material handling system according to claim 1 , wherein the platform structure further comprises a guard rail.

8. A method for offshore handling of material between a service or supply vessel having a heave compensated crane and an installation structure fixed to the seabed and projecting above sea level, said installation structure having an open trusswork that supports offshore drilling operations, said installation structure further comprising a lifting appliance on board, said method comprising:

a) bringing a platform structure as a single unit by the heave compensated crane on said service or supply vessel onto said installation structure at a level within reach of both the heave compensated crane of said service or supply vessel and the lifting appliance on board said installation structure, wherein said platform structure comprises hooks that are sized for temporary attachment onto the open trusswork of said installation structure, said platform structure further comprising at east one horizontal truss bar that is connected to said platform structure by truss beams, and that rests against said installation structure below the platform structure, and the combination of said hooks and said horizontal truss bar support said platform structure on said installation structure;

b) bringing a load from said heave compensated crane on said service or supply vessel onto said platform structure; and

c) bringing said load from said platform structure to a predetermined level and location on said installation structure by the lifting appliance.

9. The method according to claim 8 , wherein, prior to step c), the following step is performed:

bringing a second load by said heave compensated crane on said service or supply vessel from said service or supply vessel onto said platform structure.

10. The method according to claim 8 , wherein said method includes the following step:

releasing, after step c), the platform structure from the installation structure and bringing said platform structure by the service or supply vessel back from said installation structure and onto said service or supply vessel.