Installation method for water-submersible platforms and installation vessel
A method for installing a water-submersible platform is disclosed. The method includes lowering the platform in water from a vessel positioned above the platform while spuds connecting the vessel to the platform stabilize the platform during lowering. An assembly of the vessel and platform, and a vessel that is used to connect to the platform is also disclosed.
1. A method for installing a water-submersible platform at a pre-determined depth, comprising:
connecting a water-submersible platform underneath in relation to a vessel, wherein the vessel comprises a plurality of rigid elongated, vertically aligned spuds to connect the platform to the vessel, and the platform when installed is unconnected to the vessel;
transporting the platform through water underneath the vessel to an installation site;
while the platform is unconnected to a sea floor and underneath the vessel, exerting a downward force with the rigid elongated spuds by vertically driving the spuds to overcome a positive buoyancy of the platform throughout vertical lowering of the platform in the water from the vessel positioned above the platform while the rigid elongated spuds connecting the vessel to the platform stabilize the platform during lowering of the platform to a pre-determined depth without the spuds and platform reaching the sea floor,
when the platform is at the pre-determined depth, connecting the platform to the sea floor via mooring elements; and
disconnecting the platform from the spuds after the platform has been secured to the sea floor via the mooring elements, wherein the platform is moored at the pre-determined depth.
2. The method of claim 1 , further comprising, before lowering the platform in the water, placing the vessel over the platform, and connecting a lower end of the spuds to the platform.
3. The method of claim 2 , further comprising, to place the vessel over the platform, lowering the platform below a water surface to a depth that allows placing the vessel over the platform.
4. The method of claim 3 , further comprising ballasting the platform with water to assist in lowering the platform before placing the vessel over the platform.
5. The method of claim 4 , further comprising, after connecting the spuds to the platform, deballasting the platform of water and raising the spuds and raising the platform to a position underneath the vessel.
6. The method of claim 1 , further comprising, after disconnecting the spuds from the platform, raising the spuds.
7. The method of claim 1 , wherein the vessel floats on a surface of the water while lowering the platform.
8. The method of claim 1 , wherein the vessel is directly above the platform while lowering the platform.
9. The method of claim 1 , wherein the platform comprises a superstructure supported on a central hull, wherein the superstructure extends above a water surface.
10. The method of claim 1 , wherein the spuds connected to the platform are held in a fixed lateral position on the vessel, and the spuds connected to the platform are configured to lower and raise while in the fixed lateral position.
11. The method of claim 1 , wherein the platform would capsize in water when unattached to the vessel.
12. The method of claim 1 , wherein when the spuds reach a limit of downward extension, the spuds do not reach a seafloor.
13. The method of claim 1 , wherein the platform is a tension leg platform comprising a central hull and tendon arms extending radially from the central hull.
14. The method of claim 1 , wherein the spuds connected to the platform are laterally spaced from one another on the vessel.