Pulling structures into water
A structure such as a pipeline bundle is pulled into or through shallow water, for example, when launching the structure, by applying a tensile pulling force to the structure through rigging that extends to the structure from a winch of a first vessel. The pulling force is at least partially reacted through a pennant line that extends from the first vessel to a second vessel and that hangs between the first and second vessels to engage the seabed soil frictionally. The vessels can also self-propel to contribute their thrust to the pulling force. The pennant line includes a clump weight such as a bundle of chains that can be repositioned easily for additional pulls by being lifted between the vessels before being lowered to the seabed at a new location.
1 . A method of launching a structure across a shore and into water, the method comprising:
applying a tensile pulling force to the structure through rigging that extends to the structure from a near-shore tug; and
reacting the pulling force through a pennant line that extends from the near-shore tug to a far-shore tug and that frictionally engages seabed soil between the near-shore tug and the far-shore tug to augment the tensile pulling force and resist motion of the near-shore tug towards the shore, wherein the near-shore tug is located intermediate the far-shore tug and the structure.
2 . The method of claim 1 , comprising frictionally engaging the seabed soil with at least one clump weight of the pennant line.
3 . The method of claim 2 , wherein the or each clump weight comprises two or more chains attached to, or in series with, the pennant line.
4 . The method of claim 1 , comprising also reacting the pulling force by propelling the near-shore tug and/or the far-shore tug away from the structure.
5 . The method of claim 4 , comprising imparting tension in the pennant line by propelling the far-shore tug away from the structure.
6 . The method of claim 5 , comprising resisting movement of the pennant line toward the structure by propelling the far-shore tug away from the structure.
7 . The method of claim 6 , comprising moving the pennant line away from the structure by propelling the far-shore tug away from the structure.
8 . The method of claim 1 , comprising resisting movement of the pennant line toward the structure by engaging the seabed with an anchor of the pennant line.
9 . The method of claim 1 , comprising operating a winch aboard the near-shore tug to apply the pulling force to the structure.
10 . The method of claim 1 , further comprising:
relaxing the pulling force applied to the structure through the rigging;
lifting the pennant line to reduce or to interrupt frictional engagement with the seabed soil;
moving the near-shore tug, the far-shore tug and the pennant line away from the structure;
lowering the pennant line to increase or to resume frictional engagement with the seabed soil; and
reapplying the pulling force to the structure through the rigging.
11 . The method of claim 10 , comprising lifting substantially all of the pennant line clear of the seabed soil.
12 . The method of claim 10 , comprising lifting at least a portion of the pennant line onto the far-shore tug.
13 . The method of claim 12 , comprising moving the far-shore tug toward the near-shore tug for lifting the pennant line.
14 . The method of claim 10 , comprising keeping the pennant line coupled to near-shore tug and the far-shore tug while lifting, moving and lowering the pennant line.
15 . The method of claim 10 , comprising paying out the rigging from the near-shore tug while moving the near-shore tug away from the structure.
16 . The method of claim 10 , comprising keeping the rigging coupled to the structure and the near-shore tug while moving the near-shore tug away from the structure.
17 . The method of claim 1 , comprising floating the rigging on water between the near-shore tug and the structure.
18 . The method of claim 1 , comprising suspending respective ends of the pennant line from the near-shore tug and the far-shore tug in a catenary configuration.
19 . The method of claim 1 , wherein the near-shore tug is located in shallower water than the far-shore tug.
20 . A pulling arrangement for launching a structure across a shore and into water, the arrangement, in use, comprising:
a structure to be launched;
a near-shore tug and a far-shore tug disposed in series with each other and with the structure, the near-shore tug being located intermediate the far-shore tug and the structure;
rigging that extends to the structure from the near-shore tug; and
a pennant line that extends from the near-shore tug to the far-shore tug and that frictionally engages seabed soil between the near-shore tug and the far-shore tug in order to augment a tensile pulling force applied by the near-shore tug to the structure to be launched and to resist motion of the near-shore tug towards the shore.
21 . The arrangement of claim 20 , wherein the rigging extends to the structure from a winch of the near-shore tug.
22 . The arrangement of claim 20 , wherein the pennant line comprises at least one clump weight.
23 . The arrangement of claim 22 , wherein the or each clump weight comprises two or more chains attached to, or in series with, the pennant line.
24 . The arrangement of claim 20 , wherein the pennant line comprises at least one contingency anchor that is arranged to bury itself into the seabed soil in the event of longitudinal movement of the pennant line toward the structure.
25 . The arrangement of claim 24 , wherein the or each contingency anchor is arranged to disengage from the seabed soil in the event of longitudinal movement of the pennant line away from the structure.
26 . The arrangement of claim 20 , wherein the pennant line is coupled to a winch of the far-shore tug.
27 . The arrangement of claim 20 , wherein the rigging is positively buoyant.
28 . The arrangement of claim 20 , wherein the near-shore tug is located in shallower water than the far-shore tug, in use.
29 . The arrangement of claim 20 , wherein the structure is at a shore location, in use, the near-shore tug is a near shore tug and the far-shore tug is a far shore tug.