GB2089406A - A Method of Putting Down an 0ffshore Structure - Google Patents

A Method of Putting Down an 0ffshore Structure Download PDF

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Publication number
GB2089406A
GB2089406A GB8136893A GB8136893A GB2089406A GB 2089406 A GB2089406 A GB 2089406A GB 8136893 A GB8136893 A GB 8136893A GB 8136893 A GB8136893 A GB 8136893A GB 2089406 A GB2089406 A GB 2089406A
Authority
GB
United Kingdom
Prior art keywords
legs
pontoon
derrick
reached
supporting surface
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB8136893A
Other versions
GB2089406B (en
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
RSV GUSTO ENG BV
Original Assignee
RSV GUSTO ENG BV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by RSV GUSTO ENG BV filed Critical RSV GUSTO ENG BV
Publication of GB2089406A publication Critical patent/GB2089406A/en
Application granted granted Critical
Publication of GB2089406B publication Critical patent/GB2089406B/en
Expired legal-status Critical Current

Links

Classifications

    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B17/02—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto
    • E02B17/021—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto with relative movement between supporting construction and platform
    • E02B17/024—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto with relative movement between supporting construction and platform shock absorbing means for the supporting construction
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B17/02—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto
    • E02B17/021—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto with relative movement between supporting construction and platform
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B2017/0039—Methods for placing the offshore structure
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B2017/0056—Platforms with supporting legs
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B2017/0056—Platforms with supporting legs
    • E02B2017/0073—Details of sea bottom engaging footing
    • E02B2017/0082—Spudcans, skirts or extended feet

Landscapes

  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Bridges Or Land Bridges (AREA)
  • Revetment (AREA)

Abstract

A method for putting down an artificial island (2) comprising a pontoon (3) with displaceable and fastenable legs (4) comprises lowering the legs (4) at one side of the pontoon but before one or more of said legs (4) have reached the supporting surface (6) partly elevating the pontoon (3) by means of a floating derrick (7), then as soon as the legs (4) have reached the foundation surface (6) switching off the hoisting means (7). Thereafter the other legs are lowered followed by an upwards movement of the pontoon along the legs. <IMAGE>

Description

SPECIFICATION Method for Putting Down an Artificial Island The invention relates to a method for putting down an artificial island comprising a pontoon and in respect thereof displaceable and fastenable legs, which legs are lowered from the pontoon and after positioning said legs the pontoon is moved upwards along said legs.
Such a method is commonly known. When such a method is used then the legs are lowered at the place of destination until reaching the bottom or the supporting surface of a foundation construction, which is positioned at the sea bottom beforehand. When putting down such an artificial island the problem arises that the pontoon under the influence of the wave movements carries out all kinds of motions. When the lowering legs approach the bottom respectively the supporting surface, then the lower ends of said legs are continuously in motion with respect to the bottom respectively the foundation surface both in the vertical as well as in the horizontal direction. This results into multiple bumps between the legs and the bottom respectively the supporting surface which not only hinders the putting down operation but also can cause serious damage.That applies especially to the case in which the legs of the island have to be positioned unto the legs of a foundation construction which is beforehand positioned onto the sea bottom.
The object of the invention is now to provide a method in which the difficulties arising during the put down operation are removed in a simple way.
According to the invention said object is reached in that before one or more of said legs have reached the bottom respectively the supporting surface the pontoon is partly elevated at least at one side by means of a floating derrick and the hoisting means of said derrick are switched off immediately as soon as a leg or the legs at that side of the pontoon, which is partly elevated by said derrick, have reached the bottom respectively the supporting surface. Thus the hoisting means of the floating derrick carries a part of the weight of the pontoon. Therefore said part is less subject to the wave movements.
When the legs positioned at said side are lowered and the hoisting means are switched off immediately when the supporting surface is reached, then at that side the pontoon is already partially lifted out of the water and therefore presses with increased force onto the bottom respectively onto the supporting surface. The result thereof is a quick and stable dispositioning.
Under circumstances with wind and heavy waves preferably the floating derrick is positioned at the weatherboard of the pontoon. Thereby the wave movements are highly damped, which is not only an advantage in relation to the above described method, but also an advantage for positioning the non lowered legs at the side of the island opposite the floating derrick without the necessity to use the derrick also at that side.
To increase the effect of the quick elimination of the wave movement influence onto the pontoon during positioning of the legs at the side, which is elevated by means of the floating derrick, it can be advantageous according to the invention to provide the part of the pontoon to be elevated with additional ballast. As far as the wave movements are not already eliminated by the floating derrick these movements do have in that case even less chance to lift the positioned legs again from the supporting surface.
The used floating derrick preferably is a crane onto a vessel of the type provided with buoyancy bodies under the water level and with a small cross section of the parts crossing the water level.
Such a ship itself is only influenced by the waves in a minor way.
The invention will now be explained referring to the drawing. Said drawing in a side view of a crane ship 1 and an artificial island 2 comprising a pontoon 3, a number of displaceable and fastenable legs 4 and a foundation construction 5, positioned onto the sea bottom and comprising upwards directed carrier legs 6.
The crane ship 1 comprises a heavy crane 7.
The crane ship is moored by means of mooring cables 8 and is positioned at the weatherboard of the pontoon 3 which is coupled to the crane ship 1 by means of cables 9.
In the drawing the waves and wind are coming from the left and moving to the right so that the pontoon is positioned in the shelter of the crane ship. Thereby the wave movements at the place of the pontoon are strongly reduced.
According to the invention the side part of the pontoon 3 directed to the crane ship is elevated by means of the hoisting cables 10 so that the pontoon and the legs thereof are only partly carried by the pontoons own buoyancy capacity and for the other part carried by the crane ship 1.
This results into such a stabilisation that even in heavy weather the motions are minimal so that the put down operation can carry on.
In this stabilized elevated position the left hand legs 4 are lowered until they meet the upper surface of the foundation legs 6.
Because of the stabilization the bump thereby is very minimal. Directly after said bump the hoisting means are switched off so that the related side of the pontoon immediately rests with an important part of its weight on the legs 6 by means of the legs 4 and said effect can be increased by providing additional ballast in the order of magnitude of many hundreds of tons of weight for instance into the space 11. At this side the water line of the pontoon is already above the water surface so that the upwards pressure generated by the waves has thereafter little or no influence.
The legs 4 illustrated at the right hand are still free from the foundation construction 5, 6.
Because one side is already supported and because the wave movements in the shelter of the crane ship are minimal it is possible to lower said legs without using further additional means and to install said legs onto the legs 6.
It is of course also conceivable to bring the crane ship to the other side and to elevate said side and repeat the operation.
As soon as this part of the out down operation is completed the pontoon can move upwards in a known way along the legs onto a level in which it is out of reach of high waves.

Claims (3)

Claims
1. Method for putting down an artificial island comprising a pontoon and in respect thereof displaceable and fastenable legs, which legs are lowered from the pontoon and after positioning said legs the pontoon is moved upwards along said legs, characterized in that before one or more of said legs have reached the bottom respectively the supporting surface the pontoon is partly elevated at least at one side by means of a floating derrick and the hoisting means of said derrick are switched off immediately as soon as a leg or the legs at that side of the pontoon, which is partly elevated by said derrick, have reached the bottom respectively the supporting surface.
2. Method according to claim 1 characterized in that the floating derrick is positioned at the weatherboard of the pontoon.
3. Method according to claim 1 or 2 characterized in that the part of the pontoon to be elevated is provided with additional ballast.
GB8136893A 1980-12-09 1981-12-08 A method of putting down an offshore structure Expired GB2089406B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL8006678A NL8006678A (en) 1980-12-09 1980-12-09 METHOD FOR SETTING DOWN AN ARTIFICIAL ISLAND

Publications (2)

Publication Number Publication Date
GB2089406A true GB2089406A (en) 1982-06-23
GB2089406B GB2089406B (en) 1984-06-27

Family

ID=19836300

Family Applications (1)

Application Number Title Priority Date Filing Date
GB8136893A Expired GB2089406B (en) 1980-12-09 1981-12-08 A method of putting down an offshore structure

Country Status (3)

Country Link
DE (1) DE3148247C2 (en)
GB (1) GB2089406B (en)
NL (1) NL8006678A (en)

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3545539A (en) * 1967-08-28 1970-12-08 Mobil Oil Corp Subsea satellite foundation unit and method for installing satellite body therewithin
DE2545219A1 (en) * 1975-10-09 1977-04-21 Babcock Ag ARTIFICIAL ISLAND
US4109476A (en) * 1977-05-20 1978-08-29 Brown & Root, Inc. Docking an offshore structure with a submerged fixture

Also Published As

Publication number Publication date
DE3148247C2 (en) 1984-07-12
DE3148247A1 (en) 1982-07-22
NL8006678A (en) 1982-07-01
GB2089406B (en) 1984-06-27

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Legal Events

Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee