CA2440248C - A mooring buoy - Google Patents
A mooring buoy Download PDFInfo
- Publication number
- CA2440248C CA2440248C CA002440248A CA2440248A CA2440248C CA 2440248 C CA2440248 C CA 2440248C CA 002440248 A CA002440248 A CA 002440248A CA 2440248 A CA2440248 A CA 2440248A CA 2440248 C CA2440248 C CA 2440248C
- Authority
- CA
- Canada
- Prior art keywords
- buoy
- chain
- winch
- equilibrium position
- winch line
- 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.)
- Expired - Fee Related
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- Other Liquid Machine Or Engine Such As Wave Power Use (AREA)
Abstract
In a method for releasing a mooring buoy (3) from a float- ing structure (1) the buoy is lowered by means of a chain (3) to a fist equilibrium position where the net buoyancy of the buoy is balanced by the weight of mooring lines (4) and risers (5). The chain (3) is lowered further by a sec- ond winch line (6) while the chain moves through a guide in the buoy until an upper stopper on the chain abuts the buoy. By further paying out of the second winch line (6), the weight of the chain is gradually transferred to the buoy and pulls it down to a second equilibrium position at a substantial depth safe from e.g. drifting icebergs. The second winch line (6) is disconnected from the chain and retrieved to the floating structure (1).
Description
A mooring buoy The present invention relates to a method for lowering a mooring buoy from a floating structure by means of a chain which is paid out from the floating structure via a chain-s winch until the buoy is near a first equilibrium position due to the weight of mooring lines and any risers connected to the buoy, whereupon the chain is lowered further by means of a second winch line until the chain is supported by the buoy.
~o Such a method is known from US 5860840. In this prior art method the basic purpose is to minimize the size and strength of the buoy. This is obtained by avoiding any di-rect connection of the majority of mooring lines to the buoy. Instead, these mooring lines are connected directly ~s to the turret of the vessel during the normal moored condi-tion. When the buoy has to be disconnected, e.g. in an emergency situation, each of said mooring lines are discon-nected from the turret and lowered by means of lighter aux-iliary lines through guide tubes in the buoy and to the sea 2o floor in order to reduce the load on the buoy also in its disconnected condition. However, this individual disconnec-tion and lowering of some of the mooring lines will cause a considerable delay in what may be an emergency situation where time is of essence.
Zs Due to the reduced size of the buoy the size and weight of the chain used to lower the buoy may be sufficiently small for it to be stored in a central space in the buoy. How-ever, once the buoy is disconnected from the vessel, there are no longer any mooring lines to keep the vessel in 3o place. Consequently, the vessel may tend to drift off under the influence of environmental forces and cause a lateral pull in the chain. The chain will no longer be vertical and when it is lowered further by means of the second winch line, all of it may not end up in its intended central space in the buoy, but may instead be left hanging over the
~o Such a method is known from US 5860840. In this prior art method the basic purpose is to minimize the size and strength of the buoy. This is obtained by avoiding any di-rect connection of the majority of mooring lines to the buoy. Instead, these mooring lines are connected directly ~s to the turret of the vessel during the normal moored condi-tion. When the buoy has to be disconnected, e.g. in an emergency situation, each of said mooring lines are discon-nected from the turret and lowered by means of lighter aux-iliary lines through guide tubes in the buoy and to the sea 2o floor in order to reduce the load on the buoy also in its disconnected condition. However, this individual disconnec-tion and lowering of some of the mooring lines will cause a considerable delay in what may be an emergency situation where time is of essence.
Zs Due to the reduced size of the buoy the size and weight of the chain used to lower the buoy may be sufficiently small for it to be stored in a central space in the buoy. How-ever, once the buoy is disconnected from the vessel, there are no longer any mooring lines to keep the vessel in 3o place. Consequently, the vessel may tend to drift off under the influence of environmental forces and cause a lateral pull in the chain. The chain will no longer be vertical and when it is lowered further by means of the second winch line, all of it may not end up in its intended central space in the buoy, but may instead be left hanging over the
2 side of the buoy where it can get tangled in the risers and mooring lines.
The purpose of the present invention is to provide a method of the type mentioned by way of introduction which may be s used in deep water and hostile environments, where the buoy will have to reach a substantial depth in the disconnected condition in order to avoid threats from e.9. passing ice-bergs, yet without being too heavy to lift back up to re-docking position in the surface vessel. In addition, the ro method should permit quick and easy disconnection of the buoy from the vessel without the need for separate discon-nection of mooring lines.
This is obtained in the method according to the invention by letting the chain, during said further lowering, move ~s down through a guide in the buoy until an upper enlargement on the chain stops against the buoy, whereby the chain is permitted to depend below the buoy and constitute a sub-stantial ballasting element which brings the buoy to a sec-ond, substantially deeper equilibrium position.
zo By using the chain as a ballasting element the first equi-librium position may be considerably higher than the re-quired final equilibrium position, which means that the buoy will have to be lifted a shorter distance and with a lower force exerted by the chain winch. This is because the zs buoy can be made with a higher net buoyancy than what would be required if it were to obtain equilibrium at the lower depth without any removable substantial ballast like the chain. The higher net buoyancy permits the buoy to carry a heavier load from the moorings or risers, thus avoiding any 3o separate disconnection thereof.
Further advantageous features of the invention are recited in the dependent claims.
The purpose of the present invention is to provide a method of the type mentioned by way of introduction which may be s used in deep water and hostile environments, where the buoy will have to reach a substantial depth in the disconnected condition in order to avoid threats from e.9. passing ice-bergs, yet without being too heavy to lift back up to re-docking position in the surface vessel. In addition, the ro method should permit quick and easy disconnection of the buoy from the vessel without the need for separate discon-nection of mooring lines.
This is obtained in the method according to the invention by letting the chain, during said further lowering, move ~s down through a guide in the buoy until an upper enlargement on the chain stops against the buoy, whereby the chain is permitted to depend below the buoy and constitute a sub-stantial ballasting element which brings the buoy to a sec-ond, substantially deeper equilibrium position.
zo By using the chain as a ballasting element the first equi-librium position may be considerably higher than the re-quired final equilibrium position, which means that the buoy will have to be lifted a shorter distance and with a lower force exerted by the chain winch. This is because the zs buoy can be made with a higher net buoyancy than what would be required if it were to obtain equilibrium at the lower depth without any removable substantial ballast like the chain. The higher net buoyancy permits the buoy to carry a heavier load from the moorings or risers, thus avoiding any 3o separate disconnection thereof.
Further advantageous features of the invention are recited in the dependent claims.
3 The invention also relates to a buoy for use in the afore-said method, wherein the buoy is provided with a ballasting element in the form of a chain, said chain also being suit-able for lifting and lowering the buoy in the submerged po-s sition, said chain being free to move through a guide in the buoy except for end stoppers on the chain preventing it from becoming loose from the buoy.
The invention will be explained in more detail with refer-ence to the exemplifying embodiment illustrated in the ap- .
~o pended drawings, where:
Fig. 1 shows a schematic view of an 'offshore hydrocarbon, production facility incorporating a buoy according to the present invention, Fig. 2 is a view similar to fig. 1, but shows the buoy dis-~s connected and in a first equilibrium position, and Fig. 3 shows a view similar to fig. 2, but with the buoy in a second equilibrium position.
The production facility shown in fig. 1 comprises a float-ing vessel 1 having a generally axi-symmetric underwater 2o body supporting a deck structure carrying facilities well known in the art. The vessel is moored by means of a buoy 3 attached thereto, the buoy 3 being connected to mooring lines 4 and flexible risers 5 of two hybrid riser systems.
If the vessel 1 temporarily has to move from its location, zs e.g. if it is in the path of a drifting iceberg, the buoy 3 is disconnected from the vessel and lowered by means of a chain winch (not shown) on the vessel until it reaches a first equilibrium position where its net buoyancy is bal-anced by the weight of the mooring lines 4 and flexible 3o risers 5. This first equilibrium position is illustrated in fig. 2 and may be at a depth of about 130 m. This figure further shows that the chain 2 has been lowered further so I
that part of it depends below the buoy 3. This lowering of the chain continues by means of a second winch line 6 until a stopper at the upper end of the chain abuts the buoy and pulls the buoy down to a second equilibrium position s wherein the entire weight of the chain 2 is carried by the buoy 3. The buoy may now be at a depth of e.g. 250 m.
The lower end of the second winch wire 6 may be connected to the chain 2 by means of a coupling that automatically will disconnect from the chain when the second winch wire io goes slack. The vessel is now free to move off the loca-tion.
When the vessel is to be reconnected to the buoy 3 at a later stage, the second winch wire 6 has to be lowered to the buoy and reconnected to the chain 2, e.9. by the aid of ~s a remotely operated vehicle or other means well known in the art. As the winch line 6 gradually takes over the weight of the chain 2, the buoy 3 rises until it reaches the first equilibrium position illustrated in fig. 2. Fur-ther operation of the second winch pulls the chain up ?o through the buoy until the chain can be connected to its chain winch and raise the buoy to its docking position in the vessel as shown in fig. 1.
The present invention has been described in connection with its preferred embodiment. However, persons skilled in the art will recognize that modifications, alterations and variations of the invention are possible without departing from the scope of the invention. Accordingly, such modifi-cations, alterations and variations shall be deemed to be included in this invention as defined by the appended 3o claims .
The invention will be explained in more detail with refer-ence to the exemplifying embodiment illustrated in the ap- .
~o pended drawings, where:
Fig. 1 shows a schematic view of an 'offshore hydrocarbon, production facility incorporating a buoy according to the present invention, Fig. 2 is a view similar to fig. 1, but shows the buoy dis-~s connected and in a first equilibrium position, and Fig. 3 shows a view similar to fig. 2, but with the buoy in a second equilibrium position.
The production facility shown in fig. 1 comprises a float-ing vessel 1 having a generally axi-symmetric underwater 2o body supporting a deck structure carrying facilities well known in the art. The vessel is moored by means of a buoy 3 attached thereto, the buoy 3 being connected to mooring lines 4 and flexible risers 5 of two hybrid riser systems.
If the vessel 1 temporarily has to move from its location, zs e.g. if it is in the path of a drifting iceberg, the buoy 3 is disconnected from the vessel and lowered by means of a chain winch (not shown) on the vessel until it reaches a first equilibrium position where its net buoyancy is bal-anced by the weight of the mooring lines 4 and flexible 3o risers 5. This first equilibrium position is illustrated in fig. 2 and may be at a depth of about 130 m. This figure further shows that the chain 2 has been lowered further so I
that part of it depends below the buoy 3. This lowering of the chain continues by means of a second winch line 6 until a stopper at the upper end of the chain abuts the buoy and pulls the buoy down to a second equilibrium position s wherein the entire weight of the chain 2 is carried by the buoy 3. The buoy may now be at a depth of e.g. 250 m.
The lower end of the second winch wire 6 may be connected to the chain 2 by means of a coupling that automatically will disconnect from the chain when the second winch wire io goes slack. The vessel is now free to move off the loca-tion.
When the vessel is to be reconnected to the buoy 3 at a later stage, the second winch wire 6 has to be lowered to the buoy and reconnected to the chain 2, e.9. by the aid of ~s a remotely operated vehicle or other means well known in the art. As the winch line 6 gradually takes over the weight of the chain 2, the buoy 3 rises until it reaches the first equilibrium position illustrated in fig. 2. Fur-ther operation of the second winch pulls the chain up ?o through the buoy until the chain can be connected to its chain winch and raise the buoy to its docking position in the vessel as shown in fig. 1.
The present invention has been described in connection with its preferred embodiment. However, persons skilled in the art will recognize that modifications, alterations and variations of the invention are possible without departing from the scope of the invention. Accordingly, such modifi-cations, alterations and variations shall be deemed to be included in this invention as defined by the appended 3o claims .
Claims (10)
1. A method for lowering a mooring buoy from a floating structure by means of a chain which is paid out from the floating structure via a chain winch until the buoy is near a first equilibrium position due to the weight of mooring-lines and any risers connected to the buoy, whereupon the chain is lowered further by means of a second winch line until the chain is supported by the buoy, wherein, during said further lowering, the chain is permitted to move down through a guide in the buoy until an upper enlargement on the chain stops against the buoy, whereby the chain will depend below the buoy and constitute a substantial bal-lasting element which brings the buoy to a second, substan-tially deeper equilibrium position.
2. A method according to claim 1, wherein said second winch line, when the buoy is at its second equilibrium po-sition, is released from the chain and raised to the float-ing structure.
3. A method according to claim 2, wherein the second winch line is released automatically from the chain when the sec-ond winch line goes slack.
4. A method according to any one of claims 1 to 3, wherein, when the buoy at a later stage is to be connected to the floating structure, the second winch line is recon-nected to the upper end of the chain and made to raise the chain to the floating structure, whereupon the buoy is raised to said structure by means of the chain and said chain winch.
5. A method according to claim 4, wherein, when said upper end of the chain is raised to said structure, the chain is permitted to move through a guide in the buoy until a stop-per at the lower end of the chain abuts the buoy.
6. A method according to any one of claims 1 to 5, wherein the buoy is used to support risers in addition to the mooring lines.
7. A method according to any one of claims 1 to 6, wherein said second equilibrium position is at a depth of about 250 m.
8. A method according to any one of claims 1 to 7, wherein said first equilibrium position is at a depth of about 130 m.
9. A method according to any one of claims 1 to 8, wherein the floating structure used has a generally axi-symmetric underwater body, thereby obviating a rotatable turret or swivel connection between the buoy and said structure.
10. A buoy for use in the method according to any one of claims 1 to 9, wherein the buoy is provided with a ballasting element in the form of a chain, said chain being suitable for lifting and lowering of the buoy, said chain being freely moveable through a guide in the buoy, the ends of the chain being provided with stoppers preventing the chain from coming loose from the buoy.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NO20024303 | 2002-09-09 | ||
| NO20024303A NO20024303D0 (en) | 2002-09-09 | 2002-09-09 | Buoy |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2440248A1 CA2440248A1 (en) | 2004-03-09 |
| CA2440248C true CA2440248C (en) | 2008-05-13 |
Family
ID=19913976
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002440248A Expired - Fee Related CA2440248C (en) | 2002-09-09 | 2003-09-09 | A mooring buoy |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2440248C (en) |
| NO (1) | NO20024303D0 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101532234B1 (en) * | 2007-03-21 | 2015-06-29 | 세반 마린 에이에스에이 | Floating platform for operation in regions exposed to extreme weather conditions |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104890818A (en) * | 2015-06-19 | 2015-09-09 | 东南大学 | Automatically resettable buoy comprising coil spring |
| CN110341891A (en) * | 2019-07-08 | 2019-10-18 | 吴江新华航标制造有限公司 | A deep water buoy and its manufacturing process |
-
2002
- 2002-09-09 NO NO20024303A patent/NO20024303D0/en not_active Application Discontinuation
-
2003
- 2003-09-09 CA CA002440248A patent/CA2440248C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101532234B1 (en) * | 2007-03-21 | 2015-06-29 | 세반 마린 에이에스에이 | Floating platform for operation in regions exposed to extreme weather conditions |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2440248A1 (en) | 2004-03-09 |
| NO20024303D0 (en) | 2002-09-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |
Effective date: 20210909 |