GB2286173A

GB2286173A - Anchor arrangements

Info

Publication number: GB2286173A
Application number: GB9401506A
Authority: GB
Inventors: Inge Huse
Original assignee: I P Huse AS
Current assignee: I P Huse AS
Priority date: 1994-01-26
Filing date: 1994-01-26
Publication date: 1995-08-09
Anticipated expiration: 2014-01-26
Also published as: FR2716157A1; BR9400570A; FR2716157B1; GB2286173B; GB9401506D0

Abstract

An anchoring arrangement for offshore vessels includes an anchor line 12 having a first line portion 12a which passes from a winch (not shown) on the deck of the vessel downwardly towards a guide pulley 13 on a hawse pipe 14 submerged in the sea 11. The guide pulley 13 is pivotably mounted on the vessel via a force-transferring component 19 on the hawse pipe 14 about an axis 18 parallel to the first line portion 12a. A second line portion 12b of the anchor line 12 passes from the guide pulley 13 obliquely downwards and outwards to an anchor (not shown) fastened to the sea bottom. The guide pulley 13 is rotatably mounted about a first horizontal axis at 13a at the one end of a joint arm-forming fork member 24, the opposite end of which is pivotably mounted at 21 about a second horizontal axis on the force-transferring component 19. <IMAGE>

Description

Anchor Arrangements.

This invention relates to anchor arrangements for offshore vessels comprising a winch on the deck of the vessel controlling an anchor line having first and second line portions, said first line portion being arranged to pass from said winch downwardly towards a hawse pipe submerged in the sea, a guide pulley rotatably mounted about a horizontal axis as well being pivotably mounted in said vessel, via a force-transferring means, about an axis parallel to the first line portion, said second line portion being arranged to pass form the guide pulley in a path deflected obliquely downwards and outwards towards an anchor fastening on the sea bottom.

The hawse pipe of the afore-mentioned anchor arrangement shall transfer large forces between the anchor fastening on the sea bottom and the vessel. The forces which occur are extra large as a consequence of the anchor line being led downwardly and outwardly from the vessel at a significant angle of deflection in the hawse pipe, for example at an angle of deflection of between 30 and 90".

Simultaneously the vessel is to be held at rest in a specific position cn the sea under the influence of large sea and/or wind forces. In this connection, the anchor line must be able to travel in a controlled manner backwards and forwards through the hawse pipe via the guide pulley while tensile forces are transferred from the guide pulley, via the force-transferring component, to a fastening on the lower construction of the vessel, all according to the prevailing conditions at sea.

The force-transferring component can, in practice, have various designs but includes, in most instances, a rotatably mounted guide pulley where the guide groove of the guide pulley together with the anchor line shall control the movements of the guide pulley and the anchor line relative to each other.

By virtue of the occurrence of shifting winds and/or currents the anchor line can acquire different angles of incidence to the vessel in the vertical plane as well as in the horizontal plane. In order to solve this problem, hawse pipes have hitherto been employed with an associated guide pulley which is pivotably mounted about an axis so that the hawse pipe becomes self-levelling and with that assumes a favourable position when stresses arise.

A problem with known self-levelling hawse pipes is that there is a relatively large distance between upper and lower mountings of the vertically pivotable forcetransferring component. This involves problems especially when the hawse pipe is to be used on vessels (platforms) of concrete structure. It is desirable that the occurring forces shall pass more collectively in towards the concrete structure so that there is less need for extra reinforcing arrangements enclosed in the concrete structure.

With the present invention the aim is to collect tensile forces in a relatively constricted region at the lower construction component of the vessel.

Accordingly, the present invention resides in an anchor arrangement for an offshore vessel which comprises a winch on the deck of said vessel controlling an anchor having first and second line portions, said first line portion being arranged to pass from said winch downwardly towards a hawse pipe submerged in the sea, a guide pulley rotatably mounted about a horizontal axis as well as being pivotably mounted in said vessel, via force-transferring means, about an axis parallel to said first line portion, said second line portion being arranged to pass from said guide pulley in a path deflected obliquely downwards and outwards towards an anchor fastening on the sea bottom, and the guide pulley being rotatably mounted about a horizontal axis at the one end of a joint arm-forming fork member while the opposite end of the latter is pivotably mounted about a horizontal axis in the force-transferring component.

By means of the fork member, one can ensure, independently of the angle of incidence of the anchor line towards the guide pulley, reckoned in the vertical plane, that the occurring tensile forces are received in a constricted region at the fastening on the lower end of the adjacent construction components of the vessel.

In order that the invention can be more clearly understood, a convenient embodiment thereof will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a side representation of a hawse pipe in an anchor arrangement, and Fig. 2 is a plan of the hawse pipe of Fig. 1.

Referring to Figs. 1 and 2, a lower construction component 10 of an offshore vessel (drilling platform or the like) is shown submerged in the sea 11, while the deck of the vessel (not shown) is arranged above sea level. On the deck of the vessel a winch (not shown) is arranged.

An anchor line 12 passes with a first line portion 12a from said winch to a guide pulley 13 in a hawse pipe 14, which is fastened to the construction component 10, as is illustrated in Figs. 1 and 2. The anchor line 12 passes with a second line portion 12b from the guide pulley 13 in a path directed obliquely outwards and downwards to an anchor fastening on the sea bottom (not shown).

The hawse pipe 14 comprises a vertical anchor plate 15 which is secured, for example, by welding or with fastening bolts to the lower end of the construction component 10. From the anchor plate 15, an upper fastening plate 16 and a lower fastening plate 17 project horizontally outwards with respective fastenings for an intermediate pivot pin 18. On the pivot pin 18, which extends parallel to the first line portion 12 at the anchor line 12, a force-transferring component 19 is pivotably mounted. The force-transferring components 19 comprises a first vertical pivot bush 20 which is pivotably mounted in a pivot bearing (not shown) on the pivot pin 18, and a second horizontal pivot bush 21 which is arranged radially just outside the pivot bush 20 at its upper end and which is connected to the pivot bush 20 by means of a pair of vertical side plates 22,23.The pivot bushes 20, 21 and associated side plates 22,23 mutually brace one another and together constitute a relatively compact force-transferring component.

In the horizontal pivot bush 21, a joint armingforming fork member 24 is pivotably mounted. The fork member 24 comprises a first horizontal pivot pin 25 which is pivotably mounted in a pivot bearing in the pivot bush 21 and which carries, laterally outside the forcetransferring component 19, the inner end of a pair of mutually parallel fork arms 26,27. At the outer end of the fork arms, a transverse rotary shaft 28 is fastened which carries a bearing-forming pivot bush 13a rotatably mounted in the guide pulley 13.

By means of the rotary shaft 28, the fork member 24 forms a rigid ring construction which is adapted to transfer mainly tensile forces between the guide pulley 13 and the force-transferring component 19. All according to the angle at which the second line portion 12b is caused to pass obliquely downwards rom the guide pulley 13. The fork member 24 will be pivoted correspondingly about the pivot pin 25 and transfers tensile forces axially through the pivot pin 25. As illustrated in Fig. 1, the line portion 12a passes while at a relatively small angle to the horizontal plane through the rotary shaft but can, in practice, form substantially greater angles with the horizontal plane determined by the fastening point of the anchor on the sea bottom.A support-forming stop 2 is shown on side plates 26, 27 of the fork member 24 and an equivalent support-forming stop 30 on side plates 22,23 of the force-transferring component 19 in order to limit the pivot angle of the fork member 24 downwards from the position illustrated in Fig. 1.

Correspondingly, the force-transferring component 19 forms an equivalent rigid ring construction which constitutes a universal joint between the guide pulley 13 and the fastening on the construction component and which is adapted to mainly transmit tensile forces between the fork member 24 and the anchor plate 15 and associated fastening plates 16,17 and pivot pin 18.

The rigid ring constructions (the force-transferring component 19 and the fork member 24) constitute a pivot arm mechanism braced in a horizontal direction which can ensure that the guide pulley 13 is automatically adjusted in the same plane as the vertical plane through line portions 12a, 12b of the anchor line 12. In Fig. 2 there is indicated, in broken lines, a lateral outward swinging of the pivot mechanism about a vertical axis through the pivot pin 18. By broken lines 31, 32, stops are indicated for limiting outward swinging angles of the pivot arm mechanism to opposite sides of the central position shown in Fig. 2. The stops 31, 32 can, in addition, form extra bracing means between the fastening plates 16 an 17.

Claims

1. An anchor arrangement for an offshore vessel which comprises an anchor line controlled by a winch on the deck of said vessel and having first and second line portions, said first line portion being arranged to pass from said winch downwardly towards a hawse pipe submerged in the sea, a guide pulley rotatably mounted about a horizontal axis as well as being pivotably mounted in said vessel, via a force-transferring means, about an axis parallel to said first line portion, said second line portion being arranged to pass from said guide pulley in a path deflected obliquely downwards and outwards towards an anchor fastening on the sea bottom, and said guide pulley being rotatably mounted about a horizontal axis at one end of a joint-arm forming fork member while the opposite end of the latter is pivotably mounted about a horizontal axis in said force-transferring means.

2. An arrangement according to claim 1, wherein the joint arm-forming fork member is pivotably mounted at the upper end of the force-transferring means.

3. An arrangement according to claim 1 or 2, wherein a hawse pipe comprises a vertical anchor plate secured to the lower end of a submerged construction member of the offshore vessel, and first pivot means mounted on said anchor plate in laterally spaced relation therefrom upon which the force-transmitting means are pivotably mounted.

4. An arrangement according to claim 3, wherein the force-transferring means comprise a vertical first pivot bush pivotably mounted on the first pivot means and a horizontal second pivot bush connected to said first pivot bush radially outside the latter and adjacent the upper end thereof, said second pivot bush being pivotably mounted on a second pivot means at the opposite end of the fork member.

5. An arrangement according to claim 4, wherein the fork member comprises a pair of mutually parallel arms supported at their inner end on the second pivot means laterally outside the force-transmitting means while at their outer end a rotary shaft of the guide pulley is supported.

6. An arrangement according to claim 5, wherein the fork member and the rotary shaft form a rigid ring construction adapted to transfer tensile forces between the guide pulley and the force-transferring means.

7. An arrangement according to claim 3, wherein the force transferring means forms a rigid ring construction in the form of a universal joint between the guide pulley and the construction member which is adapted to transfer tensile forces between the fork member and the anchor plate plus first pivot means.

8. Arrangements for offshore vessels constructed and adapted for use substantially as described herein with particular reference to the accompanying drawings.