WO2009087559A1

WO2009087559A1 - Underwater- pipeline laying apparatus, method of operating such an apparatus, and pipeline laying vessel comprising such an apparatus

Info

Publication number: WO2009087559A1
Application number: PCT/IB2009/000012
Authority: WO
Inventors: Giancarlo De Negri; Cristian Scaini; Teresio Signaroldi
Original assignee: Saipem S.P.A.
Priority date: 2008-01-08
Filing date: 2009-01-07
Publication date: 2009-07-16
Also published as: ITMI20080021A1

Abstract

An underwater-pipeline (2) laying apparatus (6) of a pipeline laying vessel (1) has an inner ramp (14) hinged to the vessel (1) about a first axis (Al); an outer ramp (15) hinged releasably to the inner ramp (14) about a second axis (A2) parallel to the first axis (Al); a first actuating device (16) for operating the inner ramp (14) and connected to the inner ramp (14) and the vessel (1); a second actuating device (17) for operating the outer ramp (15) and connected to the outer ramp (15) and the vessel (1); and a coupling device (27) for connecting the outer ramp (15) to the vessel (1).

Description

UNDERWATER-PIPELINE LAYING APPARATUS, METHOD OF OPERATING SUCH AN APPARATUS, AND PIPELINE LAYING VESSEL COMPRISING SUCH AN APPARATUS

TECHNICAL FIELD

The present invention relates to an underwater- pipeline laying apparatus of an underwater-pipeline laying vessel.

More specifically, the present invention relates to an underwater-pipeline laying apparatus of a pipeline laying vessel, in which the laying apparatus comprises an inner ramp hinged to the vessel about a first axis; an outer ramp hinged releasably to the inner ramp about a second axis parallel to the first axis; a first inner ramp actuating device connected to the inner ramp and the vessel; and a second actuating device connected to the outer ramp and the vessel .

BACKGROUND ART A pipeline laying vessel is a floating unit comprising an underwater-pipeline assembly line known as a "firing line", and equipped at the stern with a laying apparatus, the inner and outer ramps of which form a continuation of the firing line, and which is designed to ease the pipeline onto the sea bed as the vessel advances. Though the following description refers specifically to laying pipelines in the sea, the present invention also applies to any stretch of water large and deep enough to accommodate a pipeline laying vessel.

At present, underwater pipelines are produced and laid using two methods, depending on the depth of the sea bed. A first method is to produce the pipeline on a vertical firing line, and lay the pipeline vertically, so that the portion of the pipeline between the vessel and the sea bed assumes a "J" shape. This method is particularly suitable for laying deep-sea pipelines. A second method is to produce the pipeline on a substantially horizontal firing line, and lay the pipeline using a laying apparatus, which, in the work configuration, guides and supports the pipeline along an arc-shaped path having a first portion above sea level, and a second portion below sea level. Using this method, the pipeline being laid assumes an "S" shape between the vessel and sea bed, and various types of vessels can be employed, such as pontoons, barges, semisubmersible and single-hull vessels. Pontoons and barges are the underwater-pipeline laying vessels most commonly used in the past; semisubmersible vessels are particularly suitable for laying underwater pipelines in bad weather (rough sea) ; and single-hull vessels have the advantage of being fast, have ample pipe storage space, and can accommodate relatively long firing lines with a high output rate.

Laying underwater pipelines using the second method calls for relatively good weather conditions, so much so that, in rough- sea conditions, laying is suspended: the pipeline being laid is left on the sea bed, possibly attached to a salvage cable; and the inner and outer ramps are set as high as possible above sea level in a so-called "survival configuration".

The inner and outer ramps are normally hinged to each other, and must be movable into various ■ work configurations, depending on the depth of the sea bed and the characteristics of the pipeline, into an in- transit configuration allowing unobstructed movement of the vessel, and into the "survival configuration".

A first actuating device rotates the inner ramp about the first axis, and a second actuating device rotates the outer ramp about the second axis to achieve the above configurations .

One particular type of laying apparatus, designed to assume various configurations and positions, is described in the Applicant's Patent US 4,257,718, which describes a semisubmersible underwater-pipeline laying vessel equipped with a laying apparatus comprising an inner ramp hinged to the vessel; an outer ramp hinged to the inner ramp; and a first and second actuating device for operating the inner ramp and outer ramp respectiveIy . Though proven highly efficient, the above apparatus has drawbacks when it comes to disassembling the outer ramp from the inner ramp; in which case, the outer ramp must be disconnected from the inner ramp and the second actuating device, and must be supported by an on-board crane, and lowered onto land or the deck of the vessel. The same operations must be performed to reassemble the outer ramp to the inner ramp and second actuating device. Assembling and disassembling the outer ramp are therefore painstaking, time-consuming jobs. Moreover, when out of use on deck, the outer ramp takes up valuable work space on the deck of the vessel, and, when out of use on land, is not immediately available when needed.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide an underwater-pipeline laying apparatus designed to eliminate the drawbacks of the known art .

According to the present invention, there is provided an underwater-pipeline laying apparatus of a pipeline laying vessel, the laying apparatus comprising an inner ramp hinged to the vessel about a first axis,- an outer ramp hinged releasably to the inner ramp about a second axis parallel to the first axis; a first actuating device for operating the inner ramp and connected to the inner ramp and the vessel; and a second actuating device for operating the outer ramp and connected to the outer ramp and the vessel; the laying apparatus being characterized by comprising a first coupling device for connecting the outer ramp directly to the vessel. A major advantage of the present invention lies in the outer ramp being connectable to the vessel with no need for a crane, and without disassembling the outer ramp from the second actuating device . To only set the inner ramp to the laying position, the outer ramp need therefore simply be connected to the vessel and disconnected from the inner ramp.

The present invention also relates to a method of operating a laying apparatus. According to the present invention, there is provided a method of operating a laying apparatus of a pipeline laying vessel, wherein the laying apparatus comprises an inner ramp hinged to the vessel about a first axis; and an outer ramp hinged releasably to the inner ramp about a second axis parallel to the first axis; the method comprising the steps of: selectively connecting the outer ramp to the inner ramp; rotating the inner ramp about the first axis by means of a first actuating device; rotating the outer ramp, by means of a second actuating device, about the second axis and with respect to the inner ramp to set the inner ramp and outer ramp to a number of work configurations and to a survival configuration; and the method being characterized by connecting the outer ramp directly to the vessel, both when the outer ramp is disconnected from the inner ramp, and when the outer ramp is connected to the inner ramp.

The present invention also relates to a pipeline laying vessel.

According to the present invention, there is provided an underwater-pipeline laying vessel equipped with an underwater-pipeline laying apparatus, wherein the laying apparatus comprises an inner ramp hinged to the vessel about a first axis,- an outer ramp hinged releasably to the inner ramp about a second axis parallel to the first axis; a first actuating device for operating the inner ramp and connected to the inner ramp and the vessel; and a second actuating device for operating the outer ramp and connected to the outer ramp and the vessel; the vessel being characterized in that the laying apparatus comprises a first coupling device for connecting the outer ramp directly to the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a partly sectioned side view, with parts removed for clarity, of a pipeline laying vessel equipped with an underwater-pipeline laying apparatus in accordance with the present invention;

Figure 2 shows a larger-scale, partly sectioned view in perspective, with parts removed for clarity, of the Figure 1 vessel;.

Figure 3 shows a smaller-scale, partly sectioned side view, with parts removed for clarity, of a pipeline laying vessel with the Figure 1 laying apparatus in a work configuration;

Figures 4 to 10 show partly sectioned side views, with parts removed for clarity, of the Figure 1 vessel with the laying apparatus in a number of installation configurations ;

Figure 11 shows a larger- scale front view, with parts removed for clarity, of a detail in Figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in Figure 1 indicates a pipeline laying vessel for laying an underwater pipeline 2 in relatively deep water, the level of which is indicated SL. In the example shown, vessel 1 is a single-hull ship comprising a hull 3; an aftercastle 4; and a firing line 5 for producing pipeline 2 by joining pipes not shown in the drawings .

Vessel 1 is equipped with a laying apparatus 6, which defines an extension of firing line 5, and, in the Figure 1 configuration, guides and supports pipeline 2 along a path Pl having a first portion above sea level SL, and a second portion below sea level SL.

Vessel 1 is equipped with a crane 7 located at aftercastle 4. Aftercastle 4 of vessel 1 has an upper deck 8 defining the top of a well 9, which is bounded laterally by two walls 10 (only one shown in Figure 1) partly immersed at the aft end, and is bounded by a lower deck 11 supporting firing line 5.

Two lateral walls 12 (only one shown in Figure 1) extend above upper deck 8 , and the end portion of aftercastle 4 has two opposite, substantially vertical walls 13.

Laying apparatus 6 is housed at least partly in well 9, is hinged to vessel 1, and, in the example shown, comprises an inner ramp 14 hinged to vessel 1 and, in the example shown, to lower deck 11; an outer ramp 15 which, in Figure 1, is connected directly to vessel 1 and is hinged to inner ramp 14; an actuating device 16 connected to inner ramp 14 and vessel 1; and an actuating device 17 connected to outer ramp 15 and vessel 1. In the Figure 1 example, outer ramp 15 is shown in a rest position disconnected from inner ramp 14 and connected directly to vessel 1, and inner ramp 14 is in a work configuration.

Actuating devices 16 and 17 serve to support, control and set respective inner and outer ramps 14 and 15 to a number of work configurations, an in-transit configuration, a survival configuration, and the Figure 1 configuration. The work configurations comprise configurations in which inner ramp 14 and outer ramp 15 are connected to each other and inclined at different angles with respect to vessel 1 and with respect to each other (one of these work configurations is shown in Figure 3) ; and configurations in which outer ramp 15 is connected directly to vessel 1 (Figure 1) and inner ramp 14 can be inclined at different pipeline 2 laying angles (one of these configurations is shown in Figures 1 and 2) . Inner ramp 14 is used on its own in relatively shallow water. In the Figure 3 work configuration, inner ramp 14 and outer ramp 15 define respective supporting regions for pipeline 2. More specifically, inner ramp 14 comprises a substantially rigid, trestle box structure 18, which has a first end hinged to lower deck 11 by a hinge 19 with an axis Al substantially parallel to sea level (in calm- sea conditions) ; and a second end hinged to outer ramp 15 by a releasable hinge coupling 20 with an axis A2 parallel to axis Al. In the example shown in the attached drawings, outer ramp 15 comprises two substantially rigid, tubular trestle structures 21 and 22 connected rigidly to each other, and connectable to inner ramp 14 by releasable hinge coupling 20.

In the Figure 1 example, hinge coupling 20 comprises a pin 23, of axis A2, fitted to the far end of inner ramp 14; and two pairs of end half -rings 24, 25

(only one pair shown in Figure 1) which are engaged by pin 23 as shown in Figure 9. Once pin 23 is seated inside half-rings 24, half -rings 25 are closed to secure pin 23 in rotary manner. Inner ramp 14 and outer ramp 15 comprise supports 26 for supporting pipeline 2, and which are aligned with one another, assist in feeding pipeline 2 forward, and are selectively adjustable to define the ideal curve of pipeline 2 .

Laying apparatus 6 comprises two coupling devices

27 and 28 for selectively connecting outer ramp 15 to vessel 1; two coupling devices 29 and 30 for selectively locking inner ramp 14 to vessel 1; a hydraulic assembly

31; and a control unit 32.

Actuating device 16 of inner ramp 14 comprises two opposite, parallel runners 33; two carriages 34 movable along respective runners 33; and two connecting members 35 - in the example shown, rods - each hinged to a respective carriage 34 and to inner ramp 14 about an axis A3 parallel to axis Al.

Only one runner 33, one carriage 34, and one connecting member 35 are shown in Figure 1, it being understood that the runner 33, carriage 34, and connecting member 35 not shown are specularly symmetrical, with reference to a vertical plane parallel to the Figure 1 plane, with the runner 33, carriage 34, and connecting member 35 shown in Figure 1. Runners 33 are defined by straight rails 36 sloping through an opening in upper deck 8, and carriages 34 are powered by known hydraulic jacks (not shown) connected to hydraulic assembly 31 and positively engaging a respective rail 36. Actuating device 17 of outer ramp 15 comprises two opposite, parallel runners 37; two carriages 38 movable along respective runners 37; and two connecting members 39 - in the example shown, rods - each hinged to a respective carriage 38 and to outer ramp 15 about an axis A4 parallel to axis Al .

Only one runner 37, one carriage 38, and one connecting member 39 are shown in Figure 1, it being understood that the runner 37, carriage 38, and connecting member 39 not shown are specularly symmetrical, with reference to a vertical plane parallel to the Figure 1 plane, with the runner 37, carriage 38, and connecting member 39 shown in Figure 1. With reference to Figure 4, each runner 37 comprises three straight rails 40, 41, 42. Rail 40 extends from the level of lower deck 11 to a point above upper deck 8, is slightly less than vertical, and is supported by lateral wall 13; rail 41 is located above upper deck 8, between two ends of rails 40 and 42, and adjustable about an axis Bl; and rail 42 is fixed to a respective lateral wall 12, above upper deck 8, and slopes slightly with respect to the horizontal.

With reference to Figure 4, each rail 41 is fitted to a movable assembly 43 which is hinged to a respective lateral wall 12 about axis Bl, and comprises a hydraulic actuator (not shown) for setting movable assembly 43 and respective rail 41 to the operating position shown by the continuous line (rail 41 aligned with rail 42) and to the operating position shown by the dash line (rail 41 aligned with rail 40) in Figure 4.

Each carriage 38 is powered by known hydraulic jacks (not shown) connected to hydraulic assembly 31 and positively engaging respective runner 37.

Control unit 32 controls hydraulic assembly 31, which powers carriages 34, 38 and the hydraulic actuator (not shown) of movable assembly 43 between the two operating positions. Control unit 32 comprises sensors located along runners 33, 37 and movable assembly 43, and from which it receives signals indicating the position of carriages 34, 38 and movable assembly 43.

The above setup of rails 40, 41, 42 provides for achieving extremely long, but at the same time extremely compact runners 37, and hence a long excursion of carriage 38 and a wide operating range of outer ramp 15.

In Figure 4, outer ramp 15 is shown disconnected from vessel 1 and actuating device 17, and supported by crane 7. This is an assembly stage that is only performed, using crane 7, at first assembly of outer ramp 15 or when servicing outer ramp 15 on land or on the deck of vessel 1. As will be made clear below, the present invention also has advantages when installing outer ramp 15 using crane 7.

Coupling device 27 comprises two coupling members 44 (only one shown in Figure 4) associated with outer ramp 15; and two coupling members 45 (only one shown in Figure 4) , each associated with vessel 1 and selectively connectable to a respective coupling member 44. In the example shown, each coupling member 44 comprises a pin 46 supported by a flange 47 for assembly to tubular trellis structure 21 of outer ramp 15. More specifically, tubular trellis structure 21 comprises a tubular member 48 extending between a pair of half-rings 24, 25 and axis A4 , and flange 47 is fixed to tubular member 48, close to the pair of half -rings 24, 25. Each coupling member 45 comprises two half-rings 49 and 50, and a flange 51 for fixing half-ring 49 to lateral wall 13 , in particular along the face facing the other lateral wall .

Half-ring 49 has an upward-facing seat for one of pins 46. Half -ring 50 is hinged to half-ring 49, and is fastened to half-ring 49 by a fastener inserted inside holes (not shown) in half -rings 49 and 50. Each pair of half -rings 49, 50 forms a hinge shell for a respective pin 46 when half-ring 50 is fastened. Coupling device 28 comprises two coupling members 52 fixed to upper deck 8 of vessel 1; and two coupling members 53 fixed to outer ramp 15 and for engaging respective coupling members 52.

With reference to Figure 11, each coupling member 52 comprises two facing tubular members 54 flaring towards their free ends and defining a guide perpendicular to upper deck 8.

With reference to Figure 4, each coupling member 53 comprises a T-shaped hook 55 fixed to tubular member 48 of outer ramp 15 by a flange 56 close to axis A4.

Hook 55 comprises a shank 57 which fits between tubular members 54; and a head 58 which rests against tubular members 54, is tubular in shape, and allows outer ramp 15 to rotate about the axis A6 , substantially parallel to axis Al, of head 58, when head 58 is connected to the guide .

Members 53 are removable from tubular member 48 of outer ramp 15, on account of coupling device 28 only- being used for installing outer ramp 15 using crane 7.

Coupling device 29 comprises two powered members 59 (only one shown in Figure 4) , which in the example shown are two hydraulic cylinders parallel to axis Al, fitted to inner ramp 14, and for pushing respective pistons 60 against respective lateral walls 10 to lock inner ramp 14 in an operating position.

Each lateral wall 10 preferably has an arc- shaped track 61 with its centre at axis Al. Track 61 defines a support for the free end of a respective piston 60, and powered members 59 are controlled by the hydraulic assembly and control unit 32.

Coupling device 30 comprises two connecting rods 62

(only one shown in Figure 4) ; and two flanges 63 (only one shown in Figure 4) associated with inner ramp 14.

Each connecting rod 62 has a hole, which is aligned with and adjacent to a slot in flange 63 when inner ramp 14 is set to the survival configuration by actuating device

16, as shown in Figure 9. Locking is achieved by inserting a safety pin 64 through the hole in connecting rod 62 and the flange 63.

In actual use, laying apparatus 6 assumes a number of work configurations, some of which are shown in Figures 1 and 3 ; and a survival configuration shown in Figure 9. More specifically, the work configuration in Figure 1 only employs inner ramp 14, and outer ramp 15 is locked to vessel 1 in a substantially vertical position enabling connection and disconnection to and from inner ramp 14. In other words, outer ramp 15 is locked independently in the survival or at least close to survival configuration; whereas inner ramp 14 can be connected to outer ramp 15 and also locked in the survival configuration by respective coupling device 30, or can be disconnected from outer ramp 15 and moved into work configurations by actuating device 16. Inner ramp 14 is locked into each work configuration by coupling device 29. Outer ramp 15 is manoeuvred, i.e. coupling members 44 and 45 connected or disconnected, simply by the combined action of actuating devices 16 and 17 when inner ramp 14 is connected to outer ramp 15. In other words, outer ramp 15 is lifted and lowered by actuating device 16 rotating inner ramp 14 about axis Al; whereas outer ramp 15 is moved towards and away from aftercastle 4 directly by actuating device 17 rotating it about axis A2. Control unit 32 is programmed to control hydraulic assembly 31 powering carriages 34 and 38, and to obtain a connecting and disconnecting sequence of members 44 and 45.

Coupling device 28 provides for easy assembly of outer ramp 15 when disconnected from actuating device 17, vessel 1, and inner ramp 14. In this configuration, outer ramp 15 is lifted by crane 7, as shown in Figure 4, or by another, e.g. quayside, crane.

To install outer ramp 15, this is lowered gradually, and the guides defined by coupling members 52 are engaged by coupling members 53 to ease the outer ramp onto the upper deck of the vessel (Figures 5 and 6) . When lowered further by crane 7, outer ramp 15 rotates about axis A6 to connect coupling members 44 to coupling members 45.

Once coupling members 45 are locked, connecting members 39 of actuating device 17 are hinged to outer ramp 15 about axis A4 ; crane 7 is released from outer ramp 15; and coupling members 53 are. removed from tubular member 48 as shown in Figure 7.

Next, carriage 38 rotates outer ramp 15 about axis A5 , as shown in Figures 7 and 8, to position half-rings 24 and 25 to receive pin 23.

Once pin 23 engages the seat defined by half-ring 24, half-ring 25 is closed, hinge coupling 20 is now operative, and outer ramp 15 is connected to inner ramp 14 as shown in Figure 10, which shows inner ramp 14 connected to outer ramp 15 and locked by coupling device 30, and outer ramp 15 locked by coupling device 27. To move inner ramp 14 and outer ramp 15 into a work configuration from the Figure 10 survival configuration, coupling devices 27 and 30 are simply released, inner ramp 14 is rotated clockwise in Figure 10 (i.e. outer ramp 15 is raised) , and outer ramp 15 is rotated anticlockwise in Figure 10 to release pin 46 from half- ring 49.

One of the main advantages of the present invention ^" lies in coupling device 27 connecting outer ramp 15 to vessel 1 about axis A5 and so enabling movement of outer ramp 15 to position the pairs of half -rings 24, 25 for engagement by pin 23 as inner ramp 14 rotates about axis Al. In this way, actuating devices 16 and 17 can be employed in connecting inner ramp 14 and outer ramp 15.

Coupling device 28 is equally advantageous by enabling, like device 27, isostatic connection of outer ramp 15 to vessel 1, i.e. by enabling vertical translation and rotation of outer ramp 15 about axis A6 with respect to vessel 1. These movements are particularly advantageous . when assembling outer ramp 15 using crane 7.

Claims

1) An underwater-pipeline (2) laying apparatus of a pipeline laying vessel (1) , the laying apparatus (6) comprising an inner ramp (14) hinged to the vessel (1) about a first axis (Al) ; an outer ramp (15) hinged releasably to the inner ramp (14) about a second axis

(A2) parallel to the first axis (Al); a first actuating device (16) for operating the inner ramp (14) and connected to the inner ramp (14) and the vessel (1) ; and a second actuating device (17) for operating the outer ramp (15) and connected to the outer ramp (15) and the vessel (1) ; the laying apparatus (6) being characterized by comprising a first coupling device (27) for connecting the outer ramp (15) directly to the vessel

(D •

2) An apparatus as claimed in Claim 1, characterized in that the first actuating device (16) comprises a first powered member (34) connected to the inner ramp (14) by a first connecting member (35) hinged to the inner ramp (14) about a third axis (A3) parallel to the first axis (Al) ; and the second actuating device (17) comprises a second powered member (38) connected to the outer ramp (15) by a second connecting member (39) hinged to the outer ramp (15) about a fourth axis (A4) parallel to the first axis (Al) .

3 ) An apparatus as claimed in Claim 1 or 2 , characterized in that the first coupling device (27) comprises at least one first coupling member (44) associated with the outer ramp (15) ; and at least one second coupling member (45) associated with the vessel (1) and forming, with the first coupling member (44) , a hinge by which to rotate the outer ramp (15) , with respect to the vessel (1) , about a fifth axis (A5) parallel to the first axis (Al) .

4) An apparatus as claimed in Claim 3, characterized in that the first coupling member (44) comprises a pin (46) ; the second coupling member (45) comprising a hinge shell (49, 50) selectively engaged by the pin (46) .

5) An apparatus as claimed in Claim 4, characterized in that the hinge shell (49, 50) comprises a first half-ring (49) fixed to the vessel (1) ; and a second half-ring (50) fixable to the first half-ring (49) to enclose the pin (46) inside the hinge shell (49, 50) in rotary manner about the fifth axis (A5) .

6) An apparatus as claimed in any one of the foregoing Claims, characterized by comprising a second coupling device (28) for connecting the outer ramp (15) to the vessel (1) .

7) An apparatus as claimed in Claim 6, characterized in that the second coupling device (28) comprises at least one third coupling member (52) associated with the vessel (1) ; and at least one fourth coupling member (53) associated with the outer ramp (15) and which cooperates with the third coupling member ( 52 ) .

8) An apparatus as claimed in Claim 7, characterized in that the third coupling member (52) is a guide; and the fourth coupling member (53) is a hook (55) which slides inside the guide.

9) An apparatus as claimed in Claim 8, characterized in that the guide is perpendicular to the first axis (Al) .

10) An apparatus as claimed in Claim 8 or 9, characterized in that the hook (55) rotates with respect to the guide about a sixth axis (A6) , parallel to the first axis (Al) , when the hook (55) is connected to the guide .

11) An apparatus as claimed in any one of the foregoing Claims, characterized by comprising a third coupling device (29) in turn comprising two opposed actuators (59) which push respective pistons (60) in opposite directions against facing lateral walls (10) of the vessel (1) . 12) An apparatus as claimed in Claim 11, characterized in that each lateral wall (10) comprises an arc-shaped track (61) centred about the first axis (Al) and defining a support for the pistons (60) .

13) An apparatus as claimed in any one of the foregoing Claims, characterized by comprising a fourth coupling device (30) for locking the inner ramp (14) in a survival configuration or an in-transit configuration.

14) An apparatus as claimed in Claim 13, characterized by comprising at least one fifth coupling member (62) associated with the vessel (1) ; and a sixth coupling member (63) associated with the inner ramp (14) and which cooperates with the fifth coupling member (62) to lock the inner ramp (14) in a survival or in-transit configuration.

15) A method of operating a laying apparatus of a pipeline laying vessel (1) , wherein the laying apparatus

(6) comprises an inner ramp (14) hinged to the vessel (1) about a first axis (Al) ; and an outer ramp (15) hinged releasably to the inner ramp (14) about a second axis (A2) parallel to the first axis (Al) ; the method comprising the steps of: selectively connecting the outer ramp (15) to the inner ramp (14) ; rotating the inner ramp (14) about the first axis (Al) by means of a first actuating device (16) ; rotating the outer ramp

(15) , by means of a second actuating device (17) , about the second axis (A2) and with respect to the inner ramp

(14) to set the inner ramp (14) and outer ramp (15) to a number of work configurations, to an in-transit configuration, and to a survival configuration; and the method being characterized by connecting the outer ramp

(15) directly to the vessel (1) .

16) A method as claimed in Claim 15, characterized by connecting the outer ramp (15) directly to the vessel

(1) both when the outer ramp (15) is disconnected from the inner ramp (14) , and when the outer ramp (15) is hinged to the inner ramp (14) . 17) A method as claimed in Claim 15 or 16, characterized by rotating the inner ramp (14) about the first axis (Al) by means of a first powered member (34) connected to the inner ramp (14) by a first connecting member (35) hinged to the inner ramp (14) about a third axis (A3) parallel to the first axis (Al) ; and rotating the outer ramp (15) about the second axis (A2) by means of a second powered member (38) connected to the outer ramp (15) by a second connecting member (39) hinged to the outer ramp (15) about a fourth axis (A4) parallel to the first axis (Al) .

18) A method as claimed in any one of Claims 15 to 17, characterized by connecting the outer ramp (15) to the vessel (1) , in rotary manner about a fifth axis (A5) parallel to the first axis (Al) , by means of a first coupling device (27) associated with the outer ramp (15) and the vessel (1) .

19) A method as claimed in Claim 18, characterized in that the first coupling device (27) comprises at least one first coupling member (44) associated with the outer ramp (15) , and at least one second coupling member (45) associated with the vessel (1) ; the method comprising connecting and disconnecting the first coupling member (44) to and from the second coupling member (45) by means of the first and second actuating device (16, 17) , when the outer ramp (15) is connected to the inner ramp (14) in rotary manner about the second axis (A2) . 20) A method as claimed in Claim 19, characterized in that the first coupling member (44) comprises a pin (46) ; the second coupling member (45) comprising a hinge shell (49, 50) selectively engaged by the pin (46) ; and the method comprising inserting and withdrawing the pin (46) into and from the hinge shell (49, 50) by means of the first and second actuating device (16, 17) .

21) A method as claimed in any one of Claims 15 to 20, characterized by connecting the outer ramp (15) to the vessel (1) by means of a second coupling device (28) .

22) A method as claimed in Claim 21, characterized in that the second coupling device (28) comprises at least one third coupling member (52) associated with the vessel (1) , and at least one fourth coupling member (53) associated with the outer ramp (15) ; the method comprising inserting and withdrawing the fourth coupling member (53) into and from the third coupling member (52) by means of a crane (7) , when the outer ramp (7) is disconnected from the inner ramp (14) and the second actuating device (17) .

23) A method as claimed in Claim 22, characterized in that the third coupling member (52) is a guide, and the fourth coupling member (53) is a hook (55) ; the method comprising rotating the outer ramp (15) about a sixth axis (A6) , defined by the hook (55) , when the hook (55) is connected to the guide,- said hook (55) defining the sixth axis (A6) parallel to the first axis (Al) . 24) A method as claimed in any one of Claims 15 to 23, characterized by locking the inner ramp (14), with respect to the vessel (1) , in a number of work configurations by means of a third coupling device (29) ; the method comprising selectively pushing pistons (60) in opposite directions against two facing first lateral walls (10) of the vessel (1) by means of actuators (59) supported by the inner ramp (14) .

25) A method as claimed in any one of Claims 15 to 24, characterized by locking the inner ramp (14) in a survival configuration by means of a fourth coupling device (30) .

26) A method as claimed in any one of Claims 15 to

25, characterized by connecting and disconnecting the outer ramp (15) to and from the inner ramp (14) , when the outer ramp (15) is locked by the first coupling device (27) .

21) A method as claimed in any one of Claims 20 to

26, characterized by connecting the outer ramp (15) to the second actuating device (17) when the outer ramp

(15) is locked to the vessel (1) by the first and second coupling device (27, 28) .

28) An underwater-pipeline laying vessel equipped with an underwater-pipeline (2) laying apparatus (6) comprising an inner ramp (14) hinged to the vessel (1) about a first axis (Al) ; an outer ramp (15) hinged releasably to the inner ramp (14) about a second axis (A2) parallel to the first axis (Al) ; a first actuating device (16) for operating the inner ramp (14) and connected to the inner ramp (14) and the vessel (1) ; and a second actuating device (17) for operating the outer ramp (15) and connected to the outer ramp (15) and the vessel (1) ; the vessel (1) being characterized in that the laying apparatus (6) comprises a first coupling device (27) for connecting the outer ramp (15) directly to the vessel (1) .

29) A vessel as claimed in Claim 28, characterized by comprising a lower deck (11) , and two facing first lateral walls (10) ; the inner ramp (14) being hinged to the lower deck (11) and movable between the two facing first lateral walls (10) .

30) A vessel as claimed in Claim 28 or 29, characterized by comprising two facing second lateral walls (13) ; the outer ramp (15) in the survival configuration being located between the facing second lateral walls (13) .

31) A vessel as claimed in Claim 30, characterized in that the first coupling device (27) comprises at least two first coupling members (44) fitted to the outer ramp (15) ; and two second coupling members (45) fitted to the facing second lateral walls (13) .

32) A vessel as claimed in any one of Claims 28 to 31, characterized in that the outer ramp (15) can be hinged to the vessel (1) about a fifth axis (A5) by means of the first coupling device (27) .