The invention relates to a vessel for e.g. well intervention or deep sea lowering, comprising a moon pool and a hoisting arrangement for lowering and retrieving

items, in particular equipment, tools, and/or supplies or

modules comprising the same, through the moon pool, into

respectively from the sea and onto respectively from the

seabed or an installation already present on the seabed. The invention further relates to a handling system to be

installed on such a vessel and to a method of lowering or

retrieving items into respectively from the sea.

WO 2007/027081 discloses a vessel comprising "a hoist cable 3 for lowering and retrieving subsea equipment

5. This hoist cable 3 is part of a subsea equipment hoist

system further comprising a winch (not shown) for lowering and retrieving subsea equipment in a hoist area generally

indicated with number 4. The hoist area 4 can be a moonpool located in the middle of the ship, but can also be located at the side or at the stern of the ship. ... The vessel

further comprises a subsea equipment motion restraining and guidance system for restraining subsea equipment 5 motion

relative to the vessel 1 in the hoist area 4 as the subsea equipment 5 is lowered into the sea and retrieved from the sea 6. ... The system ... comprises two spaced apart parallel

rail engaging members 8a, one of which is visible in fig. 1, mounted on said auxiliary trolley 8. Each of the rail

engaging members 8a is adapted to engage on one of two

equally spaced parallel vertical rails 11 mounted on said

subsea equipment 5 as said subsea equipment 5 passes

vertically by said auxiliary trolley 8." Once the centre of gravity of the subsea equipment 5 "is at the same level as the auxiliary trolley 8, the subsea equipment 5 is fixed in two dimensions by the main trolley 7 and auxiliary trolley 8. ... Only movement in the third, vertical direction is possible by the hoist cable 3."

The "subsea equipment motion restraining and guidance system [is] capable of more adequately avoiding collisions between the vessel and the subsea equipment."

WO 2004/020275 is related to a vessel which has a moonpool and a tower which is mounted on the vessel and a load hoist system for raising and/or lowering a load through the moonpool. The tower is located adjacent a single side of the moonpool. The tower is provided with one or more

trolleys and associated vertical trolley guides, which allow for up and down movement of the one or more trolleys along at least part of the height of the tower.

US 2004/0089215 is related to a vessel which comprises a monohull with moonpool. A multipurpose tower is mounted on the vessel and an equipment handling system is removably mounted on the vessel. A movable hatch is

installed on top of the moonpool and a hoist system is installed inside the vessel.

WO 99/11518 is related to an apparatus for an offshore vessel, which comprises a crane arranged on the deck of the vessel and a derrick provided on the vessel. The crane comprises a crane pedestal and a jib, and also a crane winch and a crane wire. The derrick comprises a derrick structure which is designed to be positioned over a moonpool in the vessel. The crane wire is arranged so as to be capable of operating a lifting means inside the derrick, thus enabling the crane to be used as a hoisting device in the derrick.

It is an object of the present invention to further improve guidance of items lowered or retrieved through a moon pool.

To this end, the vessel according to the invention is characterized by one or more guides for laterally

retaining items inside the moon pool, preferably at least two guides positioned on opposite sides or corners of the moon pool, e.g. a guide at each corner of the moon pool.

The guides suppress or, depending on the

configuration, even prevent horizontal movement, i.e.

movement in the X- and Y- directions (vertical movement defining the Z-direction) , of the items relative to the vessel, in particular the walls of the moon pool, thus providing a more controlled lowering and retrieval of the items and avoiding collision of the items with said walls.

In an embodiment, the guides extend at least partially in the moon pool and/or are provided at different heights in the moon pool, in particular both in the upper half, e.g. at or near the top, and in the lower half, e.g. at or near the bottom, of the moon pool, effectively

providing guidance over a greater length. It is preferred that the effective length of the guides is in excess of half the height of the moon pool.

Another embodiment comprises a drive mechanism, e.g. one or more hydraulic cylinders, jacks or toothed racks and driven pinions, for retaining the items in the vertical direction and for exerting (directly or indirectly) a downward or upward force on the items.

Thus, the items, while being positively guided inside the moon pool and between the guides, can be pushed through the so-called splash-zone, i.e. the surface of the water, in a controlled manner, avoiding heave of the items relative to the vessel.

In another embodiment, the vessel comprises a tower for supporting and/or receiving one or more of the items, which tower is translatingly mounted between the guides and coupled to the drive mechanism, if present.

In a further embodiment, the tower comprises fasteners, e.g. grippers, to temporarily hold a plurality of items, one stacked above the other. The tower provides an effective means for stacking separate modules and lowering, e.g. pushing, or retrieving, e.g. pulling, them in a controlled manner through the splash-zone .

Further, the tower preferably replaces the conventional tower that is usually positioned next to the moon pool, thus providing more space on deck next to the moon pool and facilitating efficient storage and handling of the items to be lowered into the sea. Also, a tower

positioned and lowered into the moon pool, e.g. such that the bottom of the tower is flush with the hull of the vessel, will have a lesser height than conventional towers, which in turn enables passing bridges that are too low for conventional towers and, in a more specific application, facilitates fitting a cover over the tower e.g. to protect it from extreme cold and wind.

In an embodiment, the tower comprises doors in its bottom end. The doors enable closing the bottom end of the moon pool during transit, thus improving safety and

increasing (fuel) efficiency.

In another embodiment the tower comprises a plurality of guide wires, preferably attached to the tower at or near its bottom end.

The invention further relates to a handling system to be installed on a vessel as described above comprising one or more guides for laterally retaining items inside the moon pool and a tower for supporting and/or receiving one or more of the items, which tower is translatingly mountable between the guides.

In an embodiment, the system comprises a drive mechanism for exerting a downward or upward force on the tower and thus indirectly on the items.

The invention further relates to a method of lowering and retrieving items, in particular equipment, tools, and/or supplies or modules comprising the same into respectively from the sea and onto respectively from the seabed or an installation on the seabed by means of a vessel as described above comprising a moon pool and a hoisting arrangement, the method comprising the steps of

suspending one or more items from the hoisting arrangement,

lowering or hoisting the items through the moon pool,

laterally retaining the items while they are being lowered or hoisted through the moon pool, preferably between at least two guides positioned on opposite sides or corners of the moon pool.

In another embodiment, the method comprises the steps of loading the items to be lowered onto and/or into a tower and translatingly lowering the tower between the guides, e.g. loading a first item onto and/or into the tower, lowering or hoisting the tower and loading a second item onto and/or into the tower, respectively above or below the first item.

In an embodiment, the method comprises exerting a downward or upward force on the items being lowered or hoisted trough the moon pool. The force can be exerted directly on the items or indirectly, e.g. via the tower.

For the sake of completeness, attention is drawn to the following prior art.

WO 2011/008835 is directed to a Self Supporting Riser (SSR) and provisions for interfacing a vessel subject to high motions to the SSR. The SSR can be installed and recovered in a wide range of water depths and in areas of high current. Figure 2 of WO 2011/008835 shows a

stabilization system (indicated by numeral 62) comprising a heave stabilized platform (66) and a pitch and roll

stabilized frame (68). Frame (68) is shown below platform (66) and held by pitch and roll cylinders (70). The platform (66) is supported by heave cylinders (72). Heave guide rails (73) are attached securely to the vessel and prevent binding and racking of the cylinders (72) .

US 2009/0151955 discloses a vessel in the form of a drillship (10) incorporating a rig assembly (38), a moon pool (40), and, at least in the embodiment shown in Figure 3, a support frame (104) positioned in the moon pool. A similar support frame is known from WO 2006/123147.

Within the framework of the present invention the term "moon pool" refers is defined as any opening in the hull through which items, in particular equipment, tools, and/or supplies or modules comprising the same, can be lowered into or retrieved from the sea, in particular openings that extend all the way up to the deck of the vessel enabling items to be stored and handled on deck and lowered directly from the deck into the sea.

The invention will now be explained in more detail with reference to the drawings, which schematically show embodiments of the vessel and method of the present

invention .

Figures 1A and 1B are top and side views of a well intervention vessel comprising a translating tower in accordance with the present invention.

Figure 2 is a detail of the vessel shown in Figure

1A.

Figure 3 is a perspective view of a translating tower in accordance with the present invention.

Figures 4A to 4G illustrate an example of the method of stacking items in a tower and lowering the items in accordance with the present invention.

Figures 1A to 3 show a well intervention vessel 1 comprising a hull 2, a deck 3, and a moon pool 4 extending through the deck and the hull. A plurality of items 5, in particular equipment, tools, and/or supplies or modules comprising the same, are placed on deck, more specifically on the so-called firing-line 6, i.e. lined up with the moon pool .

As shown in Figure IB, a plurality of guides 7, in this example four guides, are positioned in the moon pool, one in each corner of the moon pool. Each guide comprises two parts, a top part 7A mounted on deck and partially extending into the moon pool and a bottom part 7B near the bottom side of the hull, together providing effective guidance over a length of approximately 80% of the height of the moon pool.

A tower 8 for supporting and/or receiving one or more of the items is translatingly mounted between the guides. In this example, the tower is provided at each corner with a vertical toothed rack (not shown) and each of the upper parts 7A of the guides contains a pinion and a motor for driving the pinion and thus positively translating the tower up and down.

Further, the tower comprises four winches 9 for an equal number of guide cables 10, known in themselves, that, once deployed, extend from the tower to a well 11 (Figure IB) on the seabed 12 below. In the example shown in Figure 3, the winches for the guide cables are located near the top of the tower.

The tower 8 is open on the side facing the firing line 6, to allow items 5 to be entered into the tower. In this example, the tower has a U-shaped cross-section over the greater part of its length. The tower comprises grippers 13 (Figure 2), to temporarily hold a plurality of items, one stacked above the other. In its bottom end, the tower comprises a pair doors 14 closing the bottom end of the moon pool 4 during transit.

A main hoisting arrangement 15 comprising e.g. a hoist cable 16, a winch and a motor is provided on or below deck, next to or at some distance of the tower. The tower provides an effective means for stacking separate modules and 'pushing' the assembled stack in a controlled manner through the splash-zone, as follows.

Figures 4A to 4G illustrate a method of lowering a one or more e.g. four modules 5 onto a well on the seabed by means of the vessel 1 described above. During transit, the lower part of the tower 8 is in inside the moon pool 4, such that the (closed) doors 14 in the bottom of the tower are flush with the hull 2. The four modules are stored on deck, in this example lined up on the firing line (Figure 4A) .

Once the vessel is positioned over the well and the guide lines for lowering the modules are in place, the tower is translated to its uppermost position, the first module is loaded and secured in the tower, and the tower is lowered to its initial position, thus maintaining a relatively low center of gravity. Next, the second module is loaded in the tower (Figure 4C) , connected to the main hoist cable and hoisted to allow the third module to be loaded into the tower, beneath the second module. After the third module is connected to the second module the (sub) stack thus obtained is hoist to allow the fourth module to be loaded into the tower, beneath the third module (Figure 4D) .

After completing the stack of four modules by connecting the fourth module to the first and third modules (Figure 4E) , the tower containing the stack is gradually lowered through the moon pool, while laterally retaining the modules and positively avoiding any contact between the modules and the walls of the moon pool (Figure 4F) . When the tower reaches it lowermost position or at least a lower position wherein the doors clear the hull by a sufficient distance, the doors are opened, the grippers are released from the stack and the stack is lowered from the tower and along the guide wires to the well below, again while

preventing any contact between the modules and the moon pool. Further, the items, while being positively guided inside the moon pool and between the guides, are forced through the so-called splash-zone, i.e. the surface of the water, in a controlled manner.

The invention is not restricted to the above- described embodiments which can be varied in a number of ways within the scope of the claims. For instance, during retrieving items from the sea, the uppermost module could be removed first, followed by the one below that, and so on, thus continually maintaining the centre of gravity as low as possible .