HK1172300B - Offshore equipment deploying and retrieving vessel - Google Patents

Description

Offshore unit for recovering and deploying a vessel

Technical Field

The present invention relates to a vessel for recovery and deployment of equipment in offshore areas. The vessel is a semi-submersible vessel and can work as a normal seagoing vessel in a non-submersible situation. The invention also relates to a method for equipment recovery and deployment in the offshore region by using the aforementioned vessel. In particular, an offshore vessel is provided in the preamble of claim 1 of the present invention, and a method for equipment recovery and deployment in an offshore area is provided in the preamble of claims 14 and 16, whereby the equipment and the lifting device are protected from dynamic forces in the splash zone/surface.

Background

In offshore locations, it is very common to use vessels for heavy equipment deployment and recovery. These heavy equipment are mostly used for oil and gas exploration and production, mining, mineral exploration, drilling operations, etc.

For example, international patent application publication No. WO 2010/020026a2 discloses a double hull vessel in the oil industry, which vessel comprises a deck and a universal bridge for loading and unloading of operational commodities in the oil field. However, the vessel is not suitable for offshore areas where the sea waves are up to ten meters, e.g. in the north sea. In these areas, which is very disadvantageous for ships, single-hull offshore ships have been used, for example, as disclosed in WO 2009/102197 and WO 2009/102196. However, over the years these single hull offshore vessels, such as those disclosed in these two publications, are not suitable for many offshore operations where stability and safety considerations are required, particularly in the harsh environment of the ocean, e.g., the north sea, brazil and gulf of mexico.

Semi-submersible vessels are known in the prior art for various types of offshore operations. These vessels are particularly suitable for offshore areas where the environment is harsh. At the same time, safety and stability considerations are encountered in the design of these semi-submersible vessels, which is important in offshore areas where the environment is harsh. For example, WO 99/12807 discloses a semi-submersible vessel design that provides a firm and rigid base to support the deck of the superstructure. WO 2009/084950 discloses an unsupported semi-submersible vessel. WO85/03050 discloses a semi-submersible vessel improved in shape, which vessel comprises a floating core column arranged centrally around a central drill string. The design aims to significantly reduce the normal movement in marine conditions. WO99/57011 discloses a semi-submersible vessel which ensures the safety of the mineral production platform it supports. WO 2007/097611 discloses a semi-submersible vessel comprising a hull arrangement, support structures and deck structures with reinforcements for resisting storms.

However, the aforesaid vessels and the like have some drawbacks, mainly in that designing such vessels requires very high costs and long engineering time to observe their safety in harsh environments and sea conditions. Further, the design of these vessels involves the deployment of large cranes and jack-up drives, further increasing costs and inconvenience of operation. In addition, existing ships have different drafts in harbors, and are mainly connected by ships, so that multiple connections are required, and the reliability of the ships in very severe weather conditions is reduced regardless of the operation. Also, it is known from the common knowledge that since ship-shaped vessels are not suitable for a variety of offshore operations, these vessels are not ship-shaped, which also makes it impossible to operate efficiently in non-submerged conditions as normal ships. Furthermore, deployment and recovery of heavy equipment using these vessels in a splash zone can subject the heavy equipment and lifting/lowering devices to dynamically changing forces.

The above-mentioned vessel may have an optional temporary port which works on the same principle as the main vessel for receiving ships for transporting crews/supply ships/or other ships for safe transport of crews and materials. US5215024 discloses an open sea based mooring for grabbing ships or other vessels, but it is primarily for sea-based defense purposes. The mooring vessel includes a buoyant platform having a housing for receiving the vessel. The movement of the vessel drives the movement of the platform such that relative movement between the vessel and the platform is relatively reduced. This solution has not revealed a semi-submersible vessel for offshore operations which overcomes/substantially reduces the drawbacks of the prior art disclosed in the preceding paragraph and which basically has an optional temporary port which works on the same principle as the main vessel for accommodating ships carrying crews/supply ships/or other ships for safe transport of crews and materials. These problems are also present in U.S. patent application US2006/0086304 and international patent application WO 93/04914. The former discloses a ship for rescuing a ship suffering from a difficult accident. The rescue vessel includes an elongated hull and a ballast device. The rescue boat has two side hulls that surround the pool and define an upper edge of the rescue boat. When the rescue boat withdraws, the upper edge of the rescue boat is higher than the sea level. When a ship is rescued, the upper edge of the rescue ship is lower than the keel of the rescued ship. Although it is stated in US patent application publication No. US2006/0086304 that the rescue vessel is applicable to a drilling or production platform or a part of a platform, it is not clearly disclosed a semi-submersible vessel for offshore operation which overcomes/substantially reduces the drawbacks of the prior art disclosed in the preceding paragraph and which basically has an optional temporary harbour which works on the same principle as the main vessel for accommodating ships carrying crews/supply ships/or other ships for safe transport of crews and materials. These problems also exist in international patent application WO93/04914, which discloses a large barge fast offshore replenishment and harbour system comprising a trapezoidal twin hull design including a barge, at least one cargo barge, a transportable harbour system and a embankment. The system relates to the rapid transport and deployment of very large quantities of cargo to meet the requirements of humanitarian, economic and military contingencies, and strictly speaking, it does not relate to semi-submersible vessels for the deployment and retrieval of equipment in the offshore area, which is the subject of the present invention.

There has therefore been a long felt need to design a semi-submersible vessel that overcomes/substantially reduces the above-mentioned drawbacks, and in particular a mono-hull column stabilizer that is cost-effective, stable, and reliable in extremely hostile marine environments, and can travel at high speeds in non-submersible conditions as a vessel with low draft. Also, there has been a long felt need to develop a semi-submersible vessel that is in the shape of a ship and, at the same time, can be effectively used in a wide range of offshore applications. Furthermore, there has been a long felt need to design a semi-submersible vessel which overcomes/substantially reduces the above-mentioned drawbacks and which at the same time has an optional temporary port which works on the same principle as the main hull for accommodating crew ships/supply ships/other ships for safe transfer of crew and materials. In addition, there is a long felt need for a method for deploying and retrieving equipment from water in offshore operations that does not subject the equipment and the lifting/lowering devices to the dynamic forces of the splash zone/waterline by submerging and retrieving from water, rather than by lowering the equipment through the waterline.

The present invention satisfies all of the above needs and others related thereto, and the single hull column stabilized semi-submersible vessel disclosed hereinafter is the subject of the present invention.

Disclosure of Invention

The present invention aims to meet the aforementioned needs of the prior art by providing a specially constructed single hull vessel to enable deployment and recovery of equipment in offshore areas, the aforementioned disadvantages of the prior art being substantially reduced/overcome by the specific structure of the vessel.

It is a further object of the present invention to provide a single hull vessel for deployment and recovery of equipment in offshore areas that is very stable and reliable under extremely harsh ocean conditions.

It is another object of the present invention to provide a single hull vessel for deployment and recovery of equipment in offshore areas that allows for a low cost design and ensures deployment and recovery of equipment without splash effects.

It is another object of the present invention to provide a mono hull vessel for deployment and recovery of equipment in offshore areas that can achieve a higher sailing speed in low draft, non-submerged conditions.

Another object of the present invention is to provide a mono hull vessel for deploying and retrieving equipment in offshore areas, which is a mono hull column stabilized vessel constructed in a general ship shape, thereby being applicable to a wide range of applications offshore at the same time.

It is another object of the present invention to provide a single hull vessel for deployment and recovery of equipment in offshore areas, the vessel having an optional temporary port operable on the same principle as the main vessel for receiving crew boats/supply boats/other vessels for safe transfer of crew and materials.

It is another object of the present invention to provide a method of deploying and retrieving equipment from water in offshore operations that avoids the equipment and the lifting device from the dynamic forces of the splash zone by submerging and retrieving the equipment from water, rather than lowering/retrieving the equipment through the water line as in the prior art.

It is a further object of the present invention to provide a novel hull/pontoon for a single-hull vessel for deploying and retrieving equipment in offshore locations that is stable and reliable under extremely harsh ocean conditions.

In addition, the present invention also discloses some beneficial features which are not disclosed in the prior art.

Although the claims are included in the specification, the terms "vessel/installation", "deckbox", "mono hull", "upper deck", "lower deck", "hull/pontoon", "column", and "temporary harbor" are to be construed in a very broad sense, and to one skilled in the art, include all similar terms used in the art. The limitations/restrictions in the description are only intended to illustrate the invention. Further, to those skilled in the art, the terms "ship," "ship-like," and "ship-like" in this disclosure should be construed to refer to all common shipping vessels. The present invention has been explained in detail in the entire specification of the present invention, and the references to "ship", "ship-like" and "ship-like" are only for the better understanding of the present invention and are not intended to limit the present invention.

In a first aspect of the invention, there is provided a single hull vessel for equipment deployment and recovery in offshore areas comprising a deckbox with an upper deck having a lifting device at its upper portion and a hull/pontoon at the bottom of the vessel. In the present invention, the hull/pontoon is connected to the deckbox by a plurality of columns. The hull/pontoon is integrally formed and further forms a platform as a lower deck. The upper and lower decks are configured for lifting and lowering of equipment thereon, respectively.

In a preferred embodiment of the first aspect of the invention, the vessel is used for diving to lift a lower deck located at a desired depth below the water surface to another desired depth.

Preferably, the number of columns is 4 to 10, and the combination of the upper deck, the deckbox and the lower deck is designed in conformity with a hull/pontoon which is similar to the hull of a ship and is submersible, so that the ship as a whole has a ship shape. Thus, the vessel can be operated in a non-submerged condition as a normal vessel.

In a preferred embodiment of the first aspect of the invention, the deckbox has an engine room, a large space for the equipment, accommodation means and an apron on the upper deck.

In a preferred embodiment of the first aspect of the invention, the hull/pontoon includes ballast tanks, fuel tanks, fresh water tanks and a propulsion engine room, and the lower deck further includes a bow deck.

More preferably, the ballast tank is provided in the buoyancy tank and the section of the column.

In a preferred embodiment of the first aspect of the invention the displacement of the vessel in submerged condition is about 45000 tonnes, the load capacity of the upper deck is 6000 to 8000 tonnes, and a round well deck is provided in the entire path from the upper deck to the lower deck.

In a preferred embodiment of the first aspect of the invention, a temporary harbour site is provided at the stern of the vessel for crew or supply vessels or other vessels.

Preferably, the harbour site comprises a water gate arrangement in the stern area and is provided with a barrier area.

More preferably, the temporary harbour is intended to be moored to a turret system.

The vessel of the present invention may be used as any one of a deep sea structure vessel, an intervention vessel, a construction vessel, a drilling rig, an Anchor Handling Tug (AHTS), a hoisting vessel, a windmill safety vessel, a pipe laying vessel, a deep water mining vessel, a accommodation facility, and a service support facility, or as a combination of two or more thereof.

In a second aspect of the invention, a method is provided for passing a surface submersible plant such that the plant and lifting device are protected from dynamic forces of a splash zone in an offshore area. The method comprises the following steps: there is provided a mono hull column stabilized semi-submersible vessel comprising a deckbox with an upper deck having a lifting device at the upper portion thereof and a mono hull/pontoon at the bottom thereof, similar to the hull of a ship and submersible, the mono hull/pontoon being integrally formed and further forming a platform for use as a lower deck, the upper deck being configured for lowering equipment therefrom to the lower deck, respectively, the equipment being lowered from the lower deck to a desired depth below the surface of the water by the vessel by lifting device on the upper deck when placed thereon. In the present invention, the method comprises:

a) lowering the apparatus from the upper deck onto a lower deck by a lifting device;

b) submerging the lower deck to a desired depth below the surface;

c) partially lifting the apparatus from the lower deck upwardly using a lifting device;

d) the apparatus is rotated and lowered under water by a lowering device.

In a third aspect of the invention there is provided a method of passing through the water surface for recovering underwater equipment which protects the equipment and lifting means from dynamic forces in the splash zone of the offshore region, the method comprising: there is provided a semi-submersible vessel stabilized by single hull columns, the vessel including a deckbox with an upper deck having a lifting device at the upper portion thereof and a single hull/pontoon at the bottom of the vessel, the pontoon being similar to the hull of a ship and being submersible, the single hull/pontoon being connected to the deckbox by a plurality of columns, the single hull/pontoon being integrally formed and further forming a platform which serves as a lower deck, the upper and lower decks being configured for lifting equipment. In the present invention, the method comprises:

a) submerging the vessel so that the lower deck is lowered to a desired depth below the surface;

c) lifting and placing the equipment onto the lower deck by a lifting device;

d) the vessel is moved up above the water surface so that the lower deck is above the water surface.

In a fourth aspect of the invention there is provided a hull/pontoon for a mono-hulled vessel of the first aspect of the invention for recovery and deployment of equipment in offshore areas. In a fourth aspect of the invention, the hull/pontoon is integrally formed and further forms a platform for use as a lower deck, the hull/pontoon having the same shape as a ship hull.

Drawings

Having described the principal features of the invention, some exemplary embodiments thereof will be described in more detail and with no limitation subsequently made with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a preferred embodiment of the single hull vessel of the present invention;

FIG. 2 is another perspective view of a preferred embodiment of the single hull vessel of the present invention in offshore operation;

FIGS. 3 to 5 are different stages in a preferred method of submerging heavy equipment of the present invention in offshore area operations;

FIG. 6 is a schematic view of a temporary port at the end of a single hull vessel with an open port according to the present invention;

fig. 7 is another schematic view of a temporary harbor at the stern of a single hull vessel with closed water gates according to the present invention.

Detailed Description

Some non-limiting examples of the invention are described in detail below.

As shown in fig. 1, the single-hulled water craft of the present invention includes an upper deck 2, and the deck 2 has a large area for accommodating heavy equipment. The upper deck 2 is located on the upper part of a deck box provided with accommodation means 6, an apron 7 and a cross-border bridge or navigation bridge 8. The hull/pontoon 1 is formed integrally, further forming a platform as a lower deck 5. The lower deck 5 comprises a bow deck 9. The hull/buoyancy tank 1 includes ballast tanks, a fuel tank, a fresh water tank, and a propulsion engine compartment (not shown). The lower deck 5 is connected to the deckbox/upper deck 2 by a plurality of columns 4. Preferably, the number of pillars is 4 to 10. A lifting device 3 is also provided on the upper deck 2. As is clear from fig. 1, the combination of the upper deck 2, the deckbox, the columns and the lower deck 5 are designed together to conform to the hull/pontoon. The hull/buoyancy tank can be submerged like the ship hull, so that the whole single-hull ship is like the ship, and the ship can sail like a normal sailing ship when not submerged.

The mono hull column stabilization constructs work with the upper deck and the lower deck to provide the desired stability as the vessel so that extensive offshore operations can be performed efficiently in harsh marine environments. Thus, the vessel may operate as any one of a deep sea structure vessel, an intervention vessel, a construction vessel, a drilling vessel, an Anchor Handling Tug (AHTS), a hoisting vessel, a windmill safety vessel, a pipe laying vessel, a deep water mining vessel, a accommodation vessel, and a service support vessel, or a combination of two or more thereof.

Figure 2 shows a single hull vessel operating in the offshore region. Like reference numerals are the same as features referenced in fig. 1, but for clarity of description and illustration all reference numerals are shown. The hoisting device 3' as well as the crane 3 are also clearly shown in fig. 2. As is also apparent from fig. 2, the vessel of the invention has a ship-like submersible hull 1 and 4 to 8 uprights connecting the hull to the deckbox. In particular, at the bottom is a hull/pontoon. As mentioned before, the hull together with the other features described above may enable the vessel to function as a normal ship.

The vessels may have different sizes and capacities. The hull comprises ballast tanks, fuel tanks, fresh water tanks and propulsion engine compartments (not shown), preferably ballast tanks (not shown) are provided in the lower hull and part of the columns 4. Preferably the vessel has a speed of 10-11 knots when sailing, and is able to maintain its position in the submerged state at 6.5 meters high waves, 2 knots of water and 15m/s wind speed. Preferably, the deckbox has a size of 120 × 45 × 6m and includes an engine room, a large space for heavy equipment, and a hotel device 6. Preferably, the vessel is equipped with 6 to 12 propellers, the number of which depends on the vessel size and the working area. In the actual working area, the height of the uprights can be adjusted to suit the operating needs and environmental factors.

As previously mentioned, the vessels may have different sizes, which may be 100 and 300 long and 45-70 meters wide.

The vessel includes ballast tanks and a portion of the columns in the lower hull. Under submerged conditions, the displacement of the vessel was 45000 tons. When a structure/device is deployed, if it falls to the bottom, its weight can be compensated by water ballast. This construction/installation is about 1% of the total displacement and therefore has only a limited effect on the stability of the vessel. Preferably, the vessel has a loading capacity of about 6000-.

With the vessel of the present invention, it is known from experimental data that all known problems of operation in the prior art are solved by the combination of its aforementioned structural features and that a better, more stable offshore platform, greater space and ton capacity can be provided. Further, the vessel is more flexible when sailing into port than the drilling platform. In addition, when a round well deck is provided from the upper deck to the bottom hull, the vessel provides better protection for all equipment passing through the round well deck. The ship can be used as a common ship to sail, so that good stability is provided for the hoisting device. Also, due to the position of the propeller, the vessel can obtain a better maneuverability. Under the sailing state, 11-section speed can be obtained, so that large acting force on a crane, a lifting device and a building can be avoided. Need not to be provided with the lift compensator on the hoist, it is lower to the safety factor requirement to have better lifting capacity, thereby avoided the harm to building and elevating gear, have better capacity on its cross-section, have fine capacity under extremely abominable marine environment.

Fig. 3-5 illustrate how the vessel deploys (and retrieves) heavy equipment 10 by diving in the present invention, avoiding the equipment and lifting devices from the dynamic forces of the splash zone, instead of the usual method of lifting heavy equipment through the water line, which is a significant feature of the present invention. Features in fig. 3 to 5 that are referenced by the same reference numerals as in fig. 1 and 2 are the same, but for clarity of description not all reference numerals are shown.

First, large structures/installations are lowered on the upper deck 2 in ports and transported to the actual offshore location, where the vessel is in a non-submerged state like a normal sailing vessel. The spacious upper deck, which has corresponding space for the passage of the device 10, can be clearly seen in fig. 5. In fig. 3, the building/equipment 10 is lowered onto the lower deck 5. When the equipment 10 is lowered to the lower deck 5, the vessel starts to dive slowly by gradually diving the lower deck below the water line, as shown in fig. 4. The lifting device 3' is connected to the crane 3 before the apparatus is submerged approximately 3 to 4 metres below the surface. When the equipment is below the water surface, the equipment is raised to about 1 metre above the lower deck 5, the stern is turned and the vessel bottom is lowered, as shown in figure 5. By avoiding the lowering of heavy equipment as it passes through the splash zone, the dynamic forces on the equipment and the lifting device are significantly reduced. In many sea areas, such as the north sea, the waves are relatively high (up to several meters), and if the waves strike the equipment on the deck or land on the surface of the equipment, a damaging effect is created on the equipment or the lifting device. By lowering the apparatus below the sea surface (and below the range of influence of the waves) before further lowering to the sea bottom by means of a crane or the like, there are two advantages, i.e. the apparatus is not subjected to the influence of wave forces and the weight of the apparatus can also be reduced due to buoyancy.

Likewise, when the equipment is recovered, the ship avoids the effect of dynamic forces of the splash zone on the equipment and the lifting device. Obviously, the steps of recovering the plant are the reverse of the steps of deploying the plant, the process not being shown in the figures. However, as a person skilled in the art can easily understand the method for recovering heavy equipment according to the present invention, including: a step of submerging the vessel so that the lower deck can be submerged to a desired depth below the surface of the water; a step of raising the equipment from the water onto the lower deck by the lifting device 3' and the crane 3; and a step of raising the vessel so that the lower deck is above the water surface. Further, as an optional step and subsequent steps, the apparatus 10 is raised to the upper deck 2 by separation of the lifting device 3' from the crane 3.

Figures 6 and 7 further illustrate preferred structural features of the present invention. In the stern area of the vessel a temporary harbour 11 is also included. The component also has a large ship-like hull/pontoon at the bottom (not shown) and works on the same principle as the vessel. Preferably, the temporary port has a size of 300 x 70m and can accommodate a crew/supply/other vessel 14. A plurality of such vessels may also be accommodated, depending on their size. Typically, the maximum containable vessel is a 70 meter long, 6 meter draft. It will be apparent to those skilled in the art from figures 6 and 7 that the vessel 14 may be any vessel that can be used for the safe transport of crew and materials. Preferably the stern door 13 is 40 metres for quickly closing the stern. The temporary harbour can be moored to a turret system (not shown) so that it is always facing into the weather. The area behind the vessel is a barrier zone 12 so that when the vessel is submerged crew ships, supply ships or other optional ships 14 can also enter the barrier zone through gates 13 in inclement weather. When crew enters with the ship/supply/optional other ship 14, the gates 13 are closed, thereby creating a shallow port so that crew/material can be safely transported. This feature is very useful for areas that are inaccessible to helicopters.

The following is a non-limiting illustration of some of the vessels in the examples of the invention.

Matters of essentials

Capacity of

Speed of rotation

Test speed of the vessel in clean hull and unrestrained sea (max wind 2 level):

approximate speed of test 11,0 knots

Draft balance keel summer load line of 5,12m

Console hold

The vessel should be able to operate with dynamic positioning 2 under the following meteorological conditions of the ocean, wind, current and all directions of motion of the vessel:

ocean 6,5m effective wave height/Tp =10 seconds

15m/s of wind power

0,9m/s surface layer flow of the water stream

For action analysis:

ocean 6,5m effective wave height/Tp =9 to 17 seconds

Meal sleeping accommodation

Reference ship general arrangement diagram

The vessel should accommodate 120 persons, including sailors and special purpose crews.

An effort was made to standardize the cabin size and arrange in four different cabins.

Mechanical/propulsion device

8X 2600KW generator

2X 2200KW stern propeller

4 x 2200KW telescopic azimuth angle from bow to stern

2X 2200KW stem propeller

The present invention has the following advantages, but is not limited to the present invention:

ship shape, column stabilizer connected to the upper deck

Sailing like a ship, operating like a rig

As well as the rig, but at a lower cost

Lower hull damping effect less than the current vessel motion oscillations, greater

Similar devices with better stability

Higher loading capacity

Larger working deck

Can enter the port with a shallower draft

The application range is wider, and the ship can be used as an interference ship, a construction ship, a drilling tower device, an anchor handling tug unit (AHTS), a heavy lifting ship, a windmill installation ship, a pipe laying machine, a deep water mining ship, a hotel ship and a service support ship

-lowering buildings and equipment through the water surface when they are on deck

Reduced dynamic forces on cranes, lifting devices and buildings

Large capacity segmentation up to 30 x 15 x 10m can be provided

Providing safe offshore ports for crew vessels/supply vessels/other small vessels when a volume and deck space is formed by stern door, extra large space

Cost reduction

Larger, more stable work platform

The problem of splashing is prevented when deploying subsea buildings/equipment, so that the equipment and the lifting device are not affected by wave forces, while the weight of the equipment can be reduced due to buoyancy effects.

Reduced forces on the tower, riser, crane, lifting device and building

-operable in a more severe environment than existing offshore vessels

The above-mentioned embodiments are only preferred embodiments of the present invention, and the present invention should not be limited by the above-mentioned embodiments, and any modifications, equivalents and improvements made to the claims and the foregoing within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A single-hulled water craft for equipment deployment and recovery in offshore areas, comprising a deckbox with an upper deck (2) in its upper part and a hull (1) at the bottom of the craft, the upper deck (2) having a lifting device (3,3 '), characterized in that the hull (1) is connected to the deckbox by a number of columns (4), the hull (1) being integrally formed and further forming a platform as a lower deck (5), the lifting device (3, 3') being provided on the upper deck (2) for lifting and lowering equipment between the upper and lower deck, the lower deck (5) being adapted to be submerged to and raised from a desired depth below the water surface, the number of columns being 4 to 10, when the single hull (1) is in a non-submerged condition, the single hull operates as a surface vessel.

2. A mono hull vessel according to claim 1, characterised in that a round well deck is provided in the entire way from the upper deck (2) to the bottom hull (1).

3. Mono hull vessel according to claim 1 or 2, characterised in that a temporary harbour site (11) is arranged at the stern of the vessel for at least one of crew, supply and other vessels (14).

4. A mono-hull vessel according to claim 3, characterised in that the harbour site (11) comprises a gate arrangement (13) and a barrier area (12) at one end of the stern area.

5. A method for a submersible plant, the method comprising: -providing a mono hull column stabilized semi-submersible vessel, said vessel comprising a deck box with an upper deck (2) with a lifting device (3,3 ') in the upper part, and a mono hull (1) in the bottom of the vessel, said mono hull (1) being connected to said deck box by a plurality of columns (4), the mono hull (1) being integrally formed and further forming a platform for a lower deck (5), said lifting device (3, 3') being arranged on said upper deck (2) for lifting and lowering equipment between the upper deck (2) and the lower deck, said lower deck (5) being used for submerging to and raising from a first desired depth below the surface of the water, characterized in that the method of submerging equipment comprises:

a) lowering the apparatus from the upper deck onto a lower deck by a lifting device;

b) submerging the lower deck to a desired depth below the surface;

c) partially lifting the apparatus from the lower deck upwardly using a lifting device;

d) the apparatus is rotated and lowered under water by a lowering device.

6. The method of claim 5, wherein the method further comprises:

e) submerging the vessel so that the lower deck is lowered to a second desired depth below the surface;

f) lifting and placing the equipment onto the lower deck by a lifting device;

g) the vessel in the water is moved upwards so that the lower deck is above the water surface.