NO343571B1

NO343571B1 - Horizontal wireline compensator

Info

Publication number: NO343571B1
Application number: NO20161987A
Authority: NO
Inventors: Tord Martinsen; Andre Skare Berg
Original assignee: Safelink As
Priority date: 2016-12-15
Filing date: 2016-12-15
Publication date: 2019-04-08
Also published as: NO20161987A1

Description

The horizontal wireline compensator (HWC) is an installation tool designed to compensate heave motion during sensitive lifts in an offshore environment. The heave is typically induced by swells that causes floating objects, like installation vessels and barges, to move vertically up and down. The HWC is designed to operate in air or in water. The HWC is an inline tool that combines the principles of spring isolation with active cylinder control in order to generate an efficient compensation effect. The tool can operate like a traditional gas-over-hydraulic fluid spring-dampening device if the active control malfunctions. During offshore construction high and heavy structures are to be lowered by expensive working ships with big cranes of high carrying capacity. The structures have to be lifted from fixed or floating objects and be placed on either fixed or floating locations, topside or subsea. Irregular movements of working ships, barges and supply vessels generated by swell and wind can be increased a lot by the crane boom, so that even with average swell it is difficult or impossible to carry by the crane sensitive structures during violent ship and crane movements and to lower them subsea. Since daily costs of operation with working ships are very high, each delay causes enormous additional costs. Therefore, a strong demand exists to perform respective works also in less favourable weather and with average swell without damaging the structures to be moved. The prior art compensation devices, such as crane mounted active heave compensators, have a very high capital cost and have several weaknesses, where the biggest ones are; poor mobility, poor splash zone crossing performance, fatigue problems with wire rope, many lack passive backup systems, high power demand and lack of models for heavy lifts.

Thus, the present invention relates to a horizontal wireline compensator for reduction of dynamic loads and motion in offshore lifting operations. The horizontal wireline compensator is comprising an actuator with an actuator cylinder, an actuator piston rod connected to an actuator piston adapted for reciprocation with respect thereto, an accumulator connected to the actuator by conduits means, an actuator sheave and a secondary sheave applied with rope means connected to a payload via connection means.

Prior Art of US 4593885 A describes a motion compensating device installed on a lift line between the crane and object to be lifted. Hydraulic actuator, defined as a hydraulic ram, and an actuator is fluidly connected through a hydraulic manifold. Sheaves are mounted on the actuator cylinder in one end, and on the piston rod, referenced as a free end, on the other end. A third sheave is mounted at the actuator at an offset from centre line of a lift point attachment. A load line/rope means is mounted on the first, second and third sheave and terminating at a load line connection means and further the object to be lifted. The referenced document of prior art is to be used at lifts in air, while the invention relates to lifts in both air and water giving different challenges due to lift and equipment.

SUMMARY OF THE INVENTION

The main features of the present invention are given in the independent claim. Additional features of the invention are given in the dependent claims.

The HWC consists of a special actuator connected to one or more double acting gas accumulators, which further is connected to one or more gas tanks. The double acting gas accumulator allows for very efficient use of commercially available hydraulic pumps, that are used to actively control the actuator. Further, the HWC has two different ways to compensate for external water pressure, a simple and efficient passive system and an active system. Other influences like temperature variations and load variations are also handled by the active compensation system, which is able to increase or reduce gas pressure in tanks and accumulators individually by use of control valves and gas boosters. Active control of the actuator is used to compensate for heave motion. The active control is controlled by a computer that calculates the control signal based on measurements from several sensors, where the most important ones are the piston position sensor, the accelerometer and the wire rope speed sensor. Information about the wire rope speed is transferred to the compensator with wireless signals while the compensator is in air and with acoustic transmission while it is submerged. The compensator can operate in several different modes with variable stiffness and damping with or without active control of the actuator and with or without active control of the pressure levels in the various gas volumes. The compensator is energy efficient due to the fact that passive part of the compensator carries the entire load of the payload weight and the actively controlled hydraulic pumps only have to compensate for gas compression effects and friction, which typically is typically maximum 15 % of the force compared to static force, and usually much less. Energy regeneration is also used so that only friction and oil leakage and mechanical losses in the hydraulic pump contributes to the energy consumption. For HWC units with active depth compensation the power consumption is further lowered due to reduced friction at deep waters. When active control of the actuator is not required the HWC may use the active system to charge the internal battery pack. Further, acoustic communication subsea and wireless communication topside allows for control and monitoring of the compensator, on-board sensors allows the user to verify performance after a lift is concluded.

The invention has the following advantages compared to the prior art; mobile construction, lower cost for same capacity, as good performance for long wave periods and better performance for short wave periods, excellent splash zone crossing performance, well-suited for resonance protection, reduced wear of the steel wire rope, low energy consumption, reduced lifting height requirement, no upending required.

The main features of this patent application, which are new compared to previous applications:

- Horizontal design

- Increased stroke versus required lifting height

- No need for upending of the compensator (from horizontal to vertical)

- Simpler passive depth compensation

- New accumulator design, more efficient and cheaper construction

The new actuator design allows for horizontal construction of the compensator, which gives two large benefits. One, the elongation of the compensator can be long without increasing the effective vertical length of the compensator. Two, troublesome upending of the compensator from horizontal position on the vessel deck to vertical position (hanging in the crane hook) is removed as it is ready to go when lifted straight up from the vessel deck. It also worth noting that a very simple, effective and cheap passive depth compensation can be used with this actuator design. The improved gas accumulator design allows for simpler construction at a lower cost compared to prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the actuator of a compression based design with horizontally mounted sheaves on the cylinders, viewed from a horizontal plane. The advantage compared to vertical mounting is reduced lifting height requirement and no upending is required. Compression based designs also allows for more compact designs (possible to utilize more of the actuator cylinder). Gas tanks and accumulators are not shown. Note that the sheave arrangement might be modified slightly to make the two wire ropes collinear.

Figure 2 shows the actuator of a compression based design with horizontally mounted sheaves on the cylinders, viewed from a vertical plane. Gas tanks and accumulators are not shown. Note that the sheave position is for illustration purposes only and may be placed higher or lower, it is also feasible to have a sheave block at the payload connection if desired.

Figure 3 shows the actuator of a tension based design with vertically mounted sheaves on the cylinders, viewed from a horizontal plane. Tension based designs can use smaller piston rods, which cost less, due to no buckling effect. Also depth compensation is cheaper on this type of design for the same reason. The downside is the larger horizontal space requirement. Gas tanks and accumulators are not shown. Note that the sheave arrangement might be modified slightly to make the two wire ropes collinear.

Figure 4 shows the actuator of a tension based design with vertically mounted multi fall sheaves on the cylinders, viewed from a horizontal plane. Multi fall designs can increase the elongation length without increasing horizontal length. Gas tanks and accumulators are not shown. Note that the sheave arrangement might be modified slightly to make the two wire ropes collinear.

Figure 5 shows the actuator of a tension based design with vertically mounted sheaves on the cylinders, viewed from a vertical plane. Support legs are shown as well as lifting points. Note that the sheave position is for illustration purposes only and may be placed higher or lower, it is also feasible to have a sheave block at the payload connection if desired.

Figure 6 shows a depth compensated actuator. The depth compensation is performed by the tail rod, which has the same diameter as the piston rod.

Figure 7 shows a simplified hydraulic circuit for a compression based system. Note that the actuator is simplified to one cylinder.

Figure 8 shows a simplified hydraulic circuit for a tension based system. Note that the actuator is simplified to one cylinder.

Figure 9 shows a placement of the HWC in a topside lift, wherein it is located right above a payload located on a barge.

Figure 10 shows a placement of the HWC in a subsea lift, wherein it is located right above a payload, which is symbolized with a rectangle.

Figure 11 is an illustration of a prior art active heave compensator, permanently installed topside.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following section will describe how a horizontal wireline compensator (100), or HWC for short, according to the present invention works during different phases of an offshore subsea lift. One possible application is shown, where it is assumed that a payload (101) is initially on a barge (103) next to an installation vessel (102), as shown in figure 9. This payload (101) has to be retrieved by the vessel (102). Then the payload (101) needs to cross the splash zone. Next there is a descent of the payload (101) into deeper waters, and finally landing of the equipment (101) on the seabed (106), as shown in figure 10.

There are different requirements to functionality during the different phases of the lifting operation. During the first phase, which is lifting of a payload (101) that is located on a floating barge (103) from a floating vessel (101), it is beneficial if the horizontal wireline compensator (100) can compensate motion in such a way that the relative motion between the lower part of the compensator (100) and the barge (103) deck is zero, except for winch spooling. This functionality requires that three things are known:

1. Velocity of the barge (103) deck

2. Velocity of the crane hook

3. Winch speed (i.e. wire rope spooling velocity)

The first requirement is handled by a wireless MRU (104), short for motion reference unit, placed on the barge (103) deck, preferably close to the payload (101). The second requirement is either handled by an accelerometer inside the horizontal wireline compensator (100), or by a MRU (105) located on the vessel (102) or in the crane. The final requirement is normally given by the crane computer, and is transferred wirelessly while in air, or via acoustic signals when submerged, to the horizontal wireline compensator (100).

Based on the information above the computer inside the horizontal wireline compensator (100) is able to control the actuator (10) in such a way that the relative motion between the lower part of the horizontal wireline compensator (100) and the barge (103) deck is close to zero while the crane winch is not spooling out wire rope. During spooling the computer inside the horizontal wireline compensator (100) will take this into account to not cause any lag for the crane operator.

After successful connection and lifting of the payload (101) from the barge (103) deck, the payload (101) has to cross the splash zone (i.e. the border between air and sea), where different requirements apply. This phase is characterized by fast dynamics, where unpredictable forces from slamming and buoyancy occurs and is best suited for a passive heave compensator, which the horizontal wireline compensator (100) basically is. Active actuator (10) control is turned off, stiffness and damping is adjusted to the best possible settings by use of control valves (CV). During the actual crossing of the splash zone, the actuator (10) equilibrium position tends to move towards the inner position, due to buoyancy forces acting on the payload (101). This effect is compensated by adjusting the internal gas pressure in one of the following ways:

1. Release gas to the surroundings

2. Transfer gas from the double acting gas accumulator (30) to a tank with lower pressure 3. Transfer gas from the double acting gas accumulator (30) to a tank with higher pressure by utilizing the gas booster (40)

The adjustment is performed automatically by the on-board computer based on changing equilibrium position of the actuator (10).

A certain distance after crossing the splash zone, the horizontal wireline compensator (100) will often switch to a softer setting with less damping. This is done to prevent resonance in the lifting arrangement. If the passive system alone is not enough to avoid resonance, then the actuator (10) can either be locked by closing control valves or actively controlled by the computer to prevent resonance.

During the transport from shallow waters to deeper waters two effects influence the equilibrium position of the actuator (10). The first influence is that the water temperature often tends to decrease as the horizontal wireline compensator (100) is lowered into deeper waters. This affects the actuator (10) equilibrium due to the fact that the gas pressure in all gas volumes are reduced due to lowered temperature. The horizontal wireline compensator (100) compensates this either by transferring gas under higher pressure from one of the tanks to the double acting gas accumulator (30) via control valves or from a tank under lower pressure to the double acting gas accumulator (30) via the booster (40) and control valves (CV). The second and often most important effect is the increasing water pressure. The horizontal wireline compensator (100) comes in two versions that handles this issue in different ways:

1. The actuator (10) shown in figure 6 is passive depth compensated, which effectively cancels the water pressure effect by having tail rods (20) passing through the actuator cylinders (11) with the same diameter as the actuator rods (13).

2. The horizontal wireline compensators (100) shown in figure 7 and figure 8 has an active depth compensation system that adjusts pressure on both sides of the actuator pistons (12) so that the water pressure effect is cancelled. The system is controlled by the on-board computer and can in many cases provide better performance than the passive depth compensation, however the passive version is more robust and less complex.

During the final phase of the lifting operation, which is the landing phase, the active actuator (10) control is again enabled, either by acoustic commands, water pressure triggering or by an ROV, to ensure that there is minimal relative velocity between the lower end of the horizontal wireline compensator (100) and the seabed (106). The on-board computer uses the on-board accelerometer, the piston rod (13) position sensor as well as acoustically transmitted signals from the vessel about wire rope spooling to actively control the actuator (10) to a high degree of accuracy and without crane operator lag. The water pressure sensor (it indirectly measures distance) can also be used in improving the control signal.

Figure 1 and 2 illustrates an embodiment of a compression based horizontal wireline compensator (100) actuator (10) with horizontal sheaves (14) attached to the actuator rods (13) with all major subcomponents numbered seen from the above and from the side, it does not depict accumulators, tanks or other components. A compression based design allows for a more compact horizontal wireline compensator (100) in the horizontal direction compared to tension based designs as the actuator cylinders (11) can be partially adjacent to each other. Horizontal sheaves (14) reduces the vertical size of the horizontal wireline compensator (100) as the other sheaves (15) can be mounted further up, hence reducing the minimum vertical size of the horizontal wireline compensator (100).

The actuator (10) consists of minimum two actuator cylinders (11), each with an actuator piston (12) and an actuator rod (13) connected to the actuator piston (12) in one end and a horizontal sheave (14) in the other end, a framework (16) locking the actuator cylinders in position relative to each other as well as providing support for the sheaves (15) and acting as a support for the horizontal wireline compensator (100) when not in use (i.e. placed on the vessel deck), at least two rope means (19) (i.e. wire rope, fibre rope, chain, belt or similar) attached to a fixed point (e.g. framework (16)) in one end and connected to the payload (101) in the other end and being reeved over the actuator sheaves (14) and the other sheaves (15), connection means (17) used for connecting the horizontal wireline compensator (100) to the crane and to the payload (101) via connection means (17) attached to a framework (16) attached to the minimum two rope means (19). The actuator cylinders (11) have two volumes each, the first volume (V+) is used for extending the actuator rod (13), and the second volume (V-) can be used for e.g. active depth compensation or end damping. The first volume (V+) is normally connected to double acting gas accumulator(s) and is normally filled with oil.

When tension is applied to the rope means (19) a force will act on the actuator rod (13) via the actuator sheave (14) which in turn will be transferred to the first volume (V+) as pressure via the actuator piston (12). The figure shows a rope means (19) configuration which gives double the movement of the rope means (19) compared to the actuator cylinder (11) stroke. This can be increased by increasing the number of rope means (19) falls. Also the force acting on the actuator cylinder (10) is twice of the force in the rope means (19).

Figure 3-5 illustrates embodiments of a tension based horizontal wireline compensator (100) actuator (10) with vertical sheaves (14) attached to the actuator rods (13) with all major sub-components numbered, it does not depict accumulators, tanks or other components. A tension based design allows for use of smaller diameter actuator rods (13) compared to compression based designs. It is also easy to implement multiple falls, and hence easy to increase the ratio between the lower connection means (13) (i.e. connected to the payload (101)) movement and the actuator rod (13) movement. The force acting on the actuator cylinder (11) is also multiplied with the same ratio. A single fall design is shown in figure 3 and a multi fall design is shown in figure 4.

The actuator (10) consists of minimum two actuator cylinders (11), each with an actuator piston (12) and an actuator rod (13) connected to the actuator piston (12) in one end and an actuator sheave (14) in the other end, a framework (16) locking the actuator cylinders in position relative to each other as well as providing support for the sheaves (15), at least two rope means (19) (i.e. wire rope, fibre rope, chain, belt or similar) attached to a fixed point (e.g. framework (16)) in one end and connected to the payload (101) in the other end and being reeved over the actuator sheaves (14) and the other sheaves (15), connection means (17) used for connecting the horizontal wireline compensator (100) to the crane. The actuator cylinders (11) have two volumes each, the first volume (V+) is used for e.g. active depth compensation or end damping, and the second volume (V-) is used to retract the actuator rod (13). The second volume (V-) is normally connected to double acting gas accumulator(s) and is normally filled with oil.

When tension is applied to the rope means (19) a force will act on the actuator rod (13) via the actuator sheave (14) which in turn will be transferred to the second volume (V-) as pressure via the actuator piston (12).

Figure 6 shows an actuator cylinder (11) with passive depth compensation. The actuator cylinder (11) has a piston (12) connected to a piston rod (13) and a tail rod (20), both rods (13, 20) have the same diameter, so that when external pressure is applied to the rods (13, 20) the net force will be zero. This principle can be used in any of the embodiments.

Figure 7 and 8 are very similar and shows simplified hydraulic circuits of compression and tension based horizontal wireline compensators (100). They are both described below:

- a hydraulic actuator (10), comprising of minimum two actuator cylinders (11) consisting of an actuator rod (13) connected to an actuator piston (12) and extending outwardly therefrom through one end of the actuator cylinder (11), adapted for reciprocation with respect thereto, actuator sheave (14) mounted at one end of the actuator rod (13) adapted for applying force to rope means (19), a first actuator volume (V+), located between the actuator piston (12) and piston side of the actuator cylinder (11), filled with oil for compression based designs and filled with gas (at any pressure, including vacuum) on tension based designs, a second actuator volume (V-), located between the actuator piston (12) and rod side of the actuator cylinder (11), filled with oil on tension based designs and filled with gas (at any pressure, including vacuum) on compression based designs, a position measurement means (22) to register the position of the actuator piston (12)

- a double acting gas accumulator (30), comprising of a first cylinder (31), a ring shaped piston (32) mounted concentrically within the first cylinder (31) and adapted for reciprocation with respect thereto, where the lower end of the ring shaped piston (32) is on the same side as the lower end of the first cylinder (31) when the ring shaped piston (32) is at zero stroke, a first inner cylinder (33) mounted concentrically with and fixed to the upper end of the ring shaped piston (32), a second inner cylinder (34) mounted concentrically within the first cylinder (31) and fixed to the lower end of the first cylinder (31) with a leak tight connection against the lower end of the first cylinder (31) as well as a leak tight seal against the ring shaped piston (32), an inner piston (38) mounted concentrically within the second inner cylinder (34) with a leak tight seal against the second inner cylinder (34) where the lower end of the inner piston (38) is at the same level as the lower end of the ring piston (32), a third inner cylinder (35) mounted concentrically within the first cylinder (31) and fixed to the upper end of the inner piston (38) and to a cylinder connector (36) that joins the third inner cylinder (35) with the first inner cylinder (33) in a stiff connection, a stuffing box (37) is mounted on top of the second inner cylinder (34) to form a leak tight connection with the first inner cylinder (33), the cylinder connector (36) has openings that allow free flow of fluids to either side of the cylinder connector (36), the second inner cylinder (34) is equipped with means for transporting fluid from outside the double acting gas accumulator (30) to the third volume (V3) between the first inner cylinder (33) and the second inner cylinder (34), a first volume (V1), located between the lower end of the ring piston (32), the lower end of the first cylinder (31) and the outside of the first inner cylinder (34), a second volume (V2), located between the lower end of the inner piston (38), the lower end of the first cylinder (31) and the inside of the second inner cylinder (34), a third volume (V3), located between the upper end of the ring piston (32), the outside of the second cylinder (34), the inside of the first inner cylinder (33) and the lower end of the stuffing box (37), a fourth volume (V4), contains the remaining volume of the double acting accumulator (30) not occupied by any parts or any other volumes

- a gas booster (40), which can be of either single acting or double acting type, with or without area difference between gas and drive side, including means to drive it, which could be either hydraulic or gas based

- a number of tanks (T1, T2, …, TN) suitable for gas storage

- conduit means between the first actuator volume (V+) and the first volume (V1) for compression based designs and conduit means between the second actuator volume (V-) and the first volume (V1) for tension based designs, adapted with a control valve (CV1) - conduit means between the second volume (V2) and the third volume (V3) adapted with a hydraulic pump (P) adapted to transport oil under pressure between the respective volumes in any direction

- conduit means between the fourth volume (V4) and the tank (T1, T2, ..., TN) volumes adapted with control valves (CVA1, CVA2, ..., CVAN) for adjustment of the volume size connected to the fourth volume (V4)

- conduit means between the first actuator volume (V+), for tension based designs, and between the second actuator volume (V-), for compression based designs, and any number of tank (T1, T2, ..., TN) volumes, adapted with control valves (CVC1, CVC2, ..., CVCN) for adjustment of the volume size connected to the actuator

- conduit means between all gas volumes (V4, V+ for tension based designs, V- for compression based designs, T1, T2, …, TN), the gas booster (40) as well as the surroundings, adapted with control valves (CV2, CV3, CV4, CVB0, CVB1, CVB2, …, CVBN), suited for pressure adjustment, both up and down, in all volumes as well as filling from the surroundings or release of pressure to the surroundings.

Figure 9 shows the horizontal wireline compensator (100) during a lift of a payload (101) from a barge (103). A wireless MRU (105) adapted for transferring motion data to the horizontal wireline compensator (100) is used in combination with either an internal MRU or a second external MRU (104) as well as transmission of winch spooling data to calculate actuator rod (13) speed to ensure that the relative motion between the lower end of the horizontal wireline compensator (100) and the barge (103) deck is close to zero, except for winch spooling, this enables safe and efficient connection between the compensator and the payload as well as safe lift off. Actuator (10) pressure is adjusted, by transfer of gas between tanks (T1, T2, …, T3) and the double acting gas accumulator (30), to match the actual payload weight.

Figure 10 shows the horizontal wireline compensator (100) during a subsea lift of a payload (101). For most of the time, while in transit from the splash zone to a short time before landing, the horizontal wireline compensator (100) is in passive mode, i.e. there is no influence on the system from the pump (free flow). The horizontal wireline compensator (100) can be put into active mode by several means, e.g. based on water depth, time, turning an ROV switch or by acoustic communication. While in active mode the horizontal wireline compensator (100) will minimize the relative motion between the lower end of the horizontal wireline compensator (100) and the seabed (106) to ensure a safe and controlled landing. Winch spooling data is preferably transferred to the horizontal wireline compensator (100) via acoustic communication or via an umbilical to remove crane operator lag.

The horizontal wireline compensator (100) further features a sensing means adapted for measuring the vertical motion of the horizontal wireline compensator (100), one or more sensing means adapted for measuring the pressure in one or more volume, a computer adapted for controlling the pump (P), the gas booster (40) and the control valves (CV) based on input from the sensing means, communication means adapted to transfer signals between the vessel (102) and the horizontal wireline compensator (100), preferably with acoustic communication while subsea and wirelessly while in air and either a battery pack or an umbilical for energy supply.

Table 1

Claims

1. Horizontal wireline compensator (100) for reduction of dynamic loads and motion in offshore lifting operations comprising an actuator (10) with an actuator cylinder (11), an actuator piston rod (13) connected to an actuator piston (12) adapted for reciprocation with respect thereto, an accumulator connected to the actuator (10) by conduits means, an actuator sheave (14) and a secondary sheave (15) applied with rope means (19) connected to a payload (101) via connection means (17) c h a r a c t e r i s e d b y that it further comprises:

the actuator (10), comprising of minimum two horizontally mounted actuator cylinders (11);

the actuator sheaves (14) mounted at the end of the actuator rods (13) adapted for applying force to the rope means (19), such as wire rope, fibre rope, chain or belt, where the rope means (19) is connected to the payload (101) via the connection means (17), such as a padeye, and the minimum one secondary sheave (15), where the actuator sheave (14) mounting direction may be horizontal or vertical, and the number of the rope means (19) is minimum one with no upper limit;

framework (16) fixing the actuator cylinders (11) position in relation to each other, the framework (16) also supports all other components, such as secondary sheaves (15), tanks (T1, T2, …, TN), further the framework (16) may be used as anchoring points for connection means (17), like padeyes, to connect the horizontal wireline compensator (100) to a crane; a first actuator volume (V+), located between the actuator piston (12) and piston side of the actuator cylinder (11), filled with oil for compression based designs and filled with gas (at any pressure, including vacuum) on tension based designs, a second actuator volume (V-), located between the actuator piston (12) and rod side of the actuator cylinder (11), filled with oil on tension based designs and filled with gas (at any pressure, including vacuum) on compression based designs;

a position measurement means (22), such as a laser position sensor, a linear position sensor or an ultrasonic position sensor, to register the position of the actuator piston (12); at least one double acting gas accumulator (30), comprising of a first cylinder (31), a ring shaped piston (32) mounted concentrically within the first cylinder (31) and adapted for reciprocation with respect thereto, where the lower end of the ring shaped piston (32) is on the same side as the lower end of the first cylinder (31) when the ring shaped piston (32) is at zero stroke, a first inner cylinder (33) mounted concentrically with and fixed to the upper end of the ring shaped piston (32), a second inner cylinder (34) mounted concentrically within the first cylinder (31) and fixed to the lower end of the first cylinder (31) with a leak tight connection against the lower end of the first cylinder (31) as well as a leak tight seal against the ring shaped piston (32), an inner piston (38) mounted concentrically within the second inner cylinder (34) with a leak tight seal against the second inner cylinder (34) where the lower end of the inner piston (38) is at the same level as the lower end of the ring piston (32), a third inner cylinder (35) mounted concentrically within the first cylinder (31) and fixed to the upper end of the inner piston (38) and to a cylinder connector (36) that joins the third inner cylinder (35) with the first inner cylinder (33) in a stiff connection, a stuffing box (37) is mounted on top of the second inner cylinder (34) to form a leak tight connection with the first inner cylinder (33), the cylinder connector (36) has openings that allow free flow of fluids to either side of the cylinder connector (36), the second inner cylinder (34) is equipped with means for transporting fluid, such as gun drilling the cylinder walls, from outside the double acting gas accumulator (30) to a third volume (V3) between the first inner cylinder (33) and the second inner cylinder (34);

a first volume (V1), located between the lower end of the ring piston (32), the lower end of the first cylinder (31) and the outside of the second inner cylinder (34);

a second volume (V2), located between the lower end of the inner piston (38), the lower end of the first cylinder (31) and the inside of the second inner cylinder (34);

the third volume (V3), located between the upper end of the ring piston (32), the outside of the second cylinder (34), the inside of the first inner cylinder (33) and the lower end of the stuffing box (37);

a fourth volume (V4), contains the remaining volume of the double acting accumulator (30) not occupied by any parts or any other volumes;

a number of tanks (T1, T2, …, TN) suitable for gas storage;

conduit means between the first actuator volume (V+) and the first volume (V1) for compression based designs and conduit means between the second actuator volume (V-) and the first volume (V1) for tension based designs, adapted with a first control valve (CV1);

conduit means between the second volume (V2) and the third volume (V3) adapted with a hydraulic pump (P) adapted to transport oil under pressure between the respective volumes in any direction;

conduit means between the fourth volume (V4) and the tank (T1, T2, ..., TN) volumes adapted with control valves (CVA1, CVA2, ..., CVAN) for adjustment of the volume size connected to the fourth volume (V4);

a sensing means adapted for measuring the vertical motion of the horizontal wireline compensator (100);

one or more sensing means adapted for measuring the pressure in one or more volume; a computer adapted for controlling the pump (P) and the control valves (CV) based on input from the sensing means;

a communication means, such as acoustic communication while subsea and wirelessly while in air, adapted to transfer signals, such as winch spooling data, between the vessel (102) and the horizontal wireline compensator (100);

either a battery pack or an umbilical for energy supply.

2. Horizontal wireline compensator (100) according to claim 1, further comprising:

a gas booster (40), which can be of either single acting or double acting type, with or without area difference between gas and drive side, including means to drive it, which could be either hydraulic or gas based;

conduit means between the first actuator volume (V+), for tension based designs, and between the second actuator volume (V-), for compression based designs, and any number of tank (T1, T2, ..., TN) volumes, adapted with control valves (CVC1, CVC2, ..., CVCN) for adjustment of the volume size connected to the actuator;

conduit means between all gas volumes (V4, V+ for tension based designs, V- for compression based designs, T1, T2, …, TN), the gas booster (40) as well as the surroundings, adapted with control valves (CV2, CV3, CV4, CVB0, CVB1, CVB2, …, CVBN), suited for pressure adjustment, both up and down, in all volumes as well as filling from the surroundings or release of pressure to the surroundings.

3. Horizontal wireline compensator (100) according to any one of claims 1-2, further comprising:

a first Motion Reference Unit, MRU, (105) placed in a crane tip; and/or

a second MRU (104) placed on the barge (103) deck close to the payload (101).

4. Horizontal wireline compensator (100) according to any one of claims 1-3, further comprising:

tailrods (20) mounted to the actuator pistons (12), exposed to external pressure, with same diameter as the actuator rods (13).