Patent Description:
Offshore lifting cranes and their related equipment are getting increasingly larger and heavier in order to keep up with the requirements for lifting continually heavier loads, often in increasingly deep waters. Lifting cranes for deep water operations need to store a wire rope with a length in the order of <NUM> meters or more. Using a steel wire rope at great depths is undesirable or even impossible as the wire rope itself will become so heavy that it is impractical or even impossible for most commercially available lifting cranes to hoist the wire rope.

For hoisting loads in deep water operations, fibre ropes may be preferred due to their reduced weight compared to traditional steel wire ropes. Most fibre ropes are close to neutrally buoyant in water, thereby not adding significant weight to the lifting operation. However, a challenge related with the use of fibre ropes is the excessive wear, and hence reduced lifetime, when used in repeated bending cycles under load. In particular, the quick deterioration is observed when the hoisting operation is performed with heave compensation, in which the same portion of the fibre rope undergoes numerous bending cycles under load during a period of time that can be prolonged for a few days. The lifetime of a fibre rope can also be difficult to monitor and predict in a reliable manner, leading to excessive safety factors and unnecessary frequent replacements.

<CIT> discloses an apparatus according to the preamble of claim <NUM>.

The solutions disclosed in <CIT> and <CIT> solve the challenge of using a fibre rope to overcome the drawbacks of a heavy steel wire rope. This is achieved by providing hoisting systems where a load being hoisted subsea is carried between two ropes in an alternated manner: a first rope will typically be a steel wire rope with a short length, such as <NUM> meters; and a second rope will be a fibre rope with sufficient length to reach the seabed from a floating vessel, such as up to <NUM> meters or even more. Thus, the steel wire rope will not be extremely heavy, due to its shorter length, and will be the one undergoing bending cycles under load, thereby saving the fibre rope from the deterioration caused by this actuation.

A disadvantage of the known solutions is that the alternation between the two wire ropes requires the use of a remotely operated vehicle (ROV) to activate the disconnection between the two wire ropes, and this makes the alternation (often referred to as "handshake") a time-consuming process that adds cost to the hoisting operation.

The invention will now be disclosed and has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to the prior art. The invention is defined by the independent patent claims, and the dependent claims define advantageous embodiments of the invention.

According to an aspect of the invention, there is provided an apparatus for suspending a connector provided on a first elongated hoisting member during a subsea hoisting operation. The apparatus comprises a mechanism for holding the connector, in which, when the mechanism is subjected to a hydrostatic pressure above a threshold pressure, the mechanism is changeable to a configuration for moving past the connector while the apparatus is raised.

It has been realised that the hydrostatic pressure at which the apparatus is subjected to could be used for the purpose of changing the apparatus to a configuration that allows the apparatus to be raised and moved past a connector on the first elongated hoisting member. This is advantageous in that it removes the need to deploy a diver or an ROV in order to change the apparatus to the intended configuration. This is particularly advantageous in deep water operations where the operation of changing the configuration of the apparatus typically happens at depths of at least <NUM> meters. The known alternative solutions are significantly more time consuming and expensive. Also, since there is no need for ROVs or divers, the solution requires less machinery resources to be provided on the floating vessel from which the load is being suspended. Moreover, this solution requires only one operator for controlling the elongated hoisting members, whereas in the know alternative solutions there is a need for further operators, such as a diver or and ROV operator.

In an alternative embodiment, instead of containing the compressible fluid, the first chamber comprises a compression spring or another biasing member against which a hydraulic fluid from the second chamber is operated. The compression spring in the first chamber may be separated from the hydraulic fluid from the second chamber by means of a piston, a membrane, a diaphragm etc. A compressible fluid, a compression spring or any other biasing member will enable the mechanism to change to a configuration for moving past a connector. This is achieved by compressing the compression spring or the compressible fluid once a hydrostatic pressure is exerted above the mentioned threshold pressure.

Also, the apparatus may comprise a one-way valve arranged in parallel to the first control valve, the one-way valve being oriented to permit a free flow only from a hydraulic connection of the first control valve to the first chamber to another hydraulic connection of the first control valve to the second chamber.

Moreover, the apparatus may comprise a second control valve for controlling a hydraulic connection between the first control valve and the second chamber.

Furthermore, the apparatus may comprise a third control valve for controlling a hydraulic connection transmitting a hydrostatic pressure into the third chamber.

In one embodiment, the mechanism may comprise:.

Also, the hydraulic cylinder may be arranged so that the latch is actuatable by a piston rod connected to the piston of the hydraulic cylinder, the actuation by the piston rod causing the latch to rotate to a position for moving the mechanism past the connector while the apparatus is raised.

Moreover, the mechanism may comprise an elastic body for tensioning the rotation of the latch towards the stopper.

Furthermore, the latch may comprise a density configured to position the centre of mass of the latch in relation to the pivot so that the latch automatically rotates towards the stopper.

In another embodiment, the apparatus may comprise a channel for passing the connector through the apparatus, wherein the mechanism is arranged in relation to the channel so that the connector is holdable within the channel.

Also, the contact switch may be arranged for protruding into the channel.

According to another aspect of the invention, there is provided a system for moving a load between a floating vessel and a submerged position. The system comprises:.

According to a further aspect of the invention, there is provided a method for lowering a load from a floating vessel to a submerged position. The method comprises the steps of:.

According to a yet another aspect of the invention, there is provided a method for raising a load from a submerged position towards a floating vessel. The method comprises the steps of:.

In the present description, the terms "lower", "upper", "bottom" and "top" may be used for referring to parts and portions of a component as seen when the component is in a preferred orientation of use at a submerged position. Similarly, the terms "below", "above", "vertical" and "horizontal" may be used for describing a relative positioning as seen from an elevation view of a submerged position between a seabed <NUM> at the bottom of the view and a surface of seawater at the top of the view.

<FIG> and <FIG> show an apparatus embodiment <NUM> according to the present disclosure, the apparatus <NUM> being shown from a perspective view and from a cross-sectional view, respectively. The orientation of the apparatus <NUM> in relation to the page is in alignment with the preferred orientation of use, in which the top portion of the apparatus <NUM> is the closest portion to the surface of the seawater and the bottom portion of the apparatus <NUM> is the closest portion to the seabed <NUM>. Also, some details of the apparatus <NUM> have been simplified or omitted from the figures for illustrative purposes.

The apparatus <NUM> in <FIG> and <FIG> includes a channel <NUM> suitable for enclosing a portion of a first elongated hoisting member <NUM> while the latter is being used for suspending a load <NUM> from a floating vessel <NUM>. The channel <NUM> has a tubular shape and it crosses the apparatus <NUM> along a vertical axis (shown in <FIG> as a vertical dashed line). Arranging the first elongated hoisting member <NUM> through the channel <NUM> results in the apparatus <NUM> becoming restricted to only be able to move along the first elongated hoisting member <NUM>.

The apparatus embodiment <NUM> also includes four parts at the top that are suitable for connecting a second elongated hoisting member <NUM> to suspend the apparatus <NUM> from a floating vessel <NUM>. Each of the four parts projects upwards and includes a transversal circular hole for fastening the connection with the second elongated hoisting member <NUM>. The skilled person will be able to develop many alternative solutions for connecting the second elongated hoisting member <NUM> to the apparatus <NUM>.

Thus, the apparatus <NUM> may be used in a subsea hoisting operation in which a first elongated hoisting member <NUM>, such as a fibre rope <NUM>, is used for suspending the load <NUM> and a second elongated hoisting member <NUM>, such as a steel wire rope <NUM>, is used for suspending the apparatus <NUM>. With the first elongated hoisting member <NUM> arranged through the channel <NUM>, the apparatus <NUM> can be raised or lowered to a position along the first elongated hoisting member <NUM> by making the second elongated hoisting member <NUM> shorter or longer.

The apparatus <NUM> includes a mechanism <NUM> for holding a connector <NUM> provided on the first elongated hoisting member <NUM>. The mechanism <NUM> is more easily observed in <FIG>, as most of the components of the mechanism <NUM> are not visible in the perspective view shown in <FIG>.

The mechanism <NUM> includes two latches <NUM> for holding a connector <NUM> within the channel <NUM>. The latches <NUM> are rotatable around pivots <NUM> and the latches' rotations intersect with the interior of the channel <NUM> so that a connector <NUM> may be held within the channel <NUM>. The mechanism <NUM> also includes a stopper <NUM> for each latch <NUM>, each stopper <NUM> being arranged in relation to the respective latch pivot <NUM> so that the rotation of the respective latch <NUM> is stoppable at a position in which the connector <NUM> is holdable by the latch <NUM>. In <FIG>, the stop positions of the latches <NUM> can be observed as being horizontal in relation to the orientation of the page and pointing towards the interior of the channel <NUM>.

In the embodiment shown in <FIG> and <FIG>, the latches <NUM> are positioned opposite to each other around the central axis of the channel <NUM>. Other apparatus embodiments <NUM> may include a different number of latches <NUM>. For example, the skilled person may develop an apparatus embodiment <NUM> with a single latch <NUM> that is suitable for holding a connector <NUM> within the channel <NUM> without requiring any other latch <NUM>. Other apparatus <NUM> embodiments may include three or more latches <NUM> positioned around the central axis of the channel <NUM>.

When the apparatus <NUM> is raised or lowered by the second elongated hoisting member <NUM>, the first elongated hoisting member <NUM> and any connector <NUM> fixed to it will be passed through the channel <NUM>. It can be observed that, when a connector <NUM> is passed through the channel <NUM> from the bottom to the top of the apparatus <NUM>, the latches <NUM> will be pushed by the connector <NUM> to rotate upward and away from the central axis of the channel <NUM>. On the other hand, when the connector <NUM> is passed through the channel <NUM> from the top to the bottom of the apparatus <NUM>, the latches <NUM> will be pushed by the connector <NUM> towards the stoppers <NUM>. The stoppers <NUM> will block the latches <NUM> from rotating further and this will cause the connector <NUM> to be obstructed from continuing passing downward through the channel <NUM>. This mechanical obstruction results in the connector <NUM> being held by the apparatus <NUM>.

The mechanism <NUM> also includes hydraulic cylinders <NUM> for controllably rotating the latches <NUM> and allow any connector <NUM> to be passed through the channel <NUM> in a downward movement in relation to the apparatus <NUM> without getting caught by the latches <NUM>. The hydraulic cylinders <NUM> are arranged so that a piston rod <NUM> of the hydraulic cylinders <NUM> actuates on a portion of the respective latch <NUM> and causes the latter to rotate. In <FIG>, it can be observed that the actuation of the hydraulic cylinders <NUM> will cause the latches <NUM> to rotate upwards in relation to the orientation of the page and away from the central axis of the channel <NUM> (shown as a vertical dashed line in <FIG>). This creates the necessary clearance within the channel <NUM> for a connector <NUM> provided on the fibre rope <NUM> to be able to be passed through the channel <NUM> in a downward movement in relation to the apparatus <NUM> without being held by the mechanism <NUM>.

The hydrostatic pressure to which the mechanism <NUM> is subjected is used for controllably powering the actuation of the piston rod <NUM>. The hydrostatic pressure is defined by the formula: <MAT> in which ρ is the density of the fluid (the density of water is <NUM>/m3), g is the acceleration of gravity (<NUM>/s<NUM>) and h is the height of the column of fluid. It can be observed from this formula that the hydrostatic pressure is directly proportional to the depth of the submerged position at which the hydrostatic pressure is being calculated. The following table shows some example heights and corresponding pressure values:.

In order to control the actuation of the piston rods <NUM> on the latches <NUM>, the mechanism <NUM> includes two instances of a first chamber <NUM> for containing a compressible fluid and one instance of a valve module <NUM> (visible in <FIG>) for controlling hydraulic connections between each of the hydraulic cylinders <NUM> and the respective first chamber <NUM>. These three components are used for controllably subjecting the compressible fluid in the first chamber <NUM> to the hydrostatic pressure. When the valve module <NUM> allows the hydrostatic pressure accumulated in the hydraulic cylinder to be released into the first chamber <NUM>, the piston rod <NUM> will move and actuate on the respective latch <NUM>.

Using the hydrostatic pressure to controllably power the actuation of the piston rods <NUM> makes it simpler to move the latches <NUM> at submerged positions. This is also advantageous in that it avoids the added challenges and costs to deploy a human diver or a remotely operated vehicle (ROV) for the purpose of rotating the latches <NUM>.

The two first chambers <NUM> are visible in <FIG> and <FIG> at positions of the apparatus <NUM> above the latches <NUM>, and the valve module <NUM> is visible in <FIG> above and at an angle of both first chambers <NUM>. The skilled person will see that different numbers of valve modules <NUM> and first chambers <NUM> may be used for controlling the hydraulic connections between hydraulic cylinders <NUM> and first chambers <NUM>. For example, one valve module <NUM> may be provided for each first chamber <NUM>. Alternatively, one first chamber <NUM> may be provided for both hydraulic cylinders <NUM>.

<FIG> and <FIG> do not show any tubing for establishing hydraulically connections, such as hydraulic connections related to the hydraulic cylinders <NUM>, the first chambers <NUM> and the valve module <NUM>. However, the skilled person will see that any omitted tubing connections may be installed without requiring inventive skills. Also, the valve module <NUM> is shown in the perspective view illustrated in <FIG> but not in the cross-sectional view illustrated in <FIG>. This omission relates to a misalignment of the valve module <NUM> in relation to the cross-section shown in <FIG>. Other apparatus embodiments <NUM> may have a valve module <NUM> positioned differently.

<FIG> shows a schematic cross-sectional view of another apparatus embodiment <NUM> while holding a connector <NUM> provided on a first elongated hoisting member <NUM>. The apparatus embodiment <NUM> shown in <FIG> is similar to the embodiment shown in <FIG> and <FIG>. Several parts and components of the apparatus <NUM> have been omitted or simplified for illustrative purposes. For example, only one side of the cross-sectional view of the apparatus <NUM> is shown, this side being on the left-hand side of the first elongated hoisting member <NUM> as viewed in <FIG>.

One difference of the apparatus <NUM> when compared to the apparatus embodiment <NUM> shown in <FIG> and <FIG> is that the mechanism <NUM> includes an elastic body <NUM>, such as a spring, for tensioning the rotation of the latch <NUM> towards the stopper <NUM>. This is advantageous for keeping the latch <NUM> in contact with the stopper <NUM> when there is no connector <NUM> being held by the apparatus <NUM>. Also, the use of the apparatus <NUM> will, by default, be provided with a configuration for holding a connector <NUM>, and this is advantageous in that it increases the safety of using the apparatus <NUM> and eliminating the possibility of inadvertently letting the connector <NUM> fall.

In another mechanism embodiment <NUM>, the latch <NUM> may, instead or in addition to the elastic body <NUM>, be replaced by a latch <NUM> with the same shape but having a density configured to position the centre of mass of the latch <NUM> in relation to the pivot <NUM> so that the latch <NUM> automatically rotates towards the stopper <NUM>. This can be achieved by providing the portion of the latch <NUM> that intersects the channel <NUM> with a higher weight than the rest of the latch <NUM>. Causing the automatic rotation by means of a density configuration of the latch <NUM> is advantageous in that it does not require other components, such as the elastic body <NUM>, to be exposed to the seawater and thus reduces the need for maintenance. Providing both the elastic body <NUM> and the density configuration for the latch <NUM> is advantageous in that the automatic rotation behavior is stronger and more resilient should the elastic body <NUM> fail.

The controllable actuation of the piston rod <NUM> on the latch <NUM> will now be further described with reference to the components and hydraulic connections schematically shown in <FIG>.

In addition to the first chamber <NUM>, the mechanism <NUM> includes two chambers within the hydraulic cylinder <NUM>: a second chamber <NUM> (shown in the bottom portion of the hydraulic cylinder <NUM> in <FIG>) for exchanging a hydraulic fluid with the first chamber <NUM>; and a third chamber <NUM> (shown in the upper portion of the hydraulic cylinder <NUM> in <FIG>) for containing a fluid subjected to the hydrostatic pressure to which the mechanism <NUM> is subjected. The two chambers of the hydraulic cylinder <NUM> are separated by a piston <NUM>, which is connected to the piston rod <NUM> that is used for actuating on the latch <NUM>.

It can be observed that the interior of the third chamber <NUM>, shown in the upper portion of the hydraulic cylinder <NUM> in <FIG>, is subjected to the hydrostatic pressure on the exterior of the hydraulic cylinder <NUM>. This is schematically illustrated by the opening at the top left corner of the hydraulic cylinder <NUM>. Further openings may be available in the apparatus <NUM> in locations not shown in the cross-sectional view in <FIG> that result in the interior of the third chamber <NUM> being subjected to the hydrostatic pressure to which the apparatus <NUM> is subjected. In a preferred implementation, a device may be additionally provided and hydraulically connected to the third chamber <NUM> for blocking any sea water from entering the third chamber <NUM> while enabling the transmission of the hydrostatic pressure. This reduces the need for maintenance of the hydraulic cylinder <NUM>. The device may, for example, include a membrane or a fluid that is immiscible with sea water for creating a movable barrier between the sea water and a hydraulic fluid being used within the third chamber <NUM>. The skilled person will not require inventive skill to develop alternative solutions for both transmitting the hydrostatic pressure to the interior of the third chamber <NUM> and blocking the sea water from entering the third chamber <NUM>.

Also, it can be observed that the first chamber <NUM>, the second chamber <NUM> and the valve module <NUM> form a closed hydraulic circuit. In this circuit, the first chamber <NUM> and the second chamber <NUM> are hydraulically connected to each other and the valve module <NUM> is used for controlling this hydraulic connection between the first chamber <NUM> and the second chamber <NUM>. The valve module <NUM> is shown intersecting the hydraulic connection between the first chamber <NUM> and the second chamber <NUM>.

The valve module <NUM> includes a contact switch <NUM> protruding into the channel <NUM>. The contact switch <NUM> is used for opening a first valve <NUM>, provided within the valve module <NUM>, controlling the hydraulic connection between the first chamber <NUM> and the second chamber <NUM>. The protrusion formed by the contact switch <NUM> allows a connector <NUM> being passed through the channel <NUM> to contact and transversely push the contact switch <NUM>, thus activating the hydraulic connection between the first chamber <NUM> and the second chamber <NUM>. In a preferred implementation, the protrusion of the contact switch <NUM> is a semi-spherical shape. The height of the contact switch <NUM> as measured from the channel's <NUM> inner surface is suitable for intersecting the connector's <NUM> path through the channel <NUM> while allowing the connector <NUM> to move past the contact switch <NUM> when the contact switch is being pressed. A skilled person will find alternative shapes for the protrusion of the contact switch <NUM> within the interior of the channel <NUM>. The valve module <NUM> will be further described below, with reference to <FIG>.

Moreover, the first chamber <NUM> may include a barrier for blocking the hydraulic fluid, such as a liquid, from being mixed with the compressible fluid, such as a gas, while enabling the exchange of pressure between the two fluids. This advantageously reduces the need for maintenance of the first chamber <NUM>. Such a barrier may, for example, include a membrane, or the compressible fluid may be immiscible with the hydraulic fluid.

Thus, the closed hydraulic circuit formed by the first chamber <NUM>, the second chamber <NUM> and the valve module <NUM> makes it possible to transmit pressure in a controlled manner between the piston <NUM> within the hydraulic cylinder <NUM> and the compressible fluid within the first chamber <NUM>.

In a situation in which the apparatus <NUM> is being lowered in seawater, the hydrostatic pressure transmitted to the interior of the third chamber <NUM> will, according to the formula of the hydrostatic pressure, increase proportionally to the depth at which the apparatus <NUM> is positioned. The increased hydrostatic pressure transmitted to the interior of the third chamber <NUM> will increase the pressure applied on the piston <NUM>, which in turn will increase the pressure of the hydraulic fluid between the second chamber <NUM> and the valve module <NUM>.

In this situation, the piston rod <NUM> will not actuate on the latch <NUM> if the hydraulic connection between the second chamber <NUM> and the first chamber <NUM> is closed by the valve module <NUM>. This is caused due to the piston <NUM> being obstructed by the hydraulic fluid contained between the second chamber <NUM> and the valve module <NUM> and due to the hydraulic fluid typically being incompressible or approximately incompressible. Thus, when the contact switch <NUM> of the valve module is not being pressed by the connector <NUM>, the hydraulic connection between the two chambers remains closed and the piston rod <NUM> will not actuate on the latch <NUM>.

The contact switch <NUM> can be pressed by lowering the apparatus <NUM> in relation to the first elongated hoisting member <NUM> so that the connector <NUM> is passed against the contact switch <NUM>. When the contact switch <NUM> is pressed, the valve module <NUM> will open the hydraulic connection between the second chamber <NUM> and the first chamber <NUM>, and the piston <NUM> will react towards balancing the pressure applied on the piston <NUM> by the third chamber <NUM> and by the second chamber <NUM>. The piston <NUM> will move downwards (in accordance with the orientation of <FIG>) when the hydrostatic pressure applied on the side of the piston <NUM> facing the third chamber <NUM> is higher than the pressure applied on the other side of the piston <NUM> by the hydraulic fluid and the compressible fluid within the first chamber <NUM>. In that case, the hydraulic fluid from the second chamber <NUM> is pushed by the piston <NUM> and flows towards the first chamber <NUM> to pressurise the compressible fluid therein. The hydraulic fluid displacement and downward movement of the piston <NUM> will cause the piston rod <NUM> to actuate on the latch <NUM>.

Thus, by using the hydrostatic pressure, the mechanism <NUM> is capable of being changed to a configuration in which the latch <NUM> is rotated away from the centre of the channel <NUM>, and the connector <NUM> can be passed through the channel <NUM> from the top to the bottom of the apparatus <NUM> without contacting the latch <NUM>. The apparatus <NUM> can therefore move past the connector <NUM> while the apparatus <NUM> is raised.

Moreover, by configuring the initial pressure of the compressible fluid stored within the first chamber <NUM>, it is possible to establish a threshold pressure below which the hydrostatic pressure will not be capable of making the piston rod <NUM> actuate on the latch <NUM>. This behaviour is caused by the difference of pressures observed by the piston <NUM> not being favourable to move the piston downwards in accordance with the orientation shown in <FIG>. As long as the hydrostatic pressure is not higher than the pressure of the compressible fluid, the piston rod <NUM> will not actuate on the latch <NUM>.

In other words, configuring the initial pressure of the compressible fluid allows defining a threshold depth until which pressing the contact switch <NUM> will not cause the piston rod <NUM> to actuate on the latch <NUM>. For example, if the initial pressure of the compressible fluid in the first chamber <NUM> is set to <NUM>,<NUM> bar, the contact switch <NUM> will only cause the piston rod <NUM> to actuate on the latch <NUM> after the apparatus <NUM> has been lowered to more than the threshold depth of <NUM> meters because this is the depth at which the hydrostatic pressure is expected to be <NUM>,<NUM> bar. Configuring the initial pressure of the compressible fluid can be advantageous in increasing the safety of using the apparatus <NUM> because the contact switch <NUM> can be inadvertently pressed by a connector <NUM> before the apparatus <NUM> reaches an intended depth and this will not cause the latch <NUM> to be actuated by the piston rod <NUM>.

<FIG> show schematic views of valve module embodiments <NUM> that could be used as the valve modules <NUM> shown in <FIG> and <FIG>.

<FIG> shows a valve module <NUM> including a first control valve <NUM> for controlling the hydraulic connection between the first chamber <NUM> and the second chamber <NUM>. The first control valve <NUM> includes two hydraulic terminals. A top terminal is illustrated as being hydraulically connected to the top of the valve module <NUM> shown in <FIG>, and this terminal connects to the first chamber <NUM>. A bottom terminal is illustrated as being hydraulically connected to the bottom of the valve module <NUM> shown in <FIG>, and this terminal connects to the second chamber <NUM>. Also, the first control valve <NUM> can be activated by the contact switch <NUM>.

In a preferred embodiment, the first control valve <NUM> is closed unless the contact switch <NUM> is being pressed.

<FIG> shows a valve module embodiment <NUM> that has similarities with the embodiment shown in <FIG>.

A difference of the valve module <NUM> shown in <FIG> is that a one-way valve <NUM> is included and arranged in parallel to the first control valve <NUM>. The one-way valve <NUM> is oriented to permit a free flow only from the top terminal, i.e. the hydraulically connection of the first control valve <NUM> to the first chamber <NUM>, to the bottom terminal, i.e. the hydraulic connection of the first control valve <NUM> to the second chamber <NUM>.

This valve module embodiment <NUM> is advantageous in that it enables the compressible fluid within the first chamber <NUM> to depressurize whenever the pressure within the second chamber <NUM> is lower than the pressure within the first chamber <NUM>. This automatic depressurization is achieved without requiring the activation of the contact switch <NUM>. Thus, when the apparatus <NUM> is raised and the hydrostatic pressure transmitted into the third chamber <NUM> decreases, the one-way valve <NUM> will enable the transmission of any excess pressure from the top terminal to the bottom terminal of the first control valve <NUM> and thus keep the pressure of the compressible fluid within the first chamber <NUM> to be at most the pressure of the hydraulic fluid between the second chamber <NUM> and the first control valve <NUM>.

One difference of the valve module <NUM> shown in <FIG> is that a second control valve <NUM> is included for controlling the hydraulic connection between the first control valve <NUM> and the second chamber <NUM>. The second control valve <NUM> can be used for closing the hydraulic connection between the second chamber <NUM> and the first chamber <NUM> independently of the hydrostatic pressure or the activation of the contact switch <NUM>. In a preferred embodiment, the second control valve <NUM> is open by default and closed only when it has been configured to be closed.

For example, it can be useful in some hoisting operations to close the second control valve <NUM> before submerging the apparatus <NUM>. Then, the apparatus <NUM> can be controlled to perform the following movements: lowering the apparatus <NUM> to move past a connector <NUM> at a lower depth on a first elongated hoisting member <NUM>; once the apparatus <NUM> has moved past the connector <NUM>, raising the apparatus <NUM> so that the passed connector <NUM> is held and raised by the apparatus <NUM>; repeating these steps until the first elongated hoisting member <NUM> has been decreased as intended. In this hoisting operation, closing the second control valve <NUM> is advantageous in that a higher safety is provided due to the inability of the connector <NUM> to inadvertently press the contact switch <NUM> and cause the connector <NUM> to be abruptly dropped.

In one apparatus embodiment <NUM> not shown in the Figures, the apparatus <NUM> includes a third control valve <NUM> for controlling a hydraulic connection transmitting the hydrostatic pressure into the third chamber <NUM>. Closing this valve blocks the interior of the third chamber <NUM> from being subjected to the hydrostatic pressure applied on the apparatus <NUM>. Thus, the third control valve <NUM> can be advantageous in increasing the safety of the apparatus <NUM> similarly to the second control valve <NUM> described above with reference to <FIG>.

Turning now to <FIG> and <FIG>, these show a situation in which a subsea hoisting operation is being carried out. A load <NUM> is being moved by a system embodiment based on a floating vessel <NUM>. For illustrative purposes, the floating vessel <NUM> is shown as a trapezoid and the load <NUM> is shown as a square. Moreover, it can be observed that the system components and proportions in <FIG> and <FIG> are shown in a simplified manner. For example, the distance between the floating vessel <NUM> and the seabed <NUM> in a deep-water operation may be in the order of thousands of metres.

The system shown in <FIG> and <FIG> deals with the challenges of handling a heavy steel wire rope using an arrangement of ropes similar to the ones described in <CIT> and <CIT>. The system includes two elongated hoisting members: a fibre rope <NUM> for suspending the load <NUM>; and a steel wire rope <NUM> for suspending an apparatus <NUM> embodiment according to the present disclosure. The two elongated hoisting members, i.e. the fibre rope <NUM> and the steel wire rope <NUM>, can be independently made longer or shorter from the floating vessel <NUM>. This capability is illustrated by the two winches shown on the floating vessel <NUM>, one shown at the top of a crane mast on the floating vessel <NUM> and the other winch being on the main deck of the floating vessel <NUM>.

Also, the apparatus <NUM> and the fibre rope <NUM> have been arranged so that the fibre rope <NUM> runs through a channel <NUM> crossing the apparatus <NUM>. This restricts the movements of the apparatus <NUM> so that it may be moved up or down along the fibre rope <NUM>. Thus, by making the steel wire rope <NUM> longer or shorter, the system can move the apparatus <NUM> to a position along the fiber rope <NUM>. The range of positions that can be reached by the apparatus <NUM> depends on the length of the steel wire rope <NUM>.

In addition to being movable along the fibre rope <NUM>, the apparatus <NUM> can hold a component provided at a fixed position on the fibre rope <NUM>. In this respect, the fibre rope <NUM> includes two connectors <NUM> at fixed positions: a lower connector <NUM> can be observed within the apparatus <NUM> in <FIG> as a dashed circle; and an upper connector can be observed as a circle with a solid line fixed to the fibre rope <NUM> at an upper position closer to the floating vessel <NUM>. The same two connectors are observed in <FIG> but the lower connector <NUM> is no longer shown within the apparatus <NUM>.

The connectors <NUM> can be implemented as a solid objects or devices provided at a fixed position on the fibre rope <NUM>. In the <FIG>, <FIG> and <FIG>, the connector <NUM> is schematically shown as a sphere encircling a position on the fibre rope <NUM>. The skilled will be able to use a connector <NUM> based on other shapes and kinds of fixture without requiring inventive skill. In an alternative embodiment, the connectors <NUM> may be of the type disclosed in <CIT>, in which the connectors, rather than encircling a fibre rope <NUM>, are used to splice ends of fibre rope segments together. The connector may be barrel shaped with a slightly enlarged diameter over its midportion.

The apparatus <NUM> can hold a connector <NUM> when the apparatus <NUM> is raised along the fibre rope <NUM> and the connector <NUM> enters the channel of the apparatus <NUM>. By using the apparatus <NUM> to hold the connector <NUM>, the system can suspend the connector <NUM> using the steel wire rope <NUM>. Moreover, since the connector <NUM> is fixed on the fibre rope <NUM>, the system can suspend the portion of the fiber rope <NUM> between the load <NUM> and the connector <NUM> using the mechanical connection established between the apparatus <NUM> and the connector <NUM>. Thus, it becomes possible to operate the system shown in <FIG> and <FIG> in two modes of suspension.

In a first mode of suspension, shown in <FIG>, the weight of the load <NUM> is transmitted to the floating vessel <NUM> by two rope segments: a rope segment between the load <NUM> and the apparatus <NUM>, this segment being provided by a portion of the fibre rope <NUM>; and another rope segment between the floating vessel <NUM> and the apparatus <NUM>, this segment being provided by the steel wire rope <NUM>. This mode of suspension requires the apparatus <NUM> to hold a connector <NUM>, which is shown as a dashed circle within the apparatus <NUM> in <FIG>. Thus, a chain of mechanical connections is established: the weight of the load <NUM> tensions the fibre rope <NUM> segment between the load <NUM> and the apparatus <NUM>; then, within the apparatus <NUM>, the connector <NUM> is both pulled down by the fibre rope <NUM>, due to the tension from the load <NUM>, and held by the apparatus <NUM>; and the apparatus <NUM> tensions the steel wire rope <NUM> extended from the floating vessel <NUM>.

It can be observed that, in this first mode of suspension, the weight of the load <NUM> is transmitted from the apparatus <NUM> to the floating vessel <NUM> only through the steel wire rope <NUM> and this has the advantage of limiting the execution of bending cycles under load only to the steel wire rope <NUM> and keeping the fibre rope <NUM> free from deterioration due to this type of bending cycle. Moreover, it can be observed that the fibre rope <NUM> segment between the load <NUM> and the apparatus <NUM> is subjected to the weight of the load <NUM> but not subjected to bending cycles. Thus, the first mode of suspension is advantageous for moving the load <NUM> between two submerged positions.

Ensuring that the connector <NUM> is in contact with and being held by the apparatus <NUM> when the load <NUM> is being lowered is achieved by accompanying the changes of length of the steel wire rope <NUM> with similar changes of length of the fibre rope <NUM> including an additional slack. Depending on how long the additional slack is, the fibre rope <NUM> may be observed hanging next to the steel wire rope <NUM>. In one implementation of the first mode of suspension, the additional slack is sufficiently long to avoid having any weight of the load <NUM> being transmitted through the fibre rope <NUM> above the apparatus <NUM> but not long enough that it becomes possible for the fibre rope <NUM> to get inadvertently wound around or stuck into other components of the system or the load <NUM>. In another implementation of the first mode of suspension, the added slack has a length equivalent to the perimeter of at least one turn of a drum being used on the floating vessel <NUM> for controlling the extended length of the fibre rope <NUM>.

In a second mode of suspension, shown in <FIG>, the weight of the load <NUM> is transmitted to the floating vessel <NUM> entirely by the fibre rope <NUM>. This mode is useful for moving the apparatus <NUM> along the fibre rope <NUM> while maintaining the length of the fibre rope <NUM> between the floating vessel <NUM> and the load <NUM>. It can be observed in <FIG> that the apparatus <NUM> is suspended at an intermediate position between the two connectors <NUM> on the fiber rope <NUM> and can be raised or lowered as needed.

Switching the system from the first mode of suspension to the second mode of suspension can be achieved by altering the lengths of the elongated hoisting members so that the apparatus <NUM> no longer holds the connector <NUM>. By "altering the lengths" is meant to spool in/out the elongated hoisting members by means of winches provided on the floating vessel <NUM>, as will be understood by a person skilled in the art. The elongated hoisting members can be controlled to lower the apparatus <NUM> in relation to the fibre rope <NUM> and, at some moment, cause the weight of the load <NUM> to be transmitted to the floating vessel <NUM> entirely through the fibre rope <NUM>. That moment will occur when the length of the fibre rope <NUM> between the floating vessel <NUM> and the connector <NUM> being held by the apparatus <NUM> becomes shorter than the length of the steel wire rope <NUM> between the floating vessel <NUM> and the apparatus <NUM>. This also results in the apparatus <NUM> no longer holding the connector <NUM> and being positioned at a lower position of the fibre rope <NUM> than the connector <NUM>.

Switching from the second mode of suspension to the first mode of suspension can be achieved in an opposite manner. When starting from the second mode of suspension, the apparatus <NUM> can be raised until it encounters a connector <NUM> and the latter enters the channel of the apparatus <NUM>. By continuing to decrease the length of the steel wire rope <NUM>, the apparatus <NUM> will hold the connector <NUM> and this will cause the weight of the load <NUM> to be transmited to the floating vessel <NUM> in accordance with the first mode of suspension.

In order to avoid subjecting the fibre rope <NUM> to bending cycles under load, the system can be operated so that it only changes the extended length of the fibre rope <NUM> during the first mode of operation while having the steel wire rope <NUM> perform all the bending cycles under load. During both the second mode of suspension and switching between modes of suspension, the length of the fibre rope <NUM> extended from the floating vessel <NUM> may be kept constant and the steel wire rope <NUM> may be made longer or shorter to position the apparatus <NUM> as needed. Therefore, the fibre rope <NUM> is kept free from deterioration due to bending cycles under load both during the modes of suspension and the switching moments between modes of suspension. This maximizes the lifetime of the fibre rope <NUM>. Also, the predictability of when the fibre rope <NUM> should be replaced will be improved because the fibre rope <NUM> will only be used under load when kept still. The higher predictability results in a higher safety.

By observing <FIG> firstly and <FIG> secondly, it can be seen that, after the system changed to the second mode of suspension, the apparatus <NUM> was raised by the steel wire rope <NUM> and moved past the lower connector <NUM> on the fiber rope <NUM> without holding it. This was achieved by having the apparatus <NUM> change to a configuration for moving past the connector <NUM> before being raised and moved past the connector <NUM>. In such a configuration, the features in the apparatus <NUM> for holding the connector <NUM> are disabled.

In an opposite situation, i.e. by observing <FIG> firstly and <FIG> secondly, the apparatus <NUM> also requires the ability to move past the lower connector <NUM>. It can be seen that, before the system changed to the first mode of suspension, the apparatus <NUM> first had to be moved past the lower connector <NUM> to reach a position on the fibre rope <NUM> below the lower connector <NUM> and then be raised to hold the connector <NUM>. Thus, apparatus <NUM> includes features for moving past a connector <NUM> when the apparatus <NUM> is being lowered.

With the system embodiment shown in <FIG> and <FIG>, moving the load <NUM> between two submerged positions separated by a distance longer than the length of the steel wire rope <NUM> can be achieved by continuously alternating between the first and second modes of suspension until the target submerged position is reached. During the first mode of suspension, the steel wire rope <NUM> is used for performing bending cycles under load in the direction of the lowering or raising operation being carried out, and during the second mode of suspension the steel wire rope <NUM> is used for moving the apparatus <NUM> in the opposite direction. In particular, when lowering the load <NUM> the length of the steel wire rope <NUM> is increased during the first mode of suspension and decreased during the second mode, whereas when raising the load <NUM> the length of the steel wire rope <NUM> is decreased during the first mode and increased in the second mode. Thus, the system can be useful for lowering, raising, or lowering and raising a load <NUM> between two submerged positions reachable by the fibre rope <NUM>.

In order to lower the load <NUM> over a distance longer than the length of the steel wire rope <NUM>, the following steps may be repeated:.

The efficiency of these steps can be improved by maximizing a threshold length of the steel wire rope <NUM> at which the system stops extending both the fibre rope <NUM> and the steel wire rope <NUM> and switches to the second mode of suspension. For example, with a steel wire rope <NUM> embodiment with a total maximum length of <NUM> meters, it can be useful to establish a threshold length equal to the total maximum length minus a safety margin length, such as <NUM> to <NUM> meters. The safety margin length allows the system to still have some steel wire rope <NUM> available to perform the step of switching to the second mode of suspension. The skilled person will find several possibilities for suitable maximum total and safety margin lengths. Maximizing the length of the steel wire rope <NUM> at which the system switches to the second mode of suspension also has the advantage of minimizing the aggregate time during which the second mode of suspension is performed with the fibre rope <NUM> kept with a constant length waiting for the apparatus <NUM> to be repositioned and connected to the next connector <NUM> at an upper position on the fibre rope <NUM>.

In order to raise the load <NUM> over a distance longer than the length of the steel wire rope <NUM>, the following steps may be repeated:.

In these steps, the efficiency of raising the load <NUM> over a distance longer than the length of the steel wire rope <NUM> may also be improved. This can be achieved by maximizing a threshold length of the steel wire rope <NUM> at which the system switches to the first mode of suspension after having extended the length of the steel wire rope <NUM>. For example, with a steel wire rope <NUM> embodiment with a total maximum length of <NUM> meters, it can be useful to establish the threshold length as being equal to the maximum total length of the steel wire rope <NUM>. Maximizing the length of the steel wire rope <NUM> at which the system switches to the second mode of suspension also has the advantage of minimizing the aggregated time during which the second mode of suspension is performed with the fibre rope <NUM> kept with a constant length waiting for the apparatus <NUM> to be repositioned and connected to the next connector <NUM> at a lower position on the fibre rope <NUM>.

The system embodiment can be provided with appropriate dimensions and parameters for the operations that will be performed. In some situations, it may be useful to provide the fibre rope <NUM> with a length that is sufficient to reach the seabed <NUM> from the floating vessel <NUM>, while the steel wire rope <NUM> may be provided with a length corresponding to a portion of the distance between the floating vessel <NUM> and the seabed <NUM> so that a balance is established between the maximum total length of the steel wire rope <NUM> and the necessary requirements imposed on the floating vessel <NUM> in order to hoist the steel wire rope <NUM>. For example, in one embodiment suitable for deep-water hoisting operations the fibre rope <NUM> may have a total length of at least <NUM> meters and the steel wire rope <NUM> a length of at least <NUM> meters.

Generally, the terms used in this description and claims are interpreted according to their ordinary meaning the technical field, unless explicitly defined otherwise. Notwithstanding, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. These terms are not interpreted to exclude the presence of other features, steps or integers. Furthermore, the indefinite article "a" or "an" is interpreted openly as introducing at least one instance of an entity, unless explicitly stated otherwise. An entity introduced by an indefinite article is not excluded from being interpreted as a plurality of the entity.

Claim 1:
An apparatus (<NUM>) for suspending a connector (<NUM>) provided on a first elongated hoisting member (<NUM>) during a subsea hoisting operation,
the apparatus (<NUM>) comprising a mechanism (<NUM>) for holding the connector (<NUM>),
characterised in that, when the mechanism (<NUM>) is subjected to a hydrostatic pressure above a threshold pressure, the mechanism (<NUM>) is changeable to a configuration for moving past the connector (<NUM>) while the apparatus (<NUM>) is raised.