Patent Description:
Hoisting systems for hoisting vertically-suspended objects are known from the prior art. Examples of such hoisting systems are cranes, A-frames with winches mounted on them and overboard sheaves combined with winches. Such hoisting systems may typically be placed on vessels, platforms, semis and jack-up rigs. In addition, these hoisting systems may be placed at or over a moon pool or they operate directly over the sea via further sheaves that are guiding a hoisting rope from a winch to the operation point. An example hoisting system may be a crane, which typically comprises a crane pedestal, a main boom pivotable connected to the crane pedestal, a knuckle-boom (or jib) pivotable connected to the main boom. Such crane further comprises a winch having a winch drum with a hoisting rope. The hoisting rope is typically guided from the winch along the main boom and knuckle-boom to the boom tip at the end of the knuckle-boom. Wire sheaves are generally placed along this path to guide the hoisting rope.

The known hoisting systems function well, but their winches may become very bulky (and thereby costly) due to the required length and thickness of the hoisting rope, which is to be designed for the minimum breakable load required by the application. This is particularly so for offshore hoisting systems, wherein lengths of the hoisting rope may be up to several kilometres in order to be able to reach the seabed.

<CIT> discloses a cable winch for helicopter installation which comprises a guide sheave assembly utilizing a trunnion and carriage assembly for the guide pulley including a reaction bar and rollers to transmit the horizontal component of cable tension into the reaction bar. The installation further comprises a reaction strut for supporting the guide sheave assembly and which is pivoted to follow traversing motion of the guide sheave assembly. Furthermore, the installation comprises a levelwind mechanism having a two-speed drive for traversing of the guide sheave assembly and automatic means for changing traversing speed during cable deploy or retrieval. Finally, the installation comprises a load cell in the guide sheave assembly support for measuring cable tension.

In a first aspect the invention relates to a hoisting system for hoisting a vertically-suspended object, the hoisting system having a winch having a winch drum with a hoisting rope. A first part of the hoisting rope has a first diameter and a second part has a second diameter being larger than the first diameter, the first part being connected with a first end of the second part. Furthermore, the first part is an inner part on the winch drum when the winch drum is completely wound. The second part has a further end that is connectable to the object for hoisting the object, wherein a ratio between the first diameter and the second diameter is chosen such that the minimum breakable load of the first part differs less than a factor of four from the minimum breakable load of the second part, and preferably less than a factor of three.

The effects of the hoisting system in accordance with the invention are as follows.

The first important feature of the invention is that the hoisting rope on the winch comprises at least two parts having different diameter, wherein the inner part of the winch (that is unwound the latest) comprises the thinner part of the hoisting robe. Furthermore, the diameters are chosen such that the minimum breakable load between said parts does not differ more than a factor of four, and preferably less than a factor of three. The inventors have realized that this combination of features leads to an enormous advantage in offshore hoisting applications. When a heavy and bulky load is hoisted offshore, either lifted from the seabed or placed onto the seabed the buoyancy forces acting by the water on the object cause the load on the hoisting rope to be significantly smaller. In certain applications the inventors have seen a <NUM>-ton-weighing object (in air) resulting in a <NUM>-ton load on the hoisting rope (and hoisting system) when the object is fully submerged underwater. This is a factor of <NUM>,<NUM> difference, even though in most applications the weight reduction will be between <NUM>% and <NUM>%, resulting in ratio of the minimum breakable load (of the first and second part) between about <NUM>,<NUM> and <NUM>. The inventors came to the realization that this opens up the possibility to exploit this effect. Instead of designing the complete hoisting rope for the <NUM>-ton load capacity the major part of the hoisting rope may be designed for a much smaller load. In practical applications the second part does not need to be longer than <NUM> metres or <NUM> metres. The remainder, which may easily have lengths up to several thousands of meters may be designed with a significantly smaller diameter. Consequently, the winch may be designed much smaller and additionally a lot of material (and costs) are saved for the hoisting rope material. The latter effect is in fact quite large as hoisting rope is very costly, particularly fibre ropes. Nevertheless, for metal ropes the impact is also quite large. The invention is therefore not limited to any specific type of hoisting rope.

In order to facilitate understanding of the invention one or more expressions are further defined hereinafter.

A few definitions and expressions as used throughout this specification are defined hereinafter.

Wherever the word "rope" is used, this is to be interpreted as similar to the words cable and wire.

In an embodiment of the hoisting system in accordance with the invention the length of the second part of the hoisting rope is chosen such that, while, in operational use, the object is suspended in the hoisting rope and touches the water, the second part remains wound around the winch drum with at least a predefined number of windings and stretches all the way from the winch drum along the hoisting system and down to the further end of the hoisting rope near the water. The advantage of this embodiment is that it creates a safety zone during the hoisting where an effective minimum breakable strength of the hoisting rope is maintained higher in the transition from air-suspended to submerged load. In addition, for the second part to be used as hoisting rope it needs to be wound around the winch at least a predefined number of times in order to create enough friction on the winch. In practical applications this may be <NUM> times or more, for example.

In an embodiment of the hoisting system in accordance with the invention the first part and the second part are connected through a tapered transition region.

In an embodiment of the hoisting system in accordance with the invention the second part has a length between <NUM> and <NUM> metres, and preferably between <NUM> and <NUM> metres, and even more preferably between <NUM> and <NUM> metres. This embodiment gives the range for the length of the second part, which is suitable for most applications.

In an embodiment of the hoisting system in accordance with the invention the first part has a length between <NUM> and <NUM> metres, and preferably between <NUM> and <NUM> metres, and even more preferably between <NUM> and <NUM> metres. This embodiment gives the range for the length of the first part, which is suitable for most applications.

In an embodiment of the hoisting system in accordance with the invention the first diameter of the first part of the hoisting rope is between <NUM> and <NUM>. This embodiment gives the range for the diameter of the first part, which is suitable for most applications.

In an embodiment of the hoisting system in accordance with the invention the second diameter of the second part of the hoisting rope is between <NUM> and <NUM>. This embodiment gives the range for the diameter of the suitable part, which is suitable for most applications.

In a second aspect the invention relates to a method for hoisting a vertically-suspended object with a hoisting system in accordance with the first aspect of the invention. In an embodiment the method comprises a step of hoisting the object either into or from the water, in such a way that the second part of the winch drum is always at least partially wound on the winch drum before the object is lifted out of the water during lifting of the object, and that the first part is not unwound from the winch drum before the object is fully submerged in the water during lowering of the object. Even though ropes with parts with unequal diameter have been reported before, these ropes were not used in hoisting methods, and particularly not in hoisting methods, wherein the load remains vertically suspended in the hoisting rope both in air as well as when being submerged. The latter is exactly the application area where the benefits of the hoisting system (and winch) in accordance with the other aspects of the invention are most profound.

In an embodiment of the method in accordance with the invention the method comprises steps of:.

In an embodiment of the method in accordance with the invention, in the step of lowering the object, at least a predefined number of windings of the second part remain on the winch drum until the object is exactly fully submerged. The advantage of this embodiment is that it creates a safety zone during the hoisting where an effective minimum breakable strength of the hoisting rope is maintained higher in the transition from air-suspended to submerged load. In addition, for the second part to be used as hoisting rope, it needs to be wound around the winch at least a predefined number of times in order to create enough friction on the winch. In practical applications this may be <NUM> times or more, for example.

In an embodiment of the method in accordance with the invention, in the step of lifting the object, at least a predefined number of windings of the second part are wound on the winch drum before the object is no longer fully submerged. The advantage of this embodiment is that it creates a safety zone during the hoisting where an effective minimum breakable strength of the hoisting rope is maintained higher in the transition from air-suspended to submerged load. In addition, for the second part to be used as hoisting rope it needs to be wound around the winch at least a predefined number of times in order to create enough friction on the winch. In practical applications this may be <NUM> times or more, for example.

In the following is described examples of embodiments illustrated in the accompanying drawings, wherein:.

Various illustrative embodiments of the present subject matter are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present subject matter will now be described with reference to the attached figures. Various systems, structures and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

In this invention a hoisting rope used for subsea load handling (offshore). Subsea load handling is normally based on a winch and a rope for lowering and hoisting a load to and from a seabed. As discussed in the introduction these load handling systems are often operated from a floating vessel or platform. The hoisting heights are depending on the depths in the operation area. Typical hoisting heights (depths) for a global operating vessel is <NUM>.

Traditional hoisting systems use steel wire ropes as a load carrier. These systems have several challenges, such as weight of the rope, corrosion and fatigue during active-heave compensation (AHC). The main advantages of such systems are robustness, well-known and established technology and several decades of experience.

Future hoisting system are going in a direction of using fibre ropes replacing the traditional steel wire ropes. These hoisting ropes may be based on different materials or a combination of these. The main advantages of fibre ropes are light weight (neutral in water), no corrosion issues, possible to transfer data signals through optionally-integrated cables, more accurate condition monitoring, possibilities to replace damaged part of the rope by splicing. Disadvantages are rope size, high cost, temperature sensitive, more fragile ropes, less experience from subsea load handling systems and the need for larger bending radius hence large sheaves and drums.

Furthermore, as the vessel is floating, an Active Heave Compensating system (AHC) is a typical part of the system for safe load handling.

The inventors got the insight that when an item is lowered into water the weight is reduced due to buoyancy from the displaced water. The main idea in the invention is to use a rope with two different diameters and different Minimum Braking Load (MBL) to utilize the effect from buoyancy. The outer part of the hoisting rope (closest to the load) needs a higher MBL as this part of the rope is used for load handling in air. In most embodiments this part should have a length of about <NUM> to <NUM> rope, depending of the hoisting system configuration and size. The remaining part of the hoisting rope is used for load handling when the load is submerged in water, hence experiencing a reduced load and lower MBL requirements. This is the largest part of the rope and in most embodiments between <NUM> and <NUM> length.

One benefit of the invention is the reduced rope weight, but the main advantage is the reduced overall cost and size of the hoisting system (i.e. crane). The hoisting rope determines a major part of the total cost, and by reducing the hoisting rope diameter the winch may be downsized as the rope diameter is a design factor for determining the required dimension of the winch drum and rope sheaves. These reductions also affect the overall cost and size of the total hoisting system.

The invention may be used in connection with hoisting systems (i.e. cranes, A-frames with winches mounted on them, and overboard sheaves combined with winches), where fibre ropes are used for load handling offshore, but the invention also applies to steel ropes.

<FIG> shows an application field of the invention. This application field as earlier discussed concerns a floating vessel <NUM> (i.e. a boat, barge or platform) floating on water <NUM> (sea, lake, fjord and the like) as illustrated. The floating vessel <NUM> has a crane <NUM> on its deck as illustrated. Typically, such vessels comprise storage place for storing objects (not shown) that either are to be placed on the seabed or have been taken from the seabed. In the claims this place is referred to as the "first location" P1 of the object. <FIG> further illustrates the surface <NUM> of the water <NUM>.

<FIG> shows a winch <NUM> in accordance with an embodiment of the invention. For the sake of simplicity only the winch drum <NUM> of the winch <NUM> is shown. This figure illustrates an important aspect of the invention, which concerns the hoisting rope <NUM> that is wound on the winch drum <NUM>. The winch drum <NUM> comprises several known parts such as the winch drum cylinder <NUM> and the winch drum flanges <NUM>. This is all considered known to the person skilled in the art. The hoisting rope <NUM> comprises a first part <NUM>-<NUM> that is connected to a second part <NUM>-<NUM>. The first part <NUM>-<NUM>, that is located on the inner side 20i of the winch drum <NUM>, comprises a smaller diameter than the second part <NUM>-<NUM>. This means that when the winch <NUM> is being unwound first the second part <NUM>-<NUM> with the larger diameter is unwound, and then then the first part <NUM>-<NUM> with the smaller diameter is unwound. This feature is conveniently used in the current invention as will be explained with reference to <FIG>.

<FIG> show different stages of a method in accordance with an embodiment of the invention. These figures effectively show part AA of <FIG>. In the stage illustrated in <FIG> the floating vessel <NUM> of <FIG> is shown, wherein an object <NUM> (a load) has been vertically suspended using suspension ropes <NUM> in the crane <NUM> as illustrated. The crane <NUM> has a known configuration comprising a crane pedestal <NUM> to which a main boom <NUM> is pivotably mounted. Furthermore, a knuckle-boom <NUM> (or jib) is pivotably mounted to the main boom <NUM>. Furthermore, the winch <NUM> is visible, which includes the hoisting rope <NUM>, which is guided using a plurality of wire sheaves <NUM> to a boom tip 20e at the end of the knuckle-boom <NUM> as illustrated. So far, everything described is known in the field of cranes for offshore/subsea hoisting. What is special in the crane <NUM> of <FIG> is that the winch <NUM> with the hoisting rope <NUM> is the same as shown in <FIG>, having the respective first part <NUM>-<NUM> and second part <NUM>-<NUM>, wherein first part <NUM>-<NUM> has the smallest diameter. In the stage of <FIG>, wherein the object <NUM> is still suspended in the hoisting rope and hanging in the air above the surface <NUM> of the water <NUM>, the second part <NUM>-<NUM> is still partially wound on the winch <NUM>. This means that it is the second part <NUM>-<NUM>, which carries the full load, i.e. full weight of the object <NUM> that is hanging in the air.

The figure illustrates a surface S1 of the floating vessel <NUM> on a first position P1, where the object <NUM> was taken from, before it was vertically suspended in the crane <NUM>. Furthermore, the object <NUM> has already been moved to a second position P2 different from the first position P1 as illustrated.

In the stage illustrated in <FIG>, the object <NUM> has been lowered such that it touches the surface <NUM> of the water <NUM>. In this stage the second part <NUM>-<NUM> is still partially wound on the winch <NUM>. This means that it is still the second part <NUM>-<NUM>, which substantially carries the full load, i.e. full weight of the object <NUM> that is hanging in the air.

In the stage illustrated in <FIG>, the object <NUM> has been lowered such that it is partially submerged in the water <NUM>. The arrows illustrate the water <NUM> that has been pushed away by the object <NUM>, thereby creating upwardly-directed buoyancy forces. Now the weight (load) acting on the hoisting rope <NUM> is reduced by the buoyancy forces. Yet, still the second part <NUM>-<NUM> is partially wound on the winch <NUM> in this embodiment. The main reason for this is that the effective weight of the object <NUM> (load) on the hoisting rope <NUM> is still larger than the minimum breakable load of the first part (not shown) of the hoisting rope <NUM>. Thus, it is still the second part <NUM>-<NUM> of the hoisting rope <NUM> that is to carry the load.

In the stage illustrated in <FIG>, the object <NUM> has been lowered to underneath the surface <NUM> of the water <NUM>, i.e. it is fully submerged. Theoretically the crane <NUM> could be designed such that the second part <NUM>-<NUM> of the hoisting rope <NUM> is fully unwound as soon as the object is just fully submerged. However, the inventors have found out that it is safe to keep a certain safety margin, that is that the second part <NUM>-<NUM>, should preferably not be fully unwound until the object <NUM> has reached a predefined depth under the surface <NUM> of the water <NUM>. It is at that point that the first part <NUM>-<NUM> and a transition region 25t of the hoisting rope <NUM> will be visible as illustrated in <FIG>. The transition region 25t may be a tapered region, but also other solutions are possible as will be shown in the next figures.

<FIG> shows a first variant of a hoisting rope <NUM> in accordance with an embodiment of the invention. In this variant the first part <NUM>-<NUM> and the second part <NUM>-<NUM> are connected through a tapered transition region 25t as illustrated. The length of the transition region may vary and will also depend on the ratio between a (first) diameter d1 of the first region <NUM>-<NUM> and a (second) diameter d2 of the second region <NUM>-<NUM>. <FIG> also illustrates what is meant by a first end 25fe of the second part <NUM>-<NUM> that is connected to the first part <NUM>-<NUM> (via the transition region 25t), and a further end 25se at the side of the object/load (not shown).

It goes without saying that many variants of the hoisting rope <NUM> are possible. <FIG> shows a second variant of a hoisting rope 25a in accordance with an embodiment of the invention. The first end 25fe and further end 25se of the second part <NUM>-<NUM> are defined in a similar manner as in <FIG>. A main difference is the adapted transition region 25ta, which now comprises a first tapered part 25ta1 and a second tapered part 25ta3, which are connected by a cylindrical part 25ta2 as illustrated. The respective diameters d1, d2 of the first and second parts have also been illustrated. A diameter dta2 of the cylindrical part 25ta2 is chosen between the first diameter d1 and the second diameter d2. One might also define the hoisting rope 25a of <FIG> as having at least three different parts having different diameters. This is a matter of definition. The definition chosen here is in accordance with the claims, which define at least two different diameters.

There are other ways of making transitions between two parts <NUM>-<NUM>, <NUM>-<NUM> of a hoisting rope <NUM> having a different diameter. <FIG> shows a third variant of a hoisting rope 25b in accordance with an embodiment of the invention. The first end 25fe and further end 25se of the second part <NUM>-<NUM> are defined in a similar manner as in <FIG>. This variant uses a technology which has been used in rope extension systems as known from patent application publication <CIT>, owned by the same applicant. In this document a steel rope is extended using a fibre rope from a further winch. This fibre rope comprises multiple segments that are connected together using a rope connector that holds spliced ends of the fibre rope segments. This rope connector <NUM> may conveniently be used to make the transition between the first part <NUM>-<NUM> and the second part <NUM>-<NUM> of the hoisting rope <NUM> as illustrated. For details on the rope connector, including how it is built up and is connected, reference is made to the earlier-mentioned patent application publication <CIT>.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practised in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the method steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

Claim 1:
Hoisting system (<NUM>) for hoisting a vertically-suspended object (<NUM>), the hoisting system (<NUM>) having a winch (<NUM>) having a winch drum (<NUM>) with a hoisting rope (<NUM>), wherein a first part (<NUM>-<NUM>) of the hoisting rope (<NUM>) has a first diameter (d1) and a second part (<NUM>-<NUM>) has a second diameter (d2) being larger than the first diameter (d1), the first part (<NUM>-<NUM>) being connected with a first end (25fe) of the second part (<NUM>-<NUM>), wherein the first part (<NUM>-<NUM>) is an inner part (20i) on the winch drum (<NUM>) when the winch drum (<NUM>) is completely wound, wherein the second part (<NUM>-<NUM>) has a further end (25se) that is connectable to the object (<NUM>) for hoisting the object (<NUM>), characterized in that a ratio between the first diameter (d1) and the second diameter (d2) is chosen such that the minimum breakable load of the first part (<NUM>-<NUM>) differs less than a factor of four from the minimum breakable load of the second part (<NUM>-<NUM>), and preferably less than a factor of three.