There is provided a lifting tool for opposing twisting of generally submerged ropes. More precisely, there is provided a lifting tool for opposing twisting of generally submerged ropes where the lifting tool comprises a body having an operable lock that is adapted to catch a rope connector, and a structure that is designed to be connected to a hoist or a crane.

During hoisting operations at sea where heavy items having weights in the order of several hundred tonnes are to be disposed on the seabed, the availability of steel ropes having sufficient combined strength and length has become a limiting factor for the size of items that can be handled. The seabed may be located several kilometres below sea level, and the weight of the steel rope therefore becomes significant.

It may therefore be necessary to use fibre ropes that have a density close to that of water, to allow the largest items to be submerged into deep waters.

The use of fibre ropes for operations of this type requires consideration of conditions not normally being limiting when using steel ropes. For example, the effective life of a fibre rope comprising a significant proportion of carbon fibre, depends directly on the number of load-related flexures that the fibre rope is exposed to.

Oftentimes hoisting operations of this type are heave-compensated, and the lifting rope will therefore be continuously reeled in and out from a winch due to the heave motion of the lifting vessel. Even if the item being lifted is stationary relative to the seabed, the lifting rope will still be reeled in and out, whereby the effective life of a fibre rope is reduced relatively fast.

NO document 20090729 discloses a method for paying out a relatively long fibre rope, which carries a load, by means of a shorter steel rope. The method, that includes the use of parallel ropes, is explained in detail in the special part of this document.

An inherent problem when utilizing parallel ropes is the tendency of the rope to twist and to get entangled in each other. As the ropes have to be moved independently of each other in the sea, an entanglement may in a worst case lead to cutting of the ropes and loss of a valuable item.

The object of the invention is to remedy or reduce at least one of the disadvantages of the prior art.

The object is achieved according to the invention by virtue of the features disclosed in the description below and in the subsequent claims.

There is provided a lifting tool for opposing twisting of generally submerged ropes, the lifting tool comprising a body with a centre axis, and having an operable lock that is adapted to catch a rope connector, and a structure that is designed to be connected to a hoist or a crane wherein the lifting tool is equipped with at least one water flow inducing means positioned at a radial distance from the centre axis.

The water flow inducing means may be adjustable and include one or more of a thruster, a nozzle or a rudder.

When lifted or lowered through the sea, the thruster, the nozzle or rudder may be adjusted to oppose a torque from one or both ropes. By measuring one or more physical features such as the rotational acceleration or inclination, the thruster, the nozzle or the rudder may be adjusted autonomously, remote by an operator, ore by a combination thereof to counteract said torque.

Equipment and methods usable for such measurements and control are well known to a skilled person and is not explained here.

The lifting tool may have a pair of thrusters, nozzles and rudders where the thrusters, nozzles or rudders are positioned on opposite sides of the lifting tool. When adjusting the pair of thrusters, nozzles or rudders properly, a couple acting about the central axis of the payload carrying rope may be generated.

The rudder may be turnable about an axis laid out in the direction of the span of the rudder. Thus the rudder may be balanced so that less torque is needed in adjusting the rudder.

The thrusters, nozzle or rudder may be connected to an actuator for the adjustment about said axis. Energy for operation of the actuator and for the thrusters may be stored on the lifting tool. The energy may for instance be stored in the form of a pressurized fluid or an electrical charge.

Water flow for the nozzle may be generated from the speed of the lifting tool through the sea. The nozzle inlet may be positioned in the lifting direction, while the outlet of the nozzle may be directed tangentially relative the lifting tool body.

It may be advantageous to combine a thruster for use when the lifting tool is stationary in the sea, and a rudder for use when the lifting tool is at speed, this in order to conserve energy. While in motion, a thruster may be used for generating energy. The thruster and rudder may be one unit or separate items

The lifting tool may, when it is connected to the steel rope and either moving along, or carrying the fibre rope, oppose the rotational forces typically generated by torque from the ropes, sea current and vortex shredding, and acting on the lifting tool. The lifting tool may thus, when having a speed through the sea, largely prevent the twisting and entanglement between parallel ropes in the sea.

Below, an example of a preferred lifting tool is explained under reference to the enclosed drawings, where:

Fig. 1 shows the general layout of a lifting operation;

Fig. 2 shows in perspective and larger scale a lifting tool according to the invention; and

Fig. 3 shows a side view, partly sectioned, of the lifting tool in fig. 2.

On the drawings the reference number 1 denotes a lifting tool that is connected to a crane 2 on a vessel 4 by a steel rope 6 and a lifting hook 8, the lifting hook 8 includes a swivel not shown.

A first fibre rope section 10 of a fibre rope 12 is passing through the lifting tool 1. The first fibre rope section 10 is at its lower end party connected to an item 14 via a first rope connector 16 and an intermediate rope 18. At its opposite upper end the first fibre rope section 10 is connected to a second fibre rope section 20 via a second rope connector 22.

The second fibre rope section 20 extends over a sheave 24 on the crane 2, to a feed mechanism 26 on the vessel 4. In fig. 1 the second rope connector 22 is shown in a locked position in a hanger 28 on the crane 2. The lifting force generated by the item 14 is thus carried by the first fibre rope section 10 and the crane 2, and not by the second fibre rope section 20.

The lifting tool 1 includes a pipe formed body 30 having an operable lock 32 that is adapted to catch a rope connector 10, 22 as the fibre rope 12 passes through the body 30.

In the shown embodiment, see fig. 3, the lock 32 includes a first lock party 34 that is fixed to a first shaft 36, and a second lock party 38 that is fixed to a second shaft 40. Other forms of locking mechanisms may be applicable.

The two shafts 36, 40 are rotationally interconnected by toothed sectors 42. The lock parities 34, 38 are movable by a lock actuator, not shown, between an active locked position as shown in fig. 3, where the lock parties 34, 38 rest on a protrusion 44 in the body 30, and an open position, not shown, where the lock parties 34, 38 are turned upwardly so the rope connector 10 may pass through the body 30.

An upper structure 46 is pinned to the body 30 and allowed to swing a limited amount out from the centre axis 48. The structure 46 includes a padeye 50 for a shackle 52.

The body 30 is equipped with a first rudder 54 and a second rudder 56 protruding with their span 58 in a radial direction of the body 30. As the first and second rudders 54, 56 are connected to the body 30 by bearings 60, the first rudder 54 may be turned about a first axis 62 by a first actuator 64 while the second rudder 56 may be turned about a second axis 66 by a second actuator 68.

The rudders 54, 56 of the present embodiment are substantially symmetrical about the respective axis 60, 64. The axes 60, 64 are generally parallel with the span 58 and the rudder's 54, 56 root cord 70 are longer than their tip cord 72.

Eqipment, cables and pipes for the operation of for instance the actuators 62, 66 are, apart from containers 74 for pressurised drive fluid, not shown on the drawings.

When an item 14 is to be lowered into the sea 76 and down to the sea floor 78, the first rope connector 16 as shown in fig. 3 is prevented from passing through the body 30 by the lock 32.

The first fibre rope section 10 is paid out from the feed mechanism 26 while the crane 2 is carrying the payload from the item 14 via the steel rope 6, the lifting tool 1, the first rope connector 16 and the intermediate rope 18. As the lifting tool 1 descends through the sea 76, the rudders 54, 56 are adjusted to oppose torques from the sources described above.

When the second rope connector 22 interlocks with the hanger 28, the payload is taken over from the steel rope 6 by the first fibre rope section 10. The lifting tool 1 is released from the first rope connector 10 by moving the lock parties 34, 38 to their open position. The lifting tool 1 may be moved upwardly along the first fibre rope section 10, the rudders opposing rotation of the lifting tool 1, see fig. 1. The lifting tool 1 then latches in with the second rope connector 22. When the hanger 28 unlatches from the second rope connector 22, the crane may lower the first fibre rope section 10, now carrying the payload, while the second fibre rope section 20 is paid out over the sheave 24 largely unloaded.