GB2168310A

GB2168310A - Dredger

Info

Publication number: GB2168310A
Application number: GB08528815A
Authority: GB
Inventors: Wolfgang Rohr
Original assignee: Rohr GmbH
Current assignee: Rohr GmbH
Priority date: 1984-12-14
Filing date: 1985-11-22
Publication date: 1986-06-18
Also published as: EP0185859A2; EP0185859A3; AU5057285A; IT8583414A0; GB2168310B; ES8701676A1; GB8528815D0; AU580116B2; FR2574834A1; CH668059A5; CA1261790A; ES547822A0; IT1201984B; FR2574834B1

Description

SPECIFICATION Dredger The present invention relates to a dredger.

A known dredger has a floating body on which is mounted a lifting mechanism featuring a restraining winch for a grab suspended on ropes, cables, hawsers or the like. Such a dredger is employed to reclaim sand and gravel from deep or large depressions. Clamp shell grabs are used for dredging, with the grab opening and closing operation being effected either with the aid of ropes or through an hydraulic mechanism. The grab is suspended on a travelling crab which is designed to be self propelled of which features a rope drive. A lifting mechanism for raising and lowering of the grab is arranged on the travelling crab, being driven by a rope winch.

A further known dredger has a luffing jib and a lifting mechanism for a grab arranged on the jib.

Such a dredger is primarily used where a more limited capacity is adequate and for spot or concentrated dredging.

A disadvantage of these known dredgers lies in the fact that during winching or lifting operations a relatively large dead load is placed upon the lifting mechanism, since the grab constitutes about a third of the load to be lifted. As a result, a high consumption of energy is needed during lifting and the drive unit of the lifting mechanism has therefore to be of corresponding size and sturdy proportions.

It is an object of the present invention to provide an improved dredger.

Accordingly, the present invention provides a dredger comprising a floating body; a dredging means for dredging material from the sea bed; a lifting mechanism coupled to the dredging means for raising and lowering the dredging means; and counter-balance means coupled to the dredging means for counterbalancing said dredging means during raising and lowering thereof.

It will be appreciated that the term "rope" as used herein means any suitable form of flexible member and includes (but is not limited to) chains, cables and the like.

A dredger according to the present invention has the distinct advantage that the lifting mechanism can be designed for a more limited or lighter loading (i.e. greater efficiency), which is of considerable importance, particularly, for large lifting distances, which, for such dredgers, may be up to 100 metres or more.

The present invention is further described hereinafter, by way of example, with reference to the following drawings, in which: Figure 1 is a side elevation of one embodiment of a dredger according to the present invention; Figure 2 is a plan view of the dredger of Figure 1; Figure 3 is a simplified side elevation of a further embodiment of a dredger according to the present invention; Figure 4 is a plan view of the dredger of Figure 3; Figure 5 is a side elevation similar to Figure 3 of a third embodiment of a dredger according to the present invention.

Figure 6 is a plan view of the dredger of Figure 5; Figure 7 is a side elevation of a fourth embodiment of a dredger according to the present invention; Figure 8 is a plan view of the dredger of Figure 7; Figure 9 is a side elevation of a fifth embodiment of a dredger according to the present invention; Figure 10 is a plan view of the dredger of Figure 9; Figure 11 is a simplified side elevation of a sixth embodiment of a dredger having a luffing jib in elevation; and Figure 12 is a side elevation of a seventh embodiment of a dredger according to the present invention.

Figure 1 shows a dredger having a floating body 1, on which various structures are mounted, i.e. a cross beam 3 supported on girders 2, on which a traversing arm 4 is arranged for a travelling crab 5.

The travelling crab 5 is provided with a lifting mechanism 6, which has a restraining winch 7. A grab 8 is suspended from the restraining winch 7, by which the grab 8 can be raised or lowered through a rope 9.

A rope 10 is wound on the restraining winch 7 in a contra-direction to that of the rope 9 and is guided at one of the ends of the cross beam 3 over a deflecting pulley 11 and supports a counter-balance weight 12, the rope 10 being guided around a return pulley 13 on the counter-balance 12 to an anchorage 14 at or adjacent the end of the cross beam 3. The grab 8 is heavier by approximately 20 per cent in relation to the counter-balance 12 and is counterbalanced during lifting by the counterbalance 12, the latter falling as the grab is raised.

Conversely, the counter-balance 12 is raised as the grab is lowered so that only a limited braking force need be applied to the lifting mechanism 6 during the grab lowering operation. When the grab 8 is deposited on the bed of the sea, lake or similar, the lifting gear brakes are actuated to enable the grab to operate under its full weight without being affected by action of the counter-balance 12.

In the embodiment shown, an additional winding face for the rope 10 is provided on the restraining winch 7. One can also arrange the rope 10 on the restraining winch 7 such that the rope 10 wraps itself directly on to the restraining winch 7 as the latter unwinds during the lowering of the grab 8.

The described and illustrated design and arrangement of the counter-balance 12 also enables the design of the travelling crab and its drive to be effected. The crab drive unit 15 is arranged at or adjacent the end of the cross beam 3 opposite the deflecting pulley 11. The drive is effected via a rope 16, whereby a tension force is produced during movement in the direction towards the crab drive unit 15, whilst in the opposite direction, the travelling crab 5 is drawn away from the counter balance and effects a braking action on the drive 15.

The travelling crab 5 is drawn towards the drive unit 15 by actuation of the latter to wind in the rope 16, the crab 5 moving against the action of the counter-balance 12 which effects a braking action on the drive unit. Movement of the crab 5 away from the drive unit 15 is assisted by the action of the counter-balance under the effect of gravity, when the drive unit 15 releases the rope 16.

In the embodiment shown in Figures 3 and 4 the grab 8 is counterbalanced directly by the counterbalance 12, the rope 10 extending from the counter-balance 12 and being attached to the grab 8 via an additional deflecting pulley 17 on the travelling crab 5. This arrangement can be used for light-dredgeable material. As will be appreciated the winch 7 sees only a lightweight grab 8 as a result of the counter-balance 12.

In the embodiment of Figures 5 and 6 the travelling crab 5 is provided with its own drive, for which the rope 10, instead of being secured to the cross beam 3, is passed around additional deflecting pulleys 18, 19 at or adjacent respective ends of the cross beam 3 and then anchored to the crab 5, preferably to the side of the travelling crab 5 remote from the counter-balance.

The embodiment depicted in Figures 7 and 8 is similar to that of Figures 5 and 6, with the rope 10 for the counter-balance 12 being coupled to the restraining winch 7. This embodiment is suitable for a four-rope grab operation, with a further closing winch 20 being arranged on the travelling crab 5 next to the restraining winch 7.

Figures 9 and 10 show an embodiment, in which the counter-balance 12 is in two parts for hydraulic grab operation on a four rope winch. Each counterbalance part 12 is arranged as in Figure 1 with each counter-balance part being connected respectively to the restraining winch 7 and the closing winch 20. In this embodiment, the travelling crab 5 can have its own drive or an external drive such as the drive unit 15 of Figure 1.

In the embodiment of Figure 11 a luffing jib 22 is mounted on the floating body 1 and operates in conjunction with a hopper 21. By a steep positioning of this jib 22 the grab 8 which is suspended from the job can be lowered through the floating body 1 into the water. Raising and lowering of the grab 8 is effected via rope 9 and lifting mechanism 6 associated with the restraining winch 7. A sup port 23is is fixed on the floating body 1 to one side of the lifting mechanism 6, the support having a deflecting pulley 24. The counter-balance 12 is suspended from this support 23 by means of rope 10 with the rope being guided over the deflecting pulley 13, the deflecting pulley 24 and a further pulley 25 on the free end of the luffing jib 22 adjacent the grab 8.

With this arrangement the rope 10 can be connected directly to the grab 8 or guided directly to the winch 7 and be wound in a counter direction to the movement of the grab to provide a counterbalance effect during raising and lowering of the grab 8.

In the further embodiment depicted in Figure 12 the counter-balance 12 is suspended directly from the lifting mechanism 6 with the rope 10 of the counter-balance being wound on to the winch 7 in the manner illustrated, the counter-balance 12 thus being lowered as the grab 8 is raised and vice versa.

Claims

1. A dredger comprising a floating body; a dredger means for dredging material from the sea bed; a lifting mechanism coupled to the dredging means for raising and lowering the dredging means; and counter-balance means coupled to the dredging means for counterbalancing said dredging means during raising and lowering thereof.

2. A dredger as claimed in claim 1 further comprising a travelling crab supporting said lifting mechanism and movable between first and second extreme positions on guide means supported on a support means above said floating body; and wherein said counter-balance is suspended at or adjacent one end of said support means.

3. A dredger as claimed in claim 1 or 2 further comprising a drive means for moving said travelling crab, said drive means being secured relative to said floating body and coupled to said travelling crab, the travelling crab being positioned between said drive means and said counter-balance means whereby said counter-balance means assists movement of said crab away from said drive means and serves to brake movement of said crab towards said drive means.

4. A dredger as claimed in claim 1 or 2 having a four rope grab operation further comprising a closing winch, said closing winch and said restraining winch being coupled to the dredging means for raising and lowering the dredging means, and said counter-balance means being coupled to said restraining winch.

5. A dredger as claimed in claim 2 wherein said travelling crab is self-propelled, and said counterbalance means is coupled to said travelling crab by rope means one end of which is wound on said restraining winch and the other end of which is secured to said travelling crab to form a closed loop such that movement of said travelling crab does not substantially alter the position of said counterbalance means.

6. A dredger as claimed in claim 5 further comprising pulley means on said support means on the side of said travelling crab remote from said counter-balance means; and wherein one end portion of said rope means is guided over said pulley means and secured to said travelling crab.

7. A dredger as claimed in any of claims 2 to 6 wherein said counter-balance means comprises first and second counter-balance weights, each of which is suspended from said support means on respective sides of said travelling crab and coupled to one of said closing winch and said restraining winch by a four-rope winch system for hydraulic grab operation.

8. A dredger as claimed in claim 1 wherein said lifting mechanism comprises a luffing jib, and said counter-balance means is suspended from said floating body at the rear of said luffing jib.

9. A dredger as claimed in claim 8 wherein said counter-balance means is suspended laterally from the floating body on a support by way of a deflect ing pulley means.

10. A dredger as claimed in claim 7, wherein said counter-balance means is suspended by rope means directly from said winch.

11. A dredger in accordance with any of claims 1 to 10, wherein the rope means is wound on to the restraining winch of the lifting mechanism in the opposite direction to the rope means for the grab.

12. A dredger substantially as herebefore described with reference to Figures 1 and 2 or Figures 3 and 4 or Figures 5 and 6 or Figures 7 and 8 or Figures 9 and 10 or Figure 11 or Figure 12 of the accompanying drawings.