Rechtbank Den Haag, 07-06-2017, ECLI:NL:RBDHA:2017:5959, C/09/485407 / HA ZA 15-370

“1. Apparatus for accommodating a substantially vertical spud (3) of a dredging vessel with a longitudinal direction, comprising a spud carriage (6) which is mounted for limited rotation around a horizontal transverse axis (18),

characterized in that

- at least a first and a second spring means (40, 41) is arranged under bias between vessel and spud in the longitudinal direction for the purpose of absorbing a moment on the spud carriage, which first and second spring means compensate each other in the non-loaded situation of the spud; and that

- at least one spring means is provided with a spring force limiting means (50) for limiting the tension in said spring element from a determined maximum moment on the spud carriage.

en in de – onbestreden – Nederlandse vertaling:

“1. Inrichting voor het opnemen van een in hoofdzaak verticale paal (3) van een baggerschip met een langsrichting, omvattende een paalwagen (6) die beperkt draaibaar rond een horizontale dwarsas (18) gemonteerd is,

met het kenmerk dat

begrenzen van de spanning in dat veerelement vanaf een bepaald maximummoment op

de paalwagen.

"1. Apparatus for accommodating a substantially vertical spud (3) of a dredging vessel with a longitudinal direction, comprising a spud carriage (6) which is mounted for limited rotation around a horizontal transverse axis(18), wherein

the spring force limiting means (50) comprises a piston accumulator (51, 52) which is connected to the corresponding hydraulic cylinder, the piston accumulator comprising a cylinder with free piston and an accumulator, arranged such that when the tension in the at least one spring means rises above a determined maximum value which is a function of

the pressure of the accumulator, pistons of the hydraulic cylinder and the cylinder with free piston move inward and the spring force increases only slowly while the spud carriage rotates.

“1. Inrichting voor het opnemen van een in hoofdzaak verticale paal (3) van een baggerschip met een langsrichting, omvattende een paalwagen (6) die beperkt draaibaar rond een horizontale dwarsas (18) gemonteerd is,

waarin

voorspanning in de langsrichting aangebracht is voor het absorberen van een moment

op de paalwagen, welk eerste en tweede veermiddel elkaar compenseren in de onbelaste

toestand van de paal; en dat

begrenzen van de spanning in dat veerelement vanaf een bepaald maximummoment op

de paalwagen, waarin verder het eerste en tweede veermiddel door middel van

respectievelijk een eerste en tweede hydraulische cilinder (32, 33) verbonden is met het schip voor het aanbrengen van de gewenste voorspanning,

de veerkrachtbegrenzer (50) omvattende een zuigeraccu (51, 52) die verbonden is met

de overeenkomstige hydraulische cilinder, waarbij de zuigeraccu een cilinder met vrije

zuiger en een accumulator omvat, die dusdanig zijn ingericht dat wanneer de spanning

in het tenminste één veermiddel boven een bepaalde maximumwaarde, die een functie is

van de druk van de accumulator, stijgt, zuigers van de hydraulische cilinder en de

cilinder met vrije zuiger naar binnen bewegen en de veerkracht slechts langzaam

toeneemt terwijl de paalwagen roteert.”

“[0001] The present invention relates to an apparatus for accommodating a substantially vertical pole (also referred to as spud) of a dredging vessel, typically a cutter suction dredger, comprising a spud carriage which is mounted for limited rotation around a horizontal transverse axis.

[0002] Large cutter suction dredgers must often carry out operations at sea or on unsheltered waters. The waves cause the vessel to move and great forces can herein be exited on the couplings between the vessel and the bottom, these couplings being formed mainly by a spud and cutter ladder. These couplings must on the one hand be rigid in order to enable an efficient cutter process, but may not be too stiff because otherwise excessive forces are generated in the spud by the pontoon following the movements of the larger waves.

[0003] The invention has for its object to propose an apparatus of the type stated in the preamble which behaves as a spud carriage mounting in the pontoon with a variable rigidity – rigid in the case of small waves and more flexible at critical wave conditions – and in particular with a rigidity which decreases sharply at a determined maximum load of the spud plus spud carriage.

[0004] Such an apparatus is known from prior art documents NL 1011753 C, US 4033056, ( and the article by Dekker: Analyse van een Spudssysteem voor een deiningsgecompenseerde snijkopzuiger", co/85/153 ).”

“[0006] The longitudinal force F1 exerted on the spud is typically a ground reaction force on the point of the spud, and in the case of a cutter suction dredger this normally acts in the direction of the cutter head. This causes a moment on the spud carriage, whereby the

spud carriage tilts through a determined angle around the transverse axis, the first spring means is further tensioned and the second spring acting in opposite direction loses tension. This tiltability of the spud carriage in combination with the spring means thus decreases as it were the rigidity and ensures that the moment on the spud carriage is absorbed. When the moment on the spud carriage becomes greater than a determined maximum moment, the spring force then hardly increases further ( only slowly ), whereby the moment exerted on the spud carriage around an athwartship axis is limited.

(…)

[0008] According to the preferred embodiment ( invention ), the first and second spring means are connected by means of respectively a first and second hydraulic cylinder to the vessel for the purpose of applying the desired bias. In this way the bias can be adjusted in a simple manner. In this embodiment the spring force limiting means can be realized in simple manner by means of a piston accumulator which is connected to the bottom side of the hydraulic cylinder( , preferably to the bottom side thereof ). A ( The ) piston accumulator typically comprises a cylinder with free piston and an accumulator. When the tension in the spring rises above a determined maximum value which is a function of the pressure of the accumulator, pistons of main ( hydraulic ) cylinder and cylinder with free piston move inward, whereby the spring force increases only slowly while the spud carriage rotates. If the force on the spud point is acting in forward direction, the rotation will then be such that the spud point moves forward relative to the vessel, which results in a sharp fall in the force on the spud point. As soon as the force on the spud point becomes smaller than the maximum value, the piston( s ) move s outward again under the influence of the accumulator pressure.

(…)

[0018] The invention will be further elucidated on the basis of a number of non-limitative exemplary embodiments (…)

(…)

[0019] Figure 1 shows a typical embodiment of a dredging vessel with cutter suction head. The shown vessel comprises, among other parts, a ladder 1, a ladder winch 9 and two side winches 2, an auxiliary spud 4 and a working spud 3 which is accommodated in a spud carriage 6. A cutter head 5 is arranged on the outer end of ladder 1, and suction means are provided close to the cutter head which consist substantially of a suction tube 10 and a pump 8. (…)

[0020] In such a cutter suction dredger the working spud ensures that a fixed point is formed around which the suction dredger can swing during dredging. (…)

[0021] The apparatus according to the invention will now be further elucidated on the basis of an embodiment variant as shown in figures 2A and 2B. (…)

(…)

[0023] The moment M on the spud carriage caused by a longitudinal force F1 is absorbed by a system of steel wires and discs as shown schematically in figure 3. A first spring means arranged between the vessel and spud carriage 6 is formed by a first steel wire 40. At one outer end 42 the first steel wire 40 is connected to the vessel to the right of the transverse axis. This first wire 40 is guided via a double disc 34 mounted on the spud carriage to a tensioning disc 30 which also lies to the right of the transverse axis and from where the first wire is further trained diagonally to the other second side of the spud carriage along guide discs 36, 37, and is finally guided over a second double disc 35 mounted on the spud carriage and connected on the other second side, to the left of the transverse axis, to the vessel at the other outer end 44. In similar manner a second wire 41 connected to the vessel at a first outer end 43 forms together with discs 34, 31, 38, 39 and 35 a spring means between spud carriage and vessel which acts in the opposite direction.

[0024] The first and second wires are held under bias by respectively a first and second hydraulic cylinder 32, 33 which engage respectively on first tensioning disc 30 and second tensioning disc 31. During the dredging process a ground reaction force F1 is typically exerted on the spud point (see figure 2A), whereby a spud carriage moment M occurs. As a result of this moment the second wire 41 is stretched elastically, while the first wire 40 loses elastic tension. This is further illustrated by the graph in figure 4, wherein the wire load F is plotted as a function of the wire lengthening in range 1, and as a function of the cylinder displacement in range 2. The wire is biased at a force Fv. [weergegeven als Fpre-tens in figuur 4, toevoeging rechtbank] In range 1 the wire behaves elastically, while in range 2 the wire tension (spring force) limiting means ensures that the wire does not stretch further (spring force increases only slowly). Curve C' shows the wire tension of the wire which slackens. The wire tensioning means (see further) ensure that the wire tension does not fall below determined minimum value Fkrit.

[0025] Hydraulic cylinders 32, 33 are both provided with a spring force limiting means, and in this embodiment thus a wire tension limiting means which is shown schematically

in figure 5. The spring force limiting means 50 comprise a piston accumulator constructed from a cylinder with free piston 51 and an accumulator 52. The bottom side of hydraulic cylinder 32 is first brought to the desired pressure, corresponding with the desired bias in

the wire, by means of an accumulator 56. When the tension in the wires has reached a determined maximum which depends on the pressure in the piston accumulator, the free piston and the piston of hydraulic cylinder 32 will then move to the left, and the wire tension is in this way limited. When the great wire tension falls away again, the cylinder springs fully outward under the influence of the piston accumulator.

[0026] (…) The maximum wire tension in wire 40 is a measure for the maximum spud carriage moment M, and this wire tension can thus be controlled by adjusting accumulator 52 of wire tension limiting means 52 to the appropriate pressure. When the maximum allowed wire tension is reached, the piston moves in the direction of the bottom and the spud carriage can rotate through an additional angle under the influence of the spud force moment around the horizontal transverse axis. Owing to this additional tilting of the spud carriage the reaction force of the ground on the spud will be smaller (…)

[0027] When the wire tension increases in one of the wires, for instance second wire 41, the wire tension in first wire 40 will simultaneously decrease. When a wire tension FNOM is reached in second wire 41 (see figure 4), the tension in first wire 40 has fallen to a critical value FKRIT, below which value the first wire 40 becomes slack. In order to avoid this there are provided spring tensioning means, here in particular wire tightening means, in order to maintain a minimum tension in the wire. These consist here of a tensioning plunger 54 which is connected to an accumulator 55. (…)”

Figure 1 (A) is a side view (…) of a cutter suction dredger

Figure 2(A) is a side view (in alongship direction) of a possible embodiment of the apparatus according to the invention

Figure 3 is a schematic view of the wire system

Figure 4 shows a ( schematic ) graph representing the wire tension as a function of the elasticity/2 or of the cylinder displacement

Figure 5 shows a simplified diagram of a wire tension limiting means and wire tightening means

“De werking van dit spelingsvrije systeem is als volgt (figuur 3.4²): De spud (1) is gevat in een bus (2). Deze bus is scharnierend opgehangen in een glijschoen (3), welke door middel van een hydraulische cilinder (4) in het beun gefixeerd is. Het principiële verschil met een paalwagen is dat het moment in plaats van via 2 assen nu via een kruisdraadsysteem naar het ponton wordt doorgeleid. Daartoe zijn 2 x 2 draden zowel aan de bovenkant (A) als aan de onderkant (B) met de bus verbonden. Deze draden lopen over 2 x 4 vast met het ponton verbonden schijven (5). Met behulp van een hydraulische cilinder kunnen de schijven zo ingesteld worden dat de draad er niet uitloopt. (…) Omdat de draden gekruist zijn, wordt bij het verstappen (dat wil zeggen verschuiven van de glijschoen) geen moment via de draden op de spud uitgeoefend.

(…)

Bovenstaand systeem is geïnstalleerd op de Bilberg I (…) door een extra schijf op de beugels te monteren [wordt] een takeleffect bereikt zodat bij een zelfde kracht op de spud de kracht in de draad halveert (figuur 3.5).

(…) Verder wordt elk van de 4 draden (Ø 64 mm) voorgespannen met behulp van een hydraulische cilinder. Daardoor wordt bereikt dat de stijfheid van alle draden meedoen bij een hoekverdraaiing in het langsscheepse vlak. Omdat bij een bepaalde druk in de cilinder de overstort in werking treedt, is de kans op draadbreuk kleiner geworden. (…)

Het is op de 'Bilberg' mogelijk om een drukvat op de cilinder aan te sluiten. Afhankelijk van het luchtvolume ontstaat dan een gasveer met een bepaalde stijfheid. In feite komen dan 3 veren in serie te staan namelijk de gasveer, de draad en de spud. In figuur 3.6 is dit weergegeven.

“(…) Flexibility can also be introduced within the spud carriage construction. An example of such a solution is used on the CSD Ursa (former Bilberg I). On the Ursa flexibility in longitudinal direction is provided by a spud carriage support system of crossed wires and sheaves. A new development is that these wires can be tensioned/adjusted hydraulically. Because of the hydraulic tensioners the system can now act as a (peak) load limiter. When using special wires the (undesired) elasticity of the wires themselves can be minimised”