Pipeline or cable plough

The plough consists of two portions separable by rams (72). Each portion comprises a beam (14, 16) joined to a plough body part (18, 20). The portions include two pairs of longitudinally-spaced arms (69) interconnected by pivots (70). At each end of the plough a support including bearers (61) is closed by a ram (59) to entrap the pipeline (26). Another ram lifts the support to raise the pipeline between the plough body parts (18, 20). The support ram is connected to a pressurized accumulator so that the support rollers (62) are kept against the pipeline (26) as the plough rises and falls and pitches. The elevated positions of the arms (69) and the relatively short separation between the two pairs of arms (69) allows the plough to descend and pitch relatively to the pipeline. In a modification the two beams are joined by rigid bridging structure and the plough body parts are pivotally connected to their respective beams. In other modifications the supports are dispensed with; or only one is used.

CROSS-REFERENCE TO RELATED APPLICATIONS 
Reference may be made to our U.S. patent applications Ser. No. 677,025 (now 
U.S. Pat. No. 4,585,372) and Ser. No. 809,268 assigned to Soil Machine 
Dynamics Limited disclosing ploughs having features of construction 
similar to those disclosed herein. 
BACKGROUND OF THE INVENTION 
The invention relates to ploughs for entrenching pipelines, cables or the 
like, for example in the bed of a body of water. 
A plough is described in British Pat. No. 2,017,785 in which two separate 
plough body shares are connected to respective beams. The beams are 
connected at their forward ends about vertical pivot axes to structure 
extending across the pipeline. The pivots allow the beams and shares to be 
moved apart to allow the pipeline to pass between the shares, after which 
the shares are brought together beneath the pipeline. 
Another type of plough is known having a main chassis frame which extends 
across the pipeline. Two plough body shares are each pivotally connected 
to the frame and angularly separate to allow the pipeline to pass between 
them. 
Those ploughs have the disadvantage that pitching and downward movements of 
the plough relative to the pipeline impose large and damaging loads on the 
pipeline by impact with the structure or chassis frame extending across 
the pipeline. 
SUMMARY OF THE INVENTION 
The objects of the invention is to provide a plough in which that 
disadvantage is reduced or eliminated. 
In this specification hereinafter a pipeline, cable or other elongate 
construction to be entrenched is referred to by the term "pipeline" for 
convenience. 
A plough for entrenching a pipeline according to the invention comprises 
first and second portions each including a plough body part and an 
elongate chassis component extending ahead of said plough body part, said 
portions being connected by bridging structure extending above said 
chassis components across said pipeline, said plough body parts being 
separable to allow said pipeline to pass between said parts and said 
bridging structure being positioned and dimensioned to allow downward and 
pitching movements of the plough relative to said pipeline. 
In one embodiment of plough said bridging structure comprises first and 
second parts joined to said first and second portions respectively and 
interconnected by pivot means defining an axis parallel to the lengthwise 
direction of the plough about which said portions are angularly separable.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIGS. 1 to 6 show a plough comprising two portions 10, 12 extending 
side-by-side lengthwise of the plough. The portions 10, 12 include 
respective elongate chassis components 14, 16 in the form of beams joined 
to respective parts 18, 20 of a plough body. The two portions 10, 12 are 
interconnected by bridging structure in the form of one or preferably (as 
shown) two pairs of arms 22, 24. The plough is shown in FIGS. 1 and 2 
straddling a pipeline 26 already laid on the seabed 28. The plough opens a 
trench 30 into which the pipeline 26 lowers as the plough advances beneath 
the pipeline 26, which rises from the seabed 28 as the plough approaches. 
The depth at which the plough body 18, 20 works is determined by the 
setting of two skids 32, each connected at a horizontal pivot 33 to a 
respective arm 34. Each arm 34 is connected at a horizontal pivot 36 to a 
respective chassis beam 14, 16. Each arm is adjustable by a hydraulic ram 
37 connected at a horizontal pivot 38 to the respective arm 34 and 
connected at another horizontal pivot (not shown) to the respective beam 
14, 16. 
Each beam 14, 16 carries a respective rotary disc cutter 39 mounted on an 
arm 40 adjustable by a hydraulic ram 41. The cutters 39 are mutually 
inclined so as to cut slits in the ground ahead of the plough body 18, 20 
in V relationship. 
The plough is hauled along the seabed by a tow cable 42 extending from a 
surface vessel (not shown) to a bridle 43, the ends of which are connected 
to the ends of respective arms 44 connected at vertical pivots 45 to 
respective beams 14, 16. The arms 44 are pivotally connected by links 46 
to bell-cranks 47 mounted at vertical pivots 48 on the leading arms 22. 
The bell-cranks 47 are pivotally interconnected by a link 49. The arms 44 
can be turned by respective hydraulic rams 50. 
The plough can be steered by operation of the rams 50 which causes a couple 
to act on the plough in the horizontal plane. When the rams operate the 
apex of the bridle 43 describes an arc centred at 51 adjacent the centre 
of ground forces (as seen in plan) acting on the plough body. This 
minimises the forces required to steer the plough by operation of the rams 
50. 
Alternatively, the rams 50 can be locked at fixed lengths and the plough 
steered by change of course of the towing vessel. As a further alternative 
the rams 50 are allowed to change length freely, the plough being guided 
by the pipeline 26 which engages rollers on supports to be described next 
below. 
There are two similar supports mounted at respective horizontal pivots 51 
at opposite ends of the beams 14, 16. Each support comprises two arms 52 
pivotally connected to the pivots 51 and adjustable up and down by 
hydraulic rams 53. Each support also comprises two further arms 54. The 
arms 52 are linked by a crosspiece 55 (FIG. 3). 
The arms 52, 54 support two carriers 56, 57, which have inwardly-directed 
brackets 58 inter-connected by a hydraulic ram 59 (FIG. 3). 
The carriers 56, 57 each terminate at their lower ends in tapered, 
inwardly-directed bearers 60, 61 carrying rollers 62. The carriers carry 
further rollers 63. 
The beams 14, 16 carry further rollers 64. 
Each portion 10, 12 of the plough comprises two arms 69, one from each pair 
of arms forming the mechanism 22, 24. The arms 69 extend inwardly from the 
top margins of the beams 14, 16 and are joined at their upper ends by a 
horizontal pivot pin 70 (FIG. 3). The pins 70 of the two pairs of arms 22, 
24 are coaxial. The arms 69 have upper extension limbs 71 pivotally 
interconnected by respective hydraulic rams 72. Each pair of arms 22, 24 
carries a respective horizontal roller 73 (FIGS. 1 and 2). 
OPERATION 
The pipeline 26 is laid on the seabed 28 by a lay barge, for example. The 
plough is lowered from a surface vessel on, for example, four wires or a 
four-wire sling attached to the "corner" extremities of the plough, which 
is in open configuration. That is to say, the rams 72 are both retracted 
so as to pull together the limbs 71 and so separate the arms in each pair 
22, 24. The open configuration of the plough, so produced, is shown in 
FIG. 3. Also, the rams 59 are extended so as to separate the carriers 56, 
57 as shown in FIG. 3. 
The rams 53 are retracted to position the arms 52, 54 in their lowermost 
positions. The plough is lowered over the pipeline 26 and the lower edges 
of the separated beams 14, 16, the plough body parts 18, 20 and the 
bearers 60, 61 assume positions on the seabed 28 on opposite sides of the 
pipeline. 
The rams 37 are extended fully to lower the skids 32 fully to the positions 
shown in FIGS. 3 to 5. 
Note that the skids 32 rest on the seabed 28 in canted positions. 
The pipeline 26 is next picked up from the seabed. One preferred mode of 
operation is to raise the skids 32 so that the front of the plough is 
lowered. Next the rams 59 of the front support are retracted by remote 
operation from the surface vessel. The bearers 60, 61 are forced together 
and overlap beneath the pipeline 26, which is thus entrapped within the 
carriers 56, 57 and rests on the rollers 62. The skids 32 can be lowered 
again and the rear support can be engaged similarly with the pipeline 26. 
Next, the rams 53 are extended by remote control to raise the supports at 
the ends of the beams 14, 16, to the position shown in FIG. 4. Then, the 
rams 72 are extended by remote control to force the arms in each pair 22, 
24 together and to close the beams 14, 16 and plough body parts 18, 20 
together in the position shown in FIG. 5. The skids 32 are now level on 
the seabed 28. 
In the closed position, the beams 14, 16 engage each other at their lower 
longitudinal margins. It is preferred that the beams are locked together 
by locks to give optimum strength in the chassis structure. The upper 
longitudinal margins are relieved so that the beams form a trough which 
extend lengthwise of the plough and which receives the pipeline, supported 
on the rollers 64 if necessary. 
The plough can now be advanced into the seabed 28, the rams 37 being 
retracted by remote control to raise the skids 32 so that the plough body 
18, 20 is caused to bite downwardly into the seabed. The depth of working 
of the plough is determined by the setting of the skids 32. 
The plough is now advanced along the pipeline 26 for form the trench 30. As 
shown the trench 30 is just deep enough to accommodate the pipeline which 
in this case is typically some 1016 millimeters (40 inches) in diameter 
(FIG. 1). The two plough body parts 18, 20 are forced together by ground 
forces as the plough advances and the rams 72 also assist in keeping the 
plough closed. Also, the tensions in the bridle 43 counteract the tendency 
of ground forces on the skids 32 to open the plough. 
As the plough operates, it is caused to move up and down, and to pitch, 
relatively to the pipeline 26. When the plough pitches, it turns in a 
vertical plane so as to change its inclination. Pitching may occur in 
either rotary sense. The generous clearance between the top of the 
pipeline and the arms 22, 24 allows such pitching movements to occur 
without impact between the plough and the pipeline. Also, the elevated 
structure formed by the pairs of arms 22, 24 occupies considerably less 
than the overall length of the beams 14, 16 so that the ends of the beams 
can freely move up and down against the median level of the pipeline. 
The arms 69 are subjected during ploughing to only relatively low forces. 
The applied towing force is transmitted directly through the beams 14, 16 
to the plough body 18, 20. Since the forces are low, the arms 69 can be 
quite highly elevated to allow generous clearance above the pipeline and 
the mechanism formed by the arms 69 occupies quite a short overall length 
of the beams 14, 16 allowing generous clearance for pitching. The beams 
14, 16 occupy low positions and are therefore subject to minimal bending 
loads. By contrast in the known ploughs previously mentioned considerable 
loads are imposed on the bridging structure which is required to transmit 
at least a major proportion of the applied towing force, or the large 
resulting bending moment. 
The supports at the ends of the beams 14, 16, although not essential, are 
preferred for use with at least larger pipelines. Each ram 53 is connected 
to a hydraulic accumulator containing gas under pressure so that as the 
plough rises and falls or pitches the rams 53 can maintain the rollers 62 
in supporting engagement with the pipeline as the rams extend or retract 
automatically to allow the arms 52, 54 to rise and fall to accommodate the 
plough's movements. 
The pivot connections between the bell-cranks 47 and the link 49; the 
mountings of the rollers 73; and the pivot connections 51 and between the 
arms 52, 54 and the remainder of the support assemblies are such as to 
allow the separation of the beams 14, 16 when the rams 72 retract. 
MODIFICATIONS 
Some examples of modifications are: 
(a) the two portions of the plough may be moved to the pipeline separately, 
assembled together and connected by for example pins similar to the pins 
70, preferably together with additional fastening means, for example 
interconnecting the plough body parts; 
(b) the two portions of the plough are interconnected by mechanism other 
than the arms 69; for example links or slide mechanism; 
(c) one or both of the supports at the ends of the beams 14, 16 is or are 
dispensed with; or the or each support is placed on the beam at a position 
different from that shown; 
(d) the adjustable steering mechanism is dispensed with and the bridle or 
tow wire is connected directly to the plough; 
(e) the two portions 10, 12 instead of being similar may be dissimilar. For 
example, as seen in elevation the plough body parts may abut one another, 
when closed, at a plane or other surface offset from the central vertical 
plane, for example at a plane downwardly diverging from the vertical. 
(f) the two portions may be lowered from the sea surface on wires which 
pull the portions 10, 12 apart, the portions being forced together without 
ram action by ground forces when the plough is hauled forwardly. 
FIG. 6 shows the plough pitching forwadly relatively to the pipeline 26 as 
the leading point of the plough body 18, 20 is forced to ride up out of 
the trench 30 upon encountering a large boulder 80. The upper inner 
boundary of the leading pair of arms 22 of the bridging structure is the 
leading roller 73, which has moved downwardly relatively to the pipeline 
26. The roller 73 may engage the top of the pipeline 26, as shown, in 
extreme pitching. 
The pipeline 26 continues to be supported by the bearers 60, 61. Their 
rollers 62 are kept in engagement with the pipeline by the hydraulic 
accumulators connected to the rams 53, one of which pushes the leading 
parallel linkage 52, 54 upwards and the other of which yields as the 
trailing linkage is forced downwards by the pipeline 26. For example, the 
angle of pitching allowed by the pitching of the bridging structure 22, 
24, preferably in the central third of the length of the beams 14, 16, may 
be plus or minus nine degrees away from the horizontal. The downward 
movement of the plough relative to the pipeline is, for example, one metre 
or more. As great a pitching angle and as great a downward movement as 
possible are preferable. 
The condition shown in FIG. 6 is usually the most serious encountered. 
Undulating ground causes up and down movement and pitching. Soft ground 
causes the plough to sink and without the downward movement relative to 
the pipeline allowed by the bridging structure as provided by the 
invention, the plough can "hang" on the pipeline so that the plough's 
weight imposes high stress and load on the pipeline. Without the relative 
pitching movement of the plough allowed by the invention, the effects of 
boulders or rocks or undulating ground would also cause high loads, 
stresses, impacts and bending moments on both the plough and the pipeline. 
Any of those effects can damage the pipeline or its concrete, epoxy resin 
or other coating. All of those effects are caused when known ploughs 
operate. 
FIGS. 7 and 8 show a second embodiment in which many of the parts are the 
same as those already described. However, instead of pivotally connected 
arms, the two portions of the plough are rigidly connected to bridging 
structure 100 preferably in the central third of the two beams 102, 104. 
The forwad ends of the beams 102, 104 no longer meet each other at their 
lowest margins. However the plough body parts 18, 20 do meet as before to 
exclude loose rocks from entering the pipeline channel 106 within the 
plough. The mounting of the supports, the rollers 73 and the arms 47 are 
simplified since the beams 14, 16 are relatively immovable. 
The bridging structure 100 is a single structure having an inner surface 
108 bounding the roof of the structure. 
Each plough body part 18, 20 is pivotally connected to its respective beam 
102, 104 by two hinge assemblies 110 defining a pivot axis 112 parallel to 
the lengthwise direction of the plough. Each part 18, 20 has a respective 
hydraulic ram 114 operable to move the part about its axis 112 to separate 
the plough body parts to allow the pipeline 26 to pass between them. 
As with the first embodiment when the plough is to be separated from the 
pipeline, it is brought out of work by lowering the skids 32 as the plough 
comes to a halt. This brings the plough body out of the ground. The rams 
114 are operated to separate the parts 18, 20. After a check to ensure 
that the parts are clear of the pipeline 26 the plough is lifted clear on 
a three-wire sling as indicated at 116. The hoist cable is connected to 
the sling at 118. Should the hydraulics fail, the hoist can pull the body 
parts 18, 20 apart to clear the plough from the pipeline. The first 
embodiment can also be operated, and opened by the hoist in the event of 
hydraulic failure, in a similar manner.