GB2062064A

GB2062064A - Ditching Machine

Info

Publication number: GB2062064A
Application number: GB7937742A
Authority: GB
Original assignee: EZOE T; SUDA SEISKAKUSHO CO Ltd
Current assignee: EZOE T; SUDA SEISKAKUSHO CO Ltd
Priority date: 1979-10-31
Filing date: 1979-10-31
Publication date: 1981-05-20
Also published as: GB2062064B

Abstract

A ditching machine for digging a ditch or a trench for submarine cables has several blades 51-57 disposed longitudinally along a centre body 2. The lower part of each blade serves as a digging portion which digs soil, and the wider upper part serves as a soil pushing portion which pushes away the soil thus dug substantially horizontally in a direction lateral to the moving direction of the ditching machine. The opposite ends of the soil pushing portions of the forward-most blades 51-56 are slanted to the vertical so as to slope outwardly in an upward direction so as to assist in pushing the excavated soil clear of the trench. In addition, the centre body has a plurality of small holes at the bottom to allow water to flow into the region at the rear of each blade, thus assisting in preventing the excavated soil from falling back into the trench and thus considerably reducing the towing tension in the towing wire between the ditching machine and the cable ship. <IMAGE>

Description

SPECIFICATION Ditching Machine This invention relates to ditching machines or trenchers, used for burying submarine cables or the like in the sea bed and/or for exposing them at the surface of the sea bed, and more particularly to an improvement in the blades of a multi-blade ditching machine.

To protect submarine cables or the like from fishing equipment, it has been the practice in many countries of the world to bury the cables or the like in the sea bed and to expose such buried cables or the like for repair in case of faults by digging a ditch. For this purpose, ditching machines which dig the soil or sediment of the sea bed to a desired depth have been used, and such ditching machines are called cable buriers or cable searchers, depending on the purpose thereof.

Although the structure of the cable buriers is somewhat different from that of the cable searchers due to the difference in their purposes, the essential ditching portions of both the cable buriers and cable searchers are similar to each other, and include water jets or ploughs for digging trenches in the sea bed. Conventionally, two types of ditching machines with ploughs have been used, i.e. single blade type and multi-blade type ditching machines. The present invention relates to this latter type.

In order to facilitate understanding of the present invention, a prior plough type multiblade ditching machine or trencher will be described in accordance with Figures 1 to 4 of the accompanying drawings, this construction also being shown in U.S. patent No. 4,053,998 and U.K. patent No. 1,477,815.

Figure 1 shows a cable ship 105 in the process of laying a submarine cable. In the Figure, the reference numeral 100 shows a ditching machine or a trencher, 101 is the sea bed, 102 is the trench thus dug, 103 is the communication cable to be laid, 104 is a wire for towing the trencher by the cable ship and 106 is the surface of the sea.

As the ship 105 tows the trencher 100 by the towing wire 104, the trench 102 is opened up in the sea bed and the cable 103 is laid and buried in the trench.

Figures 2 and 3 show the prior ditching machine, and Figure 4 is a schematic diagram illustrating the relation between the blade arrangement of the ditching machine in Figures 2 and 3. In Figures 2 and 3, the reference numeral 1 is a stabilising wing, 2 is a centre body, 2a is a side plate connected to the centre body, 3 is a joint between the stabilising wing and the centre body and Si to 5n are blades for digging a trench and pushing away the ditched soil. In the embodiment shown in Figures 2 and 3, there are seven blades and thus n=7.Also the reference numeral 6 is a towing wire (corresponding to 104 in Figure 1), 7 are cable inlets, 8 is the bottom of the trench thus dug, 9 is a cable to be buried, 10 is a communication repeater inserted between the cables, 13 is the rotational axis of a pushing roller, 1 4 is the frame of a pushing roller, 1 5 is the pushing roller, 1 8 is a second small roller, 1 9 is a tail roller, and 20 is a guide for the pushing roller 15.

The ditching machine or the trencher shown in Figures 2 and 3 is towed by the cable ship by the towing wire 6, and digs the sea bed to a depth H from a level S, to a level S2, utilising the blades 51 to 5n The cable and the repeaters paid out from the work ship are laid in the trench thus dug through the centre body 2 of the trencher. The stabilising wing 1 of the trencher functions to stabilise the attitude of the trencher on the sea bed and the pushing roller 1 5 pushes the cable to the bottom of the trench by the weight of the roller 1 5 itself. So the cable is led off through the path between the pushing roller 1 5 and the second small roller 1 8 to the trench bottom 8.

The tail roller 1 9 is utilised when a cable is not buried but is merely laid on the sea bed. In that case, the ditching machine is lifted onto the deck of the cable ship and is arranged upside down on the deck of the ship. The cable 9 is taken off through the tail roller 1 9 to the sea bed.

Figure 4 shows the front view of the arrangement of the blades Si to 5n and for simplicity in explanation only the right halves of the blades are shown in the drawing, the left halves of the blades being, of course, symmetrical with the right halves. At first, the first blade 5,((1)^(1)) digs the wide (width W,) and shallow (depth d,) trench, which is deepened by the succeeding blades 52 to 5n When the last blade 57 passes along the trench, the trench has the width W, and the depth (d1 +d2+d3+d4+d5+d0+d7).

It should be understood in Figure 4 that the actual digging of the trench is accomplished by the ditching portion at the centre of the blades and the excavated soil is placed on the outer edge of the trench thus dug by the soil pushing portion at the top of each blade.

However, the prior ditching machine shown in Figures 2 to 4 has the disadvantage that the excavated soil has the tendency to fall back again into the trench which has just been dug, because of the shape of each blade and the low pressure generated behind each blade. Moreover, the tension in the towing wire becomes extremely high and increased towing power of the cable ship is required.

It is therefore an object of the present invention to overcome the disadvantages and limitations just described of the prior type of ditching machine, that is to say a multi-blade ditching machine comprising a stabilising wing flexibly connected to an elongated hollow centre body so as to be capable of movement in a vertical direction, the centre body also having a series of blades extending from it at intervals, the blades towards the rear of the machine having a greater vertical length and smaller horizontal extent than those towards the forward end and being capable of digging more deeply and more narrowly, at least two of the forward most of the blades having a portion or portions for digging soil and a portion or portions above the digging portion or portions for pushing the soil substantially horizontally in a direction lateral to the direction of movement of the machine, the soil pushing portion or portions having a greater horizontal width than the digging portion or portions as seen from the front of the machine when the machine is in a normal operating position.

According to the present invention, at least a part of each of the opposite ends of the soil pushing portion or portions of at least one blade is slanted to the vertical, so as to slope outwardly in an upward direction. This assists in pushing the excavated soil clear of the trench and by reducing the amount of soil falling back reduces the towing tension correspondingly.

The invention will now be described in more detail, with reference to the accompanying drawings, in which: Figure 1 is an explanatory diagram of the laying of a cable in a trench; Figure 2 is a vertical view of a prior ditching machine; Figure 3 is a plan view of the ditching machine of Figure 2; Figure 4 is a schematic diagram illustrating the relation between the blade arrangement of the conventional ditching machine shown in Figures 2 and 3; Figure 5 is an elevation of a ditching machine according to the present invention; Figure 6 is a plan view of the ditching machine shown in Figure 5; Figure 7 is a schematic diagram illustrating the relation between the blade arrangement of the ditching machine of Figures 5 and 6; Figure 8 shows separately each blade shown in Figure 7 as seen from the front; and Figure 9 is a cross sectional view on the line A-A of Figure 6.

Figures 1 to 4, which illustrate the prior construction of machine have already been described. The improved machine according to the invention is illustrated in Figures 5 to 9. In those Figures, the same reference numerals as in Figures 1 to 4 indicate corresponding parts.

Figures 5 and 6 show a caster 21, which facilitates the transportation of the ditching machine on the deck of the cable ship, which lowers the ditching machine to and lifts it from the sea bed.

As in the previous construction, the stabilising wing 1 provides the horizontal positioning of the ditching machine. The elongated hollow centre body 2 is jointed to the wing 1 so that the wing can bend up and down at the coupling point. A number of pairs of blades 51 to 5n are disposed along the centre body 2 at predetermined intervals. The blades such as 56 or S7, which are positioned at the rear portion of the ditching machine, have a greater vertical length and smaller horizontal extent transverse to the direction of movement than the more forwardly disposed blades such as 51 or 52 and the blades are adapted to dig more deeply with narrower ditching widths.At least the two forward most of the blades have a digging portion (see A in Figure 8) for digging soil and a soil pushing portion (see B in Figure 8) for pushing the soil substantially horizontally in a direction lateral to the direction of movement of the ditching machine. As apparent from the drawings, each soil pushing portion is above a corresponding digging portion and has a wider horizontal width as seen from the front of the ditching machine than that of the corresponding digging portion when the ditching machine is in a normal operating position. As illustrated, all the blades 51 to 57 have both a digging portion (A) and a soil pushing portion (B) as shown in Figure 8.In addition, the blades 5, to s have a portion shaded as shown in Figure 8 at the extreme end of each soil pushing portion B, the side end of the shaded portion being cut slantwise, that is to say at an angle to the vertical, which is one of the features of the present invention.

In Figure 8, with reference to blades 5t,52 5,, 53 and 54, the dotted line in the portion (B) shows the line of the surface of the sea bed. Accordingly, the soil dug by the blades 5, to 53 is put on the surface of the sea bed, the soil dug by the blade 54 is put on both the surface of the sea bed and at the edge of the trench thus dug and the soil dug by the blades 55 to 57 is put at the edge of the trench which is dug by the preceding blades.

In operation, the digging portions of the blades dig a trench as the ditching machine is dragged along by the towing wire from the cable ship, and the soil thus dug is pushed away horizontally in a direction lateral to the direction of movement of the ditching machine.

As mentioned above, at least a part of the side edge of the soil pushing portion of each blade is slanted in relation to the vertical line so that a pair of side edges slope outwardly in an upward direction. In the example, the side edges T, to T8 of the blades 5, to 58 are cut slantwise. The angles 0, to fl between the edges T, to Tis and the vertical are preferably approximately the same as the angle of repose of the excavated soil, which is the necessary angle to prevent the soil from slipping. The edge of the rear most blade 57 is not cut slantwise. Accordingly, the front view of each soil pushing portion is of approximately trapezoid shape.

It should be noted that the amount of the soil dug by the forward blade and slipped into the space made by the rear blade is decreased as the angle o is increased. Thus the larger the angle 0, the better for preventing the slipping of the soil.

However, an angle of approximately 40 degrees is sufficiently large. If the angles O or 06 of the rear blades is large, the width of the ditching machine itself is increased to an undesirable extent.

Accordingly, in the preferred construction, the angles are designed so that 0, to 04 are 400, and 05 and 0e are 20 . With the above angles of slant, the towing tension can be reduced to two thirds of that of a prior ditching machine, while keeping a small width of a ditching machine.

On the other hand, in the prior ditching machine shown in Figures 1 to 4, the corresponding edges (V, to V7 in Figure 4) are vertical in the front view when the ditching machine is in a normal operating position, and so the soil excavated and pushed away by the forward blade drops back into the trench, and the trench just dug is covered up. Further the dropped soil is again dug by the succeeding blades and the load of the trencher is therefore increased.

Although Figures 5 to 9 shows the edges of the blades 5, to 5 as slanted, it should be noted that an improvement is obtained even if the edge of only one blade is cut slantwise.

Another feature of the invention is the provision of a number of small holes (h) at the bottom of the centre body towards the back of each blade. The effect of these holes is as follows.

When a prior form of ditching machine is in operation, the area to the rear of each blade experiences a low pressure or vacuum condition.

The low pressure increases the towing tension of the cable ship, prevents the soil from being pushed away by the blade, and further drops the soil excavated by the preceding blades. In a construction according to the present invention, sea water is able to flow through the small holes (h) in the centre body to the back region of each blade, as a result of which the low pressure or vacuum condition at the rear of each blade is eliminated, so that the increase of tension on the towing wire is prevented and the falling down of the excavated soil is prevented. The water flowing through the holes enters the centre body through the opening of the joint 3, and it should be noted that the holes are provided so that the water is released after the water is introduced near the rear region of the digging portion of the preceding blade. It has been found experimentally that the optimum area of each hole (h) is 50 cm2.

A modification in the provision of the small holes is possible. For instance, the hole can be provided in each blade itself instead of in the centre body. In that case, water at the front of a blade is passed through the small hole to the back of the blade.

The improved construction just described may be used not only for ditching machines for submarine communication cables, but also for any multi-bladed ditching machine.

Claims

1. A multi-blade ditching machine of the type described, in which at least a part of each of the opposite ends of the soil pushing portion or portions of at least one blade is slanted to the vertical so as to slope outwardly in an upward direction.

2. A multi-blade ditching machine according to claim 1, having seven blades, all of which except the rearmost have a soil pushing portion or portions.

3. A multi-blade ditching machine according to claim 1 or claim 2, wherein holes are provided for the flow of water into the region of the rear of each blade.

4. A multi-blade ditching machine according to claim 3 in which the holes are formed at the bottom of the centre body.

5. A multi-blade ditching machine substantially as described and as illustrated with reference to Figures 5 to 9 of the accompanying drawings.