GB1595513A - Armouring elongate member - Google Patents

Description

(54) ARMOURING ELONGATE MEMBER (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company of 190 Strand, London W.C.2. England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to submarine cables, particularly but no exclusively submarine telecommunication cables.

Conventional submarine cables have been laid in area of fishing activity and in order to protect the cables from damage by fishing equipment, anchors and the like in these shallow waters, it has been normal practice to armour the cable by means of one or two layers of armouring wire according to an assessment of the level of risk in the particular area. The wires have generally been applied with a lefthand lay at an angle in the range 10 to 17 for each layer. Figure 1 of the accompanying drawing shows somewhat schematically a submarine telecommunications cable with a layer of conventional armouring.

In our experience where cables have been armoured in this way but nevertheless a fault occurs owing to damage caused by a trawler, it appears the trawling gear succeeds in hooking one or more of the armour wires, as indicated by the large arrow A.

According to the present invention there is provided a submarine cable having an outer layer of armouring wires wound round the cable to protect it against possible damage from fishing equipment, anchors and the like, the angle of lay of the wires being at least 60 , and a further layer of armouring wires wound round the cable, which further layer is underneath the outer layer and has an angle of lay for its wires not greater than 20 .

In a preferred arrangement the inner layer is applied at an angle, such as 12".

The two layers can be laid up in a contralaid construction or the two layers can both be laid up in the same direction of lay.

In order that the invention can be clearly understood reference will now be made to the remaining figures of the accompanying drawings in which: Figure 2 is a schematic view, similar to that of figure 1, showing an elongate member protected by an outer layer of armouring wires, which outer layer follows the principles of the present invention and Figure 3 shows in cross section a submarine telecommunications cable embodying the invention.

Referring to Figure 2 an elongate member 1 in the form of a submarine telecommunications cable (not shown in greater detail) is protected by an outer layer of armouring wires 2 wound with an angle of lay of at least 60". The layer of wires comprises a group 3 of wires wound simultaneously in the fashion of a multi-start thread. As shown by the large arrow B, fishing equipment or an anchor (not shown) can strike the armouring wires but is much less likely to spring a gap between adjacent armouring wires than with the conventional angle of lay indicated in Figure 1.

The arrangement described with reference to Fig. 2 would have a cable construction as shown in Fig. 3 (to be described below), except that the central strength member would preferably have high tensile steel wires which would provide a greater tensile strength.

Referring now to Figure 3 a submarine telecommunications cable comprises a central strength member 10 comprising a number of mild steel wires and an inner conductor 1 formed of conductive material, such as copper. This is surrounded by a ployethylene dielectric layer 12 which is extruded around the central strength member and inner conductor. An outer conductor 13, of for example copper, surrounds the dielectric material 12 and this in turn is surrounded by a sheath 14 of polyethylene. Around the sheath 14 is provided a layer of fibrillated polypropylene yarn 15 which is wound around the extruded sheath 14 and provides a "bedding" for the subsequent layers of armouring wires, which bedding layer is thus softer than the sheath 14.

On to the bedding the first layer of armouring wires 16 is applied with a lay of approximately 12". This angle is not critical but is less than or equal to 20 . The wires are galvanised steel. On top of the layer 16 is wound a second layer 17 comprising similar galvanised steel wires but this time with an angle of lay of at least 60". Although not shown it would be possible to have an intermediate bedding layer between the layers 16 and 17.

The two layers 16 and 17 are shown laid up in a contra-laid construction but it would be possible for both layers to have the same direction of lay, the inner layer having a small angle of lay less than 20 and the outer layer having the large angle of lay, 60 or more.

Such an armoured cable is semi-flexible, that is to say it would be required to pass around a bow sheave having a diameter not less than 6 feet of a cable-laying ship without damage to the electrical conductors. The tensile strength of the cable is provided both by the central strength member and the armouring wires. The central member would have a breaking strength of about 2 tons, and the armoured cable would be able to withstand a load of about 21 tons ignoring the contribution to the tensile strength made by the outer armouring layer. This strength of 21 tons is provided by inner armouring wires having a diameter of 0.192". It could be larger or smaller depending on the size of the wires. The outer layer in the embodiment described comprises wires having a diameter of 0.300".Thus in both Figs. 2 and 3 the outer armouring layer contributes little if any tensile strength to the armoured cable. In Fig. 2 the tensile strength would be provided wholly by the central strength member and in Fig. 3 the inner armouring layer provides the majority of the tensile strength.

It would be possible in a modification of the Fig. 3 embodiment, for the central strength member to be formed of high tensile wires.

Even under these circumstances the inner armouring layer would contribute significantly more tensile strength to the armoured cable than would the central strength member.

Our tests indicate that where the outer layer of wires has a lay of 60 or more it is less prone to being snagged by a ship's anchor or fishing gear and is thus better able to protect the inner cable from damage by such gear. The area of greatest risk are in relatively shallow waters, for example on the continental shelf around Europe, in the English Channel and in the North Sea. In deeper waters armouring wires are not required on submarine cables because the risk of damage at the depths encountered is remote.

WHAT WE CLAIM IS: 1. A submarine cable having an outer layer of armouring wires wound round the cable to protect it against possible damage from fishing equipment, anchors and the like, the angle of lay of the wires being at least 60 , and a further layer of armouring wires wound round the cable, which further layer is underneath the outer layer and has an angle of lay for its wires not greater than 20 .

2. A submarine cable as claimed in claim 1, wherein the directions of lay of the outer and the further layers are the same.

3. A submarine cable as claimed in claim 1, wherein the directions of lay of the outer and the further layers are opposite to one another.

4. A submarine cable as claimed in claim 1, 2 or 3, and which has a plastics sheath surrounded by said layers of armouring wires, there being a bedding layer of material softer than the plastics sheath between the armouring wires and the sheath.

5. A submarine cable as claimed in claim 1,2, 3 or 4, and which is of coaxial construction, having inner and outer electrical conductors.

6. A submarine cable having an inner cylindrical electrical conductor formed by a tube which encloses a central strength member, a dielectric layer overlying said tube, an outer cylindrical electrical conductor overlaying said dielectric layer, a sheath of a plastics material overlaying the outer conductor, a bedding layer of a softer material than that used for said sheath overlying said sheath, a first layer of armouring wires wound over said bedding layer with an angle of lay of its wires not greater than 20 , and a second layer of armouring wires wound over said first layer of armouring wires with an angle of lay of its wires of at least 60 , which second layer of armouring wires protects the cable against possible damage from fishing equipment, anchors and the like.

7. A submarine cable as claimed in claim 6, wherein the directions of lay of the first and the second layers of armouring wire are the same.

8. A submarine cable as claimed in claim 6, wherein the directions of lay of the first and the second layers of armouring wires are opposite to one another.

8. A submarine cable as claimed in claim 6, wherein the directions of lay of the first and the second layers of armouring wires are opposite to one another.

9. A submarine cable substantially as described with reference to Fig. 3 of the accompanying drawings.

10. A method of protecting a submarine cable from the deleterious effect of fouling by fishing equipment, anchors and the like, which includes applying two armouring layers to the cable, the inner layer of which consists of armouring wires wound about the cable with an angle of lay not greater than 20

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. wires, which bedding layer is thus softer than the sheath 14. On to the bedding the first layer of armouring wires 16 is applied with a lay of approximately 12". This angle is not critical but is less than or equal to 20 . The wires are galvanised steel. On top of the layer 16 is wound a second layer 17 comprising similar galvanised steel wires but this time with an angle of lay of at least 60". Although not shown it would be possible to have an intermediate bedding layer between the layers 16 and 17. The two layers 16 and 17 are shown laid up in a contra-laid construction but it would be possible for both layers to have the same direction of lay, the inner layer having a small angle of lay less than 20 and the outer layer having the large angle of lay, 60 or more. Such an armoured cable is semi-flexible, that is to say it would be required to pass around a bow sheave having a diameter not less than 6 feet of a cable-laying ship without damage to the electrical conductors. The tensile strength of the cable is provided both by the central strength member and the armouring wires. The central member would have a breaking strength of about 2 tons, and the armoured cable would be able to withstand a load of about 21 tons ignoring the contribution to the tensile strength made by the outer armouring layer. This strength of 21 tons is provided by inner armouring wires having a diameter of 0.192". It could be larger or smaller depending on the size of the wires. The outer layer in the embodiment described comprises wires having a diameter of 0.300".Thus in both Figs. 2 and 3 the outer armouring layer contributes little if any tensile strength to the armoured cable. In Fig. 2 the tensile strength would be provided wholly by the central strength member and in Fig. 3 the inner armouring layer provides the majority of the tensile strength. It would be possible in a modification of the Fig. 3 embodiment, for the central strength member to be formed of high tensile wires. Even under these circumstances the inner armouring layer would contribute significantly more tensile strength to the armoured cable than would the central strength member. Our tests indicate that where the outer layer of wires has a lay of 60 or more it is less prone to being snagged by a ship's anchor or fishing gear and is thus better able to protect the inner cable from damage by such gear. The area of greatest risk are in relatively shallow waters, for example on the continental shelf around Europe, in the English Channel and in the North Sea. In deeper waters armouring wires are not required on submarine cables because the risk of damage at the depths encountered is remote. WHAT WE CLAIM IS:

1. A submarine cable having an outer layer of armouring wires wound round the cable to protect it against possible damage from fishing equipment, anchors and the like, the angle of lay of the wires being at least 60 , and a further layer of armouring wires wound round the cable, which further layer is underneath the outer layer and has an angle of lay for its wires not greater than 20 .

2. A submarine cable as claimed in claim 1, wherein the directions of lay of the outer and the further layers are the same.

3. A submarine cable as claimed in claim 1, wherein the directions of lay of the outer and the further layers are opposite to one another.

4. A submarine cable as claimed in claim 1, 2 or 3, and which has a plastics sheath surrounded by said layers of armouring wires, there being a bedding layer of material softer than the plastics sheath between the armouring wires and the sheath.

5. A submarine cable as claimed in claim 1,2, 3 or 4, and which is of coaxial construction, having inner and outer electrical conductors.

6. A submarine cable having an inner cylindrical electrical conductor formed by a tube which encloses a central strength member, a dielectric layer overlying said tube, an outer cylindrical electrical conductor overlaying said dielectric layer, a sheath of a plastics material overlaying the outer conductor, a bedding layer of a softer material than that used for said sheath overlying said sheath, a first layer of armouring wires wound over said bedding layer with an angle of lay of its wires not greater than 20 , and a second layer of armouring wires wound over said first layer of armouring wires with an angle of lay of its wires of at least 60 , which second layer of armouring wires protects the cable against possible damage from fishing equipment, anchors and the like.

7. A submarine cable as claimed in claim 6, wherein the directions of lay of the first and the second layers of armouring wire are the same.

8. A submarine cable as claimed in claim 6, wherein the directions of lay of the first and the second layers of armouring wires are opposite to one another.

8. A submarine cable as claimed in claim 6, wherein the directions of lay of the first and the second layers of armouring wires are opposite to one another.

9. A submarine cable substantially as described with reference to Fig. 3 of the accompanying drawings.

10. A method of protecting a submarine cable from the deleterious effect of fouling by fishing equipment, anchors and the like, which includes applying two armouring layers to the cable, the inner layer of which consists of armouring wires wound about the cable with an angle of lay not greater than 20

and the outer layer of which consists of armouring wires wound about the cable with an angle of lay of at least 600.