CA1326743C

CA1326743C - Metal sleeve securement to metal cable

Info

Publication number: CA1326743C
Application number: CA000554429A
Authority: CA
Inventors: H. Nicolas Weyman
Original assignee: Minister of National Defence of Canada
Current assignee: Minister of National Defence of Canada
Priority date: 1987-12-10
Filing date: 1987-12-10
Publication date: 1994-02-08
Anticipated expiration: 2011-02-08

Abstract

ABSTRACT

A multi-strand metal cable having a metal sleeve secured thereto, comprising a rough surfaced metal friction layer bonded to a selected axial section of the surface of the cable, a layer of compliant material overlying the metal friction layer and the metal sleeve surrounding the layer of compliant material and compressing it against the cable, and the method of securing a metal sleeve to a stranded metal cable, comprising: applying a rough surfaced metal friction layer to the surface of a selected axial section of the cable: positioning a compliant underlay over the friction layer;
positioning the sleeve over the compliant underlay, and reducing the diameter of the sleeve so that it grips the underlay and forces the underlay to grip the cable.

Description

The present invention relates to the securement of a metal sleeve to a multi-strand metal cable and more particularly to the connection of a load bearing collar of this type to such a cable. The sleeve can be continuous, or can be split and in the form of a clamp. Furthermore, the sleeve can form part of an element and be used to secure the element to a cable.
Cable carrying sleeves according to the present invention may be employed in many different fields; however, it was made in connection with the mounting of fairings on a towing cable for a variable depth sonar and it will be described in the following with specific reference to that use. It is to be borne in mind from the outset, however, that the applications of this invention are more general in their nature.
In a variable depth sonar system, a sonar body is towed underwater behind a ship using a tow cable which also includes electrical or fibre optics cable. It is known to reduce the cable drag by attaching a series of freely rotating fairings to the cable. With increasing cable lengths, however, hydrodynamic forces acting on the fairings can cause "stacking" and binding of the fairing with each other or preventing them from rotating freely.
~ddltional mechanical loads can be induced in the chain of fairings by the cable handling system on board ship, during launching and recovery of the towed body.
The stacking forces, once established, prevent the fairings from rotating freely to align themselves in the direction of water flow. The fairings lock end on end and act together in series like a rudder, producing a A "-tow ~" or "kiting" effect.
The fairing stacking problem has been addressed by installing "anti-stacking" sleeves or collars on the tow cable at a selected spacing and hang~ng short, discrete lengths of the fairings from the sleeves. The e~ect of accumulated, and therefore ever increasing hydrodynamic ~orces on the individual fairings down to the towed body is reduced to the point that each fairing can rotate freely. A problem that has occurred with this arrangement is the securement of the stacking sleeves to the cable. Each sleeve must be capable of supporting, not only the induced hydrodynamic loading, but also the much higher loads caused by rapid, intermittent cycling of the cable under tension through the deck mounted cable handling system. The sleeves must also ideally be compliant, so that they accommodate diametral changes in the cable due to varying tensile loads and variations in the lay angle of the outer armour strand of the cable.
Because of the manner in which tow cables are constructad, sleeve designs that rely solely upon high annular clamping pressures to achieve adequate load carrying capability are likely to cause failure in the multi-conductor electrical or fibre optic core. Consequently, simple swaged A sleeve approaches and other fitting~ techniques commonly used in the wire rope industry have generally not proven suitable for this application. The currently used anti-stacking sleeve consists of a compression-fitted stainless steel slePve over a neoprene underlay. This has not proven entirely satisfactory in that slippage of the anti-stacking sleeves on the cable has been experienced in some cases.
It is therefore the objective of this invention to provide an improved method of securing metal sleeves to cables, especially electro-mechanical or fibre-optically equipped towing cables, which are subjected to varying tensile loads and subsequent diametral change, and cable produced by that method.
According to one aspect of the present invention there is provided a method of securing a metal sleeve to a stranded metal cable, comprising:

1 3267~3 Applying a metal friction layer with a rough surface to the surface of a selected axial section of the cable;
positioning a compliant underlay over the friction layer; and crimping the sleeve onto the underlay.
According to another aspect of the present invention there is provided a multi-strand metal cable having a metal sleeve secured thereto, comprising a metal friction layer with a rough surface bonded to a selected axial section of the surface of the cable, a layer of compliant material overlying the metal friction layer and the metal sleeve surrounding the layer of compliant material and compressing it against the cable.
It is preferred that the inside of the sleeve is also provided with a metal -friction layer of similar properties to match the adherence characteristic of the interface between the cable friction layer and the compliant underlay. For the specific tow cable, the preferred compliant underlay material is a urethane elastomer with a Shore A hardness from 90 to 95 and the metal friction layer is a r c greferably an aluminum bronze alloy ~ sprayed onto the cable and the sleeve after grit blasting to clean and roughen the cable and/or sleeve surface.
Other types of underlay material could be used for other applications and also other friction materials could be used to be more compatible with materials used for different cables.
In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:
Figure 1 is a schematic representation of a variable depth sonar in use;
Figure 2 is an enlarged view of detail "A" of Figure l;
Figure 3 is a perspective view of a section of the towing cable:

Figure 4 is a cross sectional view of the towing cable showing an added compliant underlay;
Figure 5 is a cross-sectional view of the cable with an anti-stacking sleeve secured thereto;
Figure 6 illustrates the initial application of an anti-stacking sleeve to the cable;
Figure 7 illustrates the final formation and welding of the ends of the anti-stacking sleeve around the cable;
Figure 8 is an end elevation illustrating the cable and the anti-stacking sleeve assembled for crimping of the sleeve onto the cable;
Figure 9 is a side elevation of Figure 8;
Figure 10 is a view, like Figure ~, showing the crimping tool closed;
and Figure 11 is a side elevation of Figure 10.
Referring to the drawings, Figure 1 lllustrates a variable depth sonar system in which a towing cable 10 is used to tow a sonar body 12 underwater behlnd a ship 14. The cable 10 is payed out from a towing winch and boom system 16 at the stern of the ship 14. The water level is indicated at 18. In accordance with known practice, the cable 10 is equipped wlth a series of fairings 20 to reduce the hydrodynamic drag on the cable. In Figure 1, the sonar body 12 and the fairings 20 are shown on an enlarged scale, and only those fa1rings adjacent to the body 12 are illustrated~ In actual practice the entire cable carries fairings.
As illustrated most particularly in Figure 2, the fairings include hangar fairings 19 that are apertured to receive anti-stacking sleeves 22 fixed to the cable, thus preventing the fairings from sliding along the cable. The hangar fairings 1~ are spaced along the cable, each engaging a respectlve ~ 1 3267~3 anti-stacking sleeve. Between the hangar Eairings 19 are suspended fairings 21 llnked ln a chaln by flat str;ps 23 fastened by such as rivett;ng between adjacent falrlngs so that hydrodynamic forces exerted on the chaln along the cable 10 wLll be resisted by the antL-stacking sleeve 22 assocLated wLth the hangar fairlng of the assoc;ated chain. The short chains of fair;ngs are thus relatLvely free of stacking forces and rema;n free to rotate about the cable 10 to align with the flow of water past the cable. ThLs substantially reduces the forces that would otherwLse produce "kLtLng" and "tow off".
Referrlng to Figure 3, a typical configuration of the cable 10 is illustrated.
This conslsts of cable core 24 that includes the various electrlcal conductors or light conducting fibres used for communLcat;on between the ship 14 and the sonar body 12. The internal structure of the core ;s not part of th;s lnventlon and consequently has not been illustrated in detall. Surrounding the cable core is a jacket of polyethylene plastic 26. This is in turn covered with an armour 28 consisting of two layers of galvanized steel w;re strands 30 wound hel;cally about the jacket 26. The armour acts both to sustain the tensile loadings on the cable and to protect the core.
A successful anti-stacking sleeve for applicat;on to the cable 10 must be capable of supporting the hydrodynamic loadings on the associated chain of fairings. It must also withstand the much h;gher loads caused by a rap;d, intermlttent cycling of the cable under tension througll the deck mounted cable handling system. The sleeve must accommodate d;ametral changes to the cable and armour strand lay angle var-;ations s;nce these change w;th varying tensile loads on the cable dur-;ng towing operat;ons. ~t the same time9 the sleeves must be able to withstand maximum loading condit;ons exerted upon them.
To meet these requirements it is proposed to secure a layer of compliant material to the cable to accommodate the movements of the cable . . .

1 3267~3 components, and to secure the anti-stacking sleeve to the compliant material.
This requires a secure connection between the cable and the compliant layer.
In this invention, the requisite secure connection is achieved by providing the cable and the inner surface of the sleeve with a rough friction layer that keys into the compliant material. For the specific variable depth sonar tow cable application described, the surface roughness is preferably no less than 500 ~uin (12.7 microns), although this limit may be varied in different applications.
The bond between the friction layer and the cable must be sufficiently strong to support the loads applied to the sleeves. The bonding technique must not weaken the cable or impair its corrosion resistance. It has been determined that thermal metal spraying is a satisfactory technique for applying an appropriate metal friction layer. Other techniques such as welding and brazing may overheat the cable and cause an unacceptable reduction in its mechanical properties. Still others, such as soldering or casting require precise control of the operating parameters to avoid excessive heating of the internal core of the cable.
Thermal spraying, also termed metalli~ing, is a process in which an alloy in either powder or wire form is melted and deposited in particles on a workpiece by a stream of gas. The particles bond to the workpiece either mechanically by interlocking with surface irregularities or metallurgically by micro-fusing with them. Possible methods of producing thermal metal spray coatings include the following:
a) Flame Spraying: Flame spraying with a powder consumable is the simplest and most versatile of the available processes and requires relatively unsophisticated and inexpensive equipment. Flame spraying can also be done with a wire consumable but the equipment required is more complex and costly.
In operating the process a wire or powder alloy is fed into a combustion flame 1 3267~3 where it is melted. The fuel gas (usually acetylene) is mixed with oxygen and the burning gas stream transports the molten particles to the workpiece. In the powder process, the alloy materials can be gravity fed or aspirated from a canister attached to the spray gun. When using a wire alloy, motor driven wheels feed the wire into the gun and a compressed gas (air) flows around the flame to atomize the molten alloy and propel it is to the workpiece. Powder spraying has an advantage that it can deposit materials ~hich cannot be produced in a wire form. Its disadvantage is that, with the more conventional alloys, the cost of the raw material is substantially greater. In comparison with other coating methods, the flame spraying technique has lower particle velocities and temperatures which contribute to more porous, lower density coatings having poorer bond strength.
b) Electric Arc Spraying: In this process two consumable wire electrodes are fed through a gun arrangement to meet a short distance in front of the gun. An electric arc is established at this point which provides the energy to melt the wire. A constant current power supply capable of amperages in the range of 150 A to 800 A and open circuit voltages of 18 to 35 volts is required. Compressed air i9 used to atomlze the molten wire and propel the droplets to the workpiece. Operating air flows and pressures are typically about 30 - 50 cfm and 40 - 90 psi. Because the arc temperature is much hotter than a flame, high deposition rates and improved adhesion are possible, compared to flame spraying.
c) Detonation Spraying: In this process, oxygen and fuel gas are mixed with a charge of coating powder in a gun-like chamber. The mi~ture is ignited to set off detonations which propel particles out of the barrel-chamber to impact on the workpiece. Very high particle velocities contribute to the productlon of low porosity, high density and high bond strength coatings. Potential drawbacks of this process are high noise levels, higher heat input to the base material and a relatively cumbersome equipment arrangement.
d) Plasma Spray: This process utilizes an inert gas which is ionized by an arc to form a hot plasma which melts the material to be sprayed. Plasma spray deposits produce coatings with better mechanical and metallurgical properties than flame sprayed deposits because higher temperatures and transfer velocities are involved. Plasma spraying equipment is similar to that used for arc spraying except that the power source must be of the constant voltage type.
Plasma also has the advantage that either powder or wire consumables can be used whereas arc spraying is limited to using materials in wire form. The benefit of a powder system is that metallic coatings of variable densities or alloy compositions can easily be achieved simply by mixing two or more powders.
Also, materials which cannot be drawn into wire form such as tungsten and ceramic compounds can easily be deposited. Plasma spraying is, however, a relatively expensive method.
The bond strength achieved with any of these methods is a functlon of several variables such as process parameters, alloy type and substrate preparation. Since the coating adhesion ls dependent on alloying and mechanical interlocking with surface irregularities, the substrate preparation is critical to a successful application. Considerable research has been done in the past to examine the influence of surface preparation techniques on the bond strength. This led to a recommendation of grit blasing. Preparation by other means such as grinding has been shown to produce lower bond strengths by as much as two orders of magnitude on a CV-steel. The type of grit (smooth vs angular) and the procedure (direct or oblique impact) can also have some influence on the strength of the deposit by as much as a factor of two.
Cleanliness of the surface to be sprayed is very important and the air supply t 326743 used for blasting must be free of oil or moisture and it is best to spray immediately after the grit~blast preparation. Degreasing solvents should be used to clean heavily contaminated parts prior to blasting and also to remove light contamination after blasting (such as finger prints) but re-blasting is preferred.
Typically, bond strengths in shear are higher than under tensile loads. Sprayed coatings are characteristically porous (< 5~) and are relatively brittle. The brittleness of the deposited material is due to two factors; first, the coatings typically have a high oxide content and second, high residual stresses exist in the deposit because of the rapid droplet solidification and contraction producing tensile loads in individual and inter-connected particles. The oxide is initially formed on the droplet surface as the molten particle contacts the atmosphere during its traverse to the workpiece. The oxide, which is typically hard and brittle itself, becomes part of the deposited layer and thus contributes to the overall brittleness of the sprayed coating. Because of this characteristic, sprayed coatings are not recommended where point loads can be experienced since fracture of the coating is more likely to occur than under evenly distributed loads. Typical applications for sprayed coatings are to rebuild worn parts and to provide wear, corrosion or thermal resistance~ They are particularly well suited for use where low heat inputs are mandatory to avoid distortion and substrate melting.
The more commonly used processes are flame and arc spraying because they require relatively inexpensive equipment and are easy to apply. Arc spraying has been shown in produce better adhesive strengths on various substrates. This is due to the higher particle temperature achieved by the arc 1 3267~3 process. The temperature :in the flame is in the order of 2500C while the arc temperature ls more than double this.
Arc spray:ing also has the capabil:ity oE depos:it:ing coat:ings with different surface roughnesses. This Ls achieved by ;ncreas.ing or decreas-Lng the velocity of the carr.ier gas by adjustments :Ln the l:ine pressure. Lower gas veloc:lties tend to produce rougher depos:its because the molten particles do not flatten as much upon impact. In flame spray:ing, thLs control :is not available because a crit.Lcal balance must be kept between the fuel and the oxygen gas to ma:intaLn a proper flame (usually neutral).
Typ:Lcal problems w-Lth sprayed coat:ings are lack of bond:Lng, cracking and spalling. These occur prLmarily because of improper techniques such as poor part preparation and cleanl:Lness, poor procedures used in the applicat:ion(improper current, voltage or gas settings, :incorrect spraying distance), overheating of components, insuEficient preheating or excessive build-up of the deposit.
Within the context of the application to a tow cable, metal spraying produces reasonable bond strengths and the process can be controlled to l:Lmit the temperature rise in the substrate to well below that at which cable damage can occur. High substrate temperatures are, in fact, detrimental to the integrity of the sprayed coating. The temperature rise exper:Lenced by the part to be sprayed depends upon .its si~e, the spraying t:Lme and mater:Lal,the spraying distance and the process used. Although data is not ava:ilable, arc spraying is likely to produce a lower temperature rise in the substrate because the heat input Ls primar:ily from the transferred droplets. In flame and plasma spraying, however, a hot gas flame envelope :issues from the gun and substantial substrate heating occurs by imp.ingement of the flame.

In order to produce an anti-stacking sleeve securement having a large load carrying capability, a very thin (0.020 in. or less) deposit is sprayed onto the cable inner and sleeve surfaces. The sleeve is then attached with an intermediate layer of compliant material. The presence of the rough sprayed layer increases the static and sliding coefficient of friction between the ad;acent surfaces permitting higher load capacities.
Corrosion resistance is another area of concern with regard to the sprayed coatings. Existing documentation on the corrosion behaviour of aluminum and zinc sprayed deposits subjected to different environmental conditions indicates that aluminum sprayed coatings (0.003 and 0.006 in. thick) give complete base metal protection from seawater corrosion. Zinc coatings of the same thickness give 19 year protection when sealed with a primer. Thicker deposits (0.012 in.) are necessary if they remained unsealed.
The cable illustrated in Figure 3 has a zone designated L that has been grit blasted to remove any layer of oxidized zinc from the galvanizing and then arc sprayed with an aluminum bronze alloy to produce a metal friction layer 32 on the cable.
The cable is grit blasted to a surface roughness of less than 250 uin.
(6.4 um) using nepheline syenite. This process does not damage either the armour material or the galvanized layer, while it does provide an adequate surface for bonding the metal friction layer 32. Chemically, nepheline may be described as sodium potassium aluminum silicate. Syenite is a quartzless granite, with potassium feldspar comprising the main component. This material is used in the form of sand, with grit size No. 24. The particles of nepheline syenite are much more friable than more conventional grit blasting materials and as a result, there are no hard particles to become wedged between the ~ 11 --- ` I 3267~3 strands 30 of the cable armour 28. Less friable embedded particles could cause damage to the armour and to its galvanized layer during service.
The aluminum bronze material used as the metal friction layer has a composition of 90% copper, 9% aluminum and 0.5% iron. This material bonds well to the cable material and provides a dense, wear resistant surface, The use of the wire arc spray technique for applying the metal friction layer produces an exceptionally strong metallurgical bond between the base material and the aluminum bronze. The alloy itself is also corrosion resistant, so that its use in a marine environment is acceptable. The arc sprayed layer of aluminum bronze provides a surface with a roughness of about 1000 ~in (25.~ um).
As illustrated in Figure 4, the metal friction layer 32 is covered with a compliant underlay 34. This material is subsequently compressed onto the cable with the anti-stacking sleeve 36, as illustrated in Figure 5.
The primary property requirements for an underlay for anti-stacking sleeves in a variable depth sonar system are as follows:
a) Tensile/Shear Strength: A high tensile strength material is required to transmit the load from the anti-stacking ring to the friction layer on the cable.
The neoprene underlay material currently used is not able to take advantage of the substantially improved mechanical properties of the arc-sprayed friction layer on the cable strand surface. This is due to the very low tensile or shear strength of the neoprene, which is in the order of 1100 psi for a hardness of 70 shore A. The neoprene fails prematurely and consistently in a tearing and shredding mode when tested.
Therefore, it is highly desirable that alternative underlay materials e~hibit tensile/shear strength properties well in excess of that for neoprene (i.e. 5000 to 8000 psi~.

1 3267~3 b) Compression Set: The underlay material must exhibit a low compression set to maintain the compressive load between the anti-stacking sleeve and the sprayed friction layer on the cable.
c) Elongation: A medium elongation is required in the underlay material, to give the sleeve some axial flexibility and to allow for variations in the diameter of the cable. It is important that the material exhibit good restorative or 'shock absorbing' capabilities, in order to meet the sleeve displacement requirements. This is also a function of the elongation properties of the material.
d) Hardness: A medium hardness is required to produce a compressive load in the underlay when the sleeve is crimped in place. However, the hardness must also be low enough to allow the cable structure to expand and contract under operational loads and to flex as it bends over the cable handling sheaves. An appropriate range is from 80 shore A to 60 Shore D.
e) Flex Cracking Resistance: A good flex cracking resistance is highly desirable to prevent any cracks or tears in the underlay from propagating.
f) Weather and Chemical Resistance: Excellent weather resistance is required to withstand the effects of salt water and solar radiation, even though the underlay is essentially covered by the sleeve. The underlay must also be resistant to oil and grease, which is generally applied to the cable to reduce corrosion.
When using with a tow cable, it has been determined that an appropria~e underlay material is a high tensile strength, relatively hard urethane such as polyurethane diisocyanate. Anti stacking sleeves with a 0.066 0.004 inch (2.68 + 0.10 mm) thick 90 shore A hardness underlay of this material are capable of supporting loads in excess of 2000 lb. (8896 nt) with a corresponding displacement of less than 0.125 in. (3.175 mm)~ The results are ~ 13 -consistent even with var;ations in the diameter of the cable 0.05 in. (1.27) mm). ~In this appllcatLon, the urethane is soft enough to flow into surface disparities of the friction layer, thus provLdLng a good key of the sleeve to the cable, while being hard enough to support the applied load.
The anti-stacking sleeves 36 are made from a stainless steel such as that known as 316 L and are formed from rectangular blanks. Before a blank Ls formed into a sleeve, it is grit blasted on Lts inner surface. A metal friction layer 38 comparable to the layer applied to the cable is arc sprayed onto the grit blasted surface. The ob9ective in applyLng a frLctLon layer 38 to the ring is to ensure that the key between the sleeve and the compliant underlay 34 is as strong as the key between the cable and the underlay.
The ring blank is inLtially preformed into a crescent shaped blank 39 as shown in Figure 6. This Ls placed between the part cylindrical forming dies 40 illustrated in Figure 6. These dies are closed with the open side of the preformed ring 39 facLng the closed side cf the die. The ring is then reversed as shown in Figure 7, so that the open side of the die contains the joLnt 41 where the ends of the formed ring meet. A copper heat shLeld 35 is inserted between the ring and the surface of the cable and the ends of the ring are welded together wLth an appropriate weldLng process such as tungsten Ln gas as shown diagramatically at 42.
Once the heat shield 35 is removed, the complLant underlay 34 is wrapped over the friction layer on the cable and the sleeve is slid over the underlay. The assembly is then placed -Ln a crLmpLng dLe 44 illustrated in Figures 8 to 11. The crLmpLng dLe has two semLcylindrical seats 48 of s]ightly smaller diameter than the outer d-Lameter of the sleeve 36. The die is closed by a press 46, 47 as sho~n ;n Figures 9 and 11 to crimp the sleeve 36 onto the ; - 14 -compliant underlay 34 and to stress the underlay and the cable. The degree of crimping applied to the sleeve is sufficient to provide a firm engagement between the applied underlay and the cable, but is not sufficient to damage either the armour strands or the electrically conducting or light conducting fibre core elements of the cable.
Only one preferred embodiment of this invention has been described in detail, however, as indicated, the sleeve need not be joined by welding but could be formed, in ~e or two parts, as a clamp utilizing bolts or the like for holding the sleeve tightly on the cable. The clamp would, of course be treated on its inner surface by being grit blasted and by being provided wi~h a metal friction layer by arc spraying or the like.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of securing a metal sleeve to a stranded metal cable, comprising:
applying a rough surfaced metal friction layer; to the surface of a selected axial section of the cable:
positioning a compliant underlay over the friction layer;
positioning the sleeve over the compliant underlay; and reducing the diameter of the sleeve so that it grips the underlay and forces the underlay to grip the cable.

2. The method of claim 1 wherein the diameter of the sleeve is reduced by crimping.

3. The method according to claim 1 or 2, comprising applying the metal friction layer by thermal metal spraying.

4. The method according to claim 1 or 2, comprising applying the metal friction layer by arc spraying.

5. The method according to claim 1 or 2, further comprising grit blasting the selected axial section of the cable before applying the metal friction layer thereto.

6. The method according to claim 1 or 2, wherein the cable is galvanized and further comprising grit blasting the selected axial section of the cable with nepheline syenite grit before applying the metal friction layer.

7. The method according to claim 1 or 2, wherein the metal friction layer is an aluminum-bronz alloy.

8. The method according to claim 1, further comprising applying a metal friction layer to the sleeve before it is positioned over the underlay.

9. The method according to claim 1, including grit blasting one side of a sleeve blank, applying the metal friction layer to the grit blasted side of the sleeve blank, and bending the sleeve blank around the cable to form the sleeve.

10. The method according to claim 9, including performing the sleeve blank into a crescent shape after application of the metal friction layer, locating the crescent shaped blank over the cable, forming the blank into a sleeve around the cable and welding together the adjacent ends of the sleeve.

11. The method according to claim 10, including locating a heat shield between the ends of the sleeve and the cable while the ends of the sleeve ends are being welded together.

12. A multi-strand metal cable having a metal sleeve secured thereto, comprising a rough surfaced metal friction layer bonded to a selected axial section of the surface of the cable, a layer of compliant material overlying the metal friction layer, and the metal sleeve surrounding the layer of compliant material and compressing it against the cable.

13. The cable according to claim 12, wherein the metal friction layer is metallurgically bonded to the outer surface of the cable.

14. The cable according to claim 13, wherein the metal friction layer is an aluminum-bronze alloy.

15. The cable according to claim 12, 13, or 14, wherein the metal friction layer has a surface roughness of no less than 500 µ in. (12.7 microns).

16. The cable according to claim 12, wherein the compliant material is a urethane elastomer.

17. The cable according to claim 16, wherein the urethane elastomer is polyurethane diisocyanate.

18. The cable according to claim 16, wherein the urethane elastomer has a hardness from between 80 Shore A and 60 Shore D.

19. The cable according to claim 16, wherein the urethane elastomer has a hardness from 90 to 95 Shore A.

20. The cable according to claim 19, wherein the compliant material has a thickness of 0.066 + 0.004 inches. (2.68 + 0.10 mm).

21. The cable according to claim 12, further comprising a rough surfaced metal friction layer on the inside of the sleeve.

22. The cable according to claim 21, wherein the metal friction layer on the inside of the sleeve is an aluminum bronze alloy.

23. The cable according to claim 21 or 22, wherein the sleeve is stainless steel.

24. The cable according to claim 14 or 22, wherein the aluminum bronze has a composition of 90% Copper, 9% Aluminum and 0.5% iron.

25. The cable according to claim 12, 13 or 14, wherein the metal friction layer has a surface roughness no less than 500 u in. (12.7) microns).

26. The cable according to claim 21 or 22, wherein the metal friction layer on the inside of the sleeve has a surface roughness no less than 500 u in. (12.7 microns).

27. A tow cable for a variable depth sonar body comprising a cable having an outer layer of stranded wire armour, a plurality of anti-stacking sleeves fixed to the cable at positions spaced therealong, a plurality of hanger fairings mounted rotatably on the anti-stacking sleeves and plural suspended fairings rotatably mounted on the cable between the hangar fairings, the suspended fairings between each two adjacent hangar fairings being connected together and to one of the adjacent hangar fairings to transmit hydrodynamic loads on the fairings to the anti-stacking sleeves and thence to the cable, wherein:
a metal friction layer with a rough surface is bonded to the armour beneath each anti-stacking sleeve, a layer of compliant material is interposed between the anti-stacking sleeve and the friction layer and the anti-stacking sleeve compresses the compliant layer against the armour.