Patent Description:
A towed trawl usually includes a headline sonar sensor for monitoring the trawl's headline height, the trawl's opening and fish schools in front of the trawl. A data transmission cable, i.e. a headline sonar cable that is sometimes called a third wire includes a conductor for transferring data signals from the headline sonar sensor to the towing vessel. Presently, strength members of conventional headline sonar cables are made from steel, and enclose a central copper conductor that is surrounded by layed, multi-layed and torsion balanced, or braided copper wires. The braided copper wires surrounding the central conductor shield the data signal carried on the central copper conductor from electromagnetic interference that degrades the quality of transmitted data signals. Headline sonar cables can be up to <NUM> meters long and, besides their main function of transferring data signals, the cable is also sometimes used to increase trawl's opening by raising the headline. This is why a headline sonar cable is sometimes called a third wire.

When used with a trawl, a headline sonar cable must absorb the stress that results from the trawler's surging on sea swells. Surging causes the stern of the trawler where the third wire winch is located to impart surging shocks to the headline sonar cable being deployed therefrom. Surging significantly increases compressive force applied to the headline sonar cable at the winch thereby correspondingly increasing the likelihood that the headline sonar cable's data signal conductor may become damaged.

One disadvantage of a conventional steel headline sonar cable is its weight. The weight of a steel headline sonar cable adversely affects trawl operation and fishing gear's performance. A long steel headline sonar cable extending between a trawler and a trawl will, between the trawler the headline sonar, descend below the trawl's headline. Furthermore, a trawler's headline sonar cable winch frequently lacks sufficient power to tense the steel headline sonar cable since the winch is supporting the cable's weight.

A steel headline sonar cable that descends below the trawl's headline necessarily passes through schools of fish that are in front of the trawl's opening. Passage of the steel headline sonar cable through a school scares the fish and the school will turn sideways. A schools' sideways turn may reduce the catch because some of the fish avoid the trawl's opening.

Another disadvantage of a steel headline sonar cable occurs if the cable breaks. A broken steel headline sonar cable, due to its weight, initially falls downward and then starts cutting through and damaging the trawl. Similarly, when the trawler turns while towing a trawl it often becomes difficult to control a steel headline sonar cable to avoid contact between the cable and the trawl's warp lines and/or the bridles. Contact between the headline sonar cable and the trawl's warp lines and/or bridles can damage either or both the headline sonar cable and the trawl's warp lines and/or bridles. Similarly, sometimes a headline sonar cable contacts a trawl door. Contact between a headline sonar cable and a trawl's door can result either in the cable being cut, or the cable becoming entangled with the door so the trawl door become uncontrollable. Curing any of the preceding problems associated with the use of a steel headline sonar cable requires retrieving, repairing and/or readjusting the fishing gear.

Over time rust also degrades a steel headline sonar cable. Furthermore, steel headline sonar cables are difficult to splice because they typically consists of two twisted layers of steel wires, one layer twisted clockwise and the layer other counterclockwise.

Cables made from synthetic polymeric materials exhibit rather different physical properties compared to conductors, e.g. optical fibers and wires made from copper, aluminum or other metals. In general, the elasticity of conductors is very low while synthetic polymeric materials generally exhibit greater inherent elasticity. Twisting stranding and/or braiding fibers and/or filaments of synthetic polymeric materials into a cable further increases elasticity of the finished cable due to voids that occur between fibers and/or filaments. A straight conductor oriented parallel to or inside a cable made from synthetic polymeric materials tends to break upon an initial application of tension which stretches the cable. The constructional elasticity of cables made from synthetic polymeric materials can be reduced by stretching the cable either while it is hot or cold. Stretching a cable made from synthetic polymeric materials reduces elasticity by compressing the fibers and/or filaments while also removing voids.

Fibers and/or filaments made from ultra high strength synthetic polymeric materials like Ultra High Molecular Weight Polyethylene ("UHMWPE"), e.g. Dyneema® and Spectra®; para-aramid, e.g. Kevlar® and Twaron®; carbon fibers; aromatic polyester, e.g. Vectran®; thermoset polyurethane, e.g. Zylon®; and aromatic copolyamid, e.g. Technora®; typically have elongation to break from <NUM>-<NUM>%. A cable made from such materials generally exhibit <NUM>-<NUM>% constructional elongation. If a conductor is placed inside or with a cable made from such a synthetic polymeric material it must be able to accept this elongation without either breaking or becoming brittle which ultimately results in premature conductor failure.

Tension bearing energy and data signal cables using synthetic fibers for a strength member are known. For example Cortland Cable Company offers such cables for seismic/magnetometer tow cables, sidescan sonar and video tow cables and seismic ocean bottom cables. Such cables when used for tethering a remotely operated vehicle ("ROV") operate at low tension and insignificant surge. Strong surge shocks are unusual for current applications of ROV tether lines and moored ocean cables or the other uses for known non-steel tension bearing energy and data signal cables. In fact, it is well known in the field that ROVs are not to be deployed with such tether cables in surge conditions in which trawler's usually routinely and actually operate. Consequently, none in the art have proposed a non- steel tension bearing data signal and energy cable capable of tolerating very high loads such as those applied to a trawl's headline sonar cable while also capable of being wound on a drum or winch under high tensions. Until the present disclosure, none in the art have proposed a non-steel bearing energy and data signal cables that can be wound and deployed from a winch subject to a fishing trawler's surging shocks while not impairing the cable in a short time, especially in less than <NUM> calendar months from a date of first use.

In fact, it is accurate to state that when high tension is required in combination with repeated windings under tension onto a winch's drum and storage under tension on that drum such as occurs with a trawl's headline sonar cable, it is contrary to the trend of the industry to form a tension bearing data signal cable having a conductor enclosed by a strength member formed of synthetic fibers. Past experiments at sheathing conductors (including fibre optic lines, copper wires, etc.) within strength members such as braided jacket layers formed of synthetic polymeric fibers have failed in high tension applications such as those described above. Moreover, attempts to pre-stretch a strength member formed from synthetic polymeric fibers en- sheathing a conductor without breaking or otherwise causing failure of the conductor have also failed.

<CIT> teaches a construction for a towed streamer designed to both protect the conductors from excessive elongation while also minimizing vibrational amplitutes along the streamer. This publication teaches a towed streamer including a buoyant core and strength members to transmit tension along the streamer. The strength members are arranged so that the streamer is compliant for a predetermined elongation of the streamer. The strength members are embedded in an inner jacket surrounded by an outer jacket. The entire assembly is encased in an extruded outer jacket. Braided data bearers can be provided between the inner jackets that are external the strength members. The strength members can be braided with interstices impregnated with gel. Alternatively to using strength members that are all non-compliant, a combination of compliant and non-compliant members strength members can be used, where the compliant members only become engaged after a predetermined elongation of the streamer.

<CIT> teaches an armored cable intended to exhibit minimal inelastic elongation in response to tension at elevated temperatures and also intended to withstanding harsh ambient conditions. The armorned cable contains a hermetically sealed tube incorporating an optical fiber. The teachings include a method of fabrication which minimizes the inelastic part of the cable's elongation by minimizing the deformability of the core. The central bundle of the cable comprises at least two inner layers, including an inner armor, which are stranded in a "unilay" configuration of a given handedness around a central hermetically sealed tube which contains at least one optical fiber coated with a suitable cushioning material such as an elastomer so as to buffer the optical fiber. The tube is fabricated so that the fibers are hermetically sealed therein with a minimum of process-induced strain and microbends.

Published Patent Cooperation Treaty ("<CIT> , International Application No. <CIT>, discloses a cable having a thermoplastic core enclosed within a braided, coextruded or pulltruded jacket. During fabrication the cable is heated to a temperature at which the thermoplastic core becomes liquid or semi- liquid. While heated to this temperature, the cable is stretched so it becomes permanently elongated. During stretching, material of the heated thermoplastic core fill voids within the surrounding jacket. For added strength and/or stiffness, the thermoplastic core may include a central, inner strength member fiber or filament that differs from that of the thermoplastic core and is made from a metal or polymeric material. Using the metal central inner strength member to carry data signals doesn't work because during cable fabrication either the metallic wire either breaks or becomes so brittle as to fail prematurely.

Document <CIT> relates to the manufacture of an ocean bottom cable comprising a core and insulated conductors separated by a matrix; the inner portion of the cable is formed by retaining the core at elevated an temperature and then passing the heated core through a cabling station, where the insulated conductors are pressed into the hot outer surface of the core.

An object of the present disclosure is to provide a non-steel headline sonar cable capable of being wound on a winch under tensions and surging shocks experienced by a fishing trawler that remains unimpaired throughout a commercially practical interval of at least <NUM> calendar months from a date of first use.

Another object of the present disclosure is to provide a non-steel headline sonar cable capable of being wound on a winch and remaining unimpaired under tensions and surging shocks experienced by fishing trawlers particularly those having displacements from <NUM> tonnes up to and exceeding <NUM> tonnes and even exceeding <NUM> tonnes, as the trawler's displacement magnifies surge shocks.

Another object of the present disclosure is to provide a non-steel headline sonar cable capable of being wound on a winch at a tension exceeding <NUM> that remains unimpaired throughout a commercially practical interval of at least <NUM> calendar months from a date of first use on trawlers exceeding <NUM> tonnes displacement, since the trawler's displacement magnifies the surge shocks.

Another object of the present invention is to provide a non-steel headline sonar cable that does not kink when relaxed.

The invention provides a method for producing a headline sonar cable according to claim <NUM>.

Further details of the invention are set forth in the dependent claims.

Disclosed is a method for producing a headline sonar cable having a high breaking-strength and lighter weight than a conventional headline sonar cable having a strength member formed of steel wire. Most broadly, the method for producing the headline sonar cable is characterized by the steps of:.

Produced in this way, the elongatable internally-located conductive structure does not break upon stretching of the strength-member jacket layer surrounding the elongatable internally-located conductive structure that lengthens the headline sonar cable.

In one embodiment of the preceding method the elongatable internally-located conductive structure is formed by wrapping a conductor that is capable of data signal transmission around a rod that deforms during subsequent stretching of the strength-member jacket layer. In another embodiment of the preceding method the elongatable internally-located conductive structure is formed by enclosing an unstretched braided conductor that is capable of data signal transmission within a non-conductive braided sheath.

For a metallic conductor or braided conductor, either of the preceding alternative embodiments includes further steps of:.

Also disclosed is a non-steel headline sonar cable fabricated in accordance with the disclosed method. An advantage of the disclosed non-steel headline sonar cable is that it is lite having a lower density than a steel headline sonar cable. Because the disclosed non-steel headline sonar cable is lighter than, and correspondingly more buoyant in water than, a conventional steel headline sonar cable, the disclosed cable:.

Due to the disclosed headline sonar cable's lite weight and buoyancy, its path from a trawler's winch down to the trawl's headline is more direct. Furthermore, due both to the disclosed headline sonar cable's lite weight and to the trawl's towing speed, the disclosed headline sonar cable tends to remain above the trawl's headline rather than descending below the headline. If a headline sonar cable remains above the trawl's headline, it cannot contact the trawl's warp lines, bridles and/or doors. Furthermore, if such a headline sonar cable breaks it will float over the trawl thereby avoiding damage to the trawl.

Another advantage of the disclosed non-steel headline sonar cable is that it can be spliced more easily and more quickly than a conventional steel headline sonar cable.

Yet another advantage of the disclosed non-steel headline sonar cable is that it corrodes less than a conventional steel headline sonar cable. Consequently, the disclosed non-steel headline sonar cable will last longer than a conventional steel headline sonar cable.

Yet another advantage of the disclosed non-steel headline sonar cable is that it exhibits less heat fatigue than a conventional steel headline sonar cable.

Possessing the preceding advantages, the disclosed non-steel headline sonar cable answers needs long felt in the industry.

These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.

<FIG> illustrates a headline sonar cable in accordance with the present disclosure that is identified by the general reference character <NUM>. <FIG> depicts a preferably insulated electrical conductor <NUM> wrapped around a rod <NUM> of deformable material and enclosed within a sequence of layers included in the particular embodiment of the headline sonar cable <NUM> illustrated in <FIG>. The steps of a first fabrication method described below assemble the headline sonar cable <NUM> depicted in <FIG>.

Fabrication of the headline sonar cable <NUM> depicted in <FIG> begins with twisting and/or wrapping the preferably insulated electrical conductor <NUM> around the rod <NUM> of deformable material as depicted in greater detail in <FIG>. The deformable material of the rod <NUM> can be a thermoplastic material, a plastic material, or any other material that deforms when exposed to pressures generated while stretching various layers of the headline sonar cable <NUM> depicted in <FIG> in the manner described in greater detail below.

An essential characteristic of the present disclosure is that all subsequent processing steps including a step of stretching various layers of the headline sonar cable <NUM> depicted In <FIG> preserves the integrity of the conductor <NUM>. Regarding the conductor <NUM>, any insulation thereon:.

There exist numerous conventional insulating materials that satisfy the preceding criteria for an insulator included in the headline sonar cable <NUM>.

Twisting the conductor <NUM> around the rod <NUM> in a direction corresponding to a lay direction of the conductor <NUM> is advantageous. The shape of the conductor <NUM> when twisted and/or wrapped around the rod <NUM> is that of a spiral, although in accordance with the present disclosure the headline sonar cable <NUM> may be twisted and/or wrapped around the rod <NUM> in shapes other than that of a spiral or helix which alternative shapes also function as well in the headline sonar cable <NUM> as the spiral shape. In fact, any suitably arranged configuration for the headline sonar cable <NUM> in which it meanders along the length of the rod <NUM> should be capable of providing sufficient slack in the headline sonar cable <NUM> that it does not break while stretching various layers of the headline sonar cable <NUM> depicted in <FIG> in the manner described in greater detail below.

The conductive material of the headline sonar cable <NUM> includes fibers and/or filaments for carrying information. In accordance with the present disclosure such information carrying fibers and/or filaments include optical fibers and electrically conductive wire. Usually, the headline sonar cable <NUM> includes filaments capable of carrying electrical energy and/or current, such as copper strands or wires. For purposes of this disclosure, the terms fiber and filament are used interchangeably.

Referring now to <FIG>, the next step in forming the headline sonar cable <NUM> is enclosing (including forming a sheath over) the conductor <NUM> and rod <NUM> within a sheath layer <NUM> of material that has a higher softening temperature than that of the rod <NUM>. If tightly braided, wrapped or extruded material of the sheath layer <NUM> has a higher softening temperature than the material of the rod <NUM>, the material of the rod <NUM> will not extrude through the sheath layer <NUM> during prestretching and/or heatsetting most of the cable layers depicted in <FIG> in the manner described in greater detail below. The sheath layer <NUM> may be formed by tightly braiding or wrapping the conductor <NUM> and the rod <NUM> with a material, e.g. polyester fibers, having higher softening temperature than that of the rod <NUM>. Alternatively, the sheath layer <NUM> may be extruded around the conductor <NUM> and the rod <NUM>. The conductor <NUM> and the rod <NUM> enclosed within the sheath layer <NUM> form an elongatable internally-located conductive structure <NUM> of the headline sonar cable <NUM>.

Referring now to <FIG>, when the conductor <NUM> is an electrical conductor the next step in forming the headline sonar cable <NUM> is overbraiding or overtwisting the conductor <NUM>, rod <NUM> and sheath layer <NUM> of <FIG> with a shielding layer <NUM> of electrically conductive material, e. g, copper wires, to shield the conductor <NUM> from electromagnet interference. The shielding layer <NUM> must remain unimpaired when elongating up to fourteen percent (<NUM>%) while stretching various layers of the headline sonar cable <NUM> depicted in <FIG> in the manner described in greater detail below.

Referring now to <FIG>, the next step in forming the headline sonar cable <NUM> is to pultrude or extrude, cover or otherwise enclose (including forming a sheath over) the conductor <NUM>, rod <NUM>, sheath layer <NUM> and shielding layer <NUM> with a water-barrier layer <NUM> to serve as a water shield. The water-barrier layer <NUM> is formed as thin as possible from a plastic, metallic or other material to bar the enclosed layers from water intrusion (i.e. formed and/or constructed so as to be impermeable to water). Preferably polyethylene forms the water-barrier layer <NUM>.

Referring now to <FIG>, the next step in forming the headline sonar cable <NUM> is to overbraid or cover the conductor <NUM>, rod <NUM>, sheath layer <NUM>, shielding layer <NUM> and water-barrier layer <NUM> with a tightly braided or wrapped extrusion-barrier layer <NUM> of a material having a higher softening temperature than the material of the water-barrier layer <NUM>. If tightly braided, wrapped or extruded material of the extrusion-barrier layer <NUM> has a higher softening temperature than the material of the water-barrier layer <NUM>, the material of the water-barrier layer <NUM> will not extrude through the extrusion-barrier layer <NUM> during prestretching and/or heatsetting most of the cable layers depicted in <FIG> in the manner described in greater detail below. For example, the extrusion-barrier layer <NUM> may be formed from braided polyester fibers (including plaits, strands and filaments and other). Alternatively, instead of braided polyester fibers the extrusion-barrier layer <NUM> may be formed from aluminum tape that is wrapped about the conductor <NUM>, rod <NUM>, sheath layer <NUM>, shielding layer <NUM> and water-barrier layer <NUM> with approximately a <NUM>% overlapping of each subsequent wrap of the aluminum tape. Forming the extrusion-barrier layer <NUM> from a wrapped aluminum tape is particularly advantageous as it reduces the diameter of the headline sonar cable <NUM> in comparison to forming the extrusion-barrier layer <NUM> from braided or wrapped polyester fibers.

Due to the importance of minimizing the diameter of the headline sonar cable <NUM>, it is important that the rod <NUM> has the smallest diameter practicable. In particular, the diameter of the rod <NUM> can be determined experimentally so that after stretching various layers of the headline sonar cable <NUM> depicted in <FIG> in the manner described in greater detail below the conductor <NUM> is either completely straightened out or so near to being completely straight that any deviation from being entirely parallel to the longitudinal axis of the sheath layer <NUM> allows only slight additional elongation of the conductor <NUM>. As used herein slight additional elongation of the conductor <NUM> means less than <NUM>% elongation, and preferably less than <NUM>% elongation, and even less than <NUM>% elongation, and even less than <NUM>% elongation of the conductor <NUM> prior to its becoming straight as contrasted with breaking or failing of the conductor <NUM>. Dissecting headline sonar cables <NUM> fabricated in accordance with this disclosure using different diameter rods <NUM> to extract the conductor <NUM> therefrom and then stretching the conductor <NUM> until it becomes straight permits experimentally determining a preferred diameter for the rod <NUM>.

Whatever combination of layers are included in the headline sonar cable <NUM> in addition to the conductor <NUM>, the rod <NUM> and the extrusion-barrier layer <NUM>, referring now to <FIG>, the next step in forming the headline sonar cable <NUM> is to overbraided over all those layers a layer of polymeric fiber such as UHMWPE, Aramids (Kevlar), carbon fibers, LCP (Vectran), PBO (Zylon), Twaron and Technora, etc. to form the strength-member jacket layer <NUM> of the headline sonar cable <NUM>.

The conductor <NUM>, the rod <NUM> and the extrusion-barrier layer <NUM> together with any other layers enclosed within the strength-member jacket layer <NUM> and the strength-member jacket layer <NUM> itself are then heat-stretch and/or heat-set, preferably in such a way as to cause the rod <NUM> to become malleable (semi-soft) so it can be permanently deformed, and otherwise in such a way as described for subsequent processing steps <NUM>, <NUM> and <NUM>, which repeat heat-stretching.

Referring now to <FIG>, the next step in forming the headline sonar cable <NUM> is to overbraid or cover the strength-member jacket layer <NUM> and everything enclosed within the strength-member jacket layer <NUM> with a final protective layer <NUM> of the headline sonar cable <NUM>. The protective layer <NUM> shields the strength member from damage caused by abrasion or cutting. One characteristic of the protective layer <NUM> is that it must be capable of tolerating further elongation of the headline sonar cable <NUM> as described in subsequent processing steps.

The next fabrication step in making the headline sonar cable <NUM> is heating the headline sonar cable <NUM> again to a temperature that causes the rod <NUM> to become malleable (semi-soft) so the rod <NUM> again becomes deformable but not so hot that material forming the rod <NUM> flows. While maintaining the headline sonar cable <NUM> in this heated state, fabrication of the headline sonar cable <NUM> concludes with performing the operations described in Steps (<NUM>) and (<NUM>) below.

The next to last fabrication step is stretching the headline sonar cable <NUM> applying sufficient tension to at least the strength-member jacket layer <NUM> so as to elongate the strength-member jacket layer <NUM> a desired amount. The desired amount of elongation of the strength-member jacket layer <NUM> is usually an amount that after the headline sonar cable <NUM> cools the strength-member jacket layer <NUM> is unable to stretch more than approximately three and one-half percent (<NUM>%) until breaking, and especially so as to permit permanent elongation of the cooled jacket layer.

A preferred temperature when stretching the protective layer <NUM> of the headline sonar cable <NUM> that is formed of UHMWPE is <NUM>. A temperature between <NUM> to <NUM> is highly useful when stretching the protective layer <NUM> of the headline sonar cable <NUM> that is formed of UHMWPE. A temperature between <NUM> to <NUM> is useful when stretching the protective layer <NUM> of the headline sonar cable <NUM> that is formed of UHMWPE, with a temperature range <NUM> to <NUM> also being useful. Depending upon the tension applied to the headline sonar cable <NUM>, and also depending upon the types of fibers and/or filaments used in making the headline sonar cable <NUM>, temperatures from <NUM> to <NUM> are useful.

In general, applying more tension to the headline sonar cable <NUM> reduces the temperature to which the headline sonar cable <NUM> must be heated, and conversely. The temperature selected and applied and the tension selected and applied are such as to maximize the strength of the jacket layer in the headline sonar cable <NUM> while also minimizing, and preferably eliminating, its ability to further elongate;.

The final fabrication step is cooling the headline sonar cable <NUM> while maintaining tension on at least the strength-member jacket layer <NUM> so that layer together with the other layers cool while under tension. In this way:.

For example, as a result of this last step, the conductor <NUM> becomes compressed against the malleable rod <NUM>, and as a result displaces some of the rod <NUM> and actually comes to occupy some of the space formerly occupied only by the rod <NUM>. Due to elongation of the headline sonar cable <NUM>, the diameter in which the conductor <NUM> is initially wrapped around the rod <NUM> shrinks with the rod <NUM> and the conductor <NUM> becoming intertwined. Depending upon how much tension is applied to the headline sonar cable <NUM> during fabrication, the combined conductor <NUM> and rod <NUM> can become an essentially cylindrical-like structure with spaces often barely discernable between the conductor <NUM> and the rod <NUM>.

Due to the heating and stretching described above all layers of the headline sonar cable <NUM> enclosed within the strength-member jacket layer <NUM> and the protective layer <NUM> assume a shape that supports and conforms to the internal wall of the immediately surrounding layer. Accordingly, during heating and stretching of the headline sonar cable <NUM> the extrusion-barrier layer <NUM> directly contacting the strength-member jacket layer <NUM> takes a shape that supports and conforms precisely to the internal shape of the strength-member jacket layer <NUM>. Layers of the finished headline sonar cable <NUM> enclosed within the extrusion-barrier layer <NUM> assume a shape similar to that of the extrusion-barrier layer <NUM> with the degree of similarity decreasing progressively toward the center of the headline sonar cable <NUM>. At the center of the finished headline sonar cable <NUM> illustrated in <FIG>, <FIG>, <FIG> and <FIG>, the shape of the combined conductor <NUM> and rod <NUM> may be almost cylindrical with deformed exterior surface.

<FIG> depict a most preferred, alternative embodiment headline sonar cable in accordance with the present disclosure that is identified by the general reference character <NUM>. Those elements depicted in <FIG> that are common to the headline sonar cable <NUM> illustrated in <FIG>, <FIG>, <FIG> and <FIG> carry the same reference numeral distinguished by a prime ("'") designation. The most preferred embodiment of the headline sonar cable <NUM> depicted in <FIG> eliminates the elongatable internally-located conductive structure <NUM> depicted in <FIG> formed my the conductor <NUM>, rod <NUM> and sheath layer <NUM>. Instead of the conductor <NUM>, the headline sonar cable <NUM> includes an initially unstretched braided conductor <NUM> that first has a non-conductive braided sheath <NUM> overbraided around the braided conductor <NUM>. Preferably, the braided sheath <NUM> formed of a polymeric material fibers such as polyester fibers. Then, if the braided conductor <NUM> is made from an electrically conductive material pultruding or extruding a polymeric layer <NUM> around the braided conductor <NUM> enclosed within the braided sheath <NUM>. The polymeric layer <NUM> is preferably formed from cellular polyethylene and has a radial thickness that establishes a proper electrical impedance for the headline sonar cable <NUM>. The use of cellular polyethylene for electrical insulation is further described at least in <CIT>, <CIT>and <CIT>. Alternatively, a polyurethane material may also be used provided that it does not tend to contract the headline sonar cable <NUM> longitudinally after stretching various layers of the headline sonar cable <NUM> depicted in <FIG> in the manner described in greater detail below.

Configured as described above, the braided conductor <NUM>, the braided sheath <NUM> and the polymeric layer <NUM> form a most preferred embodiment of an elongatable internally-located conductive structure <NUM> of the headline sonar cable <NUM>. After the elongatable internally-located conductive structure <NUM> has been assembled, fabrication of the most preferred, alternative embodiment headline sonar cable <NUM> then continues with further processing the elongatable internally-located conductive structure <NUM> as described previously for Steps (<NUM>) through (<NUM>) above.

A headline sonar cable <NUM> of the type depicted in <FIG> having the single braided conductor <NUM> or the headline sonar cable <NUM> of the type depicted in <FIG> and <FIG> having the single conductor <NUM> is useful for a trawl headline sonar cable. When the headline sonar cable <NUM> is fabricated for certain applications, such as headline cables used for towed seismic surveillance arrays, the headline sonar cable <NUM> may include several individual information carrying fibers and/or filaments rather than a single fiber and/or filament as depicted in the illustration of <FIG> and <FIG>. For the purposes of this disclosure, as many distinct conductive fibers and/or filaments as required to carry both data signals and electrical energy for any particular application are understood to be included in the headline sonar cable <NUM>, whether there be one or hundreds or even more distinct information carrying fibers and/or filaments. As is readily apparent to those skilled in the art, for a headline sonar cable <NUM> having two (<NUM>) or more distinct information carrying electrically conductive fibers and/or filaments each of those fibers and/or filaments must be electrically insulated from all of the other distinct information carrying fibers and/or filaments.

If instead of an electrically conductive material the headline sonar cable <NUM> or <NUM> uses optical fibers for the conductor <NUM> or the braided conductor <NUM> to carry the data signals, the headline sonar cable <NUM> or <NUM> no longer requires the shielding layer <NUM> or <NUM>'. If the headline sonar cable <NUM> or <NUM> omits the shielding layer <NUM> or <NUM>' because optical fibers form the conductor <NUM> or the braided conductor <NUM>, then the headline sonar cable <NUM> or <NUM> may also omit the sheath layer <NUM> or the polymeric layer <NUM>.

Because the headline sonar cable <NUM> or <NUM> is made mainly from synthetic polymeric materials, it has much lower density that a conventional steel headline sonar cable. In fact the density of the headline sonar cable <NUM> or <NUM> is approximately the same as that of water. If a particular application such as deep water trawling benefits from a more dense headline sonar cable <NUM> or <NUM>, then fibers or filaments made from a denser material, e.g. a dense metal, may replace some or all of the fibers or filaments of the protective layer <NUM> or <NUM>'. Furthermore, varying the thickness of the protective layer <NUM> or <NUM>' permits adjusting the buoyancy of the headline sonar cable <NUM> or <NUM> to a particularly desired value. Using a denser and harder material such as steel for some or all of the fibers or filaments of the protective layer <NUM> or <NUM>' also significantly enhances the abrasion resistance of the headline sonar cable <NUM> or <NUM>.

In addition to being used with trawls, headline sonar cables in accordance with the present disclosure may be used as synthetic towing warps on trawlers or other vessels, are also used as a lead-in cable for towed seismic surveillance arrays. Towing seismic surveillance arrays requires that the lead-in cable transmit both electrical energy and data signals a long distance between the towing vessel and the array with a minimum of drag, a minimum of weight, and a minimum of lead-in cable movement.

Claim 1:
A method for producing a headline sonar cable (<NUM>, <NUM>) capable of being used with trawls, or as a synthetic towing warp on trawlers or other vessels, the method for producing the cable (<NUM>, <NUM>) comprising steps of:
a. providing an elongatable internally-located conductive structure (<NUM>, <NUM>) that includes a conductor (<NUM>, <NUM>) that is capable of electrical energy and/or data signal transmission, the elongatable internally-located conductive structure (<NUM>, <NUM>) comprising a rod comprising a deformable material (<NUM>,);
b. braiding a strength-member jacket layer (<NUM>) of polymeric material to enclose the elongatable internally-located conductive structure (<NUM>, <NUM>) while ensuring that the elongatable internally-located conductive structure is slack when surrounded by the strength-member jacket layer; and
c. heating the cable (<NUM>, <NUM>) to a temperature that enables permanently elongating the cable (<NUM>, <NUM>) while stretching the strength-member jacket layer (<NUM>);
d. stretching the strength-member jacket layer (<NUM>) sufficiently to elongate the cable (<NUM>, <NUM>) and so as to permanently elongate the cable (<NUM>, <NUM>), while simultaneously not breaking the conductor (<NUM>, <NUM>) and while simultaneously preserving the integrity of the conductor (<NUM>, <NUM>); and to thereby:
i. deform the deformable material (<NUM>, <NUM>) responsive to a reduction in cross-sectional area of the strength-member jacket layer (<NUM>); and
ii permanently lengthen the strength-member jacket layer (<NUM>); and
e. while maintaining tension on the strength-member jacket layer (<NUM>), cooling the cable (<NUM>, <NUM>) until the deformable material (<NUM>, <NUM>) solidifies.