Abstract:
A marine cable cutter is provided for wirelessly severing wire responsive to an electromagnetic command signal. The cutter includes an explosive package for wrapping around the wire, and a clamshell case for containing the package around the wire. The package includes a wireless receiver to receive the command signal, an electric pulse generator triggered by the receiver, an explosive initiated by the generator, and a platform for containing the receiver, generator and explosive. The clamshell case includes a pair of envelopes connected along mutual first edges by a hinge and mutual second edges by respective clamps. The envelopes pivot on the hinge to open and receive the package with disposal of the wire therein, and subsequently to close and secure by the clamps. The envelopes can be composed of sheet metal with the clamps being flanges with aligned holes for receiving bolt fasteners.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND 
     The invention relates generally to maritime cable cutting under emergency conditions. In particular, the invention relates to a mechanism to expeditiously and reliably sever a heavy-duty cable used between ships for supply operations. 
     Naval ship replenishment at sea, also known as an undersea replenishment (UNREP) operation, involves rendezvous of approach and control ships on parallel courses, followed by connection of ships by a span cable. For liquid supplies, e.g., fuel, the delivering ship extends a hose along the cable to the receiving ship for connection to the appropriate receptacle. Other supplies, such as weapon stores can also be exchanged via cable suspension. 
       FIG. 1  shows an elevation view  100  of a conventional rigging configuration for UNREP between a delivering ship  110  and a receiving ship  120  for refueling operation. Structures and supports on the delivering ship include a wire topping pendant  125 , a wire saddle whip  130 , and an anti-toppling device  135 . A span wire or cable  140  supports an inboard saddle  145 , operating in conjunction with mezzanine and outboard saddles  150  and  155 . The span wire  140  is typically 1⅜ inches (″) thick and comprises braided steel cable resistant to spontaneous breakage. The saddles  145 ,  150  and  155  elevate a supply hose  160  accompanied by a stress wire  165 . After refueling completion a retrieving line returns the outboard saddle  155  to the delivering ship  110 . A supply outlet  180  delivers fuel through the hose  160  supported by a receiving structure  190  on the delivery ship  120  and connected to its receiver inlet  195 . 
       FIG. 2  shows an elevation view  200  of a conventional rigging configuration for weapons transfer between the delivering and receiving ships  110  and  120  to transfer a load  220  along a travel direction  225 . The delivering ship  110  includes a ram tensioner  230 , a high line winch  235 , and out-haul winch  240 , an in-haul winch  245  and a transfer head  250 , which holds a tensioned highline  255 , a tensioned in-haul line  260 , and a tensioned out-haul line  265 . The highline  255  and in-haul line  260  enable a trolley  270  to transfer the load  220 . The delivering ship  110  also includes a kingpost  275  to elevate the transfer head  250 . The receiving ship  120  includes a padeye  280  with an out-haul fairlead  285  to support the lines  255 ,  260  and  265 . 
     In the event of an emergency replenishment termination, the cable is severed manually. This process is described in section 2.2.11 of “Underway Replenishment” especially pp. 2-11 through 2-15, issued as NWP 4-01.4 under the Chief of Naval Operations and available at http://www.hnsa.org/doc/pdf/unrepnwp04-01.pdf.  FIG. 3  shows a perspective view  300  of the inboard ship  110  with its span wire  140 . A manual cable cutter  310  is positioned on the span wire  140  by an assigned operator  320  to sever the cable when authorized during an emergency and abort the inter-ship delivery operations. 
     SUMMARY 
     Conventional emergency severance devices for marine cables yield disadvantages addressed by various exemplary embodiments of the present invention. In particular, various exemplary embodiments provide a marine cable cutter for wirelessly severing wire responsive to an electromagnetic command signal. The cutter includes an explosive package for wrapping around the wire, and a clamshell case for containing the package around the wire. 
     In exemplary embodiments, the package includes a wireless receiver to receive the command signal, an electric pulse generator triggered by the receiver, an explosive initiated by the generator, and a platform for containing the receiver, generator and explosive. In further exemplary embodiments, the clamshell case includes a pair of envelopes connected along mutual first edges by a hinge and mutual second edges by respective clamps. The envelopes pivot on the hinge to open and receive the package with disposal of the wire therein, and subsequently to close and secure by the clamps. The envelopes can be composed of sheet metal with the clamps being flanges with aligned holes for receiving bolt fasteners. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and various other features and aspects of various exemplary embodiments will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like or similar numbers are used throughout, and in which: 
         FIG. 1  is an elevation view of a first conventional UNREP configuration; 
         FIG. 2  is an elevation view of a second conventional UNREP configuration; 
         FIG. 3  is a perspective view of a conventional cable severing process; 
         FIG. 4A  is a plan view of an exemplary wireless explosive package; 
         FIG. 4B  is a perspective view of the wireless explosive package; 
         FIG. 5  is a diagramic view of an electronics control for the package; 
         FIG. 6  is an isometric view of a cable case for the package; 
         FIG. 7  is a plan view of a metal sheet for constructing the case; 
         FIGS. 8A and 8B  are elevation views of the metal sheet after shaping; 
         FIG. 9  is an elevation view of a sheet metal edge flange; and 
         FIG. 10  is an elevation view of an exemplary installation operation. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
     In accordance with a presently preferred embodiment of the present invention, the components, process steps, and/or data structures may be implemented using various types of operating systems, computing platforms, computer programs, and/or general purpose machines. In addition, those of ordinary skill in the art will readily recognize that devices of a less general purpose nature, such as hardwired devices, or the like, may also be used without departing from the scope and spirit of the inventive concepts disclosed herewith. General purpose machines include devices that execute instruction code. A hardwired device may constitute an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA) or other related component. 
       FIG. 4A  shows a plan view  400  of a wireless explosive package for an exemplary emergency cable cutter. A foam rubber block  410  provides a substrate structure for the package, into which cavities can be excised to disposal therein. Within the block  410  can be included a wireless trigger switch  420  connected by first electric wires  425  to a power oscillator  430  and second electric wires  435  to a battery  440 . The power oscillator  430  boosts voltage from the battery  440  and connects a third electric wires  445  to provides a high voltage pulse to a pair of blasting caps  450  on opposite sides of the block  410 . The block  410  is preferably flexible, such as comprising foam rubber. 
     Upon initiation, the caps  450  explode with the resulting shock transmitted via corresponding blast igniters  455  to respective linear shaped charges  460  that direct their explosive forces to the span wire  140  for severance on command from a wirelessly transmitted signal. Example charges  460  can be commercially available Semtex® RAZOR flexible explosives.  FIG. 4B  shows a perspective view  470  of the exemplary package  480  showing the configuration of the shaped charges  460  as a right angle to direct their blasts upward relative to the block  410  orientation. 
       FIG. 5  shows a circuit diagram view  500  of an exemplary power oscillator  430 . The electronics form resembles a stun gun for purposes of producing a high voltage pulse. A “555” timer integrated circuit  510  provides a switchable control with pins  1  (ground),  2  (trigger),  3  (output),  4  (reset),  5  (control voltage),  6  (threshold comparator),  7  (discharge) and  8  (voltage supply). Pins  2  and  7  connect to the switch  420 , and pins  1  and  8  connect respectively to the negative and positive terminals of the battery  440 , with a switch diode  520  interposing between pin  8  and the battery  440 . 
     The timer circuit  510  also connects to capacitors  530  and  535 , and to resistors  540 ,  545  and  550 . Output pin  3  connects via the resistor  545  to an NPN transistor  560  in parallel with a rectifier diode  570 , which together with the battery  440  connect to input terminals of a voltage transformer  580 . The output terminals of the transformer  580  provide the high voltage pulse to the caps  445 . 
     Preferably, the switch diode  520  can, for example, be either 1N914 or 1N4148. The capacitor  530  is 0.1 μF or 0.47 μF, while the capacitor  535  is 0.01 μF. The resistors  540  and  545  are 1 kΩ each; the resistor  550  is 47Ω. The transistor is a TIP31 bipolar junction transistor with current flowing from collector (C) to emitter (E) when base (B) has higher voltage than emitter (E). The transformer  580  constitutes a miniature audio transformer receives input voltage from the battery  440  on the 1 kct (one-thousand loop) center-tap left side and supplies output voltage to the caps  445  from the 200 k (0.2 million loop) right side. 
       FIG. 6  shows an isometric view  600  of a clamshell housing case  610  for containing the package  480  around the span wire  140 . The case  610  can be substantially composed from sheet metal and includes radial semicircular frames to form an annular shell. The frames include lower and upper portions  620  and  625 , conformably capped at the proximal end by respective fore plates  630  and  635 , and at the distal end by respective aft plates  640  and  645 . 
     The portions  620  and  625  pivot along a laterally disposed axis along a common hinge  650  secured by a rod  655 . The portions  620  and  625  also join together laterally opposite the hinge  650  by respective flanges  660  and  665  that face each other. Each flange  660  and  665  has aligning through-holes  670  that to receive appropriate fasteners when they face each other along a common flat joint interface  680 . The housing  610  encloses an interior  690  in which the package  480  can wrap around the span wire  140 . 
       FIG. 7  shows a plan view  700  of a flat metal rectangular sheet  710  preferably having an overall length of 20½″ and width of 7″ for constructing the upper and lower portions  620  and  625 . The sheet  710  is cut along lines  725  to divide into left and right sections  730  and  740 , each having lengths of on the 10¼″ and 8.85″ on opposite sides with a transitional middle section edge of 1.40″. These sections  730  and  740  are designed to be identical and interchangeable for composing the portions  620  and  625 . At the longitudinal edges, through-holes  750  are drilled and the ends are folded along line  760  for an edge length of 1″. 
       FIGS. 8A and 8B  show elevation views of one of the metal sheet sections  730  and  740  further modified to form the portions  620  and  625 .  FIG. 8A  illustrates an elevation view  800  of the modified section with a ledge  810  that forms one of the flanges  660  and  665 . A semi-circular arc  820  joins the ledge  810  at a corner  830  formed along line  760 . The arc  820  has a radius of 2½″ and extends tangent as an extension  840  opposite the ledge  810 .  FIG. 8B  illustrates another elevation view  850  of the modified section with the extension  840  curled to form a tight arc  860  that forms part of the hinge  650 . Two such modified sections can be joined together and joined by the rod  655 . 
       FIG. 9  shows a plan view  900  of a sheet metal plate  910  that forms any of the end plates  630 ,  635 ,  640  and  645 . The plate  910  has an outer diameter of 5″ and an inner diameter of 1⅜″ for the span wire  140  to be contained along the length of the case  610 . The outer diameter conforms to the arc  820  to provide closure between the portion  620  or  625  and the span wire  140 . 
       FIG. 10  shows elevation views  1000  of the wireless cable cutter components and their assembly together with the span wire  140  (shown in cross-section). In first elevation view  1010 , the upper portion  625  pivots  1020  along the hinge  650  relative to the lower portion  620  to open the case  610 . While maintaining the shaped charge  460  straight, the package  480  can be curled for insertion  1030  into the interior of the case  610 . In second elevation view  1040 , the span wire  140  is disposed for insertion  1050  between the longitudinal sides of the package  480 . 
     In third elevation view  1060 , the upper portion pivots  1070  on the hinge  650  to close the case  610  and bolt fasteners  1080  insert into the aligned through-holes  660  of the flanges  660  and  665  facing each other. The flanges  660  and  665  with the fasteners  1080  constitute clamps for securing the case  610  upon closure, and alternative configurations can be contemplated without departing from the inventive scope. The completed and installed assembly can operate to sever the span wire  140  on command. Upon receiving an electromagnetic commanding signal from a ship-board transmitter, the trigger switch  420  can initiate a pulse from the oscillator  430  for discharging the caps  450  to detonate their charges  460 . 
     The afore-described embodiments provide a mechanism to safely and reliably cut heavy braided steel span wires  140 , in the event of an emergency during heavy underway replenishment operations. The objective is to fabricate an emergency-use explosive cable cutter (as in view  1060 ), which is safe, reliable, and can meet safety certifications necessary for shipboard use. Flexible linear shaped charges  460  represent an exemplary reliable method for cutting the braided steel span wire  140  (typically 1⅜″ in diameter). Shipboard applications would enable minimization of fragmentation and blast effects from any explosive cable cutting system—while still ensuring effective use. 
     The exemplary embodiments provide a two-part modular assembly: first a heavy blast-resistant clamshell case  610 , designed to easily clamp around and fasten onto the braided steel cable; and second, a flexible conformal cutting charge package  480 , which readily inserts into the case  610 . This package  480  contains the secure wireless remote detonation switch  420 , a voltage multiplier-charge capacitor pulse generator  430 , a long-life battery  440 , two strips of flexible linear shaped charge  460  with industry-standard igniters  455  and blasting caps  450 . In the event of an emergency, such as the fouling of cables interconnecting two ships  110  and  120  during UNREP in heavy seas, the UNREP supervisor could press a button to remotely trigger the explosive cable cutting device, and sever the fouled span wire  140  or other similar cable. 
     Within the United States joint and international military community, such a device would have general applicability to combat engineering brigades, and potentially for purpose applications faced by special operations forces. Building demolition companies could employ such a device for dismantling bridges, and other structures with steel reinforcement bar of significant dimensions. 
     Conventional explosive cable cutters are not approved for shipboard operation due to blast and fragmentation considerations. Mechanical cutting systems, e.g., electric drive or hydraulic drive, are relatively slow and require unacceptably many seconds (or minutes) to sever a heavy braided steel cable. Further, these systems require support systems such as electricity, wiring, hydraulics, and hydraulic lines. Reliability and maintenance of these electrical and hydraulic systems over the long-haul are perceived to be cost prohibitive, as well as creating additional ship modifications. The described exemplary designs provide an effective alternative for such emergency cable severing operations. 
     While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.