US 3104220 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
H. PREISER FLEXIBLE TRAILING ANODE 2 Sheets-Sheet 1 INV ENTOR HERMAN S. PREIS ER ATTORNEYS Sept. 17, 1963 Filed April 27, 1960 2225;/ o u M .;...Eom
Sept. 17, 1963 H. s. PREISER FLEXIBLE TRAILING ANoDE 2 Sheets-Sheet 2 Filed April 27. 1960 INV ENTOR HERMAN S. PREISER ATTORNEYS United States Patent O 3,104,220 FLEXIBLE TRAILING ANODE Herman S. Preiser, North Springfield, Va. Filed Apr. 27, 1960, Ser. No. 25,179 l2 Claims. (Cl. 20e- 196) (Granted under llitle 3S, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
This invention relates to an inert, flexible trailing anode cathodic protection system for ships. The primary purpose of this invention is lto provide a reliable, rugged improved trailing anode and cable for the cathodic protection of ships which will allow the desired electrical current to be passed and ywill not be broken, twisted, or severed in actual use.
ln the past the disadvantages of heavy, consumable magnesium anodes which are fixed on the outside of a ships hull have been overcome by using an inert, rigid trailing anode, such as described in Patent No. 2,863,819 by H. S. Preiser, issued December 9, 195 8, where a trailing anode and cable place the anode at a distance or over 5G() anode diameters away from the ship to provide a relatively uniform current distribution and thereby effective and eiicient cathodic protection to the entire ship.
In actual operation the rigid trailing anode proved not fully satisfactory for several reasons. The primary reason was the difliculty of balancing the weight per foot of the anode section with that of the tow cable. This unequal weight distribution caused a severe twisting and bending of the anode around the connection to the tow cable when the anode was trailed from a fast moving ship, which resulted in early fatigue failure. A secondary factor was the permanent bowing of the rigid anode rod due to rough handling when the anode was tossed over- 'board and payed out from a moving ship. The impact of the anode rod with the surface of a rough sea caused the anode rod to be bent slightly out of axial alignment. V-fhen this deformed anode rod was trailed through the water, the unbalanced hydrodynamic forces on the rod caused it to oscillate and vibrate, which gradually Aweakened the connection to the tow cable and finally caused mechanical failure.
ln order to overcome these disadvantages of critical weight balance and permanent bowing, this invention comprises a combined cable and trailing anode which are made of flexible wires so that any hydrodynamic bending or twisting is reeoted throughout the entire cable and anode without being concentrated at any one location or connection, and where uniform weight per foot distribution is no longer critical.
Another object of this invention is Ito disclose a iiexible trailing anode and cable which may be completely wound on a towing winch without damage, such as when the ship is in port or when the anode is retrieved at sea.
Another object of this invention is to disclose a flexible trailing anode cable which is relatively easy to manufacture with automatic machinery.
Another object of this invention is to disclose a connection means bet-Ween a trailing anode and a cable which will allow a great deal of mechanical strain and bending without twisting or breaking and a detachable means for reinstalling another anode section in the event of damage.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
FIG. l is a view, partly in cross-section, of the stern Patented Sept. 17, 1963 of a ship showing the arrangement of the trailing anode, automatic cable winch, and power supply;
FIG. 2 is a cross-sectional view to scale of a preferred embodiment of the liexible trailing anode assembly showing details of the anode, the towing cable construction, and a drogue fitted to the trailing end of the anode; and
FIG. 3 is a cross-sectional view to scale of another embodiment of the flexible trailing anode assembly showing details of the anode, the towing cable construction and a detachable connection between the anode and cable.
Referring to the drawings, FIG. l is a View, partly in cross-section, of the stern of a ship 1li traveling through the ocean 12 and trailing a cathodic protective anode 14 by tow cable 16. Cable 16 passes through opening 18 in the hull 20 and over nubber covered metal or plastic sheaves 22 to reel 24 on automatically controlled winch 26 driven by motor 28.
A D.C. power supply 30 has its positive terminal connected through a brush and slip ring arrangement to the end of cable 16 mounted on reel 24 and has its negative terminal connected to the hull 20. The rudder stock 23 and propeller shat L27 are grounded to the hull 2li for electrical continuity for propeller and rudder protection by means of a flexible grounding strap 2l. and a slip ring and brush assembly 25, respectively. A cathodic protective current is supplied through cable 16, anode 14E and the ocean 12 to the ship appendages and hull 26u The cathodic protective current from anode i4 lowers the electrical potential of the hull 2@ to around .8 volt to negatively polarize the hull and thereby prevent anodic corrosion. In addition a layer of monatomic hydrogen is formed over the hull and .metallic salts are deposited to insulate the hull from the corrosive effects of the sea water.-
For a typical tanker or large freighter having a 60,000 square foot underwater surface area, an electrical current of l milliampere per square foot (60 amperes) will provide sufficient protection to a newly painted hull. This current will gradually increase to about 3 milliamperes per square foot amperes) as the paint wears and abrades in service. The bronze propeller for the ship, which is `about 22 feet in diameter, will require 50 milliamperes per square foot of surface area (30 amperes) for cathodic protection due to the higher water velocities over the bare blades which strip off the monatomic hydrogen and metallic salts. This means that the flexible trailing anode cathodic protection system will have to provide up to 210 amperes with as small a voltage drop as is reasonably practical.
These relatively large currents required highly conductive anodes which would not be rapidly corroded by the anodic current and reaction products (oxygen, chlorine, etc.) and which would trail easily and smoothly through the water without breaking or bending.
Referring to FIG. 2, a preferred embodiment of the .iiexib'le trailing anode i4 is shown in cross-section to scale including part of the cable 32, titanium connector 34, flexible strip anode 36 and a drogue 3S.
Flexible strip anode 36 is made of 7 x 19 stranded titanium wire 40 of .045 diameter to a .675 inch anode diameter. A 1A inch wide, .020 inch thick, titanium strip 42 having a coat of .00025 inch thick platinum bonded to the outer surface is swaged to the titanium wire 40 in a spiral wrap with Ms between turns to allow the wire 40 to liex.
A titanium ball yfitting 44 is swaged to the trailing end of the anode 36 and the cab-le end of the anode 36 is swaged in .titanium connector 34 to prevent unraveling of the anode.
resistance of .05 ohm `to permit the 210 ampere cathodic protective current to ow with `only a 10.5 volt drop. Titanium is a so-called rectilier metal that forms an insulating oxide on an exposed surface under anodic conditions where the oxide will not break down or conduct an electrolytic cu-rrent until 12 to 15 volts are applied across the oxide.
The inert platinum coated strip 42 will therefore conduct the cathodic protective current to the sea water without corroding the anode 36 or requiring frequent anode replacement.
The streamlined connector 34 is also swaged to the composite tow cable, indicated at 32, having a 7 x 7 stranded steel wire core 46 of .021 inch `diameter wire with a layer of an .010 inch nylon coat 48 to allow the core 46 to move relative to the rest of the cable. A 6 X 19 stranded copper conductor 50 of .O34 inch diameter wire carries most of the cathodic protective current to connector 34. As shown in FIG. 2, the layer 50 is about and longer than layer 48, but short of the extreme end of cable 48. This structure insures good electrical contact between tow cable 46 and connector 34.
A fiber reinforced neoprene insulator llayer 52 covers the copper conductor 50 and a polyvinyl chloride sheath 54 of .030 inch thick provides a layer that covers the outside of the layer 52 so as to provide Oxy-chlorine resistance for the cable 32. The -cable yv2 has an outer diameter of .87 inch and has a 2000 pound tensile strength.
Titanium connector 34 is swaged to wire core 46 and conductor 50 for good mechanical and electrical connection and has a series of concentric grooves 56 to rmly grip the insulator 52 and sheath 54 after light swaging to keep the water and electrolytic currents away from the steel core 46 and copper conductor 50.
The anode, cable, and connector construction thus described in FIG. 2 provides an inert platinum anode coating to conduct the protective :anode currents to the sea water.
The exible strip anode 36 trails easily and smoothly through the water without excessive twisting and bending of connector 34 since any exing of the ano-de is distributed over its entire length without being distributed at any one point to cause Ifatigue and failure.
In addition the exible anode 36 may be retrieved by winch 26 and wound ou reel `24 and over sheaves 22 without bending or breaking the anode.
Drogue 38 includes a swivel fitting section 58 around ball fitting 44 and has a 5 inch diameter cone 60 with 1A inch diameter holes uniformly spaced on 1/2 inch centers to provide a drag resistance of 50 pounds at 20 knots. The drogue 3S dampens a large part of the wire anode 36 oscillations while towing. Since part of the drogue resistance is in the downward direction when fthe retrieving winch and sheaves are mounted above the ship water line, a depressive force is thus exerted at the end of the anode to keep the anode and cable below the water surface at high ship speeds.
Referring to FIG. 3, another flexible trailing anode, detachable connector and cable are shown in cross-section and drawn to scale.
The flexible trailing anode 62 is designed for 105 ampere service and comprises a 3A; inch diameter, 7 x 19 stranded titanium wire rope 64 where each wire is .025 inch in diameter. The titanium wire rope 64 is 171/2 feet long and is given a to 30 micro-inch thick flash coat of inert platinum to conduct the cathodic protective current to the sea water.
A streamlined titanium sleeve fitting 66 is swaged .onto the end lof the trailing end of the anode 62 to prevent unraveling of the wire rope 64.
The other end of the anode is swaged into a female connector 68 for detachable connection to a titanium male connector 70 that is swaged to the composite tow cable 72. Female connector 68 'has a circular groove 74 to hold a neoprene Oring 76 to seal the threaded connection between the -two connectors. In order to minimize any added resistance between the two connectors by the formation of a partially insulating tlm on the titanium threads, 4the O-ring 76 seals the threaded connection from the sea water.
A tapered titanium locking pin 78 is driven through a hole in female connector 68 at the threaded connector section to prevent loosening of the connectors or loss of the anode 62 during service.
Cable *72 may be rnade smaller for the l05 ampere service `than the cable in FIG. 2 and has a central core S0 of 6 x 19 stranded wire of .O14 inch diameter copper wire.
A layer of 19 strands of .014 inch diameter steel wire, indicated by number 82, is wound around and forms a layer about the copper core 80 to provide a 1000 pound tensile strength for the cable 72.
A .030 inch thick layer 84 of polyethylene is extruded around the steel wire 82 and a .030 inch thick sheath 86 of nylon is extruded around the polyethylene layer 84 for abrasion and corrosion resistance.
The composite cable 72 has an outer diameter of .42 inch and is sealed to male connector 70 by light swaging with the help of grooves 88. The copper core 80 and steel wire 82 are bare at 90 and extend beyond layers 52 and 54 for firm swaging in Ithe male connector 70.
The llexible anode 62 and cable 72 as shown in FIG. 3 will trail easily and smoothly through the water and may be wound over the sheaves 22 and reel 24 without breaking or bending.
Flexible trailing anodes can be built to almost any current carrying capacity. However, the primary limiting factor is the anode size necessary to carry the current and still be relatively light weight, small diameter, and supple for easy towing. rIhe applicants experience indicates that, for systems up to 250 ampere capacity, platinum coated titanium cable can be used for the anode section and can still retain its flexibility.
Above 250 ampere capacity, platinum coated tantalum cable is preferred because tantalum has about one fourth the electrical resistivity of titanium and will withstand voltages across the oxide ihn of up to volts. As a typical example, for a 400 ampere system constructed in accordance with FIG. 2 or 3, a tantalum cable would use a M1 inch cable 'by 12 feet in length.
The flexible trailing anodes as thus described are simple `to manufacture on automatic cable and wire machines while the inert platinum coatings may be applied in the form of very thin or flash coatings to minimize the total cost.
Since the anodes are exible and therefore distribute any torsion, tension, or bending along their whole length without concentrating it at the connection between the anode and cable, the anodes, connectors, and cables will have a long life. Also, variations between the weight per foot and outer dimensions of the anodes, connectors, and cable will not create undesirable oscillations or vibrations.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
What is claimed is:
1. An inert, exible trailing anode system for the cathodic protection of ocean going ships adapted for reeling onto a retrieving -reel mounted aboard a ship comprising a trailing anode cable connectable at one end to the reel and the other end adapted to trail a cathodic protective anode through the ocean, wherein said cable comprises a central steel wire core to provide a mcchanically strong connection between the ship and anode, a nylon coat molded on an end of said core, a coaxial stranded copper conductor mounted around said core to provide a high conductivity electrical connection between the ship and said anode, a neoprene plastic insulator molded around said copper sleeve and a polyvinyl ohloride plastic sheath molded around said insulator; the inert, exible trailing anode attached to the said other end of said cable comprising a plurality of Wires made from a metal selected from the group consisting of titanium and tantalum and a platinum coated titanium strip swaged around said wires for transmitting a cathodic protective current to the ship; a first streamlined titanium fitting swaged around said -cable and anode; a titanium ball fitting swaged around the trailing end of said anode; and means connected between said cable and ship for passing a cathodic protective current between said anode and ship.
2. An inert, fiexible trailing anode system according to claim 1 wherein said wires are titanium.
3. An inert, flexible trailing anode system according to claim l and further characterized by a plastic drogue having a plurality of holes held at the trailing end of said anode by said ball fitting for vibration damping of said anode.
4. An inert, flexible trailing anode and fiexible cable for the cathodic protection of ships where the anode and cable may be wound on a ship board retrieving reel without breaking, comprising a central copper conductor core, coaxial stranded steel wires mounted around said core, a polyvinyl chloride plastic insulating layer around said steel wires, a trailing anode comprising a plurality of flexible stranded titanium wires having an inert, conductive coating, a connector between said anode and cable, said connector having aligned holes in which ends of said anode and cable are secured, said connector consisting essentially of a metal selected from the group consisting of titanium and tantalum, and a sleeve mounted around the trailing end of said anode to prevent unraveling.
5. An inert, exible trailing anode and cable according to claim 4 and further characterized by said connector comprising a female member swaged to said anode and a male member swaged to said cable, the male member having lhreads formed thereon, said female member having complementary threads formed therein, and said male member being screwed into said female member to detachably connect the male and female members whereby said anode may be easily detached from said cable.
6. An inert, exible trailing anode and cable according to claim -5 and further characterized by a neoprene O-r-ing, said `female connector having means for holding said neoprene O-ring for sealing the threaded connection between said connectors.
7. An inert, flexible trailing anode and cable according to claim 6 and further characterized by said female connector member having a hole adjacent said threaded section and a tapered locking pin for mounting in said hole for locking said connector members together.
8. An inert, exible trailing anode system for the cathodic protection of ships, the anode being towed by a cable from the ship, said system comprising an intermediate separable titanium connector elongated lengthwise, said connector having a lengthwise hole at each end, a fiexible stranded cathodic protection anode wire, means securing a bare end of said anode wire in a first of said holes, said means comprising a swage joint, a flexible tow cable, means securing a bare end of said tow cable in the second of rsaid holes, said connector comprising two detachable parts, the first of said holes being in one of said parts and the second of said holes being in t-he second of said parts, and removable means for locking said parts together in connected relation, said means securing a bare end of said tow cable in the second of said holes including a plurality of adjacent layers on the outside of an end portion of said cable, said layers comprising a metallic layer and an insulating layer, and further including a swage joint securing said layers and cable to said connector; said anode wire comprising a plurality of metallic strands, the metal of said strands being selected from the group consisting of titanium and tantalum, a platinum coating on said wires, and a fitting around the trailing end of said anode wire, whereby to prevent unraveling of said strands.
9. A system as defined in claim 8 wherein said fitting comprises a drogue, and swivel socket means centrally of said drogue connecting said drogue to the trailing end of said anode wire.
10. A system as defined in claim 9 wherein said drogue comprising an outwardly extending plate having a plurality of holes.
11. A system as defined in claim 8 wherein said fitting is streamlined.
12. An inert fiexible trailing anode system as defined in claim 8 wherein said two parts of said connector are interconnected by mating threaded portions thereon and an O-ring seal is positioned between said two parts whereby said threaded portions are protected from contact with ambient water.
References Cited in the file of this patent UNITED STATES PATENTS 833,252 Schwennker Oct. 16, 1906 945,917 Cottrell Ian. 11, 1910 2,106,004 lInglee Jan. 18, 1938 2,258,435 Adolph et al. Oct. 7, 1941 2,396,734 Williams Mar. 19, 1946 2,795,541 Muller June 11, 1957 2,863,819 Preiser Dec. 9, 1958 2,865,832 Pitzer Dec. 23, 1958 2,894,366 Leckie July 14, 1959 2,908,623 Doring Oct. 13, A1959 2,916,429 Vossnack et al. Dec. 8, 1959 3,010,891 Anderson Nov. 28, 1961 FOREIGN PATENTS 13,971 Great Britain 1890 OTHER REFERENCES Cotton: Platinum Metals Review, volume 2, No. 2, 204-290F, 1958.