GB868167A - Improvements relating to the electrolytic protection of ships against corrosion - Google Patents

Abstract

868,167. Preventing corrosion. SHELL RESEARCH Ltd. May 1, 1959, No. 14942/59. Class 123(1) In an impressed current cathodic protection system of the kind in which a direct electric current is passed along a trailing aluminium wire 6 coiled upon the drum 5 of a power-driven winch 3 mounted in the stern of the hull of a ship, means are provided for automatically driving the winch 3, regularly at a controlled rate, to pay out the wire 6 and compensate for consumption due to the passage of current. The drum 5 is mounted in bearings 8 through which direct current from a lead 9 is passed to the wire 6 and returned from its submerged end 7 to the hull 4, the magnitude of the current being controlled in accordance with the indications of a reference electrode 11. An electric motor 12, which drives the drum 5 through worm and worm gear 13, 14, is supplied with electric power through two solenoid-controlled, multiplegauged, switches 19, 20 which respectively control the rotation of the motor 12 in the haul and pay-out directions. The solenoids of the switches 19, 20 are controlled by current from a transformer 21 whose secondary includes a wire chute switch 22. To haul in the wire 6 either a local or a remote push-button switch 25 or 26 is pressed to close solenoid holding contacts, break the circuit to the solenoid of the switch 20, and supply current to the motor 12. Paying out can be carried out manually by making a switch 29 to supply current to the actuating solenoid of the switch 20, open the circuit to the solenoid of the switch 19, and energise the motor 12. Automatic pay out is effected by a process timer 31 which is supplied with current through a limit switch 20, a switch 32, which is closable by the timer 31 at regular intervals, periodically completing the circuit to the solenoid of the switch 20 to energise the motor 12. The delay action of a mechanism 34 allows an initial rotation of the drum 5 until the particular cam, of a number of cams 25 on the drum 35, is cleared from a switch 33 which then closes to complete a holding circuit. The drum 5 continues to be driven in the pay-out direction until the next cam 35 opens the switch 33 to de-energise the solenoid of the switch 20 and stop the motor 12. When the tension of the wire 6 being paid out becomes excessive the shaft of the motor 12 is moved axially against a spring 15 to open the limit switch 16. In rough weather it may be expedient to close the switch 32 by hand so that the wire 6 is paid out until a tension sufficient to open the limit switch 16 is reached, the tension of the wire being determined by the adjustment of a spring 15. The current, supplied by a source 36, is returned through an ammeter 38 and an adjustable resistance 37 and also through a parallel path comprising the propeller shaft 42, a slip ring 4, an ammeter 40, and an adjustable resistance 39. Specification 816,417 is referred to.