APPARATUS FOR HARMING OR KILLING FOULING FLORA OR FAUNA AND AN ITEM CARRYING THE SAME

Abstract: Apparatus for harming or killing fouling flora or fauna, for example on boat hulls, comprises two conductors (16, 20; 28) and an AC power source (24). The first conductor (16) is a conductive coating while the second conductor is a spaced sheet (20) in one embodiment and a grid (28) on a dielectric insulating coating (26) in another embodiment.

Description: APPARATUS FOR HARMING OR KILLING FOOLING FLORA OR FAUNA AND AN ITEM CARRYING THE SAME The invention relates to apparatus for harming or killing fouling flora or fauna and an item carrying the same. Fouling of items placed in the water, such as boat hulls, is a well known problem. The fouling problem is usually combated by the use of a toxic, anti- fouling paint which should kill animal or plant life which attaches itself to the painted surface. The use of toxins in this way is environmentally undesirable and other methods of control or elimination of fouling have been investigated. One such method is described in International patent application no. WO92/17061 in the name of the present applicant. The disclosure of that prior document is incorporated herein by reference. WO92/17061 discloses a trap for swimming larvae such as the larvae of fresh water mussels. The trap comprises two metal plates which are coated with insulating material and spaced apart in fresh water. The plates are connected to a high voltage AC generator to provide an electric field across the plates. Fresh water has low conductivity and so the leakage current between the plates is low. As the polarity of the water around a larvae changes, the induced polarity of the body liquid of the larvae also changes and this is sufficient to disable or kill the larvae relatively quickly. More than 90% of the internal content of a larvae is highly conductive aqueous liquid. Providing two insulated conducting plates closely spaced apart so that larvae can swim between them may be relatively difficult to achieve. According to the first aspect of the invention there is provided apparatus for harming or killing fouling flora or fauna, the apparatus comprising two conductors and a dielectric member, the conductors being provided on either side of the dielectric member and an AC power source connected to the conductors. In this way, the two conductors can simply be mounted on the dielectric member and close spacing need not be achieved. As the electric field generated by the two conductors will extend beyond the two conductors, this apparatus is effective in reducing or eliminating foul ing. Preferably, at least one of the conductors has a no more than semi-insulating coating. It had been believed that, in order to reduce leakage current and obtain the maximum polarisation, the conductors should be insulated. Experiments with semi-insulated and uninsulated conductors, however gave improved effectiveness, surprisingly. Preferably, at least one of the conductors is bare. According to another aspect of the invention, there is provided apparatus for harming or killing fouling flora or fauna, the apparatus comprising two conductors, each connected to an AC power source, one of the conductors being bare or having no more than a semi-insulating coating. Preferably one of the conductors is bare. Preferably, the apparatus further includes a dielectric member and the conductors are provided on either side of the dielectric member. In either case, one of the conductors may define apertures therein. The conductor may take any suitable form and in a preferred embodiment, one of the conductors comprises a grid. The apertures in the grid may be of any suitable size dependent on the power of the power source used and may typically be 3 to 6mm where the apparatus is for use in fresh water or 50 to 100mm where the apparatus is for use in sea water. The electric field provided by a structure of this kind is particularly effective. Material may be provided in the said apertures to reduce water resistance, for example, and also reduce the surface area of the apparatus. Insulating material may be provided in the said apertures and/or, non-toxic, anti-foul ing paint may be provided in the apertures. One of the conductors may conveniently comprise a conducting coating. Where the conductors have a gap between them, the gap may be any suitable distance dependent on the power of the power source used and may be 3 to 6mm where the apparatus is for use in fresh water or 50 to 100mm where the apparatus is for use in sea water. The power source may be arranged to apply a potential across the conductors of preferably at least 3kV. The frequency of the power source is preferably at least 300Hz. The AC power source preferably outputs a substantially square wave signal. In this way the transition from positive to negative potential is achieved quickly and so the induced polarisation within a larva, for example, will also change quickly increasing the effectiveness of the apparatus. Preferably, the duration of the transition stage of the AC cycle is less than 500 micro seconds. According to a further aspect of the invention there is provided an item to be placed in water, a part of the item which is to lie under water having a non¬ conducting surface or a non-conductive surface coating and the item including the apparatus of either aspect of the invention carried on the said part thereof. The item may be any item which is placed in water and suitably may be a boat in which case the said part of the boat may be the hull of the boat. The first conductor may conveniently comprise a coating applied to the said part of the item. In that case, an insulating coating is preferably provided on the first conductor. The insulating coating may constitute the aforesaid dielectric member where the same is provided. The second conductor may be provided on the insulating coating in that case. Two embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 a parti-ally schematic detail σross- sectional view of the apparatus of the first embodiment of the invention; and, Fig. 2 a partially schematic detail cross- sectional view of the apparatus of the second embodiment . Fig. 1 shows part of the hull 10 of a boat 12 which is 5 shown in inset. An insulating coating 14 is applied to the hull 10 and a conductive coating 16 is applied to the insulating coating 14. A further insulating coating 18 incorporating anti-fouling paint is applied to the conductive coating 16. A bare electrode 20 is 10 provided spaced from the surface of the outer insulating coating 18 by a distance of about 3mm. A plurality of insulating spacers 22, one of which is shown in Fig. 1, mount the electrode 20. The electrode 20 and the conductive coating 16 constitute 15 the aforesaid conductors and each is wired to an AC power source 24 which has a 300Hz, 3kV, sσuare wave AC output . In use, with the AC power source operating, the 20 oscillations in the electric field produced between the conductive coating 16 and the electrode 20 will be sufficient to disable or kill Daphnia larvae in over 80% of cases and, with the use of a 4.8Kv source, a success rate of 95%-l00% was obtained. ? Fig. 2 shews the second embodiment which is similar to the first and the same reference numerals will be used for equivalent features. Thus, an insulating coating 14 is supplied to the hull 10 of a boat 12. A conductive coating 16 is applied to the insulating coating 14, but a further insulating coating 26 is then applied to the conductive coating 16. A metal wire grid 28 is mounted on the second insulating coating 26. The grid apertures are about 6mm square. The apertures between the wires of the grid 28 are filled with an insulating coating 30 which may include anti-fouling material. The insulating coating 30 does not cover the wires of the grid 28 which are bare to the water. The same AC power source 24 is used as before which in this case is connected to the conductive coating 16 and to the wire grid 28. This embodiment is also extremely effective in killing and/or disabling Daphnia larvae which approach the grid 28. The apparatus of either embodiment can be used either with or without normal toxic anti-fouling paint and where used not in conjunction with anti-fouling paint or in conjunction with non-toxic anti-fouling paint it provides a particularly environmentally friendly method of reducing or eliminating fouling and, as mentioned above, is extremely effective. The apparatus of the first embodiment could be used in sea water with increased spacing between the conductive coating 16 and the electrode 20. Similarly the apparatus of the second embodiment could be used in sea water with increased grid aperture size. Clearly the apparatus of either embodiment will be effective in harming or killing a wide variety of water life.

Claims: CLAIMS 1. Apparatus for harming or killing fouling flora or fauna, the apparatus comprising two conductors and a dielectric member, the conductors being provided on either side of the dielectric member and an AC power source connected to the conductors. 2. Apparatus as claimed in claim 1, wherein at least one conductor has a no more than semi-insulating coating. 3. Apparatus as claimed in c aim 1, wherein at least one of the conductors is bare. 4. Apparatus for harming or killing fouling flora or fauna, the apparatus comprising two conductors, each connected to an AC power source, one of the conductors or having no more than a se i- insulating coating. 5. Apparatus as claimed in claim 4, wherein at least one of the conductors is bare. 6. Apparatus as claimed in claim 4 or claim 5, wherein the apparatus further includes a dielectric member and the conductors are rovided on either side of the dielectric member. 7. Apparatus as claimed in any preceding claim, wherein at least one of the conductors defines apertures therein. 8. Apparatus as claimed in claim 7, wherein at least one of the conductors comprises a grid. 9. Apparatus as claimed in claim 8, wherein the apertures in the grid are 3 to 6mm across. 10. Apparatus as claimed in claim 8, wherein the apertures in the grid are 50 to 100mm across. 11. Apparatus as claimed in any of claims 7 to 10, wherein less conducting material is provided in the said apertures. 12. Apparatus as claimed in claim 11, wherein insulating material is provided in the said apertures. 13. Apparatus as claimed in any of claims 7 to 12. wherein anti-fouling paint is provided in the said apertures. 14. Apparatus as claimed in any preceding claim, wherein one of the conductors comprises a conducting 15. Apparatus as claimed in any preceding claim, wherein the distance between the conductors is 3 to 6m . 16. Apparatus as claimed in any of claims 1 to 14, wherein the distance between the conductors is 50 to 100mm. 17. Apparatus as claimed in any preceding claim, wherein the power source is arranged to apply a potential across the conductors of at least 3kV. 18. Apparatus as claimed in any preceding claim, where the frequency of the power source is at least 300Hz. 19. Apparatus as claimed in any preceding claim, wherein the AC power source is arranged to output a substantially square wave signal. 20. Apparatus as claimed in claim 19, wherein the duration of the transition stage of the AC cycle is less than 500 micro seconds. 21. An item to be placed in water, a part of the item which is to lie under water having a non¬ conducting surface or a non-conductive surface coating and the item including the apparatus as claimed in any preceding claim carried on the said part thereof. 22. An item as claimed in claim 21, wherein the item is a boat . 23. An item as claimed in claim 22, wherein the said part of the boat is the hull of the boat. 24. An item as claimed in claim 21, 22 or 23, wherein the first conductor comprises a coating applied to the said part of the item. 25. An item as claimed in claim 24, wherein an insulating coating is provided on the first conductor. 26. An item as claimed in 25, wherein the insulating coating constitutes the dielectric member where the same is provided.

Inventors: OSTLIE LARS STEINAR, OSTLIE, LARS, STEINAR
Applicants: OSTLIE LARS STEINAR, OSTLIE, LARS, STEINAR
Application year: 1995
Main classification: A01M1
IPC codes: A01M1, A01M21, B63B59