Technical field

The proposed technology relates to the reduction of biofouling on watercraft .

Background

Biofouling is the accumulation of microorganisms , plants , algae , or small animals on surfaces exposed to water . This is a problem for watercraft that relies on a hull for buoyancy . The biofouling can increase the weight of the watercraft , thus increasing the displacement and reducing the tonnage . Biofouling is a particular problem for watercraft for transport since it can lead to a signi ficant increase in drag .

Biofouling can be divided into microfouling and macrofouling . The former relates to biofilm formation and bacterial adhesion and the latter relates to the attachment of larger organisms , such as seaweed and barnacles .

Existing fouling technologies for preventing accumulations from forming typically rely on non-toxic coatings or boat paint compositions with biocides . The latter is typically more ef ficient . However, the use of biocides is restricted and should be avoided, particularly in lakes and river . Thus , there is a need for an alternative to using biocides . There is further a need for an anti- fouling that is ef ficient , easy to apply, and has a long durability .

Summary

It is an obj ect of the proposed technology to meet one or more of the abovementioned needs .

According to a first aspect of the proposed technology, a hull arrangement for a watercraft is provided for preventing biological growth or biofouling . The arrangement comprises : a hull having an inside and an outside ; an electrically conductive first film covering the outside of the hull on a first portion of the hull ; a first electrical connector connecting to the conductive first film; a second electrical connector connecting to the conductive first film and spaced apart from the first electrical connector ; and an electric power source connected to the first electrical connector and the second electrical connector and configured for supplying a first electric current via the first electrical connector and the second electrical connector . The conductive first film constitutes an unbroken, or uninterrupted, electrical conductor between the first electrical connector and the second electrical connector .

According to a second aspect of the proposed technology a method for providing a hull arrangement for a watercraft is provided for preventing biological growth or biofouling . The watercraft has a hull having an inside and an outside . The method comprises : applying an electrically conductive first film on the outside of the hull on a first portion of the hull ; connecting a first electrical connector to the conductive first film; connecting a second electrical connector to the conductive first film spaced apart from the first electrical connector, wherein, or such that , the conductive first film constitutes an unbroken, or uninterrupted, electrical conductor between the first electrical connector and the second electrical connector ; and connecting an electric power source to the first electrical connector and the second electrical connector, wherein the electric power source is configured for supplying a first electric current via the first electrical connector and the second electrical connector . The conductive first film may be composed of the same material between the first electrical connector and the second electrical connector . The conductive first film may be biocide- free . For example , it does not contain copper compounds or the like for preventing biological growth or biofouling . Worded di f ferently, the conductive first film may be copper free . The conductive first film may be , or form a corrosion barrier, which is advantageous in combination with the hull being a metal hull .

Here , a watercraft is understood to encompass a ship, boat , or barge for transport . It is also understood to encompass structures relying on a hull for buoyancy, such as buoys , of fshore semi-submersible platforms , and floating production/ storage/of f loading systems used in oil production .

It is speci fied that the proposed technology is for preventing biological growth or biofouling . It is understood that there may be di f ferent applications of the technology . The technology may be for preventing biological growth or biofouling in freshwater, saltwater, or brackish water .

In the above aspects of the proposed technology, the hull may have a waterline and the first portion of the hull may extend below the waterline of the hull or may be located at least in part below the waterline . The first portion may extend from above the waterline to below the waterline .

It is understood that the first electrical current is supplied to the conductive first film in operation . It is further understood that the conductive first film can conduct the first current between the first electrical connector and the second electrical connector . The conductive first film, the first electrical connector, and the second electrical connector may be positioned, or arranged, for conducting the first electric current through the conductive first film between the first electrical connector and the second electrical connector . It is understood that this may be below, or at least partly below, the waterline of the hull . Here , the waterline may represent , or correspond to , a line where the hull meets a water surface when the watercraft is unloaded, for example without carrying passengers or cargo . Additionally, the waterline may represent , or correspond to , the line where the hull of the watercraft meets the water surface when the watercraft is at rest relative to the water surface .

According to a third aspect of the proposed technology, an operation method for hull arrangement according to the first aspect of the proposed technology is provided . The operation method comprises : supplying a first electrical current via the first electrical connector and the second electrical connector using the electric power source . It is understood that supplying the first electrical current is supplied to the conductive first film . It is speci fied that the conductive first film constitutes an unbroken, or uninterrupted, electrical conductor between the first electrical connector and the second electrical connector . Worded di f ferently, the conductive first film established an unbroken, or uninterrupted, electrical , or resistive , connection between the first electrical connector and the second electrical connector . Worded di f ferently, the first electrical connector, the conductive first film, and the second electrical connector form, or constitute , a complete , or uninterrupted, electrical conductor . This means that the conductive first film does not form a cathode and anode pair that together with the water surrounding the hull form an electrolytic cell . The first electric current is essentially confined to the conductive first film .

It is speci fied that the electric power source is configured for supplying a first electric current via the first electrical connector and the second electrical connector . Worded di f ferently, the electric power source is arranged to generate a first electric current in the conductive first film that flows between the first electrical connector and the second electrical connector . Worded di f ferently, the electric power source is arranged to generate a first electric current in the conductive first film that flows from the first electrical connector to the second electrical connector, or vice versa . In the third aspect of the proposed technology, the electric power source is used to achieve the speci fied ef fects .

The electric power source , the first electrical connector, the conductive first film, and the second electrical connector may form a closed electric circuit . The first electrical connector, the conductive first film, and the second electrical connector may be coupled in series with, or relative to , the electric power source . It is understood that this is at a pre-launching of the watercraft , or without the conductive second film being exposed to water . Worded di f ferently, the electric power source , the first electrical connector, the conductive first film, and the second electrical connector may be arranged to conduct the first current from the electric power source to the first electrical connector, from the first electrical connector to the conductive first film, from the conductive first film to the second electrical connector, and from the second electrical connector to the electric power source , or in the reverse direction . This way, electrolytic corrosion or calcareous deposits on the conductive first film is avoided or reduced .

The first electrical connector and the second electrical connector may connect physically, or directly, to the conductive first film . The first electrical connector, the second electrical connector, the electric power source , and the conductive first film may form part of a closed electrical circuit . The shortest path in the conductive first film between the first electrical connector and the second electrical connector may pass below the waterline . It is understood that the first electrical connector and/or the second electrical connector may be positioned, or connected to the conductive first film, above the waterline . This contributes to reduce electrolytic ef fects . Alternatively, the first electrical connector and/or the second electrical connector may be positioned, or connected to the conductive first film, below the waterline .

It has been found that the electric current speci fied here inhibits microfouling and the formation of biofilm on the conductive first film . This in turn inhibits macrofouling that depends on the presence of a biofilm . The electric current may also directly inhibit macrofouling . Thus , the proposed technology contributes to inhibit biofouling, thus reducing the need for anti- fouling paint containing biocides .

The conductive first film may be permanently fixed to , or permanently attached to the watercraft , or more speci fically to the hull . This means that the conductive first film cannot be removed from the hull without causing structural damage to the conductive first film . Worded di f ferently, the conductive first film may be non-removable . It is understood that the conductive first film has a thickness transverse to the hull . The conductive first film may have an average thickness , and the thickness of the conductive first film may vary by less than 50% , or less than 25% , from the average thickness along the shortest path in the conductive first film between the first electrical connector and the second electrical connector .

The conductive first film may have a width transverse to the shortest path between first electrical connector and the second electrical connector . The conductive first film may have an average width, and the width of the conductive first film may vary by less than 80% , 40% , or 20% from the average width when following, or traversing, the shortest path between the first electrical connector and the second electrical connector . Worded di f ferently, the conductive first film may be arranged to provide a smooth drop in electric potential between the first electrical connector and the second electrical connector in operation, which contributes to reduce or prevent electrolytic ef fects on the conductive first film as such . The average width transverse to the shortest path between first electrical connector and the second electrical connector may be less than 10 m, or less than 5 m . The average width may be greater than 0 . 5 m, greater than 1 m, or greater than 2 m .

The conductive first film may be a layer of electrically conductive paint . For example , the conductive paint may be an underwater hull paint containing carbon black . Alternatively, the conductive first film may be a sheet of an electrically conductive material . For example , the sheet may be of an electrically conductive polymer containing carbon black . The carbon black contributes to improve the electrical conductivity of the first film . Worded di f ferently, the conductive first film may be polymer based . For example , the polymer may be an epoxy, polyurethane , or polyester . The polymer as such may be electrically conductive . Alternatively, the conductive first film may comprise additives making the conductive first film electrically conductive . For example , the additive may be carbon black . Alternative to the conductive first film being a paint , it may be a layer of an electrically conductive gelcoat . For example , the gelcoat may comprise carbon black, which contributed to make the gelcoat electrically conductive . Gelcoats are commonly used to provide the visible surface of a fibre-reinforced composite .

It is speci fied that the electrically conductive first film covers the outside of the hull on the first portion of the hull . This means that the conductive first film forms , or constitutes , an outermost layer at , or of , the first portion of the hull . It also means that there is no other layer outside the conductive first film . This contributes to improve the prevention of biological growth or biofouling but makes the conductive first film susceptible to electrolytic ef fects . Worded di f ferently, the conductive first film may be arranged to contact water in use of the watercraft .

The first and second electrical connectors may each comprise a net of metal contacting the conductive first film . It is understood that a net encompasses a mesh and a web . Alternatively, the first and second electrical connectors may each comprise a plate , or sheet , of metal . For example , the net or plate may be of stainless steel . It is understood that the net or plate is operationally connected to the electric power source , for example by a cable connection forming part of the first and second electrical connectors .

The net or plate may be an elongated strip aligned with, or extending parallel with, the waterline of the hull . The net may be at least in part , or fully, embedded in the conductive first film, which is particularly advantageous for establishing an electrical connection i f the conductive first film is a layer of electrically conductive paint . The paint may contribute to hold the net in place on the hull . The plate may be fully covered by the conductive first film, which is advantageous i f the conductive first film is a sheet . It is understood that the net , or plate , may be aligned with or conform to the hull or the conductive first film . The first portion of the hull may be electrically insulating, or of an electrically insulating material . For example , the hull may be a monocoque fiberglass hull . This prevents the first electric current from passing through the hull instead of through the conductive first film, thus improving the inhibiting ef fect on the microbiological growth .

The first portion of the hull may be electrically conductive . For example , the hull may be a metal hull , such as a steel hull or aluminum hull . The hull arrangement may further comprise : an electrically insulating first film arranged, or located, between the electrically conductive first film and the hull . It is understood that the insulating first film insulates the conductive first film from the hull and that it covers the first portion of the hull . The electrically insulating first film may be permanently fixed to , or permanently attached to the watercraft , or more speci fically to the hull . The electrically conductive first film may then be permanently fixed to , or permanently attached to the electrically insulating first film .

The first electrical connector may comprise an electric first cable arranged to couple the electric power source to the conductive first film, or to the abovementioned net or plate of metal of the first electrical connector . Similarly, the second electrical connector may comprise an electric second cable arranged to couple the electric power source to the conductive first film, or to the abovementioned net or plate of metal of the second electrical connector . The first and/or the second cable may be located above the waterline , which contributes to avoid electrolytic ef fects involving the cables as such . Alternatively to the second electrical connector comprising an electric second cable , the hull may be electrically conductive , and the hull may form part of the second electrical connector . This means that the hull is arranged to conduct the first electric current between the conductive first film and the electric power source . This is advantageous i f the current is an alternating current , as further described below, with the hull forming, or constituting, ground or neutral for the electric power source .

The method of the second aspect of the proposed technology may comprise prior to applying the electrically conductive first film : applying an electrically insulating first film on the outside of the hull on the first portion of the hull . The insulating first film prevents the first electric current from passing through the hull instead of through the conductive first film, thus improving the ef fect on the microbiological growth, in particular for electrically conductive hulls . It is understood that the conductive first film is applied on top of the insulating first film . The material of the insulating first film may have an electrical resistivity that is at least two orders of magnitude , or at least three orders of magnitude greater than the electrical resistivity of the conductive first film .

The insulating first film may be an electrically insulating paint . Alternatively, the insulating first film may be a sheet of an electrically insulating material . For example , the sheet may be of an electrically insulating polymer . The conductive first film may be polymer based . For example , the polymer may be an epoxy, polyurethane , or polyester . Alternative to the insulating first film being a paint , it may be a layer of electrically insulating gelcoat .

The hull may have a bow and a stern . The first portion may extend from a point at the bow to a point at the stern . The first electrical connector may be positioned at the bow and the second electrical connector may be positioned at the stern . The conductive film may extend above the waterline at the bow and at the stern . These features are advantageous for smaller boats .

The hull may have a centerline , or keel . The first portion of the hull may extend across the centerline . The centerline may bisect the first portion of the hull . The conductive film may extend above the waterline on opposite sides of the centerline . The first electrical connector and the second electrical connector may be positioned on opposite sides of the centerline . These features are advantageous for larger ships .

The hull arrangement according to the first aspect of the proposed technology may further comprise : an electrically conductive second film covering the outside of the hull on the first portion of the hull , wherein the conductive second film is spaced apart , or disj oint , or electrically insulated, from the conductive first film; a third electrical connector connecting to the conductive second film; and a fourth electrical connector connecting to the conductive second film and spaced apart from the third electrical connector . The electric power source is connected to the third electrical connector and the fourth electrical connector and configured for supplying a second electric current via the third electrical connector and the fourth electrical connector . It is understood that the conductive first film and the conductive second film may be spaced apart along the hull . This means that the conductive first film and the conductive second film are not overlapping . The conductive first film and the conductive second film may be spaced apart by an electric insulator, such as an electrically insulating film, and the conductive first film and the conductive second film may be overlapping and spaced apart by the electric insulator .

The method according to the second aspect of the proposed technology may further comprise : applying an electrically conductive second film on the outside of the hull on the second portion of the hull ; connecting a third electrical connector to the conductive second film, connecting a fourth electrical connector to the conductive second film and spaced apart from the third electrical connector, wherein, or such that , the conductive second film constitutes an unbroken, or uninterrupted, electrical conductor between the third electrical connector and the fourth electrical connector ; and connecting the electric power source to the third electrical connector and the fourth electrical connector, wherein the electric power source is configured for supplying a second electric current via the third electrical connector and the fourth electrical connector .

The method according to the third aspect may comprise : supplying a second electrical current via the third electrical connector and the fourth electrical connector using the electric power source .

The second portion of the hull may extend below the waterline of the hull . The conductive second film, the third electrical connector, and the fourth electrical connector may be positioned, or arranged, for conducting the second electric current through the conductive second film between the third electrical connector and the fourth electrical connector below, or at least partly below, the waterline of the hull .

It is speci fied that the electric power source is configured for supplying a second electric current via the third electrical connector and the fourth electrical connector . Worded di f ferently, the electric power source is arranged to generate a second electric current in the conductive second film that flows between the third electrical connector and the fourth electrical connector . Worded di f ferently, the electric power source is arranged to generate a second electric current in the conductive second film that flows from the third electrical connector to the fourth electrical connector, or vice versa .

The electric power source , the third electrical connector, the conductive second film, and the fourth electrical connector may form a closed electric circuit . The third electrical connector, the conductive second film, and the fourth electrical connector may be coupled in series with, or relative to , the electric power source . Worded di f ferently, the electric power source , the third electrical connector, the conductive second film, and the fourth electrical connector may be arranged to conduct the first current from the electric power source to the third electrical connector, from the third electrical connector to the conductive second film, from the conductive second film to the fourth electrical connector, and from the fourth electrical connector to the electric power source , or in the reverse direction .

It is speci fied that the conductive second film is spaced apart , or disj oint , from the conductive first film . This means that the second portion of the hull is spaced apart , or disj oint , from the conductive first portion of the hull . The conductive second film allows for larger ship hulls to be covered with a more even distribution of electric currents across the hull .

It is speci fied that the electrically conductive second film covers the outside of the hull on the second portion of the hull . This means that the conductive second film forms , or constitutes , an outermost layer at , or of , the second portion of the hull . This means that there is no other layer outside the conductive second film . Worded di f ferently, the conductive second film may be arranged to contact water in use of the watercraft .

The conductive second film may have any of the features described above for the conductive first film . For example , the conductive second film may be a layer of conductive paint . Similarly, the third electrical connector and the fourth electrical connector may have any of the features described above for the first electrical connector and the second electrical connector, respectively . The electric power source may be configured to cooperate with the conductive second film, the third electrical connector, and the fourth electrical connector as speci fied above for the conductive first film, the first electrical connector, and the second electrical connector .

The second portion of the hull may be electrically insulating, or of an electrically insulating material . Alternatively, the second portion of the hull may be electrically conductive . The hull arrangement may further comprise : an electrically insulating second film arranged, or located, between the electrically conductive second film and the hull . The method of the second aspect of the proposed technology may comprise prior to applying the electrically conductive second film : applying an electrically insulating second film on the outside of the hull on the second portion of the hull . The insulating second film may have any of the features described above for the insulating first film . For example , the insulating second film may be a layer of insulating paint .

The electric power source may be configured for alternating between supplying the first electric current via the first electrical connector and the second electrical connector and supplying the second electric current via the third electrical connector and the fourth electrical connector . This means that electric power source does not supply the first electric current and the second electric current at the same time . This may prevent electrical interactions , for example by saltwater acting as an electrolyte , between the conductive first film and the conductive second film that could cause the electric current to traverse an unintended path . In extension, this allows for the conductive first film and the conductive second film to be positioned closer to one another, improving the coverage of the hull .

The first electrical connector establishes a first connection to the conductive first film, the second electrical connector establishes a second connection to the conductive first film, the third electrical connector establishes a third connection to the conductive second film, and the fourth electrical connector establishes a fourth connection to the conductive second film . The first connection and the third connection may be closer to one another than the first connection and the second connection . Similarly, the second connection and the fourth connection may be closer to one another than the first connection and the second connection .

The first electric current may be a direct current . Similarly, the second electric current may be a direct current . The electric power source , and optionally the electrical connectors , may be configured to establish the same electric polarity for the first electrical connector and the third electrical connector . Similarly, the electric power source may be configured to establish the same electric polarity for the second electrical connector and the fourth electrical connector . For example , the first electrical connector and the third electrical connector may be coupled in parallel to the electric power source . Similarly, the second electrical connector and the fourth electrical connector may be coupled in parallel to the electric power source . This contributes to reduce electrolysis between the conductive first film and the conductive second film i f both are supplied with a current at the same time , and in extension corrosion is reduced .

With the first electric current being a direct current , the electric power source may be arranged to regularly switch the poles of the first terminal and the second terminal . The electric power source may be arranged to regularly switch the electric polarity between the first electrical connector and the second electrical connector . Similarly, with the second electric current being a direct current , the electric power source may be arranged to regularly switch the electric polarity between the third electrical connector and the fourth electrical connector . Worded di f ferently, the electric power source may be arranged to regularly change the direction of the first electric current . Similarly, the electric power source may be arranged to regularly change the direction of the first electric current . This contributes to a more even distribution of the currents within the conductive films i f there is a current leakage to the surroundings of the conductive films . The electric power source , and optionally the electrical connectors , may be arranged to supply the first electric current and the second electric current with the same directions across the centerline . Worded di f ferently, the first electric current and the second electric current may have the same direction relative to the hull .

The electric power source may be arranged to supply the first current at a positive potential . Similarly, the electric power source may be arranged to supply the second current at a positive potential . This contributes to reduce the formation calcareous deposits on the cathode if there is a current leakage to the surroundings, which could eventually block the conductive films.

The first electric current may be an alternating current. Similarly, the second electric current may be an alternating current. The alternating current may have a frequency between 0.5 kHz and 10 kHz, between 1 kHz and 5 kHz. The alternating current may have a frequency between 0.5 and 1.5 kHz, between 1.5 and 2.5 kHz, between 2.5 and 3.5 kHz, and/or between 3.5 and 4.5 kHz. Alternatively, the alternating current may have a frequency below 500 Hz, below 200 Hz, below 100 Hz, or below 50 Hz. The first electric current and the second electric current may be in phase. This contributes to reduce electrolysis between the conductive first film and the conductive second film.

The electric power source may be configured for supplying a pulsed, or intermittent, electric current. The pulses may have a combined pulse length over a period of time that is equal to or less than 50%, less than 25%, or less than 10% of the length of the period.

The first electric current may be below 50 mA, below 10 mA, below 1 mA, between 0.02 mA and 50 mA, between 0.1 mA and 1 mA, or between 0.3 mA and 0.7 mA. Similarly, the second electric current may be below 50 mA, below 10 mA, below 1 mA, between 0.1 mA and 1 mA, or between 0.3 mA and 0.7 mA.

The first electric current may be supplied at a potential difference between the first electrical connector and the second electrical connector that is below 50 V, below 10 V, below 1.5 V, below 0.5V. Similarly, the second electric current may be supplied at a potential difference between the first electrical connector and the second electrical connector that is below 50 V, below 10 V, below 1.5 V, below 0.5V.

The conductive first film and the electric power source may be arranged to give an average drop in electric potential in the conductive first film that is below 1 V/m, below 0.5 V/m, below 0.1 V/m, or below 0.05 V/m between the first connector and the second connector. The conductive second film and the electric power source may be arranged in the corresponding way . This contributes to a reduced electrolytic ef fect on the first layer . Here , the drop in electric potential may be along the shortest path between first electrical connector and the second electrical connector . For example , the shortest path between first electrical connector and the second electrical connector may be 10 m and the potential di f ference between the first electrical connector and the second electrical connector may below 10 V . At a first current of 10 mA, this means that the conductive first film has an average resistance of 100 Q/m . The power consumed in the first layer is then below 10 mW/m .

The conductive first film may have an average electric resistance below 1000 Q/m, below 100 Q/m, below 10 Q/m between the first connector and the second connector . The conductive second film may be arranged in the corresponding way . This contributes to a reduced electrolytic ef fect on the first layer . The higher electric resistances can be used in freshwater applications , and the lower electric resistances can be used in saltwater applications .

The conductive first film and/or the conductive second film may be of a material that has an electrical resistivity below 2 Qm, below 0 . 2 Qm, or below 0 . 02 Qm. The conductive second film may be arranged in the corresponding way . The higher resistivity is an order of magnitude lower than the typical resistivity of freshwater, and the lower resistivity is an order of magnitude lower than the resistivity of saltwater . This contributes to a reduced electrolytic ef fect . More speci fically, the resistivity may be less than 0 . 01 Qm, or less than 0 . 05 Qm, which is suitable for high-salinity applications .

For example , i f the resistivity is 0 . 02 Qm, the width of the first layer is 1 m, the thickness of the first layer is 1 mm, the resistance will be 20 Q/m . The first electric current may be 50 mA, which gives a power consumption, or resistive heating, of 0 . 05 W/m ² . The conductive first film and the electric power source may be arranged to give a power consumption that is less than 0 . 05 W/m ² , less than 0 . 01W/m ² , or less than 0 . 005 W/m ² . The conductive second film and the electric power source may be arranged in the corresponding way .

Brief description of the drawings

A more complete understanding of the proposed technology and other features and advantages of the proposed technology, will be apparent from the following detailed description of the figures , where : Fig . 1 schematically illustrates a starboard view of a boat with an embodiment of the proposed hull arrangement , Figs . 2a and 2b schematically illustrates starboard respective port views of a section of a ship with another embodiment of the proposed hull arrangement , Figs . 3a and 3b schematically illustrate front views of di f ferent embodiments of an electrically conductive film and an electrical connector,

Figs . 4a and 4b schematically illustrate side views of di f ferent embodiments of an electrically conductive film and an electrical connector, and

Figs . 5a and 5b schematically illustrate side views of di f ferent embodiments of an electrically conductive film, an electrical connector, and an electrically insulating film .

Detailed description

A boat 10 is shown in Fi g . 1 having an embodiment of the proposed hull arrangement 12 . The boat 10 has a hull 14 forming part of the hull arrangement 12 . The hull 14 is a monocoque fiberglass hull , which means that it is electrically insulating . The hull 14 has an inside , an outside , and a waterline 16 corresponding the line where the hull 14 meets a water surface when the of the boat 10 is unloaded .

An electrically conductive first film 18 covers a first portion on the outside of the hull 14 . The conductive first film 18 is a layer of electrically conductive paint that has been applied on the hull 14 , as shown in Fig . 4a . The conductive first film 18 extends from above to below the waterline 16 . A first electrical connector 20 and a second electrical connector 22 are physically connected to the conductive first film 18 . The hull 14 has a bow and a stern and the first portion extends from a point at the bow to a point at the stern . The first electrical connector 20 is positioned at the bow and connect to the conductive first film 18 above the waterline 16 , as shown in Fig . 3a . The second electrical connector 22 is positioned at the stern and connected to the conductive first film 18 below the waterline 16 , as shown in Fig . 3b . This means that the first electrical connector 20 and the second electrical connector 22 are spaced apart . They are positioned such that the shortest path in the conductive first film 18 between the first electrical connector 20 and the second electrical connector 22 passes below the waterline 16 .

An electric power source 24 is connected to the first electrical connector 20 and the second electrical connector 22 and is configured for supplying a first electric current via the first electrical connector 20 and the second electrical connector 22 . This way, the first electrical connector 20 , the second electrical connector 22 , the electric power source 24 , and the conductive first film 18 form part of a closed electrical circuit . The first electric current is a direct current below 10 mA and is supplied at a potential di f ference between the first electrical connector 20 and the second electrical connector 22 that is below 50 V . The electric power source 24 is configured to supply an intermittent electric current with pulse lengths of 5 min separated by gaps of 60 min .

The conductive first film 18 , the first electrical connector 20 , and the second electrical connector 22 are positioned such that the first electric current will pass through the conductive first film 18 between the first electrical connector 20 and the second electrical connector 22 at least partly below the waterline 16 of the hull 14 . The conductive first film 18 constitutes an unbroken, or uninterrupted, electrical conductor between the first electrical connector 20 and the second electrical connector 22 .

A ship 10 is shown in Figs . 2a and 2b with an alternative embodiment of the proposed hull arrangement 12 . The ship 10 has a hull 14 forming part of the hull arrangement 12 . The hull 14 is a steel hull , which means that it is electrically conductive . The hull 14 has an inside , an outside , and a waterline 16 corresponding the line where the hull 14 meets a water surface when the of the ship 10 is unloaded .

An electrically conductive first film 18 covers a first portion on the outside of the hull 14 and an electrically conductive second film 28 covers a first portion on the outside of the hull 14 . The conductive first film 18 and the conductive second film 28 are spaced apart and disj oint . Each of the conductive first film 18 and the conductive second film 28 is a sheet of an electrically conductive polymer that has been applied on the hull 14 and extends from above to below the waterline 16 . A first electrical connector 20 and a second electrical connector 22 are physically connected to the conductive first film 18 . Similarly, a third electrical connector 30 and a fourth electrical connector 32 are physically connected to the conductive second film 28 .

The hull 14 has a centerline 26 and the first portion and the second portion extend across the centerline and the centerline 26 bisects the first portion and the second portion . The first electrical connector 20 and the third electrical connector 30 are connected to the conductive first film 18 and the conductive second film 28 above the waterline 16 on the starboard side , and the second electrical connector 22 and the fourth electrical connector 32 are connected to the conductive first film 18 and the conductive second film 28 positioned above the above the waterline 16 on the port side . The first electrical connector 20 and the third electrical connector 30 are positioned closer to one another than the first electrical connector 20 and the second electrical connector, and the second electrical connector 22 and the fourth electrical connector 32 are positioned closer to one another than the first electrical connector 20 and the second electrical connector 22 .

The connection between first electrical connector 20 and the conductive first film 18 and the connection between and the third electrical connector 30 and the conductive second film 28 are closer to one another than the connection between the first electrical connector 20 and the conductive first film 18 and the connection between the second electrical connector and the conductive first film 18 . The connection between the second electrical connector 22 and the conductive first film 18 and the connection between the fourth electrical connector 32 and the conductive second film 28 are closer to one another than the connection between the first electrical connector 20 and the conductive first film 18 and the connection between the second electrical connector 22 and the conductive first film 18 .

The hull arrangement 12 further has an electrically insulating first film 34 arranged between the electrically conductive first film 18 and the hull 14 . It further has an electrically insulating second film 36 arranged between the electrically conductive second film 28 and the hull 14 . Each of the insulating first film 34 and the insulating second film 28 is a sheet of an electrically insulating polymer that has been applied on the first portion and the second portion of the hull 14 prior to applying the electrically conductive first film 18 and the electrically conductive second film 28 . The corresponding arrangement is shown in Fig . 5b . This inhibits a current in the conductive first film 18 and the conductive second film 28 from passing to the steel hull 14 .

An electric power source 24 is connected to the first electrical connector 20 , the second electrical connector 22 , the third electrical connector 30 , the fourth electrical connector 22 . The power source 24 is configured for supplying a first electric current via the first electrical connector 20 and the second electrical connector 22 , and a second electric current via the third electrical connector 30 and the fourth electrical connector 32 . This way, the first electrical connector 20 , the second electrical connector 22 , the electric power source 24 , and the conductive first film 18 form part of a closed electrical circuit . Similarly, the third electrical connector 30 , the fourth electrical connector 32 , the electric power source 24 , and the conductive second film 28 form part of another closed electrical circuit . In an alternative embodiment , the first electrical connector 20 and the third electrical connector 30 are coupled together to form a parallel coupling, and the second electrical connector 22 and the fourth electrical connector 32 are coupled together to form a parallel coupling .

The electric power source 24 is configured to operate in three modes . In the first and second mode , the first electric current and the second electric current are alternating currents below 10 mA and having a frequency between 0 . 5 kHz and 10 kHz . The first current is supplied at a potential between the first electrical connector 20 and the second electrical connector 22 below 1 . 5 V . Similarly, the second electric current is supplied at a potential between the third electrical connector 30 and the fourth electrical connector 32 below 1 . 5 V . In the first mode , current is supplied to the conductive first film 18 and the conductive second film 20 at the same time with the first current and the second current in phase . In the second mode , the electric power source 24 is configured for alternating between supplying the first electric current and supplying the second electric current .

In the third mode , the first electric current and the second electric current are direct currents below 10 mA and supplied at a potential di f ference below 50 V between the first electrical connector 20 and the second electrical connector 22 and between the third electrical connector 30 and the fourth electrical connector 32 . The electric power source 24 supplies an intermittent electric current with pulse lengths of that is an order of magnitude smaller than the separating gaps . It is further configured to establish the same electric polarity for the first electrical connector 20 and the third electrical connector 30 and for the second electrical connector 22 and the fourth electrical connector 32.

Figs. 3a and 3b schematically illustrate two different positions of an electrical connector 20, 22, 30, or 32. In Fig. 3a the electrical connector 20, 22, 30, or 32 has a net 38 of stainless steel that is connected to the electric power source 24 by a cable 42. In Fig. 3b the electrical connector 20, 22, 30, or 32 has a plate 40 of stainless steel that is connected to the electric power source 24 by a cable 42. The net 38 and plate 40 contact the conductive film 18, 28 and allows a current to flow between the electrical connector 20, 22, 30, or 32 and the conductive film 18, 28. The net 38 and plate 40 are elongated strips aligned with the waterline 16 of the hull 14. In Fig. 3a the net 38 is above the waterline, which means that the electrical connector 20, 22, 30, or 32 connects to the conductive film 18, 20 above the waterline 16. In Fig. 3b the plate 40 is below the waterline, which means that the electrical connector 20, 22, 30, or 32 connects to the conductive film 18, 20 below the waterline 16.

Figs. 4a and 4b schematically illustrate side views of embodiments with an electrically insulating hull 14. In Fig. 4a the electrical connector 20, 22, 30, or 32 has a net 38 of stainless steel connected to the electric power source 24 by a cable 42. The conductive film 18, 20 is an electrically conductive paint applied directly on the hull 14 and in which the net 38 is embedded. In Fig. 4b the electrical connector 20, 22, 30, or 32 has a plate 40 of stainless steel connected to the electric power source 24 by a cable 42. The conductive film 18, 20 is a sheet of an electrically conductive polymer applied directly on the hull 14 with the plate sandwiched between the conductive film 18, 20 and the hull.

Figs. 5a and 5b each schematically illustrate side views of an embodiment with an electrically conductive hull 14. In Fig. 5a an electrically insulating film 34, 36 in the form of an electrically insulating paint is applied on the hull. The electrical connector 20, 22, 30, or 32 has a net 38 of stainless steel connected to the electric power source 24 by a cable 42 . The conductive film 18 , 20 is an electrically conductive paint applied on the insulating film 34 , 36 and the net 38 is embedded in the conductive film 18 , 20 . In Fig . 5b an electrically insulating film 34 , 36 in the form of a sheet of an electrically insulating polymer is applied on the hull 14 . The electrical connector 20 , 22 , 30 , or 32 has a plate 40 of stainless steel connected to the electric power source 24 by a cable 42 . The conductive film 18 , 20 is a sheet of an electrically conductive polymer applied on the insulating film 34 , 36 and the plate 40 is sandwiched between the conductive film 18 , 20 and the insulating film .

Item list

10 watercraft

12 hull arrangement

14 hull

16 waterline

18 conductive first film

20 first electrical connector 22 second electrical connector 24 electric power source 26 centerline 28 second film

30 third electrical connector

32 fourth electrical connector

34 insulating first film 36 insulating second film 38 net 40 plate 42 cable