GB2434374A

GB2434374A - Immersed electrode

Info

Publication number: GB2434374A
Application number: GB0601164A
Authority: GB
Inventors: Malcolm John Perrins
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-01-20
Filing date: 2006-01-20
Publication date: 2007-07-25
Also published as: GB0601164D0; EP1974074A2; GB2434375A; WO2007083103A3; GB2434375B; WO2007083103A2; GB0701126D0

Abstract

An immersed electrode, such as a sacrificial anode for use in cathodic protection of underwater metal components on boats or a grounding electrode is described. The electrode 22 is located on the structure 58 via a though hull fitting 10. The fitting 10 may also possess a valve (not shown) to prevent water ingress, and the electrode 22 can have a line of weakness 56 to prevent damage to the metal structure 58. The electrode 22 can also be retracted through the hull fitting 10 without being removed from said fitting 10.

Description

-I-

Immersed Electrode Assembly This invention relates to an immersed electrode assembly.

The invention is particularly, but not exclusively, concerned with electrodes mounted at the underwater surfaces of boats, and one particular application for the invention is as a sacrificial anode for providing cathodic protection to underwater metal components on boats or other marine craft. The electrode may alternatively be a grounding electrode for providing an earth connection for electronic equipment on a boat and/or to reduce the adverse impact of lightning strikes. Still further the invention may be used in other circumstances where an electrode is required at metal/liquid interfaces, for example in liquid storage tanks to give cathodic protection.

In this specification, the term "boat" will be used to refer to a craft to which the anode is fitted, but the term "boat" is to be construed in its widest sense.

Underwater metal components on boats are at risk of corrosion through an electrochemical process. This risk is particularly great in seawater as seawater is a relatively good conductor of electric currents, such that an electrolytic cell is created between metals of differing electrochemical potential when they are both in the same electrolytic cell. The metal with a lower potential in the electrolytic cell will be anodic and will corrode. The same effect can occur in areas of different electrochemical potential in a single piece of metal such as a steel plate.

Cathodic protection is a process which prevents the corrosion reaction by creating an electric field so that current flows to the metal to be protected. This prevents the formation of metal ions by setting up a potential gradient at the surface, which opposes the electric current produced by flow of electrically charged ions away from the metal surface as the product of corrosion. The electric field must be of adequate strength to counter the field produced by the corrosion reaction to ensure that metal ions are fully prevented from escaping.

A source of the electric field which opposes the corrosion reaction may be a current supplied from the preferential corrosion of a metal anode with different electrochemical properties in the environment, and which has a stronger anodic reaction with the environment than does the metal surface to be protected.

Thus, current flows to the metal to be protected from the additional, sacrificial anode, which itself progressively corrodes in preference to the structure.

It is well known to mount a sacrificial anode on the underwater surface of a boat and to make an electrical connection between the anode and the metal to be protected (for example a propeller, a metal rudder blade or a metal stern gear).

According to a first aspect of the invention, there is provided an immersed electrode assembly that can be mounted in the hull of a boat, the assembly comprising a through hull fitting, an electrode of a dimension able to pass through the through hull fitting and means for making an electrical connection inside the hull between the electrode and a metal surface within the hull.

The electrode may be a sacrificial anode for protecting an underwater metal surface of the boat, and the electrical connection inside the hull will then be made, directly or indirectly, to the metal surface to be protected.

Alternatively the electrode may be a grounding electrode for grounding metal components and/or radio receivers to water. In this application, the invention can provide underwater electrode connections to enhance the electrical earth bonding of marine vessel circuits. This will be of value for example enhancing the performance of RF radio transmission and receiving equipment such as Single Side Band (SSB) transceivers or to reduce the adverse impact of lightning strikes.

It is conventional in boats to mount sensors (eg speed, depth, temperature sensors) using through hull fittings, so that the sensor itself is in contact with the water but the electrical connections to the sensor are made inside the hull.

These through hull fittings are also sometimes termed skin fittings. For example, the through hull fitting may be of the type sold by Airmar Technical Corporation and described in US Patent 5 186 050 which incorporates a flap valve to prevent substantial ingress of water when the sensor is withdrawn through the fitting.

Mounting the electrode so that it can be inserted and removed through a through hull fitting has a number of advantages. In particular, the electrode can be easily withdrawn and inspected from within the hull. Thus the degree of usage of a sacrificial anode can be easily monitored, and the anode can be replaced when necessary without having to take the boat out of the water.

Also, different anodes of different materials can be easily used when the boat moves from one marine environment to another. For example, it is conventional to use a zinc anode in salt water and an aluminium alloy anode in fresh or brackish water.

In the case of a sacrificial anode, the anode can be mounted on a non-sacrificial support which locates in the through hull fitting to close the hole in the hull, and to support the anode outside the hull outer skin. The anode itself can be detachably mounted on the support, so that the anode and support can be withdrawn from the through hull fitting as a unit, the anode itself can be removed and a fresh anode attached to the support which can then be replaced through the through hull fitting.

Preferably the anode diameter is slightly less than that of the anode support, so that the anode can still pass through the through hull fitting, even though the anode surface has become slightly blistered and enlarged, for example through oxidisation having taken place.

The invention also extends to an anode adapted to form part of an anode assembly as set forth above.

The electrode will typically be cylindrical in form. The assembly will be for mounting on a part of the hull underwater surface where it is shielded from possible damage, eg when the boat takes the ground. However there may be instances where the electrode could either catch something in the water, eg a mooring line or a net or where the electrode comes into contact with a fixed surface, and it may be desirable for the electrode to be provided with a point of weakness so that it can snap off before damage occurs to the hull in which it is mounted. Alternatively, the mounting of the electrode to an electrode support may be designed to fail if a particular force is applied to the electrode.

In a second aspect, the invention provides a removable sacrificial anode assembly that can be mounted through a wall where one side of the wall is in contact with a liquid in which a metal surface to be protected from electrochemical corrosion is immersed, the assembly comprising a tubular housing forming a passage through the wall with the exterior of the housing being sealed to the wall, an anode of a dimension able to pass through the tubular housing to close the passage through the wall and means for making an electrical connection on the opposite side of the wall between the anode and a metal surface to be protected.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an external view of a through hull fitting; Figure 2 is a cross-section through the fitting of Figure 1; Figure 3 shows an electrode assembly in accordance with the invention, with the electrode and its support separated from one another; Figure 4 shows an electrode assembly in accordance with the invention, mounted in a boat hull; Figure 5 shows a second embodiment of an electrode assembly in accordance with the invention; Figure 6 shows a third embodiment of an electrode assembly in accordance with the invention with an electrode extended; and Figure 7 shows the embodiment of Figure 6 with the electrode retracted.

The through hull fitting 10 shown in Figures 1 and 2 is generally tubular in form and made from suitable marine grade materials with a central bore 12 ending in a flange 14 which, in use, will either butt up against the outer surface of a boat hull or be recessed into the hull outer surface so as to be flush with the surface.

A threaded ring 16 engages on an externally threaded surface of the fitting 10, and can be screwed onto the fitting from inside the hull after the fitting has been passed through a hole in the hull. A sealing gasket or washer 18 will be fitted to ensure a watertight joint between the outside of the through hull fitting and the hull. A threaded cap 20 screws onto the top of the fitting 10 to retain the anode assembly, as will be described below.

The bore 12 may be hollow and unobstructed but it is also possible for the through hull fitting to have a self-sealing mechanism incorporated in the bore, such as a flap valve as described in US 5 186 050 which is closed by water pressure below the fitting when there is nothing inserted in the bore.

In the embodiments of the invention shown in the figures (which are some of many different ways in which the invention may be put into practice), the electrode takes the form of a sacrificial anode.

Figure 3 shows an anode 22 and an anode support 24. The anode 22 is a cylindrical body of a suitable sacrificial anode material. This invention is not concerned with the nature of the material, and those skilled in the art will be able to select a suitable material from which this anode will be formed, in accordance with the environmental conditions and the nature of the metal to be protected against corrosion.

The anode will preferably be formed entirely from the sacrificial anode material or may consist of the anode material formed around an armature of some description. The anode may include an embedded wear indicator which gives a visual indication of when the anode has been corroded away to the extent that it needs replacement. It would also be possible to incorporate in the anode some form of sensor such as that described in Patent Specification W02004 101851 which, when exposed, causes a signal to be sent to a remote indicator to indicate that anode replacement is necessary.

The anode 22 is to be detachably connected to the anode support 24, and for this purpose has a central counter-bored bore 26 for accepting a bolt 28, the head of which will be accommodated within the counterbored area 30. The anode also has a projection at 32 which will fit into a corresponding depression 34 on the anode support 24.

To connect the anode to that anode support, the bolt 28 passes through the bore 26 and is screwed into a threaded socket 36 in the anode support. When this bolt is tightened, the projection 32 is pulled into the recess 34 to centralise the anode and anode support and to provide a tight mechanical and electrical connectionS The projection could alternatively be provided on the support and the recess on the anode. Other joining configurations are also possible, provided they allow the joined anode and support to pass through the bore 12 of the through hull fitting.

The anode support 24 has a diameter adapted to pass through the bore 12 of the through hull fitting and, with the help of 0-rings in grooves 38, 40 and 42 to make a water-tight seal with the internal surface of the bore 12.

At its top end which, in use, will be inside the boat hull, the anode support 24 will project above the top of the through hull fitting and will have a terminal from which an electrical connection can be made, directly or indirectly, to the metal structure to be protected against corrosion. In Figure 3 a blind bore 44 extends radially into the top of the support, and this bore is intersected by another, threaded, bore 46 extending axially along the support. An electrical cable (not shown) can be inserted into the bore 44 and then a bolt 48 in the bore 46 can be screwed down onto the cable to make an electrical connection between the cable and the anode support. A lock nut 50 can then be screwed down to prevent accidental slackening of the bolt 48. Before entering the blind bore 44, the cable can be passed through a transverse bore 52 which will act as a cable grip to prevent any snagging of the cable resulting in the cable being pulled out of the bore 44.

The anode support can be made of any suitable material, either as a single piece or as an assembly of different parts. A plastics material is likely to be suitable for most of the support, but in this case it will be important to ensure that (a) there is sufficient strength in the socket 34,36, and (b) there is electrical continuity between the anode and the cable bore 44.

The top of the anode support can carry a ring 54 to assist in pulling the anode and its support out of the through hull fitting 10 when inspection and/or replacement is called for.

Figure 3 also shows where the anode has been provided with a point of weakness 56, which is designed to fail if the anode is subjected to unexpected forces. Additionally or alternatively the bolt fixing 28 may be constructed from a material with a low shear strength, such as nylon, that would intentionally fail in extreme circumstances in preference to stressing the hull.

Figure 4 shows the assembly of the through hull fitting 10, anode 22 and anode support 24 in place in a boat hull 58. The fitting 10 has been mounted through a hole in the hull 58 and the ring 16 has been screwed down from the inside of the hull to compress the gasket 18 to seal the fitting to the hull.

The anode 22 and anode support 24 have then been introduced through the fitting 10 until the anode projects outside the hull 58, and a shoulder 60 of the anode support 24 comes to rest on the top of the fitting 10, The cap 20 is then screwed down onto the fitting 10 to retain the assembly in position. 0-rings 62, 64, 66 provide a seal between the anode support and the internal bore 12 of the fitting 10.

An electrical cable (not shown) can then be passed through the transverse bore 52 and inserted in the bore 44 before the bolt 48 is tightened down to make an electrical connection between the cable and the anode, via the support 24. The other end of the cable will then be connected to a suitable point in the boat, close to the place where external metal components are to be protected.

The embodiment in Figure 5 illustrates an alternative method of connecting an electrical cable 68 to a terminal 70, within an anode holder 124 made of a metal component 72 and a hollow plastics component 74.

Figures 6 and 7 show an embodiment in which the anode can be retracted into, without complete removal from, the through hull fitting. In these figures, components which correspond to components shown in the preceding figures are indicated by the same reference numerals, increased by 200.

In this embodiment, the through hull fitting 210 is relatively tall when compared with the fitting shown in the preceding figures, and will accommodate both the anode 222 and the anode support 224 when the anode is retracted into the fitting 210. A connecting rod 276 carries the pull ring 254 and the electrical connection features 244, 246 and 252, passes through the cap 220 and screws into the top of the anode support 224. When the anode is retracted as shown in Figure 7, this rod extends within the hull of the boat.

To ensure a flush surface at the hull exterior, the anode is fitted with a fairing plug 278 which lies flush with the hull surface (or the flange 214) when the anode is retracted. This fairing plug can be a plastics component which is a push fit into the bore 26 of the anode.

0-rings 262, 264 and 266 provide the necessary water-tightness through the fitting 210. An additional water seal 280 can be provided where the rod 276 passes through the cap 220.

The anode assemblies as described have many advantages over existing sacrificial anodes.

-they can be fitted when the boat is new, or as an aftermarket addition.

-fitting requires no particular skill -the anode can be easily removed (and replaced by a watertight, flush-fitting plug or retracted as shown in Figures 6 and 7) when drag is to be reduced to a minimum, eg for racing, being subsequently replaced or extended after racing.

-the anode material can be easily exchanged for a different material when the boat is in a different marine environment -the anode can be cleaned of surface oxide or marine growth while the boat is still afloat and without having to enter the water -the anode can be easily replaced when exhausted while the boat is still afloat and without having to enter the water -the removable anode can function as a reference anode to indicate the level of electrochemical attack that may be occurring on non-removable anodes mounted elsewhere on the same boat -the anode may alternatively be permanently or temporarily replaced with a electrode made of sintered bronze or similar material for improved radio performance the anode assembly may incorporate a mechanism that allows retraction and extension of the anode without water ingress.

To check whether the anode should be replaced, a template can be provided which can be used to measure a partly corroded anode against the size at which the anode should be replaced.

In an alternative embodiment (not shown) the electrode which projects into the water can be an alternative component made to similar external dimensions but constructed of a material with significantly more active surface area for enhanced electrical conductivity in seawater, such as sintered bronze. The invention is not concerned with the detailed nature of such a material, and those skilled in the art will be able to select a suitable material or form of construction, in accordance with the environment required to increase the quality of the electrical ground or counterpoise required for either improved radio transmission in marine vessels or to enhance vessel electrical grounding to reduce the adverse impact of lightning strikes.

It is envisaged that the main use of this invention will be on leisure craft (motor or sail), but the invention is not restricted to such applications.

Claims

Claims 1. An immersed electrode assembly that can be mounted in the

hull of a boat, the assembly comprising a through hull fitting, an electrode of a dimension able to pass through the through hull fitting and means for making an electrical connection inside the hull between the electrode and a metal surface within the hull.

2. An electrode assembly as claimed in Claim 1, wherein the electrode is cylindrical in form.

3. An electrode assembly as claimed in Claim I or Claim 2, wherein the electrode and/or the electrode support is provided with a point of weakness so that it can snap off before damage occurs to the hull in which it is mounted.

4. An electrode assembly as claimed in any preceding claim, wherein the electrode may be retracted into the through hull fitting without being removed from the fitting.

5. An electrode assembly as claimed in any preceding claim, wherein the electrode is a sacrificial anode for protecting an underwater metal surface of the boat.

6. An electrode assembly as claimed in Claim 5, wherein the anode is mounted on a non-sacrificial support which locates in the through hull fitting to close the hole in the hull, and to support the anode outside the hull outer through hull.

7. An electrode assembly as claimed in Claim 6, wherein the anode itself is detachably mounted on the support.

8. An electrode assembly as claimed in Claim 6 or Claim 7, wherein the anode diameter is slightly less than that of the anode support, so that the anode can still pass through the through hull fitting, even though the anode surface has become slightly enlarged.

9. A sacrificial anode adapted to form part of an electrode assembly as claimed in any one of Claims 5 to 8.

10. An electrode assembly as claimed in any one of Claims I to 4, wherein the electrode is a grounding electrode for grounding metal components and/or radio receivers to water.

II. A grounding electrode adapted to form part of an electrode assembly as claimed in Claim 10.

12. An electrode assembly as claimed in any preceding claim, wherein the through hull fitting is a standard through hull fitting adapted to support sensors in contact with the water.

13. An electrode assembly as claimed in any preceding claim, wherein the through hull fitting has a valve to substantially prevent ingress of water when the electrode is withdrawn through the fitting.

14. A removable sacrificial anode assembly that can be mounted through a wall where one side of the wall is in contact with a liquid in which a metal surface to be protected is immersed, the assembly comprising a tubular housing forming a passage through the wall with the exterior of the housing being sealed to the wall, an anode of a dimension able to pass through the tubular housing to close the passage through the wall and means for making an electrical connection on the opposite side of the wall between the anode and a metal surface to be protected.

15. An electrode assembly substantially as herein described with reference to any one embodiment shown in the accompanying drawings.