I have had my Oceanis 311 for 4 years, and change the shaft anode annually. Three months ago I started berthing my boat on our club's new marina, and on diving the hull recently (which I do regularly using a hookah)I noticed the shaft anode to be degrading much quicker than it had when the boat was on a mooring. Does anyone have any useful advise on the topic, particularly with respect to the design of a second anode-type device hung from the backstay (for example) into the water. The boat is fitted with shore power, but I have not been leaving this connected constantly, though over Xmas/New Year it had a couple of weeks of constant connection.
Excessive anode degradation in marina
- Thread starter tuddy
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I have had my Oceanis 311 for 4 years, and change the shaft anode annually. Three months ago I started berthing my boat on our club's new marina, and on diving the hull recently (which I do regularly using a hookah)I noticed the shaft anode to be degrading much quicker than it had when the boat was on a mooring. Does anyone have any useful advise on the topic, particularly with respect to the design of a second anode-type device hung from the backstay (for example) into the water. The boat is fitted with shore power, but I have not been leaving this connected constantly, though over Xmas/New Year it had a couple of weeks of constant connection.
Zinc-itis
G'day Mate, My marine electrician discovered that the big red ignition switch in the starboard aft cabin on my 390 was not actually switching off properly. The ignition was actually live all the time when I thought I was dutifully turning it off each time I left the boat. I was probably electrifying the whole neighbourhood. Prior to that, my prop zinc was corroding at an alarming rate. Now I also have a properly grounded stern zinc that I toss off the stern each time I leave the boat. My zinc depletion rate is now minimal. The only problem with stern zincs is you have one more thing to remember when leaving the dock. I have only had to replace it once in 2 years after driving off with it still dangling. A neighbour boat could also be pouring power into the water and wearing out your zincs. Marinas are famous for elevated levels of stray power in the water. I think you can test for this somehow using a meter. Seem to remember a post some time ago which told how to check for the level of stray power in the water around your boat. Maybe someone else knows this trick. There are some serious electro-geeks on this site. Good luck, Pete (Former Kiwi, left there in 1972)
G'day Mate, My marine electrician discovered that the big red ignition switch in the starboard aft cabin on my 390 was not actually switching off properly. The ignition was actually live all the time when I thought I was dutifully turning it off each time I left the boat. I was probably electrifying the whole neighbourhood. Prior to that, my prop zinc was corroding at an alarming rate. Now I also have a properly grounded stern zinc that I toss off the stern each time I leave the boat. My zinc depletion rate is now minimal. The only problem with stern zincs is you have one more thing to remember when leaving the dock. I have only had to replace it once in 2 years after driving off with it still dangling. A neighbour boat could also be pouring power into the water and wearing out your zincs. Marinas are famous for elevated levels of stray power in the water. I think you can test for this somehow using a meter. Seem to remember a post some time ago which told how to check for the level of stray power in the water around your boat. Maybe someone else knows this trick. There are some serious electro-geeks on this site. Good luck, Pete (Former Kiwi, left there in 1972)
Zinc-itis
G'day Mate, My marine electrician discovered that the big red ignition switch in the starboard aft cabin on my 390 was not actually switching off properly. The ignition was actually live all the time when I thought I was dutifully turning it off each time I left the boat. I was probably electrifying the whole neighbourhood. Prior to that, my prop zinc was corroding at an alarming rate. Now I also have a properly grounded stern zinc that I toss off the stern each time I leave the boat. My zinc depletion rate is now minimal. The only problem with stern zincs is you have one more thing to remember when leaving the dock. I have only had to replace it once in 2 years after driving off with it still dangling. A neighbour boat could also be pouring power into the water and wearing out your zincs. Marinas are famous for elevated levels of stray power in the water. I think you can test for this somehow using a meter. Seem to remember a post some time ago which told how to check for the level of stray power in the water around your boat. Maybe someone else knows this trick. There are some serious electro-geeks on this site. Good luck, Pete (Former Kiwi, left there in 1972)
G'day Mate, My marine electrician discovered that the big red ignition switch in the starboard aft cabin on my 390 was not actually switching off properly. The ignition was actually live all the time when I thought I was dutifully turning it off each time I left the boat. I was probably electrifying the whole neighbourhood. Prior to that, my prop zinc was corroding at an alarming rate. Now I also have a properly grounded stern zinc that I toss off the stern each time I leave the boat. My zinc depletion rate is now minimal. The only problem with stern zincs is you have one more thing to remember when leaving the dock. I have only had to replace it once in 2 years after driving off with it still dangling. A neighbour boat could also be pouring power into the water and wearing out your zincs. Marinas are famous for elevated levels of stray power in the water. I think you can test for this somehow using a meter. Seem to remember a post some time ago which told how to check for the level of stray power in the water around your boat. Maybe someone else knows this trick. There are some serious electro-geeks on this site. Good luck, Pete (Former Kiwi, left there in 1972)
curious about stern zinc
Pete, I'm curious about your stern zinc. I seen other boats at my marina have a wire (or a line) coming out and hanging in the water but I never understood what that was, I though it was lightening protection or something.... can you explain a bit more about how you installed it ? I'm still working on getting my galvanic isolator in place and its a slow process... its too big to fit where the main breaker is... we change zinc about every 4-5 month and its abotu half at that point. thanks Gaute
Pete, I'm curious about your stern zinc. I seen other boats at my marina have a wire (or a line) coming out and hanging in the water but I never understood what that was, I though it was lightening protection or something.... can you explain a bit more about how you installed it ? I'm still working on getting my galvanic isolator in place and its a slow process... its too big to fit where the main breaker is... we change zinc about every 4-5 month and its abotu half at that point. thanks Gaute
curious about stern zinc
Pete, I'm curious about your stern zinc. I seen other boats at my marina have a wire (or a line) coming out and hanging in the water but I never understood what that was, I though it was lightening protection or something.... can you explain a bit more about how you installed it ? I'm still working on getting my galvanic isolator in place and its a slow process... its too big to fit where the main breaker is... we change zinc about every 4-5 month and its abotu half at that point. thanks Gaute
Pete, I'm curious about your stern zinc. I seen other boats at my marina have a wire (or a line) coming out and hanging in the water but I never understood what that was, I though it was lightening protection or something.... can you explain a bit more about how you installed it ? I'm still working on getting my galvanic isolator in place and its a slow process... its too big to fit where the main breaker is... we change zinc about every 4-5 month and its abotu half at that point. thanks Gaute
secondary zinc
is simply another zinc tossed over the side and connected (hopefully by a low impedence connection) to the boat's bonding system. They can help but more often than not, they have such a long and resistive path to the prop and shaft that they do little more than make you feel better. One reason they are often ineffective is that the conductivity from the shaft and prop is compromized because of the interconnecting stuff like the shaft coupling, transmission case and engine ground post to which the batteries are connected. Another drawback is that galvanic action on underwater metals is primarily caused by shore power connction problems and not the boat's Dc systems for which this is only a bandaid, not a cure. Still another problem for which a secondary zinc is of little efficacy has to do with the fundamental cause of the galvanic action which can often be traced to a leaky or reversed bilge pump power cable in which case no amount of zinc will prevent further corrosion. It can easily be determined where the source of the corrosion originates by measuring stray current between your boat and the water. Similarly, it is easy to trace the source of a shore power leakage by measurement. As this probably far exceeds the interest level of anyone reading thus far, I'll post the rest of the story separately
is simply another zinc tossed over the side and connected (hopefully by a low impedence connection) to the boat's bonding system. They can help but more often than not, they have such a long and resistive path to the prop and shaft that they do little more than make you feel better. One reason they are often ineffective is that the conductivity from the shaft and prop is compromized because of the interconnecting stuff like the shaft coupling, transmission case and engine ground post to which the batteries are connected. Another drawback is that galvanic action on underwater metals is primarily caused by shore power connction problems and not the boat's Dc systems for which this is only a bandaid, not a cure. Still another problem for which a secondary zinc is of little efficacy has to do with the fundamental cause of the galvanic action which can often be traced to a leaky or reversed bilge pump power cable in which case no amount of zinc will prevent further corrosion. It can easily be determined where the source of the corrosion originates by measuring stray current between your boat and the water. Similarly, it is easy to trace the source of a shore power leakage by measurement. As this probably far exceeds the interest level of anyone reading thus far, I'll post the rest of the story separately
secondary zinc
is simply another zinc tossed over the side and connected (hopefully by a low impedence connection) to the boat's bonding system. They can help but more often than not, they have such a long and resistive path to the prop and shaft that they do little more than make you feel better. One reason they are often ineffective is that the conductivity from the shaft and prop is compromized because of the interconnecting stuff like the shaft coupling, transmission case and engine ground post to which the batteries are connected. Another drawback is that galvanic action on underwater metals is primarily caused by shore power connction problems and not the boat's Dc systems for which this is only a bandaid, not a cure. Still another problem for which a secondary zinc is of little efficacy has to do with the fundamental cause of the galvanic action which can often be traced to a leaky or reversed bilge pump power cable in which case no amount of zinc will prevent further corrosion. It can easily be determined where the source of the corrosion originates by measuring stray current between your boat and the water. Similarly, it is easy to trace the source of a shore power leakage by measurement. As this probably far exceeds the interest level of anyone reading thus far, I'll post the rest of the story separately
is simply another zinc tossed over the side and connected (hopefully by a low impedence connection) to the boat's bonding system. They can help but more often than not, they have such a long and resistive path to the prop and shaft that they do little more than make you feel better. One reason they are often ineffective is that the conductivity from the shaft and prop is compromized because of the interconnecting stuff like the shaft coupling, transmission case and engine ground post to which the batteries are connected. Another drawback is that galvanic action on underwater metals is primarily caused by shore power connction problems and not the boat's Dc systems for which this is only a bandaid, not a cure. Still another problem for which a secondary zinc is of little efficacy has to do with the fundamental cause of the galvanic action which can often be traced to a leaky or reversed bilge pump power cable in which case no amount of zinc will prevent further corrosion. It can easily be determined where the source of the corrosion originates by measuring stray current between your boat and the water. Similarly, it is easy to trace the source of a shore power leakage by measurement. As this probably far exceeds the interest level of anyone reading thus far, I'll post the rest of the story separately
More on galvanic action and testing
Blanket statements such as 'all underwater metal should be bonded' or 'all underwater metal should be unbonded' does not take into account the individual situation the boat may be in. There are three types of corrosion underwater metals are subjected to---Electrolytic, Galvanic, and Stray current. Bonding underwater metals (and installing a zinc) will cure/prevent the first two types of corrosion but will cause or speed up the last. It is best to find out what type of corrosion your boat is experiencing before deciding on the cure and if you are not experiencing a problem, leave well enough alone. Galvanic & Electrolytic (Stray Current) corrosion are two similar, yet different ,types of corrosion. Galvanic corrosion results when two dissimilar metals, of sufficiently different potentials (about 0.1 V on the galvanic series) (a galvanic couple can also occur within regions of a single alloy), are electrically connected (bonded; deliberately or not), and immersed in a common electrolyte (water). The same electro-chemical reaction creates the current flow in a storage battery. Stray Current (or Electrolytic) corrosion results when an applied current flows through immersed conductive materials, other than an intended electrical circuit. Stray currents can come from an outside source either internal or external to your boat. Internal sources involve a short in your boat’s wiring system, such as a poorly insulated wire in the bilge, an electrical accessory that may be improperly wired, or a wire with a weak or broken insulation that is intermittently wet. External sources are most often related to shore power connections, or other boats on the dock . To generate electrolytic corrosion, the stray current must flow onto the metal at one location and then flow off the metal at another location. When an applied current passes in and out of a metal part, an electrolytic cell is set up, resulting in a localized anodic site, where the positive current exits the metal part. This causes the local oxidation (corrosion reaction) of the metal piece, which may lead to a very rapid metal loss, which is limited only by the amount of current available. TESTING: An ohm meter is a poor way to check bonding connections. I use a 12 volt lamp and make a probe using a screwdriver. Hook a long enough wire to the positive terminal of the starting battery and then poke the screwdriver into each of the through hull fittings and make sure the lamp lights. An ohm meter is only testing the circuit at micro-amps. The following applies mainly to boats left in the water. Trailered boats rarely spend enough time in the water for electrolysis to be a problem. ELECTROLYSIS 101. I've worked with electrolysis for 18 years including live-aboard on a steel yacht for 14. We have sold thousands of our galvanic isolators and handle numerous emails/phone calls daily on electrolysis situations. BONDING STRAPS Although your copper straps look impressive they are totally unnecessary. The wire at the most only carries a few milliamps and there is no concern for voltage drop so the copper only needs to be heavy enough to resist deterioration from oxidation. A 10 gauge copper wire is more than adequate. I use non stranded 10 gauge bare copper wire for my installations, being careful to secure it so it is not subject to flexing from boat motion. Non stranded wire has much less surface area and avoids the cavities between the strands where moisture and corrosion/oxidation can progress. THEORY Electrolysis only happens when two dissimilar metals are immersed in an electrolyte and connected together. The dissimilar metals have different electrolysis voltages so if you connect them together current flows through the connecting wire one direction and through the water the other. As the current leaves one metal to travel to the other, it causes metal to come off one surface and be deposited on the other like battery plates so the higher voltage metal suffers electrolysis. Electrolysis can also occur when an adjacent structure or boat is injecting DC current into the water and that current goes in one end of your boat and out the other on its way to the destination. This can cause electrolysis even though your boat is not an offender. PROTECTION There are basically 2 ways to reduce electrolysis. The PREFERABLE one is to DISCONNECT the electrical circuit. If this can't be done, the second method is to provide a sacrificial anode (Zinc) so it deteriorates rather than your expensive equipment. a) DISCONNECTING Electrolysis cannot occur on an isolated piece of metal in salt water. It is all at the same voltage but if it is isolated no current can flow so there is no electrolysis. When it is connected to another piece of metal, ESPECIALLY if the other piece is a different metal, you just created a shorted battery and electrolysis will start. By following the wrong advise and bonding everything in the boat you are creating batteries where it is unnecessary and making electrolysis problems worse. Only bond underwater items that are showing symptoms of electrolysis. If it ain't broke, DON'T fix it. Once you bond it unnecessarily you have CREATED the circuit rather than DISCONNECTING it. You are now stuck with providing Zincs since you have removed the first line of protection. Although some through hulls appear to be isolated due to sitting in fiberglass and using non-metallic tubing, they quite often are not and WILL need bonding. For example the raw water cooling inlet for an inboard engine is in fact connected to the engine block by the salt water in the tubing and may need bonding so the current flows though copper rather than the water and in/out of the through hull. b) SACRIFICIAL ZINC There are situations where different metals cannot be disconnected and you are stuck with putting zincs on them to provided a target for the electrolysis. Zincs have a higher electrolytic voltage than marine metals so it is the first to deteriorate. Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they were not needed will still cause the zincs to erode away since they create the battery situation where none may have existed. The range of protection a zinc can supply to other metals bonded to it is limited by the conductivity of the water. In salt water you get coverage for a radius of about 4 to 6 feet. A zinc on the stern of a 14 ft boat where everything is bonded is only protecting half the boat. This range gets even less in fresh water and may reduce to only inches. Often magnesium is substituted for zinc in fresh water to provide an even higher voltage to push through the fresh water. USE A CONDOM Over 90% of our customers electrolysis problems are created by the shore power connection. You could theoretically disconnect the ground connection in the shore power and avoid electrolysis (and in some cases this is a solution) but ABYC regulations require the AC ground be connected to the DC ground so an electrical fault on the boat won't electrocute swimmers in the vicinity. When you connect your underwater metal to the shore power ground you have "bonded" with every other boat on the docks who have the same connection. Now electrolysis currents are free to flow anywhere in the marina and it only takes one boat with a 12 volt DC leakage to eat up every boat within a wide radius even though the offender has zero electrolysis evidence. Your protection is a Galvanic Isolator in the ground connection of the shore power lead. You don't have to purchase ours (although they are typically less than 1/2 the price of our competitors). Any Galvanic Isolator that meets AYBC specifications will do - they are not rocket science and extremely reliable. On most boats you cannot isolate the DC ground from the underwater metal because the starter motor is bolted to the engine block which in turn connects to the propeller shaft and the water. So without the ground, an internal failure of the battery charger could put 120 or 230 volts AC on your DC ground and into the water.
Blanket statements such as 'all underwater metal should be bonded' or 'all underwater metal should be unbonded' does not take into account the individual situation the boat may be in. There are three types of corrosion underwater metals are subjected to---Electrolytic, Galvanic, and Stray current. Bonding underwater metals (and installing a zinc) will cure/prevent the first two types of corrosion but will cause or speed up the last. It is best to find out what type of corrosion your boat is experiencing before deciding on the cure and if you are not experiencing a problem, leave well enough alone. Galvanic & Electrolytic (Stray Current) corrosion are two similar, yet different ,types of corrosion. Galvanic corrosion results when two dissimilar metals, of sufficiently different potentials (about 0.1 V on the galvanic series) (a galvanic couple can also occur within regions of a single alloy), are electrically connected (bonded; deliberately or not), and immersed in a common electrolyte (water). The same electro-chemical reaction creates the current flow in a storage battery. Stray Current (or Electrolytic) corrosion results when an applied current flows through immersed conductive materials, other than an intended electrical circuit. Stray currents can come from an outside source either internal or external to your boat. Internal sources involve a short in your boat’s wiring system, such as a poorly insulated wire in the bilge, an electrical accessory that may be improperly wired, or a wire with a weak or broken insulation that is intermittently wet. External sources are most often related to shore power connections, or other boats on the dock . To generate electrolytic corrosion, the stray current must flow onto the metal at one location and then flow off the metal at another location. When an applied current passes in and out of a metal part, an electrolytic cell is set up, resulting in a localized anodic site, where the positive current exits the metal part. This causes the local oxidation (corrosion reaction) of the metal piece, which may lead to a very rapid metal loss, which is limited only by the amount of current available. TESTING: An ohm meter is a poor way to check bonding connections. I use a 12 volt lamp and make a probe using a screwdriver. Hook a long enough wire to the positive terminal of the starting battery and then poke the screwdriver into each of the through hull fittings and make sure the lamp lights. An ohm meter is only testing the circuit at micro-amps. The following applies mainly to boats left in the water. Trailered boats rarely spend enough time in the water for electrolysis to be a problem. ELECTROLYSIS 101. I've worked with electrolysis for 18 years including live-aboard on a steel yacht for 14. We have sold thousands of our galvanic isolators and handle numerous emails/phone calls daily on electrolysis situations. BONDING STRAPS Although your copper straps look impressive they are totally unnecessary. The wire at the most only carries a few milliamps and there is no concern for voltage drop so the copper only needs to be heavy enough to resist deterioration from oxidation. A 10 gauge copper wire is more than adequate. I use non stranded 10 gauge bare copper wire for my installations, being careful to secure it so it is not subject to flexing from boat motion. Non stranded wire has much less surface area and avoids the cavities between the strands where moisture and corrosion/oxidation can progress. THEORY Electrolysis only happens when two dissimilar metals are immersed in an electrolyte and connected together. The dissimilar metals have different electrolysis voltages so if you connect them together current flows through the connecting wire one direction and through the water the other. As the current leaves one metal to travel to the other, it causes metal to come off one surface and be deposited on the other like battery plates so the higher voltage metal suffers electrolysis. Electrolysis can also occur when an adjacent structure or boat is injecting DC current into the water and that current goes in one end of your boat and out the other on its way to the destination. This can cause electrolysis even though your boat is not an offender. PROTECTION There are basically 2 ways to reduce electrolysis. The PREFERABLE one is to DISCONNECT the electrical circuit. If this can't be done, the second method is to provide a sacrificial anode (Zinc) so it deteriorates rather than your expensive equipment. a) DISCONNECTING Electrolysis cannot occur on an isolated piece of metal in salt water. It is all at the same voltage but if it is isolated no current can flow so there is no electrolysis. When it is connected to another piece of metal, ESPECIALLY if the other piece is a different metal, you just created a shorted battery and electrolysis will start. By following the wrong advise and bonding everything in the boat you are creating batteries where it is unnecessary and making electrolysis problems worse. Only bond underwater items that are showing symptoms of electrolysis. If it ain't broke, DON'T fix it. Once you bond it unnecessarily you have CREATED the circuit rather than DISCONNECTING it. You are now stuck with providing Zincs since you have removed the first line of protection. Although some through hulls appear to be isolated due to sitting in fiberglass and using non-metallic tubing, they quite often are not and WILL need bonding. For example the raw water cooling inlet for an inboard engine is in fact connected to the engine block by the salt water in the tubing and may need bonding so the current flows though copper rather than the water and in/out of the through hull. b) SACRIFICIAL ZINC There are situations where different metals cannot be disconnected and you are stuck with putting zincs on them to provided a target for the electrolysis. Zincs have a higher electrolytic voltage than marine metals so it is the first to deteriorate. Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they were not needed will still cause the zincs to erode away since they create the battery situation where none may have existed. The range of protection a zinc can supply to other metals bonded to it is limited by the conductivity of the water. In salt water you get coverage for a radius of about 4 to 6 feet. A zinc on the stern of a 14 ft boat where everything is bonded is only protecting half the boat. This range gets even less in fresh water and may reduce to only inches. Often magnesium is substituted for zinc in fresh water to provide an even higher voltage to push through the fresh water. USE A CONDOM Over 90% of our customers electrolysis problems are created by the shore power connection. You could theoretically disconnect the ground connection in the shore power and avoid electrolysis (and in some cases this is a solution) but ABYC regulations require the AC ground be connected to the DC ground so an electrical fault on the boat won't electrocute swimmers in the vicinity. When you connect your underwater metal to the shore power ground you have "bonded" with every other boat on the docks who have the same connection. Now electrolysis currents are free to flow anywhere in the marina and it only takes one boat with a 12 volt DC leakage to eat up every boat within a wide radius even though the offender has zero electrolysis evidence. Your protection is a Galvanic Isolator in the ground connection of the shore power lead. You don't have to purchase ours (although they are typically less than 1/2 the price of our competitors). Any Galvanic Isolator that meets AYBC specifications will do - they are not rocket science and extremely reliable. On most boats you cannot isolate the DC ground from the underwater metal because the starter motor is bolted to the engine block which in turn connects to the propeller shaft and the water. So without the ground, an internal failure of the battery charger could put 120 or 230 volts AC on your DC ground and into the water.
More on galvanic action and testing
Blanket statements such as 'all underwater metal should be bonded' or 'all underwater metal should be unbonded' does not take into account the individual situation the boat may be in. There are three types of corrosion underwater metals are subjected to---Electrolytic, Galvanic, and Stray current. Bonding underwater metals (and installing a zinc) will cure/prevent the first two types of corrosion but will cause or speed up the last. It is best to find out what type of corrosion your boat is experiencing before deciding on the cure and if you are not experiencing a problem, leave well enough alone. Galvanic & Electrolytic (Stray Current) corrosion are two similar, yet different ,types of corrosion. Galvanic corrosion results when two dissimilar metals, of sufficiently different potentials (about 0.1 V on the galvanic series) (a galvanic couple can also occur within regions of a single alloy), are electrically connected (bonded; deliberately or not), and immersed in a common electrolyte (water). The same electro-chemical reaction creates the current flow in a storage battery. Stray Current (or Electrolytic) corrosion results when an applied current flows through immersed conductive materials, other than an intended electrical circuit. Stray currents can come from an outside source either internal or external to your boat. Internal sources involve a short in your boat’s wiring system, such as a poorly insulated wire in the bilge, an electrical accessory that may be improperly wired, or a wire with a weak or broken insulation that is intermittently wet. External sources are most often related to shore power connections, or other boats on the dock . To generate electrolytic corrosion, the stray current must flow onto the metal at one location and then flow off the metal at another location. When an applied current passes in and out of a metal part, an electrolytic cell is set up, resulting in a localized anodic site, where the positive current exits the metal part. This causes the local oxidation (corrosion reaction) of the metal piece, which may lead to a very rapid metal loss, which is limited only by the amount of current available. TESTING: An ohm meter is a poor way to check bonding connections. I use a 12 volt lamp and make a probe using a screwdriver. Hook a long enough wire to the positive terminal of the starting battery and then poke the screwdriver into each of the through hull fittings and make sure the lamp lights. An ohm meter is only testing the circuit at micro-amps. The following applies mainly to boats left in the water. Trailered boats rarely spend enough time in the water for electrolysis to be a problem. ELECTROLYSIS 101. I've worked with electrolysis for 18 years including live-aboard on a steel yacht for 14. We have sold thousands of our galvanic isolators and handle numerous emails/phone calls daily on electrolysis situations. BONDING STRAPS Although your copper straps look impressive they are totally unnecessary. The wire at the most only carries a few milliamps and there is no concern for voltage drop so the copper only needs to be heavy enough to resist deterioration from oxidation. A 10 gauge copper wire is more than adequate. I use non stranded 10 gauge bare copper wire for my installations, being careful to secure it so it is not subject to flexing from boat motion. Non stranded wire has much less surface area and avoids the cavities between the strands where moisture and corrosion/oxidation can progress. THEORY Electrolysis only happens when two dissimilar metals are immersed in an electrolyte and connected together. The dissimilar metals have different electrolysis voltages so if you connect them together current flows through the connecting wire one direction and through the water the other. As the current leaves one metal to travel to the other, it causes metal to come off one surface and be deposited on the other like battery plates so the higher voltage metal suffers electrolysis. Electrolysis can also occur when an adjacent structure or boat is injecting DC current into the water and that current goes in one end of your boat and out the other on its way to the destination. This can cause electrolysis even though your boat is not an offender. PROTECTION There are basically 2 ways to reduce electrolysis. The PREFERABLE one is to DISCONNECT the electrical circuit. If this can't be done, the second method is to provide a sacrificial anode (Zinc) so it deteriorates rather than your expensive equipment. a) DISCONNECTING Electrolysis cannot occur on an isolated piece of metal in salt water. It is all at the same voltage but if it is isolated no current can flow so there is no electrolysis. When it is connected to another piece of metal, ESPECIALLY if the other piece is a different metal, you just created a shorted battery and electrolysis will start. By following the wrong advise and bonding everything in the boat you are creating batteries where it is unnecessary and making electrolysis problems worse. Only bond underwater items that are showing symptoms of electrolysis. If it ain't broke, DON'T fix it. Once you bond it unnecessarily you have CREATED the circuit rather than DISCONNECTING it. You are now stuck with providing Zincs since you have removed the first line of protection. Although some through hulls appear to be isolated due to sitting in fiberglass and using non-metallic tubing, they quite often are not and WILL need bonding. For example the raw water cooling inlet for an inboard engine is in fact connected to the engine block by the salt water in the tubing and may need bonding so the current flows though copper rather than the water and in/out of the through hull. b) SACRIFICIAL ZINC There are situations where different metals cannot be disconnected and you are stuck with putting zincs on them to provided a target for the electrolysis. Zincs have a higher electrolytic voltage than marine metals so it is the first to deteriorate. Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they were not needed will still cause the zincs to erode away since they create the battery situation where none may have existed. The range of protection a zinc can supply to other metals bonded to it is limited by the conductivity of the water. In salt water you get coverage for a radius of about 4 to 6 feet. A zinc on the stern of a 14 ft boat where everything is bonded is only protecting half the boat. This range gets even less in fresh water and may reduce to only inches. Often magnesium is substituted for zinc in fresh water to provide an even higher voltage to push through the fresh water. USE A CONDOM Over 90% of our customers electrolysis problems are created by the shore power connection. You could theoretically disconnect the ground connection in the shore power and avoid electrolysis (and in some cases this is a solution) but ABYC regulations require the AC ground be connected to the DC ground so an electrical fault on the boat won't electrocute swimmers in the vicinity. When you connect your underwater metal to the shore power ground you have "bonded" with every other boat on the docks who have the same connection. Now electrolysis currents are free to flow anywhere in the marina and it only takes one boat with a 12 volt DC leakage to eat up every boat within a wide radius even though the offender has zero electrolysis evidence. Your protection is a Galvanic Isolator in the ground connection of the shore power lead. You don't have to purchase ours (although they are typically less than 1/2 the price of our competitors). Any Galvanic Isolator that meets AYBC specifications will do - they are not rocket science and extremely reliable. On most boats you cannot isolate the DC ground from the underwater metal because the starter motor is bolted to the engine block which in turn connects to the propeller shaft and the water. So without the ground, an internal failure of the battery charger could put 120 or 230 volts AC on your DC ground and into the water.
Blanket statements such as 'all underwater metal should be bonded' or 'all underwater metal should be unbonded' does not take into account the individual situation the boat may be in. There are three types of corrosion underwater metals are subjected to---Electrolytic, Galvanic, and Stray current. Bonding underwater metals (and installing a zinc) will cure/prevent the first two types of corrosion but will cause or speed up the last. It is best to find out what type of corrosion your boat is experiencing before deciding on the cure and if you are not experiencing a problem, leave well enough alone. Galvanic & Electrolytic (Stray Current) corrosion are two similar, yet different ,types of corrosion. Galvanic corrosion results when two dissimilar metals, of sufficiently different potentials (about 0.1 V on the galvanic series) (a galvanic couple can also occur within regions of a single alloy), are electrically connected (bonded; deliberately or not), and immersed in a common electrolyte (water). The same electro-chemical reaction creates the current flow in a storage battery. Stray Current (or Electrolytic) corrosion results when an applied current flows through immersed conductive materials, other than an intended electrical circuit. Stray currents can come from an outside source either internal or external to your boat. Internal sources involve a short in your boat’s wiring system, such as a poorly insulated wire in the bilge, an electrical accessory that may be improperly wired, or a wire with a weak or broken insulation that is intermittently wet. External sources are most often related to shore power connections, or other boats on the dock . To generate electrolytic corrosion, the stray current must flow onto the metal at one location and then flow off the metal at another location. When an applied current passes in and out of a metal part, an electrolytic cell is set up, resulting in a localized anodic site, where the positive current exits the metal part. This causes the local oxidation (corrosion reaction) of the metal piece, which may lead to a very rapid metal loss, which is limited only by the amount of current available. TESTING: An ohm meter is a poor way to check bonding connections. I use a 12 volt lamp and make a probe using a screwdriver. Hook a long enough wire to the positive terminal of the starting battery and then poke the screwdriver into each of the through hull fittings and make sure the lamp lights. An ohm meter is only testing the circuit at micro-amps. The following applies mainly to boats left in the water. Trailered boats rarely spend enough time in the water for electrolysis to be a problem. ELECTROLYSIS 101. I've worked with electrolysis for 18 years including live-aboard on a steel yacht for 14. We have sold thousands of our galvanic isolators and handle numerous emails/phone calls daily on electrolysis situations. BONDING STRAPS Although your copper straps look impressive they are totally unnecessary. The wire at the most only carries a few milliamps and there is no concern for voltage drop so the copper only needs to be heavy enough to resist deterioration from oxidation. A 10 gauge copper wire is more than adequate. I use non stranded 10 gauge bare copper wire for my installations, being careful to secure it so it is not subject to flexing from boat motion. Non stranded wire has much less surface area and avoids the cavities between the strands where moisture and corrosion/oxidation can progress. THEORY Electrolysis only happens when two dissimilar metals are immersed in an electrolyte and connected together. The dissimilar metals have different electrolysis voltages so if you connect them together current flows through the connecting wire one direction and through the water the other. As the current leaves one metal to travel to the other, it causes metal to come off one surface and be deposited on the other like battery plates so the higher voltage metal suffers electrolysis. Electrolysis can also occur when an adjacent structure or boat is injecting DC current into the water and that current goes in one end of your boat and out the other on its way to the destination. This can cause electrolysis even though your boat is not an offender. PROTECTION There are basically 2 ways to reduce electrolysis. The PREFERABLE one is to DISCONNECT the electrical circuit. If this can't be done, the second method is to provide a sacrificial anode (Zinc) so it deteriorates rather than your expensive equipment. a) DISCONNECTING Electrolysis cannot occur on an isolated piece of metal in salt water. It is all at the same voltage but if it is isolated no current can flow so there is no electrolysis. When it is connected to another piece of metal, ESPECIALLY if the other piece is a different metal, you just created a shorted battery and electrolysis will start. By following the wrong advise and bonding everything in the boat you are creating batteries where it is unnecessary and making electrolysis problems worse. Only bond underwater items that are showing symptoms of electrolysis. If it ain't broke, DON'T fix it. Once you bond it unnecessarily you have CREATED the circuit rather than DISCONNECTING it. You are now stuck with providing Zincs since you have removed the first line of protection. Although some through hulls appear to be isolated due to sitting in fiberglass and using non-metallic tubing, they quite often are not and WILL need bonding. For example the raw water cooling inlet for an inboard engine is in fact connected to the engine block by the salt water in the tubing and may need bonding so the current flows though copper rather than the water and in/out of the through hull. b) SACRIFICIAL ZINC There are situations where different metals cannot be disconnected and you are stuck with putting zincs on them to provided a target for the electrolysis. Zincs have a higher electrolytic voltage than marine metals so it is the first to deteriorate. Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they were not needed will still cause the zincs to erode away since they create the battery situation where none may have existed. The range of protection a zinc can supply to other metals bonded to it is limited by the conductivity of the water. In salt water you get coverage for a radius of about 4 to 6 feet. A zinc on the stern of a 14 ft boat where everything is bonded is only protecting half the boat. This range gets even less in fresh water and may reduce to only inches. Often magnesium is substituted for zinc in fresh water to provide an even higher voltage to push through the fresh water. USE A CONDOM Over 90% of our customers electrolysis problems are created by the shore power connection. You could theoretically disconnect the ground connection in the shore power and avoid electrolysis (and in some cases this is a solution) but ABYC regulations require the AC ground be connected to the DC ground so an electrical fault on the boat won't electrocute swimmers in the vicinity. When you connect your underwater metal to the shore power ground you have "bonded" with every other boat on the docks who have the same connection. Now electrolysis currents are free to flow anywhere in the marina and it only takes one boat with a 12 volt DC leakage to eat up every boat within a wide radius even though the offender has zero electrolysis evidence. Your protection is a Galvanic Isolator in the ground connection of the shore power lead. You don't have to purchase ours (although they are typically less than 1/2 the price of our competitors). Any Galvanic Isolator that meets AYBC specifications will do - they are not rocket science and extremely reliable. On most boats you cannot isolate the DC ground from the underwater metal because the starter motor is bolted to the engine block which in turn connects to the propeller shaft and the water. So without the ground, an internal failure of the battery charger could put 120 or 230 volts AC on your DC ground and into the water.
thats a lot of information
Don, thanks for the detailed information.... After finding what the line was I have read articles of owners swearing by it and others saying it does nothing. I think I'll revive my project of installing the isolator since I went thru the trouble of getting one. I think what I need to get is a cable, join it to the one coming out at the circuitbreaker (anyone know if the ground is all the way to the breaker ?) and take it out under the nav station then back in where it came out.... what type of cable shold be used for this ? what type of "joiners" shold be used ? I'm thinking the twisties that comes with lamps for home isnt reliable enough... if I get some basic ideas perhaps its not as hard as I made it out. thanks ! Gaute
Don, thanks for the detailed information.... After finding what the line was I have read articles of owners swearing by it and others saying it does nothing. I think I'll revive my project of installing the isolator since I went thru the trouble of getting one. I think what I need to get is a cable, join it to the one coming out at the circuitbreaker (anyone know if the ground is all the way to the breaker ?) and take it out under the nav station then back in where it came out.... what type of cable shold be used for this ? what type of "joiners" shold be used ? I'm thinking the twisties that comes with lamps for home isnt reliable enough... if I get some basic ideas perhaps its not as hard as I made it out. thanks ! Gaute
thats a lot of information
Don, thanks for the detailed information.... After finding what the line was I have read articles of owners swearing by it and others saying it does nothing. I think I'll revive my project of installing the isolator since I went thru the trouble of getting one. I think what I need to get is a cable, join it to the one coming out at the circuitbreaker (anyone know if the ground is all the way to the breaker ?) and take it out under the nav station then back in where it came out.... what type of cable shold be used for this ? what type of "joiners" shold be used ? I'm thinking the twisties that comes with lamps for home isnt reliable enough... if I get some basic ideas perhaps its not as hard as I made it out. thanks ! Gaute
Don, thanks for the detailed information.... After finding what the line was I have read articles of owners swearing by it and others saying it does nothing. I think I'll revive my project of installing the isolator since I went thru the trouble of getting one. I think what I need to get is a cable, join it to the one coming out at the circuitbreaker (anyone know if the ground is all the way to the breaker ?) and take it out under the nav station then back in where it came out.... what type of cable shold be used for this ? what type of "joiners" shold be used ? I'm thinking the twisties that comes with lamps for home isnt reliable enough... if I get some basic ideas perhaps its not as hard as I made it out. thanks ! Gaute
Electrolytic, Galvanic, and Stray Current
Great post Don. I have printed it for future reference. Jim
Great post Don. I have printed it for future reference. Jim
Electrolytic, Galvanic, and Stray Current
Great post Don. I have printed it for future reference. Jim
Great post Don. I have printed it for future reference. Jim
Syversens
are you asking about the connecting cable for a secondary zinc to the boat or the cable wiring for the isolator? Regardless, the conventional wisdom on twist conenctors is to never use them aboard for a few reasons, the primary one being they can disconnect over time due to vibration. Butt connectors are preferable and can be found at any hardware store or chandlery, some have heat shrink tubing with adhesive so as to ensure a good water-tight seal. For single point connections, ring terminals are typically recommended, again with adhesive heat shrink covers. Having said that, I must admit to having used twist connectors as "temporary" and they worked great - right up to the time they either corroded away of loosened.
are you asking about the connecting cable for a secondary zinc to the boat or the cable wiring for the isolator? Regardless, the conventional wisdom on twist conenctors is to never use them aboard for a few reasons, the primary one being they can disconnect over time due to vibration. Butt connectors are preferable and can be found at any hardware store or chandlery, some have heat shrink tubing with adhesive so as to ensure a good water-tight seal. For single point connections, ring terminals are typically recommended, again with adhesive heat shrink covers. Having said that, I must admit to having used twist connectors as "temporary" and they worked great - right up to the time they either corroded away of loosened.
Syversens
are you asking about the connecting cable for a secondary zinc to the boat or the cable wiring for the isolator? Regardless, the conventional wisdom on twist conenctors is to never use them aboard for a few reasons, the primary one being they can disconnect over time due to vibration. Butt connectors are preferable and can be found at any hardware store or chandlery, some have heat shrink tubing with adhesive so as to ensure a good water-tight seal. For single point connections, ring terminals are typically recommended, again with adhesive heat shrink covers. Having said that, I must admit to having used twist connectors as "temporary" and they worked great - right up to the time they either corroded away of loosened.
are you asking about the connecting cable for a secondary zinc to the boat or the cable wiring for the isolator? Regardless, the conventional wisdom on twist conenctors is to never use them aboard for a few reasons, the primary one being they can disconnect over time due to vibration. Butt connectors are preferable and can be found at any hardware store or chandlery, some have heat shrink tubing with adhesive so as to ensure a good water-tight seal. For single point connections, ring terminals are typically recommended, again with adhesive heat shrink covers. Having said that, I must admit to having used twist connectors as "temporary" and they worked great - right up to the time they either corroded away of loosened.
galvanic isolator wire
thanks Don, I know the type and used it for the 12V things I done, never for 120... guess there isnt that much difference as long as I get a permanent connection. sorry for hijacking the post but I felt it was still on topic as it seems galvanic isolator is the way to go to protect boat from stray currents. anyone know what dimension the ground cable going into the boat has and if its taken all the way up to the breaker before being split wherever it goes ? thanks Gaute
thanks Don, I know the type and used it for the 12V things I done, never for 120... guess there isnt that much difference as long as I get a permanent connection. sorry for hijacking the post but I felt it was still on topic as it seems galvanic isolator is the way to go to protect boat from stray currents. anyone know what dimension the ground cable going into the boat has and if its taken all the way up to the breaker before being split wherever it goes ? thanks Gaute
galvanic isolator wire
thanks Don, I know the type and used it for the 12V things I done, never for 120... guess there isnt that much difference as long as I get a permanent connection. sorry for hijacking the post but I felt it was still on topic as it seems galvanic isolator is the way to go to protect boat from stray currents. anyone know what dimension the ground cable going into the boat has and if its taken all the way up to the breaker before being split wherever it goes ? thanks Gaute
thanks Don, I know the type and used it for the 12V things I done, never for 120... guess there isnt that much difference as long as I get a permanent connection. sorry for hijacking the post but I felt it was still on topic as it seems galvanic isolator is the way to go to protect boat from stray currents. anyone know what dimension the ground cable going into the boat has and if its taken all the way up to the breaker before being split wherever it goes ? thanks Gaute
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