Probably a dumb question but here goes. I've noticed on a friends boat that all his thru-hulls have a large grounding wire from the valve to ground (I presume the engine, I didn't follow them all the way). Is this for electrolysis, lightning protection or what?? My boat doesn't have it and has been surveyed recently with no mention of it. Thoughts on this appreciated.
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Reply to grounding thru-hulls
Scott, We are often confused by what we read or are told and what we see on our boats. The following is a quote from the USPS Marine Electronics course regarding bonding systems. I apologize in advance for the length of the reply; however, it answers your question about bonding thru-hulls. "Even a sailboat without electricity should have a bonding system for lightning protection. This consists of a wire running from the air terminal, down the mast, to a large underwater metallic surface. This should be a minimum of #4 AWG copper or equivalent cross-sectional area. Attached to this vertical conductor is the bonding system which should be a minimum of #8 AWG. All metal objects that could normally contact a human should be connected to this bonding system. The bonding conductor consists of a normally NON-CURRENT-CARRYING CONDUCTOR (my bold-face), running fore and aft, and used to connect the NON-CURRENT-CARRYING (my bold-face) parts of the DC devices and metallic parts of the boat construction to a local ground of the wetted hull, the same point as the negative terminal of the battery. The purpose of bonding is to keep all metallic parts from getting either a static charge or a magnetically induced potential due to a lightning strike. The bonding conductor need not be insulated. Preferably, for ease of attachment a 1/16inch x 1/2inch copper strap, or a length of soft 1/2inch copper tubing makes a more workable and durable installation. This conductor should be supported well above the bilge-flooding level. ... The bonding conductor is normally grounded through the engine casting and drive-shaft assemblies or to a submerged, wetted-surface, copper ground plate. Bonding conductors should be extended to contact: a. Metallic enclosures of all DC electrical equipment. b. Motor, generator, and pump frames. c. Fuel tank, deck fuel fittings, fresh-water tank. d. Metallic mast, stanchions, railings, standing rigging. DO NOT BOND METALLIC THRU-HULL FITTINGS SUCH AS SEA COCKS OR HEAD VALVES.(my bold-face) These should be isolated from the bonding system for two reasons: TO ELIMINATE A PATH FOR LIGHTNING TO BLOW OUT AN UNDERWATER FITTING, AND TO PREVENT GALVANIC ATTACK FROM AN ELECTRICALLY CONNECTED BRONZE FITTING ACCELERATING DESTRUCTION OF LESS NOBLE UNDERWATER MATERIALS OR ZINCS. (my bold-face) No portion of the bonding system should carry an electric current for any device or any other system." After taking the Marine Electronics course this Fall, I checked the bonding system on my '86 ODay 272. The underwater thru-hulls were indeed bonded and I will disconnect them from the bonding system before launch this Spring. I don't understand why this was done by the manufacturer, but the explanation in the Marine Electronics manual which I just quoted to you convinces me to do the prudent thing and disconnect them. Again I apologize for sharing more information than you maybe wanted to know... Tom
Scott, We are often confused by what we read or are told and what we see on our boats. The following is a quote from the USPS Marine Electronics course regarding bonding systems. I apologize in advance for the length of the reply; however, it answers your question about bonding thru-hulls. "Even a sailboat without electricity should have a bonding system for lightning protection. This consists of a wire running from the air terminal, down the mast, to a large underwater metallic surface. This should be a minimum of #4 AWG copper or equivalent cross-sectional area. Attached to this vertical conductor is the bonding system which should be a minimum of #8 AWG. All metal objects that could normally contact a human should be connected to this bonding system. The bonding conductor consists of a normally NON-CURRENT-CARRYING CONDUCTOR (my bold-face), running fore and aft, and used to connect the NON-CURRENT-CARRYING (my bold-face) parts of the DC devices and metallic parts of the boat construction to a local ground of the wetted hull, the same point as the negative terminal of the battery. The purpose of bonding is to keep all metallic parts from getting either a static charge or a magnetically induced potential due to a lightning strike. The bonding conductor need not be insulated. Preferably, for ease of attachment a 1/16inch x 1/2inch copper strap, or a length of soft 1/2inch copper tubing makes a more workable and durable installation. This conductor should be supported well above the bilge-flooding level. ... The bonding conductor is normally grounded through the engine casting and drive-shaft assemblies or to a submerged, wetted-surface, copper ground plate. Bonding conductors should be extended to contact: a. Metallic enclosures of all DC electrical equipment. b. Motor, generator, and pump frames. c. Fuel tank, deck fuel fittings, fresh-water tank. d. Metallic mast, stanchions, railings, standing rigging. DO NOT BOND METALLIC THRU-HULL FITTINGS SUCH AS SEA COCKS OR HEAD VALVES.(my bold-face) These should be isolated from the bonding system for two reasons: TO ELIMINATE A PATH FOR LIGHTNING TO BLOW OUT AN UNDERWATER FITTING, AND TO PREVENT GALVANIC ATTACK FROM AN ELECTRICALLY CONNECTED BRONZE FITTING ACCELERATING DESTRUCTION OF LESS NOBLE UNDERWATER MATERIALS OR ZINCS. (my bold-face) No portion of the bonding system should carry an electric current for any device or any other system." After taking the Marine Electronics course this Fall, I checked the bonding system on my '86 ODay 272. The underwater thru-hulls were indeed bonded and I will disconnect them from the bonding system before launch this Spring. I don't understand why this was done by the manufacturer, but the explanation in the Marine Electronics manual which I just quoted to you convinces me to do the prudent thing and disconnect them. Again I apologize for sharing more information than you maybe wanted to know... Tom
the real ground?
sounds good if the real lighting gound is connected to the bolts to the lead keel on the 272. but then again with that much lead being used at the main ground ... maybe better to leave the through hulls grounded as well?
sounds good if the real lighting gound is connected to the bolts to the lead keel on the 272. but then again with that much lead being used at the main ground ... maybe better to leave the through hulls grounded as well?
Vic-the real ground?
Vic, On my 272 the bonding system is bolted to the keel bolts and that is indeed a lot of lead, but I don't get the logic behind leaving the thru-hulls bonded because of a large amount of lead in the keel. It is possible for lightning to find its way out of the hull at a thru-hull regardless of the amount of lead in the keel if the thru-hulls are part of the bonding system. Or am I still missing something in your reply? Tom
Vic, On my 272 the bonding system is bolted to the keel bolts and that is indeed a lot of lead, but I don't get the logic behind leaving the thru-hulls bonded because of a large amount of lead in the keel. It is possible for lightning to find its way out of the hull at a thru-hull regardless of the amount of lead in the keel if the thru-hulls are part of the bonding system. Or am I still missing something in your reply? Tom
Thru hull puzzle
Thomas, I agree with removing the bonding from the thru hulls. However, Nigell Calder indicates that they should be grounded to eliminate stray-current corrosion (page 140 to 144). This is going to get confusing. The reason Calder bonds the thru-hulls is stray-current traveling through water in the bilge or salt bridges from thru-hulls to the electric system. Also his thought is to actively use zincs. Meaning that he likes to create a battery to protect the thru-hulls. If a battery is not connected, no current flows. Calder creates a battery by bonding the bronze and zinc. The zinc constantly sacrifices itself to protect the bronze. My thought is if the thru-hulls are not connected, would it not be like opening a switch on a circuit and stopping current flow? I really thought I understood bonding and grounding till this thru-hull thing came up. r.w.landau
Thomas, I agree with removing the bonding from the thru hulls. However, Nigell Calder indicates that they should be grounded to eliminate stray-current corrosion (page 140 to 144). This is going to get confusing. The reason Calder bonds the thru-hulls is stray-current traveling through water in the bilge or salt bridges from thru-hulls to the electric system. Also his thought is to actively use zincs. Meaning that he likes to create a battery to protect the thru-hulls. If a battery is not connected, no current flows. Calder creates a battery by bonding the bronze and zinc. The zinc constantly sacrifices itself to protect the bronze. My thought is if the thru-hulls are not connected, would it not be like opening a switch on a circuit and stopping current flow? I really thought I understood bonding and grounding till this thru-hull thing came up. r.w.landau
Ground
It is not a dumb question Scott. Follow the large wire, it should be going to a sacrifical plate on the exterior of the hull. Then if no non thru hulls are attached Calder is correct.
It is not a dumb question Scott. Follow the large wire, it should be going to a sacrifical plate on the exterior of the hull. Then if no non thru hulls are attached Calder is correct.
stray current corrosion
R.W. Let's continue the chase. I haven't read Calder and perhaps you haven't read the USPS Marine Electronics Manual which is based upon the ABYC Standards and Recommended Practices For Small Craft. Even if the reward is small, let's see if we can figure out WHY there seems to be a contradiction. Here's what the manual says about stray current corrosion and its recommendations about not bonding the thru-hulls. Forgive my long quotes, but I would rather not paraphrase. "Stray-current flow is due to the application of an external source of electricity, unintentional or uncontrolled, that causes current to flow from wetted metal surfaces to a related return circuit of lower potential. ...With stray-current flow, it makes little or no difference if metals are similar or different. Current flow is from the positive battery terminal, through the electrolyte, to the negative electrode and negative battery terminal. The electrode at which the current flow leaves to enter the solution-that connected to the positive side of the current source of higher potential-will corrode. With stray-current flow, it makes little or no difference if metals are similar or different. Current flow will be from the hot side (higher potential) to ground... The higher the voltage and the lower the resistance of the electrical path, the faster the rate of destruction. This stray-current leakage path may be across any moist surface, through bilge water or wet wood or from ungrounded equipment frames. A common source is from a hot wire with deteriorated insulation, or a connection exposed to moisture or bilge water... In other words, THE BEST FORM OF PROTECTION AGAINST CORROSIVE ACTION FROM STRAY-CURRENT FLOW IS A PROPERLY INSTALLED WIRING SYSTEM, REGULARLY CHECKED AND MAINTAINED. (my boldface) Here comes the controversial part (I think) "There has been much debate about what to bond to prevent both galvanic and stray current corrosion. The American Boat and Yacht Council (ABYC) publishes "Standards and Recommended Practices for Small Craft" which makes specific recommendations that should be followed completely and consistently. In addition to the sections requiring metal masses above and below decks to be bonded, the ABYC Section E-9.13 c requires that all exposed electrical conductive non-current carrying parts of fixed DC electrical equipment and appliances that may be normally in contact with bilge water or seawater shall be connected to the DC grounding system. THIS WILL TEND TO PREVENT CONCERNS ABOUT STRAY LEAKAGE AT UNGROUNDED THRU-HULL FITTINGS, WHICH ARE SPECIFICALLY EXEMPT FROM BONDING BY ABYC SECTION E-1.4C(1).(my bold-face) In fact, ABYC Section E-1.6(2) requires isolation of the thru-hull fittings on metal hulled boats...The intent here is to prevent overloading any cathodic protection system. Otherwise the cathode system must be increased. Another reason for not bonding bronze underwater fittings is that this would INCREASE (my bold-face) the consumption of sacrificial zincs, since the very noble bronze is already protected against galvanic corrosion and the bronze would take current protection from bonded ferrous items that are in contact with the water. THE BOAT-OWNER'S MECHANICAL AND ELECTRICAL MANUAL by Nigel Calder says that this current tends to generate alkaline peroxides and hydroxides around thru-hulls that will attack organic materials such as wooden hulls or wood backed fibergalss, which could weaken the joint. Furthermore, many USPS members have written the Marine Electronics Committee about their exerience with the combination of bonded zincs and bronzes tending to promote the growth of barnacles. Apparently, the normal biocidal action of the copper compound that would form a corrosion film repelling growth is inhibited by the zinc." So... what does this mean to me? It means that, at this time, the best solution to this apparent dilemna is to maintain the integrity of the DC wiring to prevent stray current corrosion, and to disconnect the bronze thru-hulls from the bonding system to prevent the possibility of a lightning strike blowing a hole in the hull below the waterline. And, R.W., to put all of this into perspective, many people will respond to this discussion, by saying "Who cares? What are the chances of this occuring on MY boat?"
Tom
R.W. Let's continue the chase. I haven't read Calder and perhaps you haven't read the USPS Marine Electronics Manual which is based upon the ABYC Standards and Recommended Practices For Small Craft. Even if the reward is small, let's see if we can figure out WHY there seems to be a contradiction. Here's what the manual says about stray current corrosion and its recommendations about not bonding the thru-hulls. Forgive my long quotes, but I would rather not paraphrase. "Stray-current flow is due to the application of an external source of electricity, unintentional or uncontrolled, that causes current to flow from wetted metal surfaces to a related return circuit of lower potential. ...With stray-current flow, it makes little or no difference if metals are similar or different. Current flow is from the positive battery terminal, through the electrolyte, to the negative electrode and negative battery terminal. The electrode at which the current flow leaves to enter the solution-that connected to the positive side of the current source of higher potential-will corrode. With stray-current flow, it makes little or no difference if metals are similar or different. Current flow will be from the hot side (higher potential) to ground... The higher the voltage and the lower the resistance of the electrical path, the faster the rate of destruction. This stray-current leakage path may be across any moist surface, through bilge water or wet wood or from ungrounded equipment frames. A common source is from a hot wire with deteriorated insulation, or a connection exposed to moisture or bilge water... In other words, THE BEST FORM OF PROTECTION AGAINST CORROSIVE ACTION FROM STRAY-CURRENT FLOW IS A PROPERLY INSTALLED WIRING SYSTEM, REGULARLY CHECKED AND MAINTAINED. (my boldface) Here comes the controversial part (I think) "There has been much debate about what to bond to prevent both galvanic and stray current corrosion. The American Boat and Yacht Council (ABYC) publishes "Standards and Recommended Practices for Small Craft" which makes specific recommendations that should be followed completely and consistently. In addition to the sections requiring metal masses above and below decks to be bonded, the ABYC Section E-9.13 c requires that all exposed electrical conductive non-current carrying parts of fixed DC electrical equipment and appliances that may be normally in contact with bilge water or seawater shall be connected to the DC grounding system. THIS WILL TEND TO PREVENT CONCERNS ABOUT STRAY LEAKAGE AT UNGROUNDED THRU-HULL FITTINGS, WHICH ARE SPECIFICALLY EXEMPT FROM BONDING BY ABYC SECTION E-1.4C(1).(my bold-face) In fact, ABYC Section E-1.6(2) requires isolation of the thru-hull fittings on metal hulled boats...The intent here is to prevent overloading any cathodic protection system. Otherwise the cathode system must be increased. Another reason for not bonding bronze underwater fittings is that this would INCREASE (my bold-face) the consumption of sacrificial zincs, since the very noble bronze is already protected against galvanic corrosion and the bronze would take current protection from bonded ferrous items that are in contact with the water. THE BOAT-OWNER'S MECHANICAL AND ELECTRICAL MANUAL by Nigel Calder says that this current tends to generate alkaline peroxides and hydroxides around thru-hulls that will attack organic materials such as wooden hulls or wood backed fibergalss, which could weaken the joint. Furthermore, many USPS members have written the Marine Electronics Committee about their exerience with the combination of bonded zincs and bronzes tending to promote the growth of barnacles. Apparently, the normal biocidal action of the copper compound that would form a corrosion film repelling growth is inhibited by the zinc." So... what does this mean to me? It means that, at this time, the best solution to this apparent dilemna is to maintain the integrity of the DC wiring to prevent stray current corrosion, and to disconnect the bronze thru-hulls from the bonding system to prevent the possibility of a lightning strike blowing a hole in the hull below the waterline. And, R.W., to put all of this into perspective, many people will respond to this discussion, by saying "Who cares? What are the chances of this occuring on MY boat?"
TomWell Stated!
Thomas, Well stated. May boaters wonder why they go through zincs like crazy, I think this is a big reason. Is your boat grounded to a plate, through the engine drive train, or keel? Where are your zincs located? I know your boat is fresh water, do you see zinc loss through a season? Scott, I know this is your thread, but hopefully your are benifiting from this. r.w.landau
Thomas, Well stated. May boaters wonder why they go through zincs like crazy, I think this is a big reason. Is your boat grounded to a plate, through the engine drive train, or keel? Where are your zincs located? I know your boat is fresh water, do you see zinc loss through a season? Scott, I know this is your thread, but hopefully your are benifiting from this. r.w.landau
Through hulls and electrolysis
Let me join this discussion. My boats through hulls are all bonded to the ground system as done by O'Day at the factory in the mid 80's. Electrolysis and corrosion are funny things and many chemical and electrical processes are at work. Most of what you read in the ABYC and so forth are a macro view of the problem. If you delve a little deeper into the microscopic world what you have are all kinds of anomalies that result in corrosion even despite your zincs. Zincs provide a great solution for macro level problems. At the micro level you have impure metals and surface contaminants and so forth that create microscopic batteries within the metal itself. All of these materials are alloys and all of them have some amount of impurities. When the metal is originally created and then later melted and poured you can get non-homogeneous mixtures where certain alloying elements are in non uniform concentrations. The manufacturing process (machining, etc) can also result in impurities on the surface imbedded in the metal, then of course handilng, packaging and local environment can add to this problem. Any way it is very possible despite all your efforts to have a metal in an electrolyte corrode. Small potentials are created at these suface defects and impurities that can result in corrosion due to electrolysis. Bonded or not it is good practice to check your through hulls frequently and replace them as required. One of the bad aspects of bonding them is if you lose your zincs without knowing it, worn out, or fall off then your through hulls will be the next most noble metal and disintegrate leaving you very wet. You can read some good literature on corrosion in general (not necessarily marine related) and then adapt what you learn to your boat environment. This is a huge problem in industry trying to prevent metals in manufacturing processes from corroding. I have seen aluminum get shot peened (steel shot imbedding steel dust in the surface) and turn black in one weekend due to corrosion from the dissimilar metals. We use a chemical etch to clean the aluminum before anodize. I have also seen reactions due to dissolved iron in machine coolants (remember the machine itself is iron). So in short corrosion requires a microscopic as well as macroscopic analysis and there is no one magic wand to eliminate the problem. Best bet is to remove all through hulls and glass over the holes and not worry about it. Or put all through hulls above the water line, obviusly not practical for heads and gravity drains. Search the net on Corrosion and you'll find some good reads. dave
Let me join this discussion. My boats through hulls are all bonded to the ground system as done by O'Day at the factory in the mid 80's. Electrolysis and corrosion are funny things and many chemical and electrical processes are at work. Most of what you read in the ABYC and so forth are a macro view of the problem. If you delve a little deeper into the microscopic world what you have are all kinds of anomalies that result in corrosion even despite your zincs. Zincs provide a great solution for macro level problems. At the micro level you have impure metals and surface contaminants and so forth that create microscopic batteries within the metal itself. All of these materials are alloys and all of them have some amount of impurities. When the metal is originally created and then later melted and poured you can get non-homogeneous mixtures where certain alloying elements are in non uniform concentrations. The manufacturing process (machining, etc) can also result in impurities on the surface imbedded in the metal, then of course handilng, packaging and local environment can add to this problem. Any way it is very possible despite all your efforts to have a metal in an electrolyte corrode. Small potentials are created at these suface defects and impurities that can result in corrosion due to electrolysis. Bonded or not it is good practice to check your through hulls frequently and replace them as required. One of the bad aspects of bonding them is if you lose your zincs without knowing it, worn out, or fall off then your through hulls will be the next most noble metal and disintegrate leaving you very wet. You can read some good literature on corrosion in general (not necessarily marine related) and then adapt what you learn to your boat environment. This is a huge problem in industry trying to prevent metals in manufacturing processes from corroding. I have seen aluminum get shot peened (steel shot imbedding steel dust in the surface) and turn black in one weekend due to corrosion from the dissimilar metals. We use a chemical etch to clean the aluminum before anodize. I have also seen reactions due to dissolved iron in machine coolants (remember the machine itself is iron). So in short corrosion requires a microscopic as well as macroscopic analysis and there is no one magic wand to eliminate the problem. Best bet is to remove all through hulls and glass over the holes and not worry about it. Or put all through hulls above the water line, obviusly not practical for heads and gravity drains. Search the net on Corrosion and you'll find some good reads. dave
grounding thru-hulls-response to W.W.
W.W. As you observed, my boat is in fresh water(?),specifically in Lake Erie. Although I've upgraded the electrical system in the boat somewhat, I'm far from the laptop, refrigerator, hot water and electric water pump level of consumption. I am meticulous about wiring both AC and DC and follow the ABYC directions as to type of wire (tinned), connectors (crimped), type of wire insulation (marine grade) and protection from mechanical brakeage (plastic rough boxes and wire ties) and protection against vibration (grommets at all drilled holes). The only wires that I'm nervous about are the wires to and from the bilge pump although I have the waterproof connectors raised so that they do not rest in bilge water. For these reasons I have no measureable problems with stray current leakage. As to galvanic corrosion, I have replaced the pencil zinc in the heat exchanger of the exhaust system once since 1995. I seriously doubt that it had been replaced by the previous owner before that time. The boat was new in 1986, and the old zinc looked good enough that I kept it as a spare. That is the only zinc on board that I know of. I would rate the zinc consumption as minimal. By the way, I see no visible damage or loss of metal to anything below the waterline when I inspect in the Spring or Fall. The bonding system connects the engine, transmission, thru-hulls, keel and mast. There is no external ground plate, nor do I have anything that I can secure overboard in the event of a thunderstorm. The bonding system does NOT connect the stanchions, pushpit or pulpit. The bonding system consists of a green-shielded #4 wire which is crimped to connectors which are secured to the components listed above, as specified at commissioning by ODay. I have made no modifications up until now other than tightening the bolts at some of the connections. I'm not worried about compromising the grounding system by disconnecting the thru-hulls because there is no (measureable) problem with stray current corrosion or galvanic corrosion. Stay in touch. I've learned a lot from you. Tom
W.W. As you observed, my boat is in fresh water(?),specifically in Lake Erie. Although I've upgraded the electrical system in the boat somewhat, I'm far from the laptop, refrigerator, hot water and electric water pump level of consumption. I am meticulous about wiring both AC and DC and follow the ABYC directions as to type of wire (tinned), connectors (crimped), type of wire insulation (marine grade) and protection from mechanical brakeage (plastic rough boxes and wire ties) and protection against vibration (grommets at all drilled holes). The only wires that I'm nervous about are the wires to and from the bilge pump although I have the waterproof connectors raised so that they do not rest in bilge water. For these reasons I have no measureable problems with stray current leakage. As to galvanic corrosion, I have replaced the pencil zinc in the heat exchanger of the exhaust system once since 1995. I seriously doubt that it had been replaced by the previous owner before that time. The boat was new in 1986, and the old zinc looked good enough that I kept it as a spare. That is the only zinc on board that I know of. I would rate the zinc consumption as minimal. By the way, I see no visible damage or loss of metal to anything below the waterline when I inspect in the Spring or Fall. The bonding system connects the engine, transmission, thru-hulls, keel and mast. There is no external ground plate, nor do I have anything that I can secure overboard in the event of a thunderstorm. The bonding system does NOT connect the stanchions, pushpit or pulpit. The bonding system consists of a green-shielded #4 wire which is crimped to connectors which are secured to the components listed above, as specified at commissioning by ODay. I have made no modifications up until now other than tightening the bolts at some of the connections. I'm not worried about compromising the grounding system by disconnecting the thru-hulls because there is no (measureable) problem with stray current corrosion or galvanic corrosion. Stay in touch. I've learned a lot from you. Tom
wow, thats a lot of info!!
Thanx everyone, that is certainly more than I asked for but some great stuff here. Thanx for everyone's input, you all have some good things to say.
Thanx everyone, that is certainly more than I asked for but some great stuff here. Thanx for everyone's input, you all have some good things to say.
Last july, I got zapped
I got hit with a bolt that disentergrated my mast antennae, all is left is the bracket and coaxiel cable, I have ham, cb,2 vhf's, scanner, & am/fm, it toasted my 3 bank battery charger, but not my inverter, or my wind generator or solar panel, I was on the boat at the tim, (live aboard) and the pop was very loud, the only grounding is to the engine, I too, don't have any valves grounded, my ham has a 50ft coaxiel on the inside along the toe rail, and connected to a shroud chain plate, I got hit because my mast is taller the most boats, you never know what is safe and what is not.
I got hit with a bolt that disentergrated my mast antennae, all is left is the bracket and coaxiel cable, I have ham, cb,2 vhf's, scanner, & am/fm, it toasted my 3 bank battery charger, but not my inverter, or my wind generator or solar panel, I was on the boat at the tim, (live aboard) and the pop was very loud, the only grounding is to the engine, I too, don't have any valves grounded, my ham has a 50ft coaxiel on the inside along the toe rail, and connected to a shroud chain plate, I got hit because my mast is taller the most boats, you never know what is safe and what is not.
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