I am halfway through Nigel Caders "Marine Diesel Engines" and have a question about the use of sacrificial zincs. If you only sail in Fresh water lakes , are the still needed ? Thanks Bill
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Justin - O'day Owners' Web
Not Zincs exactly
You should have some protection from electrolosis even in fresh water, though many people get away without it. The electrical conductivity of water depends on the amount of stuff dissolved in it. (I seem to remember a high school science demonstration where deionized water was totally non-conductive). Seawater is therefore much more conductive than fresh water by virtue of the higher dissolved salt content. The issue is that even fresh water is not pure water. The dissolved minerals make it possible to get galvanic corrosion, albiet at a much slower rate. The solution is to put magnesium anodes on your boat instead of zinc. I can't tell you why magnesium is better than zinc but that's apparently the way it works. Justin - O'day Owners' Web
You should have some protection from electrolosis even in fresh water, though many people get away without it. The electrical conductivity of water depends on the amount of stuff dissolved in it. (I seem to remember a high school science demonstration where deionized water was totally non-conductive). Seawater is therefore much more conductive than fresh water by virtue of the higher dissolved salt content. The issue is that even fresh water is not pure water. The dissolved minerals make it possible to get galvanic corrosion, albiet at a much slower rate. The solution is to put magnesium anodes on your boat instead of zinc. I can't tell you why magnesium is better than zinc but that's apparently the way it works. Justin - O'day Owners' Web
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R.W.Landau
Justin
Magnesium is less noble than zinc. Bill, You will see the chart of nobility in metals on page 133 of Calder's book. I have never heard of magnesium anodes but it seems logical. Magnesium would disappear twice as fast as zinc in salt water but would provide good protection in a less conductive medium such as fresh water. Thomas Emkee (?spelling, sorry Thomas) just talked about how little zinc decay he has had in the west end of Erie. r.w.landau
Magnesium is less noble than zinc. Bill, You will see the chart of nobility in metals on page 133 of Calder's book. I have never heard of magnesium anodes but it seems logical. Magnesium would disappear twice as fast as zinc in salt water but would provide good protection in a less conductive medium such as fresh water. Thomas Emkee (?spelling, sorry Thomas) just talked about how little zinc decay he has had in the west end of Erie. r.w.landau
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R.W.Landau
Bill
My reference was to Calder's "Boatowner's Mechanical and Electrical Manual" not "Marine Diesel Engines", sorry. r.w.landau
My reference was to Calder's "Boatowner's Mechanical and Electrical Manual" not "Marine Diesel Engines", sorry. r.w.landau
A word to the wise.
If you haven't had the chance to see what happens when you connect galvanized pipes to copper pipe in a home with dielectric couplings it is something to behold. Have you seen what happens when you put stainless steel screws in aluminum. All of the reactions are from having disimilar metals in contact with each other. The biggest problem is usually with stray power in the marinas causing these type of problems. It can come from your boat or from your neighbors. So regardless of where you are located in fresh or salt water environments be sure to have a sacraficial anode on the boats metal parts. Just remember how cheap a zinc is and how expensive a repair is. Is there any reason not to have them even if your *really don't need them*.
If you haven't had the chance to see what happens when you connect galvanized pipes to copper pipe in a home with dielectric couplings it is something to behold. Have you seen what happens when you put stainless steel screws in aluminum. All of the reactions are from having disimilar metals in contact with each other. The biggest problem is usually with stray power in the marinas causing these type of problems. It can come from your boat or from your neighbors. So regardless of where you are located in fresh or salt water environments be sure to have a sacraficial anode on the boats metal parts. Just remember how cheap a zinc is and how expensive a repair is. Is there any reason not to have them even if your *really don't need them*.
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R.W. Landau
Steve
I think you missed the point. It is not that an anode should not be used but what kind and how do they last. The fact that fresh water is no where near the electrolyte that salt water is very important. I think what Justin was saying was that he had heard of magnesium being used instead of zinc. I find that interesting and worth further investigation.The problem that may occur if magnesium (or to much zinc)is used is that if it is to active, is that it will over protect and cause alkalinity which is corrosive to many metals including steel, aluminum. Actually Steve you are talking of two different animals. Electrolysis and galvanic action. Stray current is an electrolysis problem and the dissimilar metals are a galvanic reaction problem. Since fresh water is not as good an electrolyte as salt water, the chances of stray current is much less. Galvanic reaction will be present due to dissimilar metals but it is in no way as taxing on zincs( anodes) as stray current. Just throwing zincs every where is not a good idea. Calder speaks of sizing zincs in his book, Page 147 and explains over protection pages 144 to 150. r.w.landau
I think you missed the point. It is not that an anode should not be used but what kind and how do they last. The fact that fresh water is no where near the electrolyte that salt water is very important. I think what Justin was saying was that he had heard of magnesium being used instead of zinc. I find that interesting and worth further investigation.The problem that may occur if magnesium (or to much zinc)is used is that if it is to active, is that it will over protect and cause alkalinity which is corrosive to many metals including steel, aluminum. Actually Steve you are talking of two different animals. Electrolysis and galvanic action. Stray current is an electrolysis problem and the dissimilar metals are a galvanic reaction problem. Since fresh water is not as good an electrolyte as salt water, the chances of stray current is much less. Galvanic reaction will be present due to dissimilar metals but it is in no way as taxing on zincs( anodes) as stray current. Just throwing zincs every where is not a good idea. Calder speaks of sizing zincs in his book, Page 147 and explains over protection pages 144 to 150. r.w.landau
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Justin - O'day Owners' Web
Wouldn't it stand to reason?
Ok - I so Mag is less noble than zinc, which will allow it to corrode more quickly in the less conductive freshwater environment. What I don't get is this: why do you need mag instead of zinc since your through-hulls, propshaft, etc will also corrode more slowly? Electrolytic corrosion is dependent on the relationship between the two metals involved. Isn't the relationship the same in fresh as it is in salt? I can see the rate of the reaction slowing but beyond that it doesn't make sense to me. The only thing I can figure is that zinc manufacturers wanted to sell something that would wear out faster in fresh waters. I'm sure there is a less sinister reason, but I can't guess it. Justin - O'day Owners' Web
Ok - I so Mag is less noble than zinc, which will allow it to corrode more quickly in the less conductive freshwater environment. What I don't get is this: why do you need mag instead of zinc since your through-hulls, propshaft, etc will also corrode more slowly? Electrolytic corrosion is dependent on the relationship between the two metals involved. Isn't the relationship the same in fresh as it is in salt? I can see the rate of the reaction slowing but beyond that it doesn't make sense to me. The only thing I can figure is that zinc manufacturers wanted to sell something that would wear out faster in fresh waters. I'm sure there is a less sinister reason, but I can't guess it. Justin - O'day Owners' Web
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R.W. Landau
Trial explaination
This trial stuff is for you Justin. Galvanic action is the creation of electricity through chemical change. Two metals in an electrolyte that are connected together,( if they are not connected together electrically, there is no current flow.)create electricity chemically by the lesser noble metal passing electrons to the more noble metal, thus deteriorating the less noble metal. That is why zincs are added. Instead of the bronze, stainless, steel etc deteriorating, the zinc does. In electrolysis, the deterioration occurs due to current being applied, not created. Therefore, the zincs don't actually corrode, they deteriorate according to the reactions of galvanic or electrolysis process. If there is little corrosive action, there is little deterioration to the anode (zinc). Justin, there is still some corrosion and thus zincs ( I still don't know about this mag thing.) are still needed. I could be that Magnesium is more sensitive to the corrosion than zinc. Come on, someone out there must know about this magnesium thing. HELP! r.w.landau
This trial stuff is for you Justin. Galvanic action is the creation of electricity through chemical change. Two metals in an electrolyte that are connected together,( if they are not connected together electrically, there is no current flow.)create electricity chemically by the lesser noble metal passing electrons to the more noble metal, thus deteriorating the less noble metal. That is why zincs are added. Instead of the bronze, stainless, steel etc deteriorating, the zinc does. In electrolysis, the deterioration occurs due to current being applied, not created. Therefore, the zincs don't actually corrode, they deteriorate according to the reactions of galvanic or electrolysis process. If there is little corrosive action, there is little deterioration to the anode (zinc). Justin, there is still some corrosion and thus zincs ( I still don't know about this mag thing.) are still needed. I could be that Magnesium is more sensitive to the corrosion than zinc. Come on, someone out there must know about this magnesium thing. HELP! r.w.landau
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Rick Webb
I'll Give it A Shot
A magnesium anode would work great in salt water. Problem is it would work too great and be gone way too soon. The reason it is used in fresh water is it gives greater protection than would a zinc anode that sluffs off way too slow in fresh water. The zinc anode in the fresh water is not reactive enough to provide any real protection. Someone else could probably explain it better but it is late and it has been a long day.
A magnesium anode would work great in salt water. Problem is it would work too great and be gone way too soon. The reason it is used in fresh water is it gives greater protection than would a zinc anode that sluffs off way too slow in fresh water. The zinc anode in the fresh water is not reactive enough to provide any real protection. Someone else could probably explain it better but it is late and it has been a long day.
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Thomas Ehmke
Bill-fresh water zincs
I sail on Lake Erie on an ODay 272. There is only one sacrificial zinc on the boat that I know of, and it is located in the heat exchanger. As I explained in a recent post to W.W., I replaced the old zinc last year and the old zinc was in such good shape that I decided to keep it as a spare for zinc emergencies(?). The thread we were discussing dealt with galvanic corrosion, stray current leakage and bonding systems. Now speaking to the question on this thread, I find no noticeable loss of the more noble bronze underwater fittings, and the boat has been in the water every season since 1986. What do I conclude from this? Number one, an absence of galvanic corrosion from on board; number two, an absence of stray current leakage from on board the boat; number three, the absence of shoreside current leakage where I dock the boat. I must be one lucky son-of-a-gun because I find no evidence of corrosion problems. What is my advice? Put the zincs in place and watch carefully for their consumption... better safe than sorry. Conditions here may change, and I will add zincs at the cutlass bearing or prop shaft this season. Tom
I sail on Lake Erie on an ODay 272. There is only one sacrificial zinc on the boat that I know of, and it is located in the heat exchanger. As I explained in a recent post to W.W., I replaced the old zinc last year and the old zinc was in such good shape that I decided to keep it as a spare for zinc emergencies(?). The thread we were discussing dealt with galvanic corrosion, stray current leakage and bonding systems. Now speaking to the question on this thread, I find no noticeable loss of the more noble bronze underwater fittings, and the boat has been in the water every season since 1986. What do I conclude from this? Number one, an absence of galvanic corrosion from on board; number two, an absence of stray current leakage from on board the boat; number three, the absence of shoreside current leakage where I dock the boat. I must be one lucky son-of-a-gun because I find no evidence of corrosion problems. What is my advice? Put the zincs in place and watch carefully for their consumption... better safe than sorry. Conditions here may change, and I will add zincs at the cutlass bearing or prop shaft this season. Tom
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Tom
Here is West Marines take on Zincs
Go to this website http://www.westmarine.com/webapp/commerce/command/ExecMacro/west_advisor.d2w/show_advisor?fn=galvaniccorrosion.htm&store_num=4
Go to this website http://www.westmarine.com/webapp/commerce/command/ExecMacro/west_advisor.d2w/show_advisor?fn=galvaniccorrosion.htm&store_num=4
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