For the past few summers I have had a major problem with electrolysis.It has completely destroyed my prop on two different sseasons.I now use a composite prop but am still having problems! MY Zinc has been completly used up during one season leaving a bare shaft This has happened twice. My boat is kept on a mooring in a small cove with approx. a dozen small power boats.There are homes around the area with docks and boats. My boatyard could not find the cause. I would appreciate any input ! Thanks P.S. I am now worried about my seacocks and keel bolts! I want to mention that the Zincs were OK on some seasons with the composite prop ! I am puzzled !!!!
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Paul Akers
IMHO...
...finding the culprit in your cove is like finding a needle in a haystack. Are others in the area experiencing the same thing? This will be difficult to trace. You might want to add one or two more zincs to your shaft. I use 3 in my marina. Another thought would be to hang a zinc "fish" over the side while on the mooring. Scour local marinas for old zincs that have been discarded and thread them onto a wire that you can also hang over the side. Good Luck!
...finding the culprit in your cove is like finding a needle in a haystack. Are others in the area experiencing the same thing? This will be difficult to trace. You might want to add one or two more zincs to your shaft. I use 3 in my marina. Another thought would be to hang a zinc "fish" over the side while on the mooring. Scour local marinas for old zincs that have been discarded and thread them onto a wire that you can also hang over the side. Good Luck!
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Phil Teter
wiring problem
I assume you are not connecterd to shore power. If you are I think it likely the wiring problem is on the dock. Shore power or not, corrosion is caused by current flowing from - to + through the water. You could have a wiring problem on your boat. Your - should be connected to ground in one and only one place. I would expect the battery - to be connected to the boat grounding system. Disconnect this ground connection and see if your - conductor is still connected to ground. If it is, find the connection and get rid of it. Reconnect your battery ground, this should make your zinks last a lot longer. Phil Teter
I assume you are not connecterd to shore power. If you are I think it likely the wiring problem is on the dock. Shore power or not, corrosion is caused by current flowing from - to + through the water. You could have a wiring problem on your boat. Your - should be connected to ground in one and only one place. I would expect the battery - to be connected to the boat grounding system. Disconnect this ground connection and see if your - conductor is still connected to ground. If it is, find the connection and get rid of it. Reconnect your battery ground, this should make your zinks last a lot longer. Phil Teter
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Brian Pickton of BeneteauOwners.net
Follow Phil and Paul's advice
Dec.26, 2000 Dear Bril, Did you see the testing done by the yard? The reason I ask is because if they didn't conduct the test described by Phil they are not going to find the cause of the problem on your boat. If they in fact did do the test I would have to say they missed something given the magnitude of the problem. That means you are going to have to do it yourself or hire an electrician to do it for you. The other thing I find intriguing is the apparantly sporadic nature of the electrolysis, like something is being turned off and on on your boat. We ran into this issue on The Legend and the prospect of laboriously tracing every wire and disconnecting it to find out if it was the culprit was truly daunting, given the amount of wiring on board. In addition, the boat has been completely rewired once and some of the wires were not removed, which only serves to compound the problem. It occured to me that the most likely location for a short would be in the bilge and that was where I started the search. Sure enough a wire to one of our electric bilge pumps had actually worn a hole through its plastic coating and was shorting into the bilge whenever it got wet, which it would do if the bilge pump cycled and water splashed out of the banjo box. Needless to say it was replaced. It occurs to me that you may have a similar problem , but nonetheless you still have to conduct the test described by Phil to find it. In the meantime while you are getting around to it take Paul's advice and wire up and hang a large sacrificial zinc over the side. Fair winds this holiday season. Brian Pickton of BeneteauOwners.net Aboard The Legend, Rodney Bay, St. Lucia
Dec.26, 2000 Dear Bril, Did you see the testing done by the yard? The reason I ask is because if they didn't conduct the test described by Phil they are not going to find the cause of the problem on your boat. If they in fact did do the test I would have to say they missed something given the magnitude of the problem. That means you are going to have to do it yourself or hire an electrician to do it for you. The other thing I find intriguing is the apparantly sporadic nature of the electrolysis, like something is being turned off and on on your boat. We ran into this issue on The Legend and the prospect of laboriously tracing every wire and disconnecting it to find out if it was the culprit was truly daunting, given the amount of wiring on board. In addition, the boat has been completely rewired once and some of the wires were not removed, which only serves to compound the problem. It occured to me that the most likely location for a short would be in the bilge and that was where I started the search. Sure enough a wire to one of our electric bilge pumps had actually worn a hole through its plastic coating and was shorting into the bilge whenever it got wet, which it would do if the bilge pump cycled and water splashed out of the banjo box. Needless to say it was replaced. It occurs to me that you may have a similar problem , but nonetheless you still have to conduct the test described by Phil to find it. In the meantime while you are getting around to it take Paul's advice and wire up and hang a large sacrificial zinc over the side. Fair winds this holiday season. Brian Pickton of BeneteauOwners.net Aboard The Legend, Rodney Bay, St. Lucia
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Rick
Disappearing Zincs
Installing additional zincs is not a good solution to the problem. The stray current will disolve the zincs and leave a plating of zinc oxide on your prop and shaft that will degrade performance just like bottom growth - but alot harder to scrape off. For a full discourse on stray currents that eat zincs, check out this web page: http://marinesurvey.com/yacht/corrosion_in_marinas.htm If you are handy with a multi-meter you can check to see if you have current flowing from your AC grounding wire to your DC grounding system (or engine). Or you might determine (depending on direction of current flow) that other boats are grounding to water and the current is flowing thru your prop, shaft, engine and then across to your AC side to finally ground out to the marina ground. A good solution for that is to install a galvanic isolator between your AC and DC grounding system (or it can be installed on the green AC ground wire). The isolator uses diodes to stop small currents (less than 1 volt or so) but still allows higher current to pass so that normal grounding occurs. Good Luck.
Installing additional zincs is not a good solution to the problem. The stray current will disolve the zincs and leave a plating of zinc oxide on your prop and shaft that will degrade performance just like bottom growth - but alot harder to scrape off. For a full discourse on stray currents that eat zincs, check out this web page: http://marinesurvey.com/yacht/corrosion_in_marinas.htm If you are handy with a multi-meter you can check to see if you have current flowing from your AC grounding wire to your DC grounding system (or engine). Or you might determine (depending on direction of current flow) that other boats are grounding to water and the current is flowing thru your prop, shaft, engine and then across to your AC side to finally ground out to the marina ground. A good solution for that is to install a galvanic isolator between your AC and DC grounding system (or it can be installed on the green AC ground wire). The isolator uses diodes to stop small currents (less than 1 volt or so) but still allows higher current to pass so that normal grounding occurs. Good Luck.
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Bryce Grefe
disappearing zincs
I've had a similiar problem last year on my H410. I'm on a mooring in the old Hingham MA shipyard. I went thru 5 zincs, including two on the prop during the previous season. Did two things this season, 1 went to a higher quality zinc, sold by Boat US at around $20 ea vs $4-$5 for the more common zincs and secondly moved to a different mooring about 50 feet from the one I had last year. On pull out both shaft zincs were in place along with the prop zinc. I queried the shipyard about the problem, their feeling was because the mooring field is in on old ship yard, a number of magnetic hot spots were on the bottom due to metals having been dumped in the bay during the hay days of shipbuilding in the 40's. These magnetic hot spots were causing stray currents at various places in the mooring field. Don't know if its really the answer, but no problems this year. Bryce S/V Spellbinder H410
I've had a similiar problem last year on my H410. I'm on a mooring in the old Hingham MA shipyard. I went thru 5 zincs, including two on the prop during the previous season. Did two things this season, 1 went to a higher quality zinc, sold by Boat US at around $20 ea vs $4-$5 for the more common zincs and secondly moved to a different mooring about 50 feet from the one I had last year. On pull out both shaft zincs were in place along with the prop zinc. I queried the shipyard about the problem, their feeling was because the mooring field is in on old ship yard, a number of magnetic hot spots were on the bottom due to metals having been dumped in the bay during the hay days of shipbuilding in the 40's. These magnetic hot spots were causing stray currents at various places in the mooring field. Don't know if its really the answer, but no problems this year. Bryce S/V Spellbinder H410
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