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Hi Rick....
I just went down to the marina (brackish water right off the ICW) and measured the voltage difference when I put the black lead of my digital volt meter on the back-stay, and dropped the red lead into the water. I set my meter on 20 VDC and much to my surprize read .97 volts DC. I went over to the aluminum 35ft deep sea fishing boat in the next slip over and measured .66 volts DC between one his fittings and the marina water. When I detached the 30 amp shore power cable from our boat, I could visable see the .97 voltage drop about .01 volt DC per second. I didn't wait around to see how low it would drop with the shore cable removed. I'll check that out tomorrow. I know that the voltage potential is due to the ground (green) line in my shore power cable, so throwing the breaker in my light-house will not solve my problem since it only breaks the hot leg of the shore cord. One of my boat neighbors has cable TV attached to his boat, and I suspect the coax cable as well a source. I am glad that an aluminum boat is next door, because I know his boat is less noble that the bronze or stainless below the water line on our boat, and his entire boat will rot away before something on our boat gets eaten away. I still plan to keep my zincs replaced, but for the time being, I plan to disconnect my shore power when it's not needed.
I just went down to the marina (brackish water right off the ICW) and measured the voltage difference when I put the black lead of my digital volt meter on the back-stay, and dropped the red lead into the water. I set my meter on 20 VDC and much to my surprize read .97 volts DC. I went over to the aluminum 35ft deep sea fishing boat in the next slip over and measured .66 volts DC between one his fittings and the marina water. When I detached the 30 amp shore power cable from our boat, I could visable see the .97 voltage drop about .01 volt DC per second. I didn't wait around to see how low it would drop with the shore cable removed. I'll check that out tomorrow. I know that the voltage potential is due to the ground (green) line in my shore power cable, so throwing the breaker in my light-house will not solve my problem since it only breaks the hot leg of the shore cord. One of my boat neighbors has cable TV attached to his boat, and I suspect the coax cable as well a source. I am glad that an aluminum boat is next door, because I know his boat is less noble that the bronze or stainless below the water line on our boat, and his entire boat will rot away before something on our boat gets eaten away. I still plan to keep my zincs replaced, but for the time being, I plan to disconnect my shore power when it's not needed.
Not all shore power electrical
work meets code. Check to see if ground is "ground" Make sure neutral is neutral. And make sure the hot breaks when you trip the breaker. You have no way to know if the other boats are wired properly. Don't touch "ground" on the dock and "ground" on one of the boats.
work meets code. Check to see if ground is "ground" Make sure neutral is neutral. And make sure the hot breaks when you trip the breaker. You have no way to know if the other boats are wired properly. Don't touch "ground" on the dock and "ground" on one of the boats.
Ross
You had me convinced to go out tomorrow to buy the same meter until I did a web search for the specs. I'm sure you are reading the meter scale okay but the tech specs for the meter would indicate it's precision down to only 200 microamps which is .2 ma. Regardless, we're talking about two different things. By way of example, if your boat is moving or there is current, the voltage and current measured with your voltmeter will change simply by virtue of the differential movement (of the water and boat) which is unrelated to the original topic, stray current corrosion. There are no magic bullets to obtaining a true current reading. I could refer you to some not so light reading for a far more eloquent explanation than I can give.
You had me convinced to go out tomorrow to buy the same meter until I did a web search for the specs. I'm sure you are reading the meter scale okay but the tech specs for the meter would indicate it's precision down to only 200 microamps which is .2 ma. Regardless, we're talking about two different things. By way of example, if your boat is moving or there is current, the voltage and current measured with your voltmeter will change simply by virtue of the differential movement (of the water and boat) which is unrelated to the original topic, stray current corrosion. There are no magic bullets to obtaining a true current reading. I could refer you to some not so light reading for a far more eloquent explanation than I can give.
Don, as with any meter
the scales are full scale limits. With a 200 microamp range it is posible to use the low end of the scale because it is from 0 to 200 microamps. In the same manner a 20 amp meter on the instrument panel can read any current between 0 and 20 amperes. I am no stranger to electronics with an Air Force career in radio maintainance and post Air Force in Research and Developement I have been involved in measuring currents from the very small to the very large. Edit to add: Don, I too have checked the specs on the Tenma meter. Here is a link: http://www.spctechnology.com/prodinfo/specs/52f7976.PDF
the scales are full scale limits. With a 200 microamp range it is posible to use the low end of the scale because it is from 0 to 200 microamps. In the same manner a 20 amp meter on the instrument panel can read any current between 0 and 20 amperes. I am no stranger to electronics with an Air Force career in radio maintainance and post Air Force in Research and Developement I have been involved in measuring currents from the very small to the very large. Edit to add: Don, I too have checked the specs on the Tenma meter. Here is a link: http://www.spctechnology.com/prodinfo/specs/52f7976.PDF
Sherry: In Short, Don't Worry, Be Happy!
Assuming nothing is grossly wrong with either your marina or your boat's wiring, all a zinc on a fresh water boat does is prevent the the prop from hitting the rudder when the prop shaft pulls out of the coupling (a very unlikely event that I have actually observed). Although zincs are absolutely required in salt water, and STRONGLY recommended in brackish water to prevent galvanic corrosion, fresh water is a terrible conductor of electricity, and galvanic corrosion is therefore negligiable because it is very difficult to set up the required (corrosion) circuit, even without a zinc. On Lake Michigan (usually considered to be fresh water), there are a few older boats that have zincs, but I have never seen anyone actually change one. If you have electrolytic corrosion (due to stray currents), a zinc may protect the part of the boat that it is actually connected to for a short time (e.g. if you have stray electrons running around the boat and a zinc attached to your prop shaft, the prop shaft should be OK, but any metal through hulls may be eaten), but electrolytic corrosion is fast, and the zinc will go away if this occurs. In short Sherry, a zinc on your boat won't hurt, but of you don't have one, don't worry about it. Steve Alchemist C-320
Assuming nothing is grossly wrong with either your marina or your boat's wiring, all a zinc on a fresh water boat does is prevent the the prop from hitting the rudder when the prop shaft pulls out of the coupling (a very unlikely event that I have actually observed). Although zincs are absolutely required in salt water, and STRONGLY recommended in brackish water to prevent galvanic corrosion, fresh water is a terrible conductor of electricity, and galvanic corrosion is therefore negligiable because it is very difficult to set up the required (corrosion) circuit, even without a zinc. On Lake Michigan (usually considered to be fresh water), there are a few older boats that have zincs, but I have never seen anyone actually change one. If you have electrolytic corrosion (due to stray currents), a zinc may protect the part of the boat that it is actually connected to for a short time (e.g. if you have stray electrons running around the boat and a zinc attached to your prop shaft, the prop shaft should be OK, but any metal through hulls may be eaten), but electrolytic corrosion is fast, and the zinc will go away if this occurs. In short Sherry, a zinc on your boat won't hurt, but of you don't have one, don't worry about it. Steve Alchemist C-320
relocating zinc
Steve, Hmmm...... sounds like I may need to pay special attention to the location of my zinc, if its purpose is to keep the prop from hitting the rudder
I really wonder about how much stray current is running around my dock. We have several boats that are, uh, how to say this nicely, somewhat neglected? I suspect that most of them probably have wiring issues, but I don't know that. I'll be curious to see what my zinc looks like when I inspect it. A friend has an underwater remote control video camera; I am going to borrow it if we can get together before the water gets warm enough to just swim and check it. Thanks again!
Steve, Hmmm...... sounds like I may need to pay special attention to the location of my zinc, if its purpose is to keep the prop from hitting the rudder
I really wonder about how much stray current is running around my dock. We have several boats that are, uh, how to say this nicely, somewhat neglected? I suspect that most of them probably have wiring issues, but I don't know that. I'll be curious to see what my zinc looks like when I inspect it. A friend has an underwater remote control video camera; I am going to borrow it if we can get together before the water gets warm enough to just swim and check it. Thanks again!
Sherry, If there is stray AC in the
water then swimmers are in danger. But if you just place the leads from a multimeter in the water a few feet apart then you can measure the voltage per foot in the water. The current in the water isn't, in and of its self, deadly but it can interfere with a persons ability to breath while in the water and thus drown them.
water then swimmers are in danger. But if you just place the leads from a multimeter in the water a few feet apart then you can measure the voltage per foot in the water. The current in the water isn't, in and of its self, deadly but it can interfere with a persons ability to breath while in the water and thus drown them.
Fresh water?
Hi Steve from Holland; WE are in Elk Rapids, and have been using magnesium anodes for the last several years. After one year, ours shows considerable pitting. When using zincs, they would last for years. Believe me, some of the shore power set ups I see on some boats leads me to believe there is surely stray current around in fresh water. Magnesium is available at least in 1" diameter sizes at WM and other boat stores. It is much more reactive in fresh water than zinc. Fair winds Dave
Hi Steve from Holland; WE are in Elk Rapids, and have been using magnesium anodes for the last several years. After one year, ours shows considerable pitting. When using zincs, they would last for years. Believe me, some of the shore power set ups I see on some boats leads me to believe there is surely stray current around in fresh water. Magnesium is available at least in 1" diameter sizes at WM and other boat stores. It is much more reactive in fresh water than zinc. Fair winds Dave
My money is on the zincs being lost
In reply #3 Steve writes: "As I recall, I had to use an allen wrench and I tightened them until the wrench started to bend." Considering the friability of zincs, overtightening them (or banging them hard with hammers) as advised by some responders would seem to risk cracking the arch and/or flanges of the anode. Once the zinc is cracked it will just be a matter of time before it simply drops off. Moreover, there is no real point in tightening very strongly since the material is inelastic and the unavoidable loss of even a tiny amount of anode material will soon take the pressure off the nut again. IMHO, it is more important to use nuts that fit pretty tightly around the bolt or are equipped with some kind of locking device. Flying Dutchman
In reply #3 Steve writes: "As I recall, I had to use an allen wrench and I tightened them until the wrench started to bend." Considering the friability of zincs, overtightening them (or banging them hard with hammers) as advised by some responders would seem to risk cracking the arch and/or flanges of the anode. Once the zinc is cracked it will just be a matter of time before it simply drops off. Moreover, there is no real point in tightening very strongly since the material is inelastic and the unavoidable loss of even a tiny amount of anode material will soon take the pressure off the nut again. IMHO, it is more important to use nuts that fit pretty tightly around the bolt or are equipped with some kind of locking device. Flying Dutchman
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