Jim Shafer: My name is Jim Shafer. I’m a marine surveyor and marine electrician. One of the areas I specialized in as what’s referred to is Galvanic Corrosion among the water metals of boats. Sometimes it referred to, as like electrolysis but that is an incorrect usage of the word its Galvanic Corrosion. It’s very important to remember the Galvanic Corrosions are natural occurrence, physical phenomenon, when you connect a bronze prop stainless steel shaft in a sacrificial Zinc altogether you put them in a electro lite.
Galvanic Corrosion is caused because its current flow causes the anodic component with this case to Zinc, anodic component to give up electrons to protect the stainless called the cathodic component and in doing solid, misses or looses metallic ions and it waste the way and that instant is called sacrificial anode. When anode looks like this, when its starts to be consumed to protect the stainless and bronze prop its looks like that. It’s very important to remember if this zinc sacrificial element these elements to maintain their function, you must maintain electrical contact with the other metel, the stainless steel in this case to stainless steel shaft.
So the manufacture has cast in this case a copper ball, which maintains contact with the stainless. In this little pad zinc, which goes on rudder possibly our trim tab is casting a brass insert or bronze insert. In the case of this whole zinc manufactures casting in aluminium bar. All these components will maintain their contact with stainless fasteners because these casting components. Without this you would disconnect and become electrically unhooked within matter of months. The Galvanic Corrosion occurs no matter what’s you do, because you put the some metals in the water. Because how much metals in the shaft, how much metal in the prop, how much in the zinc wise we can’t control the rate at which we consume anode to protect the shaft.
Normal you should plug the boat in to a dark, however we have the whole marine all the other boats, just you see well anything else it’s buried in the ground we have to protect all of that. Now we loose control, we loose control we get rapid zinc loss we might have a fairly damaged prop or Michal so far has to loose an entire aluminium attires in this little less six months because of the Galvanic Corrosion, so this became the sacrificial component of the battery. After zinc on the shaft to whole attire and we do about --
We can leave the boat on plugged this cuts two half from the marine then your zinc’s will protect only your metal. The shafts in the props, you can plug the boat and install the isolation transformer, which we talk about here but that comes of many boats as special aluminium and steel hose or have a Galvanic isolator and we don’t open that, we are going to get down and make a test of this boat and see if you supplying current of the dock using this zincs protect the dark. To determined and this boat is going to have problems, with sacrificing at zinc with applying protection of a whole dark. We have to remove this short code which we have done, we put in the water, next to the boat a reference cell is a standard use to measure Galvanic voltages, we connect a digital voltmeter to the reference cell set it on the milliampere scale and connect the ground, understand that the ships burning system and Ic ground are common to boat-to-boat this is very important to establish this by the way for safety.
We never cut the ground on a yacht to protect it from galvanic corrosions dark. We loose our set; our IC safety and we could create these potentials, which could which could cause injury. Take the ground pin on the plug and with the prop on the ground pin compare the voltage to our reference cell in the water. This is 0.9 volts but I would expect the both it has bronze prop stainless shafts in the copper, manganese, zinc. I would expect about 0.9 volts. Galvanic Corrosion when we plug the boat in and we’ll show you that the dock voltage by going to the grounding, shallow on the dock or let measures 4.4 volts. Doesn’t have all immediately accept this. We you have two differences of potential it cracking together with current flow. We don’t want current flow means our zincs are providing sacrificial electrons swelling off the boat to protect something else in the marine, which will lose control of our zinc protection for the boat.
Whatever we know we probably have a problem, we probably have problem because this measures 0.9 and this measure is 0.4 and we connecting together we are going to have some other voltage but how we do that lets look at the current that might flow from the boat to the dock. In this case we take our digital voltmeter turned into a digital ammeter connect the negatively to the burning system which we access through that pin on the plug and other way we connect the, so they shell otherwise skeptical that is bouncing around with that almost half an hour, 500 millions almost half an hour of sacrificial current running off the boat somewhere else marine. We would expect there for substantial increase in our weight up zinc lose not to protect our boat protect the whole marine. But we don’t want to do that. Luckily do about that, besides leaving the plug out heaving freezer get -- many boats have an isolation transformer throughout going to here the alternative, the third option was called galvanic isolator. It provides a door or gate to prevent the galvanic current fall at very low levels that what you saw less then involved and less than amp, yeah we retain the very important integrity of our ground weight for IC safety.
If I install this galvanic isolator in series with my needle, this is in series now its connected so that its in the line as if I had cut the green ground in a both the boat and install this device to handle electrical panel on the something here. Now I connect by leads to the body, it’s zero current fall, so I just cut off galvanically from the rest of the dock and retain my very critical green ground safety link. We do not disconnect green safety links to produce this zero current result. Mostly if we establish this we can really tell why this boats loosing zincs and rapidly and assured providing protection for rest of the dock. Another way to confirm this test to confirm the problem is to connect is to gain access to the dock ground, after you plug your code in, so I made up this jumper, which gives me access to the ground. As that works.
We are going to connect this again show galvanic voltage using the reference cell. The galvanic we had before on the dock was about 0.4 volts, 400 kilovolts or 0.12 volts. We had on the short code; we had disconnected about 0.9 volts. Now if we have we demonstrate current flow between the short code and the dock we hope that up what happens when we plug this in to the dock now. We can further demonstrate this problem if the voltage was different in the first two readings.
See what it is and with have my access here is 0.7 some where between 0.4 and 0.9 this indicates that we have a combine battery now with a new potential, so tip of right away something is wrong. We confirm that by measuring the actual current flow of the boat was a with the plug on boat.
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