What is the general opinion about the value of these? I have read various articles and think I understand what they are supposed to do. Is the "finned box" installed behind and to the left of the Electrical Switch Panel (above the Chart table) such an "isolator"? I cant read what is says on the label which is mostly hidden from view. The wiring manual is also not helpful. How do you know if it is working ok as there does not appear to be any guage? The Cruising World magazine for Oct 2012 has an article which outlines why they work. The zinc on my prop shaft seems to last a year easily between haulouts.
Cheers, Geoff. C350 #392 Taeko 1V Blaine WA.
Galvanic Isolator
Moderator: KenKrawford
Re: Galvanic Isolator
Ah! So many questions, so many answers. Thanks for the chance.... 
A Galvanic Isolator is simply a type of transformer that lives between your boat's 110 VAC ground wire and the marina's 110 VAC ground wire.
Are they worth having and do they work depends almost entirely upon two separate issues : 1) the "health" of the electrical system that your marina maintains and 2) the "health" of the electrical system each and every boat in your marina and on the same ground maintains.
Addressing 1) : A well maintained marina will have nearly no ground leakage voltage. The maintenance crews are probably seen every couple of weeks or so checking each and every outlet with a weird looking , usually hand made , contraption. It consists of 10 loops of the ground wire between two 30 amp plugs. The crew will insert this device between each residents shore power cord and the dock outlet and then use a digital amp meter to read any flow ( multiplied by 10 ) of current in the ground wire. There should be next to none. If they find it, they are by law ( finally!! ) required to chase down the source and address it. Why? Because there have been deaths. You may recall the event just a few years ago where a child was electrocuted when he tried to climb out of the water in a 'hot' marina - kid was fine just swimming until his hand came in contact with the steel ladder. Ultimate cause was tracked down to a microwave on a boat with a poor ground and a corroded terminal in a shore side box a few boats away.
Addressing 2) : Everything you plug into your boat's 110 VAC receptacles that has a ground wire can have a poor ground and thus leak some current. In a house you'll never notice it and it usually doesn't matter. But in a boat, that leak sets up a loop outside of your boat. Almost every boat has a connection between the shore side 110 VAC ground and the 12 VDC ground in the boat. This connection is usually in the battery charging system. That connection allows stray currents in the ground wire to flow from the shore side ground through your entire boat and out through the prop, shaft and any metal through hulls that are grounded ( they are , aren't they? ) . If two or more boats have these stray currents, you now have many loops, each of which can enhance the already present galvanic current. What? What did I say? ... I said you already have some currents just by having a boat in the water. These currents are found between the dissimilar metals that live in the water. Your prop is probably bronze, your shaft is probably steel, and you probably have a zinc. And if you live in salt water, you have an electrolyte. Galvanic Currents form when ever dissimilar metals are immersed in a electrolyte. Stick a penny in a lemon at one end and a dime in the other and put a good quality voltmeter on the two coins and you will see some voltage thus current. Back at your boat, your zinc is "less noble" than the other two metals and sacrifices itself to the electrolyte to protect the prop and shaft metals. That's why it eventually gets eaten up - it's doing it's job. Back to the point of the question, a bad ground in an appliance can make your zinc disappear in no time at all.
The device behind the electrical panel , at least on Halona , actually reads "Zinc Saver" , and if it's working correctly , it breaks the connection between the 110 VAC ground and the 12 VDC ground. Thus there can be no enhancement of the naturally occurring galvanic current already present AND it isolates your boat from your neighbors boat. That's right, YOUR zinc can be protecting your neighbors boat as well. If his grounding system is poor and your's is just fine, then your zinc is in the same electrolyte as his prop and you ( with no isolators ) share the same ground. Now you have a current loop between your boat, to the shore side power ground, to his boat , to his charger , to his prop and into the water and back to your boat. These currents are not enough to harm, but can quickly erode zincs. I have seen my zinc over the course of one winter lose 80% of it's weight in two months. This kept up until the port tracked down the culprit and had the boat owner remedy the many problems on his vessel. His boat was moored six slips away and everyone was going through zincs like candy. Think also about every time you travel and show up at some barely maintained marina and plug in.
Final comment, there is a procedure that will allow you to test the galvanic isolator already on your boat, but it's generally not something normal folks can or will attempt. So the black box just sits there and you hope it works. Or , you do as I did , and install a really good quality GI into your system, one that by it's design when and if it fails , it fails in protection mode. A year on a zinc sounds good and in the end that's what you want. If your zinc starts lasting only six months or less, it's time to get aggressive. Are the GI's worth it? You bet.
Please excuse my windy-ness.
A Galvanic Isolator is simply a type of transformer that lives between your boat's 110 VAC ground wire and the marina's 110 VAC ground wire.
Are they worth having and do they work depends almost entirely upon two separate issues : 1) the "health" of the electrical system that your marina maintains and 2) the "health" of the electrical system each and every boat in your marina and on the same ground maintains.
Addressing 1) : A well maintained marina will have nearly no ground leakage voltage. The maintenance crews are probably seen every couple of weeks or so checking each and every outlet with a weird looking , usually hand made , contraption. It consists of 10 loops of the ground wire between two 30 amp plugs. The crew will insert this device between each residents shore power cord and the dock outlet and then use a digital amp meter to read any flow ( multiplied by 10 ) of current in the ground wire. There should be next to none. If they find it, they are by law ( finally!! ) required to chase down the source and address it. Why? Because there have been deaths. You may recall the event just a few years ago where a child was electrocuted when he tried to climb out of the water in a 'hot' marina - kid was fine just swimming until his hand came in contact with the steel ladder. Ultimate cause was tracked down to a microwave on a boat with a poor ground and a corroded terminal in a shore side box a few boats away.
Addressing 2) : Everything you plug into your boat's 110 VAC receptacles that has a ground wire can have a poor ground and thus leak some current. In a house you'll never notice it and it usually doesn't matter. But in a boat, that leak sets up a loop outside of your boat. Almost every boat has a connection between the shore side 110 VAC ground and the 12 VDC ground in the boat. This connection is usually in the battery charging system. That connection allows stray currents in the ground wire to flow from the shore side ground through your entire boat and out through the prop, shaft and any metal through hulls that are grounded ( they are , aren't they? ) . If two or more boats have these stray currents, you now have many loops, each of which can enhance the already present galvanic current. What? What did I say? ... I said you already have some currents just by having a boat in the water. These currents are found between the dissimilar metals that live in the water. Your prop is probably bronze, your shaft is probably steel, and you probably have a zinc. And if you live in salt water, you have an electrolyte. Galvanic Currents form when ever dissimilar metals are immersed in a electrolyte. Stick a penny in a lemon at one end and a dime in the other and put a good quality voltmeter on the two coins and you will see some voltage thus current. Back at your boat, your zinc is "less noble" than the other two metals and sacrifices itself to the electrolyte to protect the prop and shaft metals. That's why it eventually gets eaten up - it's doing it's job. Back to the point of the question, a bad ground in an appliance can make your zinc disappear in no time at all.
The device behind the electrical panel , at least on Halona , actually reads "Zinc Saver" , and if it's working correctly , it breaks the connection between the 110 VAC ground and the 12 VDC ground. Thus there can be no enhancement of the naturally occurring galvanic current already present AND it isolates your boat from your neighbors boat. That's right, YOUR zinc can be protecting your neighbors boat as well. If his grounding system is poor and your's is just fine, then your zinc is in the same electrolyte as his prop and you ( with no isolators ) share the same ground. Now you have a current loop between your boat, to the shore side power ground, to his boat , to his charger , to his prop and into the water and back to your boat. These currents are not enough to harm, but can quickly erode zincs. I have seen my zinc over the course of one winter lose 80% of it's weight in two months. This kept up until the port tracked down the culprit and had the boat owner remedy the many problems on his vessel. His boat was moored six slips away and everyone was going through zincs like candy. Think also about every time you travel and show up at some barely maintained marina and plug in.
Final comment, there is a procedure that will allow you to test the galvanic isolator already on your boat, but it's generally not something normal folks can or will attempt. So the black box just sits there and you hope it works. Or , you do as I did , and install a really good quality GI into your system, one that by it's design when and if it fails , it fails in protection mode. A year on a zinc sounds good and in the end that's what you want. If your zinc starts lasting only six months or less, it's time to get aggressive. Are the GI's worth it? You bet.
Please excuse my windy-ness.
Last edited by AynB on Mon Sep 24, 2012 9:32 am, edited 1 time in total.
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KenKrawford
- Posts: 614
- Joined: Wed Nov 02, 2005 8:54 pm
- Location: Atlanta, GA
Re: Galvanic Isolator
Thanks for the nice write up on isolators. I'm in fresh water so I assume everything you wrote still applies (other than using magnesium instead of zinc) but to a lesser extent due to fresh water being less conductive than salt.
Ken Krawford
Message Board Moderator
C350 # 351
Lake Lanier, GA
Message Board Moderator
C350 # 351
Lake Lanier, GA
Re: Galvanic Isolator
Ken, yes - it all applies but to a greatly reduced degree when a boat is in fresh water. Most lakes and such are not pure enough to have no galvanic action so there is still some small amount. The whole part about the dockside electronics is still valid though. You bring up a good point by noting the different kinds of protection for fresh water also. Magnesium for fresh and Zinc for salt. If you do a web search for "Galvanic Table" or "Noble metal" , you should get a great deal of information.
Al
Al
Re: Galvanic Isolator
Al,
You post implied that your replaced the standard 'Zinc Saver' with a more robust GI. What did you use? Did you replace it, or add an additional GI? Where is the standard 'Zinc Saver' located? Is it behind the switch panel in the cabin, or near the 30-amp AC breakers at the transom? Apparently, according the the schematic, there is a second 'zinc saver' for the air conditioner system. Do you know where it's located, and did you replace it as well?
Thanks
You post implied that your replaced the standard 'Zinc Saver' with a more robust GI. What did you use? Did you replace it, or add an additional GI? Where is the standard 'Zinc Saver' located? Is it behind the switch panel in the cabin, or near the 30-amp AC breakers at the transom? Apparently, according the the schematic, there is a second 'zinc saver' for the air conditioner system. Do you know where it's located, and did you replace it as well?
Thanks
Gary & Janet
The Best of Times (Hull #422)
The Best of Times (Hull #422)
Re: Galvanic Isolator
I left the Zinc Saver in place and purchased a DariyLand brand unit and installed it on the back wall near the Master Breaker. DariyLand has been making GI's for years to protect cows in the milking machines. If one of these units fails in 'short' mode, the cow would get shocked or at least a bad tickle and be out of production for weeks. I did a lot of research and found that a lot of GI's fail in 'short' mode but that DairyLand's units, if they fail, fail in 'open' mode. Don't ask me to explain THAT difference.
Anyway, it's a nice small robust unit that really can't be installed incorrectly, only two terminals, completely waterproof. Get your self some good marine grade green wire and connect it up.
Al
Anyway, it's a nice small robust unit that really can't be installed incorrectly, only two terminals, completely waterproof. Get your self some good marine grade green wire and connect it up.
Al
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nedenborough
- Posts: 6
- Joined: Fri Jul 06, 2012 10:48 am
Re: Galvanic Isolator
I have had a terrible ground problem at the dock where my boat is kept. I have decided to install an isolation transformer to protect the boat in the future.
I just have received the transformer and note that the instructions call for a 30 amp breaker in front of the transformer. My choice is to either install an additional breaker or to use one of the existing breakers. As you all know, Catalina installed two 30 amp breakers, boat and ac. However, I have only one 30 amp cord and have always used it with a splitter at the plugs.
I am now thinking that I could combine the boat and ac feeds at one breaker and use the other as the main feed. It makes sense to me, but what do you all think?
Neville Hull #413
I just have received the transformer and note that the instructions call for a 30 amp breaker in front of the transformer. My choice is to either install an additional breaker or to use one of the existing breakers. As you all know, Catalina installed two 30 amp breakers, boat and ac. However, I have only one 30 amp cord and have always used it with a splitter at the plugs.
I am now thinking that I could combine the boat and ac feeds at one breaker and use the other as the main feed. It makes sense to me, but what do you all think?
Neville Hull #413