Hello,
It is difficult for me to understand the principles of a bonding system for prevent the galvanic corrosion.
Aboard CD, it seems that all thru hull fittings (included engine and the negative of the battery) are connected to the bonding system.
First question : is it necessary to add a sacrifial zinc in the circuit (I had read a theory whitch said the bonding system put of the fittings at the same potential : if this is true, a zinc is unnecessary) ?
Second question : what is the fonction of the grounding plate interconnected to the bonding circuit ?
Thank you by advance
Best Regards
Jacques
HELP BONDING SYSTEM
Moderator: Jim Walsh
Yes, the zinc is still necessary, possibly more than one (prop zinc plus hull zinc elsewhere).
Just because all the metals are connected doesn't mean corrosion stops. Unless all the metallurgy (and crystallography, for that matter) of each fitting is absolutely identical (read: not possible), something will be the most anodic part of the bonded system, and will corrode preferentially. This even occurs within a single metal object, which is what causes pitting (one small part of the object serves as the anode in a galvanic cell).
The grounding plate serves several purposes. One is as an earth ground for your electrical system. Another purpose can be as a signal ground for an SSB radio. If it's large enough and connected to your mast by a large enough conductor, it can serve as a lightning protection system, reducing the probability of hull damage in the event of a lightning strike.
I have a copper plate thru-bolted and epoxied to the outside of my hull near the mast, connected with 1/0 battery cable to serve as a way of getting a lightning strike from the mast to the water. It also serves as an earth ground for the electrical system (yes, I know, not exactly the way I'm supposed to do it, but it's better than nothing), and have a separate teardrop zinc thru-bolted and connected to the bonding system. In addition, I have a collar zinc on the propshaft. It might seem like a belt and suspenders approach, but bonding wires aren't perfect, zero-resistance circuit elements.
Also, if you have a flexi-coupler between your transmission and propshaft, you might want to put a grounding wire across the coupler if you're depending only on a collar zinc to protect your entire boat.
Allen
Just because all the metals are connected doesn't mean corrosion stops. Unless all the metallurgy (and crystallography, for that matter) of each fitting is absolutely identical (read: not possible), something will be the most anodic part of the bonded system, and will corrode preferentially. This even occurs within a single metal object, which is what causes pitting (one small part of the object serves as the anode in a galvanic cell).
The grounding plate serves several purposes. One is as an earth ground for your electrical system. Another purpose can be as a signal ground for an SSB radio. If it's large enough and connected to your mast by a large enough conductor, it can serve as a lightning protection system, reducing the probability of hull damage in the event of a lightning strike.
I have a copper plate thru-bolted and epoxied to the outside of my hull near the mast, connected with 1/0 battery cable to serve as a way of getting a lightning strike from the mast to the water. It also serves as an earth ground for the electrical system (yes, I know, not exactly the way I'm supposed to do it, but it's better than nothing), and have a separate teardrop zinc thru-bolted and connected to the bonding system. In addition, I have a collar zinc on the propshaft. It might seem like a belt and suspenders approach, but bonding wires aren't perfect, zero-resistance circuit elements.
Also, if you have a flexi-coupler between your transmission and propshaft, you might want to put a grounding wire across the coupler if you're depending only on a collar zinc to protect your entire boat.
Allen
Ah to bond or not to bond, that is the question!
Ahoy Jacques,
Ah to bond or not to bond, that is the question? There are two schools on bonding everything metal together and the other is keeping them all separated. You put 10 sailors together and it will be half and half. As for Cape Dory they bond everything together which I tend to agree with, that is I think you should bond all metal together.
As for the zinc get one on as soon as possible because if there is no sacrificial zinc anode that means that something else is getting eaten away! And it doesn’t matter which way you go with the bonding system, if it is in water, (especially salt water), galvanic corrosion is going to happen! That’s why they call them “sacrificial zinc anodesâ€
Ah to bond or not to bond, that is the question? There are two schools on bonding everything metal together and the other is keeping them all separated. You put 10 sailors together and it will be half and half. As for Cape Dory they bond everything together which I tend to agree with, that is I think you should bond all metal together.
As for the zinc get one on as soon as possible because if there is no sacrificial zinc anode that means that something else is getting eaten away! And it doesn’t matter which way you go with the bonding system, if it is in water, (especially salt water), galvanic corrosion is going to happen! That’s why they call them “sacrificial zinc anodesâ€
Fair Winds,
John
John
Isolated Engine Electrical System
Jaques,
The short answer is probably not much else would happen that isn't happening anyway. Then engine isn't immersed in salt water, so the zincs in the bonding system aren't doing much to protect it. In theory, a raw water cooled engine could have a complete circuit through saltwater with the zinc via the intake, but it's going to be a pretty resistive path and offers little galvanic protection.
I'm not sure how you're going to isolate the engine block from battery negative, if you have an electric starter. The return current path for the high-current-draw starter motor is through the block. There are 40+ year old marine engines out there still chugging along that have current return through the engine block, so in a boat with a properly designed (and implemented!) DC electrical system and bonding system, it's not an issue.
It sounds like what you're really asking is whether the battery can drive corrosion, and how to prevent it. Yes, the battery can certainly drive corrosion. The way to prevent it is to make sure there is a low-resistance path through legitimate wiring so you're not driving current through the water (or a layer of salty moisture on a non-immersed surface) between conductive components of your boat. That means making sure you use adequate gauge wiring and that connections are kept clean of corrosion. I'm not talking about the outside of the connections; it's the mating surfaces that cont and these can only be cleaned by disassembly. Prevention is even better, such as using products like Tef-Gel or other water-repellent greases to keep moisture out of the junction or crimp. No water or water vapor, no corrosion. No corrosion, current flows unimpeded and isn't tempted to flow back by another path that would drive corrosion.
Hopefully all this addresses what you're thinking about.
Allen
The short answer is probably not much else would happen that isn't happening anyway. Then engine isn't immersed in salt water, so the zincs in the bonding system aren't doing much to protect it. In theory, a raw water cooled engine could have a complete circuit through saltwater with the zinc via the intake, but it's going to be a pretty resistive path and offers little galvanic protection.
I'm not sure how you're going to isolate the engine block from battery negative, if you have an electric starter. The return current path for the high-current-draw starter motor is through the block. There are 40+ year old marine engines out there still chugging along that have current return through the engine block, so in a boat with a properly designed (and implemented!) DC electrical system and bonding system, it's not an issue.
It sounds like what you're really asking is whether the battery can drive corrosion, and how to prevent it. Yes, the battery can certainly drive corrosion. The way to prevent it is to make sure there is a low-resistance path through legitimate wiring so you're not driving current through the water (or a layer of salty moisture on a non-immersed surface) between conductive components of your boat. That means making sure you use adequate gauge wiring and that connections are kept clean of corrosion. I'm not talking about the outside of the connections; it's the mating surfaces that cont and these can only be cleaned by disassembly. Prevention is even better, such as using products like Tef-Gel or other water-repellent greases to keep moisture out of the junction or crimp. No water or water vapor, no corrosion. No corrosion, current flows unimpeded and isn't tempted to flow back by another path that would drive corrosion.
Hopefully all this addresses what you're thinking about.
Allen
A long article, but the best I've found on this topic:
http://www.westmarine.com/webapp/wcs/st ... ng-Systems
http://www.westmarine.com/webapp/wcs/st ... ng-Systems
Bit of Controversy
That article makes a controversial recommendation: which is isolating your thru-hulls from the grounding/bonding system. They make a good point about stray current-driven corrosion in marinas. But the danger introduced by isolation is flashover in event of a lightning strike. This applies primarily to thru-hulls near your mast. Even with battery cable to the keel or grounding plate, flashover is still possible. Lightning is a high voltage driven, high-frequency, large current pulse, and doesn't have to completely follow the path we so nicely lay out for it.
So, bond everything and risk driven corrosion that can destroy metal fittings and sink the boat. Or, isolate, and risk the possibility (albeit low probability - less than that of a lightning strike itself) of flashover with potentially lethal effects. My boat has already taken a lightning strike, so I know the probability of a strike is not zero and I'm preferring to bond everything. But it's an equally valid argument that a corroded thru-hull is a safety threat, too. I plan to haul annually, so I can keep an eye out for driven corrosion.
Spark gaps in the bonding lines might be a solution for both problems simultaneously. But now you're adding design and maintenance complexity, with its own set of issues,
Allen
So, bond everything and risk driven corrosion that can destroy metal fittings and sink the boat. Or, isolate, and risk the possibility (albeit low probability - less than that of a lightning strike itself) of flashover with potentially lethal effects. My boat has already taken a lightning strike, so I know the probability of a strike is not zero and I'm preferring to bond everything. But it's an equally valid argument that a corroded thru-hull is a safety threat, too. I plan to haul annually, so I can keep an eye out for driven corrosion.
Spark gaps in the bonding lines might be a solution for both problems simultaneously. But now you're adding design and maintenance complexity, with its own set of issues,
Allen