Quote:
Originally Posted by Uncle Bob
Why is it that mainly north american boat owners are so obsessed with bonding every piece of metal on their boats. Is there something special about that part of the world that requires it whereas most of the rest of us don't have this problem, or is it some sort of custom or belief that one must follow that which is passed down, or what? I have zero bonding on my old fibreglass tub, with no issues, no one around me has either and the only bonded boats that I have heard of around here are steelies or American imports. Is this a routine practice in Europe as well?
Please, what would the cause of the differing experience/custom be?
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Indeed, many surveyors and thus boat owners and servicers are obsessed with the green wires between every piece of metal in sight. And there is a misconception that sea strainers and pipework can be protected through the bonding system (protection is only effective for a distance of aprox 3X the inside diameter, from the outside of the hull).
In the US and
Canada recreational boat manufacturers are required by federal law to bond all underwater metal
parts and connect to the
Equipment Safety Grounding conductor if the vessel has an
electrical service of higher than 50 volts. Debate of merits is irrelevant, compliance is required, so all production boats made in or for the North American market that have AC
electrical service are made so. In the UK and
Australia, NZ, and I guess much of
Europe Ground Fault Protection is widely universal. I don't know about the
regulations abroad, but the necessity for bonding metal
parts is much less so because of this. Requirements for more extensive GF protection are just starting to be implemented here, so boats will continue to be bonded for a long time, probably forever.
Besides satisfying the
government, the bonding system reduces the risk of electrical shock. Besides that, it allows the
delivery of protective
current from a common anode to the underwater parts. Once upon a time,
hull fittings were by and large all made from very high quality alloys, bronze with 3-4% silicon, less than 1-2% zinc and lead combined, and the attention to process that produced a consistent composition throughout the metal. These parts did indeed last 30 or more years without cathodic protection, but with it they would last much longer. The good stuff just isn't made much anymore, few are willing to pay for it and not many manufacturers remain dedicated to that level of quality. As noted up the thread, some pretty low standards have been set. Accountants
rule in business. One buys a boat, or goes to a shipyard or
chandlery with a good name and assumes the material will be fit for the purpose, at least, but even that much may be a leap of faith.
Every piece of metal is an array of dissimilar metals. Each grain is different. In some materials the differences are infintesimally small but that's not so with the stuff under our boats today. Though arguments may be made to except certain
marine aluminium alloys and high-silicon bronze, all of our underwater metal parts need protection if they are to last. You got to protect the
cheap stuff so it doesn't
rot out from under you, and the good stuff cause you never want to have to pay to replace it.
Simply connecting fittings together without an anode in the circuit makes anodes of the lower grade materials. Anodes corrode, cathodes are protected. Where each part had its own small reaction potential much greater differences are now involved. A proper bonding system and zinc makes one anode, everything else cathodes. The differences between the range of
marine bronze and stainless alloys is nullified, they all react with the one anode as cathodes.
Debates over whether any underwater part is protected or corroding due to reaction with other parts can be answered with a multimeter and a home made probe using a zinc pencil. The relative
corrosion resistance of any bronze/brass part can also be determined. I made a detailed post on this years ago and will see if I can locate it.