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On 1/02/2021 at 9:23 AM, Tamure said:

Pretty much

Not sure where that comes from. ASNZS 3004.2 requires equipotential bonding, as does the US ABYC E11. The ISO standard is equivocal but then they are the same crowd who ok'd high zinc content skin fittings.

From a reality perspective any boat with an engine has several different types of metals all in contact with each other via an electrolyte called seawater so the least noble is going to corrode. If a boat is wired for AC then you must have a grounding system. If not, I would have all the engine components, strut and shaft interconnected and protected by an anode or 2. Saildrives have their own anodes which need to be religiously maintained. Would not worry about bronze skin fittings and valves as these are not in the circuit.

Older wooden boats have had some issues with "over zinccing", check out www.waitematawoodys.com for Chris Mc Mullen's advice.

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There used to be two trains of thought. Bond nothing, or bond everything. There are no in betweens. Today, we now have an A/NZ wiring standard that requires everything to be bonded and tied to a ground plate and tied to shore power Earth. The ground plate seems to be allowed to be ignored.

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"Would not worry about bronze skin fittings and valves as these are not in the circuit."

🙂 I would. ....and they are. 

Particularly on a timber vessel. They are highly prone to becoming brittle , and to be blunt...snapping clean off.

They also inhance local timber "electrolysis"  ..but better you do some more research.. ( off line..).

 

 

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Total electrical isolation is very difficult. It becomes harder as the vessel becomes older ( regardless of what material it is made of) . Complete electrical isolation of the motor to hull is also difficult even if you have polymer engine mounts and prop couplings. Bonding of metal through hull fittings of all types and uses on plastic, timber and Ferro boats will save a lot of grief .....

( Unless you are not going to keep the boat and pass it on to someone else who will then ask me and l will tell them to replace all the pink ...bronze hull fittings..which they will then break off when trying to remove....)

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6 hours ago, idlerboat said:

"Would not worry about bronze skin fittings and valves as these are not in the circuit."

🙂 I would. ....and they are. 

Particularly on a timber vessel. They are highly prone to becoming brittle , and to be blunt...snapping clean off.

They also inhance local timber "electrolysis"  ..but better you do some more research.. ( off line..).

 

 

maybe you should do the research, the problem of brittle skin fittings has been due to using high zinc content fittings (to save money), this will help you

https://www.boatsurveyor.net/cathodic-protection-in-yachts/the-dangers-of-cw617n-european-brass-valves-skin-fittings-and-hose-tails/

as for electrolysis in wood, this is due to "over zincing", refer to Chris Mc Mullen article I previously referenced 

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MH I totally agree with that article. It confirms what l have said. 

It's not new. Changing the skin fittings to corrosion resistant ones is the best option..

But l am talking about the great many vessels that have bronze through hulls. Ask yourself what causes de zincing ? ...and apart from changing the fittings what reduces this from happening. 

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So ? Are you telling me that cheap fittings have not been put on boats ? 

In my world, the assumption is that all bronze through hulls without a known history are suspect. It's not worth the risk. Also given that, why replace them with anything metal ? 

 

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🙂.. that would be nice...in older timber "wet bilge " boats it's almost impossible to keep lower fittings electrically isolated. 

It is possible to design a new boat with a limited amount of through hulls. Not so easy to retrofit an older boat. My 38 foot yacht has no seacocks . The diesel engine is unmarinised and does not use plumbed raw water cooling ( direct or heat exchanger) . 

I would suggest that at the least , tapered emergency bungs of the right size should be kept with any older seacocks, as they tend to break off where the threads are between the through hull and seacocks.

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