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Old 30-11-2014, 17:15   #1
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Thru Hulls- Should They Be Connected Electrically?

Should a thru hull be connected to the negative of the battery or to anything? i have rec'd various answers from the local dock folks
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Old 30-11-2014, 17:59   #2
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Re: thru hulls- should they be connected electrically?

in north America they should all be bonded together with green 8 awg. perfibably not daisy chained but a wire from each to a bus. then a common bond point should connect to the dc neg somewhere at one point only. also the ac ground should connect there.


for metal... plastic doesn't mater.
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Old 30-11-2014, 18:06   #3
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Re: thru hulls- should they be connected electrically?

Is this really true? A lot of builders DONOT ground through hulls. Lighting strike has caused them to blow out, a real pain in the sea.
There is a lot we don't know about lighting.


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Old 30-11-2014, 18:06   #4
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Re: thru hulls- should they be connected electrically?

It's a matter of opinion. You should doubt anyone who makes declarative statements on the issue. If. It was that definitive an issue, all manufacturers would bond every seacock but not all do indicative of the subjective nature of bonding.

About the only generality which is true here is that if you don't have a problem, don't bother trying to find a solution.
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Old 30-11-2014, 18:32   #5
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Re: thru hulls- should they be connected electrically?

Quote:
Originally Posted by smac999 View Post
in north America they should all be bonded together with green 8 awg. perfibably not daisy chained but a wire from each to a bus. then a common bond point should connect to the dc neg somewhere at one point only. also the ac ground should connect there.


for metal... plastic doesn't mater.
So do you disconnect the grounds when reaching international waters or non-north american waters? LOL
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Old 30-11-2014, 18:42   #6
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Re: Thru Hulls- Should They Be Connected Electrically?

Maybe an ideal world would have them bonded as smac999 suggests, with a quick circuit breaker shut-off switch to isolate if there is any lightning in the area?
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Old 30-11-2014, 18:48   #7
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Re: Thru Hulls- Should They Be Connected Electrically?

Your boat. your choice.

Marine Grounding Systems | West Marine
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Old 30-11-2014, 18:52   #8
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Re: Thru Hulls- Should They Be Connected Electrically?

Berg's law:
Bond or don't, but if you do bond, bond well.

A well bonded boat is a battery shedding zinc.

A partially bonded boat is a battery shedding bronze...





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Old 01-12-2014, 05:51   #9
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Re: Thru Hulls- Should They Be Connected Electrically?

Greetings and welcome aboard the CF, Madehn.
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Old 01-12-2014, 08:25   #10
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Re: Thru Hulls- Should They Be Connected Electrically?

For electrolytic erosion to occur, current must flow through the underwater metal item. But it has to flow to or from somewhere to complete the electrical circuit. If your through hull is isolated it is like a disconnected battery and no current flows. If you bond it you risk completing the circuit and creating problems. On its own it would not have needed protection, once bonded it needs a sacrificial zinc somewhere to protect it.

But determining if the through hull is isolated is not simple. For example a through hull with a metal strainer on the raw intake for engine cooling is connected to the engine by the salt water inside it, even if the plumbing is non-metallic.

My approach is only bond an underwater item if you see evidence of electrolytic action.

The currents flowing in the bonding system are negligible so in theory a 22 gauge wire would be sufficient however located in the bilge you need mechanical protection so solid copper wire has the lowest surface area and will last longer. With negligible currents the voltage drop is also negligible so the only downside of daisy chain wiring is a bad connection at one point will isolate all down the line.
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Old 01-12-2014, 10:41   #11
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Re: Thru Hulls- Should They Be Connected Electrically?

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...If your through hull is isolated it is like a disconnected battery and no current flows...On its own it would not have needed protection...
This is not true.
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Old 01-12-2014, 10:44   #12
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Re: Thru Hulls- Should They Be Connected Electrically?

Not bonded here. No corrosion either. Seen and sailed plenty of bonded boats too. No corrosion either ...

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Old 01-12-2014, 11:09   #13
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Re: Thru Hulls- Should They Be Connected Electrically?

The jury is out on this I think. I would say I've seen more problems with bonded thru hulls than unbonded...just extreme instances though.... mostly due to marina stray current. I like unbonded personally.
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Old 01-12-2014, 11:14   #14
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Re: Thru Hulls- Should They Be Connected Electrically?

Quote:
Originally Posted by Andina Marie View Post
For electrolytic erosion to occur, current must flow through the underwater metal item. But it has to flow to or from somewhere to complete the electrical circuit. If your through hull is isolated it is like a disconnected battery and no current flows. If you bond it you risk completing the circuit and creating problems. On its own it would not have needed protection, once bonded it needs a sacrificial zinc somewhere to protect it.
I think that I have to disagree. You are forgetting that your ungrounded thru-hull is still connected to salt water which is a very good conductor!

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Old 01-12-2014, 12:19   #15
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Re: Thru Hulls- Should They Be Connected Electrically?

Galvanic corrosion occurs when two dissimilar metals connected together are immersed in an electrolyte (sea water). This in effect creates a battery caused by the different potential of the metals and that potential difference causes a current to flow through the connection between them. There must also be an identical current flowing through the electrolyte (Kirchoff's law). The damage is caused by this current which migrates metal (ion migration) from one electrode to the other.



So if you break the electrical connection between the metals, the current through the electrolyte must be the same - ie now zero. Hence the problem goes away. Basic physics.


Bonding is required where there is a danger of accidental connections and must always be accompanied by an anode of a metal high in the galvanic series - usually zinc which then suffers the ion migration and hence sacrificially is eaten away. If there is no chance of an accidental connection then deliberately providing one by bonding creates the problem you are trying to overcome.
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