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Old 23-09-2015, 07:54   #1
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DC Negative Grounding to grounding plate - Isolated shaft

Hi there,

In our boat, shaft is isolated from the engine block. We have a very simple electrical system, GPS, VHF, LED lights and basics (bilge pumps etc). There is no AC or we do not use shore power except occasionally charging the batteries in the marinas with extension cable.

All battery negatives goes to the negative bus bar and to the engine. I have a gournding plate a sam copper plate connected to a dynaplate on the hull. (Currently there is nothing connected to it)

As shaft is isolated,
- should I connect the negative bus bar to the ground plate?
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Old 23-09-2015, 09:03   #2
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Re: DC Negative Grounding to grounding plate - Isolated shaft

* correction : "square meter copper plate"
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Old 23-09-2015, 09:25   #3
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Re: DC Negative Grounding to grounding plate - Isolated shaft

Are your thru hulls bonded? If so then I think you need an anode in the water.
Which did not answer your question, but did your boat ever have an HF radio?
I think that may be the reason you have that ground plate, but thru hulls may be even more important to protect than the shaft and prop
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Old 23-09-2015, 09:30   #4
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Re: DC Negative Grounding to grounding plate - Isolated shaft

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Originally Posted by Thistle1969 View Post
...I have a gournding plate a sam copper plate connected to a dynaplate on the hull. (Currently there is nothing connected to it)

As shaft is isolated,
- should I connect the negative bus bar to the ground plate?
Leave it disconnected.
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Old 23-09-2015, 09:57   #5
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Re: DC Negative Grounding to grounding plate - Isolated shaft

Several considerations:

It the thru hulls are bonded together then she needs a zinc in the system, typically this is on the prop shaft and for this to work shaft must be electrically connected to the thru hulls.

If you care about a propeller then typically need a zinc electrically connected to the prop (shaft zinc again).

If you are concerned about lightning then the mast or mast ground wire should be connected to a ground plate (near the mast base).

Dynaplate is typically for HF radio and don't make great lightning grounds.

If the thru hulls are not bonded then leaving them that way typically works providing that they are high quality bronze and not brass.

I have one bonded ship (IP) and one unbonded (Hunter), both on shore power and neither was taking on water when I last checked.
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Old 23-09-2015, 10:18   #6
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Re: DC Negative Grounding to grounding plate - Isolated shaft

There are only two try-hulls under water, both are bronze and seacocks are Marelon. Also they are positioned on opposite sides of the hull. Almost an inch thick hull and corrosion is not concern there.

Shaft has zinc for the propeller.

I am not clear about the answers I've received.

All batteries are connected to the Negative Bus Bar and to the engine. But engine has no electrical connection to the shaft.

- Should I connect negative bus bar to the ground plate to establish connection to the sea?
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Old 23-09-2015, 10:23   #7
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Re: DC Negative Grounding to grounding plate - Isolated shaft

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Originally Posted by Thistle1969 View Post
...

Shaft has zinc for the propeller.

I am not clear about the answers I've received.

All batteries are connected to the Negative Bus Bar and to the engine. But engine has no electrical connection to the shaft.

- Should I connect negative bus bar to the ground plate to establish connection to the sea?
Quote:
Originally Posted by Terra Nova View Post
Leave it disconnected.
How can I make this more clear?

Don't...do...anything!
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Old 23-09-2015, 10:48   #8
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Re: DC Negative Grounding to grounding plate - Isolated shaft

Marine Grounding Systems | West Marine
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Old 23-09-2015, 11:19   #9
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Re: DC Negative Grounding to grounding plate - Isolated shaft

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Originally Posted by Thistle1969 View Post
Hi there,

In our boat, shaft is isolated from the engine block. We have a very simple electrical system, GPS, VHF, LED lights and basics (bilge pumps etc). There is no AC or we do not use shore power except occasionally charging the batteries in the marinas with extension cable.

All battery negatives goes to the negative bus bar and to the engine. I have a gournding plate a sam copper plate connected to a dynaplate on the hull. (Currently there is nothing connected to it)

As shaft is isolated,
- should I connect the negative bus bar to the ground plate?
You should be OK from corrosion standpoint.

Donīt even think about bonding throughulls. That will expose you to stray current corrosion in and around marinas and around other boats.

The question is about lightning. My preference would be to ground the rig to a single metal element in seawater but making sure the rig is isolated from battery negative (check VHF antenna and mast-mounted nav lights). All that said, if the keel is a bolt on keel then why not use the keel?

I confess I did not quite understand the wording about having a Dynaplate and some other plate.
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Old 23-09-2015, 22:24   #10
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Re: DC Negative Grounding to grounding plate - Isolated shaft

Ah Terra Nova, this is clear. Thanks for the input. So, all negatives are connected to the engine, that's all. My confusion was coming from the idea, if I had to establish connection with seawater or not. Engine remains not bounded to shaft electrically.
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Old 24-09-2015, 09:33   #11
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Re: DC Negative Grounding to grounding plate - Isolated shaft

My Cape Dory 31 has all the Spartan bronze sea valves bonded to the lightning ground plate in the keel from the factory. From what I'm reading they shouldn't be! Now I'm confused. Do I disconnect them after 30 years connected or not?
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Old 24-09-2015, 15:40   #12
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Re: DC Negative Grounding to grounding plate - Isolated shaft

The usual setup is bond everything or bond nothing. I.e. don't mix and match.
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Old 24-09-2015, 15:50   #13
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Re: DC Negative Grounding to grounding plate - Isolated shaft

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Originally Posted by Xthewater View Post
My Cape Dory 31 has all the Spartan bronze sea valves bonded to the lightning ground plate in the keel from the factory. From what I'm reading they shouldn't be! Now I'm confused. Do I disconnect them after 30 years connected or not?
I'm in the camp that if it has little or minimal corrosion, leave it alone. I lean slightly toward non bonded seacocks myself. But if you have a lightning ground plate, personally I would not connect it to the bonded system.
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Old 24-09-2015, 17:09   #14
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DC Negative Grounding to grounding plate - Isolated shaft

Curious, do you have some kind of elastomeric damper or something between the transmission and the shaft flange?

Let me clarify why I'm asking and why I asked if your thru hulls were bonded.
I've seen boats with drive savers, which of course electrically isolated the shaft because they didn't use a jumper to keep electrical connectivity, This boat's only Zincs were on the shaft and prop, but it's thru hulls were bonded from the factory, It's thru hull were being de-zincified and had to be replaced as they were no longer connected electrically to a sacrificial anode.
Owner thought they were doing a good thing with the drive saver, but it isolated the zincs from the rest of the underwater metals, all of which were bonded together, now if yours is like there's was a simple jumper wire across the drive saver will restore the bonding of all the underwater metals to the sacrificial anodes.
I'm in the bond everything together and watch your anodes camp, anodes protect everything and just as importantly if you notice them rapidly wasting away, investigate why


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Old 24-09-2015, 17:39   #15
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Re: DC Negative Grounding to grounding plate - Isolated shaft

This may not apply but after years of replacing zincs only because the diver was there on a bonded boat I became lazy/cheap and stopped having them replaced ! after a about a year a diver stopped by and checked and there was no zinc and the ends of the prop blades were missing at the advice of a some one else in the marina I cut all the bonding and the problem was solved THINGS CHANGE This was in a marina with 200 hundred boats and new neighbors all the time ! just telling you my story not advising!
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