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Old 19-03-2012, 13:01   #46
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Re: How Important is this Ground Thingy ?

I for one don't care if the ground is 1000 volts or not......it's the difference of potential between two "grounds" that creates problems for me. Such as in this case, the DC ground had potential X, the AC ground had potential 1.1X. Now we have a current flow situation that eats zinc.
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Old 19-03-2012, 13:05   #47
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Re: How Important is this Ground Thingy ?

Ground schmound. Voltage never ate any metal. It's the current that does it. No current, no electrolysis. Does not matter what the voltages are. Put the meter on mA to see what is happening.
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Old 19-03-2012, 13:16   #48
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Re: How Important is this Ground Thingy ?

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Ground schmound. Voltage never ate any metal. It's the current that does it. No current, no electrolysis. Does not matter what the voltages are. Put the meter on mA to see what is happening.
My point exactally............and that's what I found on the OP's boat, current from the shore ground through the boats' earth connection.
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Old 19-03-2012, 20:19   #49
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Re: How Important is this Ground Thingy ?

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Ground schmound. Voltage never ate any metal. It's the current that does it. No current, no electrolysis. Does not matter what the voltages are. Put the meter on mA to see what is happening.
Which is why NEWMAR has sold a lot of AC Shorepower Galvanic Isolators over the years. See: DC Power Onboard with Newmar offering AC Shore Power Accessories for yachts and commercial vessels.

The Newmar isolator allows shorts to your boat's AC ground to go to shorepower safety ground but does not allow any current from the shorepower safety ground to get into your system.
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Old 19-03-2012, 20:29   #50
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Re: How Important is this Ground Thingy ?

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Which is why NEWMAR has sold a lot of AC Shorepower Galvanic Isolators over the years. See: DC Power Onboard with Newmar offering AC Shore Power Accessories for yachts and commercial vessels.

The Newmar isolator allows shorts to your boat's AC ground to go to shorepower safety ground but does not allow any current from the shorepower safety ground to get into your system.
As does any galvanic isolator.
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Old 20-03-2012, 04:38   #51
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Quote:
Originally Posted by Sailmonkey
I for one don't care if the ground is 1000 volts or not......it's the difference of potential between two "grounds" that creates problems for me. Such as in this case, the DC ground had potential X, the AC ground had potential 1.1X. Now we have a current flow situation that eats zinc.
No it's not. A digital multimeter has an input impedance in excess of 10mohms. because you get a voltage reading means nothing in practice the circuits may not even have a common ground. Remember everything is connected to everything as everything has a finite resistance.. Establishing whether grounds are floating and hence not connected or merely due to current differences is a little more involved.

Dave
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Old 20-03-2012, 07:37   #52
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Re: How Important is this Ground Thingy ?

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No it's not. A digital multimeter has an input impedance in excess of 10mohms. because you get a voltage reading means nothing in practice the circuits may not even have a common ground. Remember everything is connected to everything as everything has a finite resistance.. Establishing whether grounds are floating and hence not connected or merely due to current differences is a little more involved.

Dave
When they're hooked together......they have a common ground. When one separates them and places the meter between them and measures 70ma one has current flow. Unless I'm really dense, a difference of potential is required for current flow.
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Old 20-03-2012, 09:27   #53
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Re: How Important is this Ground Thingy ?

I've been following this thread for a while, there is some pretty funny stuff here.... isolation transformers that stop galvancic corrosion ....you're kidding right ? How come nobody called him on this ? or how about the repeated use of the word "electrolysis", you guys let this one go too.

Hilarious
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Old 20-03-2012, 09:51   #54
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Re: How Important is this Ground Thingy ?

True, nothing here is really about galvanic corrosion. When you get right down to it the sum of the OP's real problem is a ground on the dock that is hot. A "galvanic" isolator will help in this instance.
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Old 20-03-2012, 11:01   #55
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Re: How Important is this Ground Thingy ?

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I've been following this thread for a while, there is some pretty funny stuff here ...
Then please educate us. We'd all appreciate accurate and useful information, much more than ridicule.
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Old 20-03-2012, 12:12   #56
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Re: How Important is this Ground Thingy ?

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Originally Posted by Sailmonkey View Post
True, nothing here is really about galvanic corrosion. When you get right down to it the sum of the OP's real problem is a ground on the dock that is hot. A "galvanic" isolator will help in this instance.
I agree, we can nit pick on semantics, or solve the OP's problem.

Galvanic potential of two metals, IE zinc vs prop is irrelevant if an outside voltage, (current) is applied.

Chances are any outside current IE 12volts from battery or AC leakage is going to be orders of magnatude greater than the few tenths of a volt generated by a zinc plate in seawater.
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Old 20-03-2012, 18:44   #57
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Then please educate us. We'd all appreciate accurate and useful information, much more than ridicule.
Zing!

I think boatpoker is going by the old rule - its better to keep one's mouth shut and appear a fool than to open it and confirm it...

Or maybe it's - It is aleays easier to burn a barn than build one...
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Old 18-06-2012, 17:04   #58
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Re: How Important is this Ground Thingy ?

Maybe this deserves a new thread, but given all this hassle - how much simpler or safer would it be to simply install a large metal plate on the hull, and avoid all this risk of corroding your prop, throughhulls, driveshafts,etc?

Sorry for the obviously naive question, but isn't it true that the engine doesn't need any electrical connections at all, except at start? It seems unnecessarily risky given the risk for corrosion of the vital metal parts that separate the dry part of the boat from the wet part.
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Old 18-06-2012, 19:23   #59
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Re: How Important is this Ground Thingy ?

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Maybe this deserves a new thread, but given all this hassle - how much simpler or safer would it be to simply install a large metal plate on the hull, and avoid all this risk of corroding your prop, throughhulls, driveshafts,etc?

Sorry for the obviously naive question, but isn't it true that the engine doesn't need any electrical connections at all, except at start? It seems unnecessarily risky given the risk for corrosion of the vital metal parts that separate the dry part of the boat from the wet part.
I believe the propeller would still be at risk as it is the cathodic metal underwater.
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Old 19-06-2012, 01:56   #60
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Re: How Important is this Ground Thingy ?

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Originally Posted by ArtM View Post
Maybe this deserves a new thread, but given all this hassle - how much simpler or safer would it be to simply install a large metal plate on the hull, and avoid all this risk of corroding your prop, throughhulls, driveshafts,etc?

Sorry for the obviously naive question, but isn't it true that the engine doesn't need any electrical connections at all, except at start? It seems unnecessarily risky given the risk for corrosion of the vital metal parts that separate the dry part of the boat from the wet part.
Although a diesel engine does not need electricity to run - it does need electricity which includes a battery ground for starting; oil pressure; coolant temperature; shut-down solenoid (sometimes); and alternator.

Both the starter motor and alternator are quite high power so need a substantial cable connection to the batteries.

However, for both DC and those boats with AC power systems it is a good idea to have a dedicated "Dynaplate" to establish a good ground to "earth/water." But most production boats only have the "earth/water" ground established by the metallic connection between the engine block to the transmission to the prop shaft to the propeller. The use of proper zincs attached to the propeller shaft and/or the propeller normally takes care of any electrolysis. In more sensitive equipment like heat exchangers, etc. separate "pencil" zincs assist in keeping things from dissolving too quickly.
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