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Old 28-02-2012, 13:13   #16
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Re: How important is this ground thingy?

Capn Bill is right. It sounds more like stray current corrosion, than galvanic corrosion. Anodes (what you called zincs) are there to prevent galvanic corrosion, but any stray current will eat them for lunch. So it would be good to sort out your electrical system first.
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Old 28-02-2012, 13:28   #17
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Re: How important is this ground thingy?

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Yes we seriously believe it.

Every electrical system standard for boats says to ground the battery and the system to the engine block.
Yes but the "ground" as far as the electrical system goes is really the battery. It is not intended that current is flowing into the engine and out via the shaft into the water. If you connect all your ground to the engine you will pay the price as everything starts corroding.
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Old 28-02-2012, 13:34   #18
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Re: How important is this ground thingy?

Only reason I can think of that the engine needs a ground is for it's own stuff: ie: starter etc... certainly not for other non engine items.... ?
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Old 28-02-2012, 13:45   #19
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Re: How important is this ground thingy?

Not so. The point is zero voltage potential. If the voltage potential is zero, nothing is flowing. And your bonding system, lightning protection if you have it, and grounds from things like tanks, should all be connected to the main ground at the engine block. If you have an AC electrical system the green grounding wire should also be connected to the main ground. The whole point is to prevent current from flowing. If that is happening then you will have corrosion. If it's DC, then stray current will cause corrosion. If it's because of dissimilar metals then it is galvanic corrosion. But if all of these are connected to the ground nothing will flow because they are all at the same potential.
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Old 28-02-2012, 16:14   #20
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Quote:
Originally Posted by Ike
Not so. The point is zero voltage potential. If the voltage potential is zero, nothing is flowing. And your bonding system, lightning protection if you have it, and grounds from things like tanks, should all be connected to the main ground at the engine block. If you have an AC electrical system the green grounding wire should also be connected to the main ground. The whole point is to prevent current from flowing. If that is happening then you will have corrosion. If it's DC, then stray current will cause corrosion. If it's because of dissimilar metals then it is galvanic corrosion. But if all of these are connected to the ground nothing will flow because they are all at the same potential.
This may be practice in the US. So obviously our electrons this side of the pond are different.

First let's not mix up code and electrics.

DC negative does not need to be "grounded". Ie held at earth potential. It's an isolated system. It's connected ( In the US ) purely to include the DC system in the Ac protective earth wire.

However due to varying resistance in ground systems there is currents flowing and many experts have stated that the DC link is a primarily facilitator.

I'm not aware that there's any need to provide a seawater path for AC protective earth. When not connected to shore power, it would serve no purpose even with on board AC generation. And with shorepower the normal "code" is to provide one central earth connection on land

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Old 28-02-2012, 16:37   #21
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Yikes. My understanding is lightening ground is separate from everything. Gord has a great link on a very good set up posted in prior threads. DC ground can be isolated from the engine and AC gets green wire to sea water when not on shore power. You can bond your thru hulls but this is separate from all of the above grounds. ssb ground is separated as well.
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Old 28-02-2012, 17:11   #22
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Re: How Important is this Ground Thingy ?

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This may be practice in the US. So obviously our electrons this side of the pond are different.
I suppose they are anti-electrons. LOL

If your country uses the RCD, then they use the ISO standard cited above. If you're not following the RCD well then........ Since I don't know what the laws are on your side of the pond, I can't say.

In the US the USCG regulations are mandatory for Manufacturers. Not for boat owners or even repairers, and ABYC standards are voluntary. But there is a catch 22 called liability. Insurance companies, surveyors and civil courts all use ABYC as the standard for how it should be done. So simply from that point most everybody uses ABYC. (And so does the Canadian Coast Guard) But it is also the safe way to do it. As with most things there are some who prefer to do it their own way and claim it provides an equivalent level of safety. And there is a lot of argument over how electrical systems should be installed (especially on metal boats) but ABYC is a consensus standard that is put together by many people who spend many hours and days agonizing over how it should be done. I have sat on those committees and I can tell you first hand that some of the arguments get pretty heated. But, eventually they reach a consensus which is then put out to all of the members of ABYC (thousands) for comments. So the process starts again evaluating the comments and deciding whether or not to incorporate them. Everyone gets to have their say including any non member who cares to comment. Eventually a consensus is reached, voted on and published. Same thing happens at ISO.

So this is the consensus. If you don't agree well that's your right. Having an over 40 year background in electrical systems on boats and ships, I think it's right on. But then that's my opinion.
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Old 28-02-2012, 17:27   #23
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Re: How important is this ground thingy?

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Not so. The point is zero voltage potential. If the voltage potential is zero, nothing is flowing. And your bonding system, lightning protection if you have it, and grounds from things like tanks, should all be connected to the main ground at the engine block. If you have an AC electrical system the green grounding wire should also be connected to the main ground. The whole point is to prevent current from flowing. If that is happening then you will have corrosion. If it's DC, then stray current will cause corrosion. If it's because of dissimilar metals then it is galvanic corrosion. But if all of these are connected to the ground nothing will flow because they are all at the same potential.
Yeah.... I meant as far as those things "operating". Other than that there's the "bond everything " crowd and "dont bond anything" crowd. Based on my observations, neither has been proven right or wrong....
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Old 28-02-2012, 17:46   #24
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Re: How Important is this Ground Thingy ?

And the plastic through hulls, and metal through hulls only crowd, and the crowd that likes to use welding cable, the wood versus FRP crowd, mono vs multi crowd, and so on. That's what keeps it interesting.
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Old 28-02-2012, 18:18   #25
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Quote:
Originally Posted by Ike

I suppose they are anti-electrons. LOL

If your country uses the RCD, then they use the ISO standard cited above. If you're not following the RCD well then........ Since I don't know what the laws are on your side of the pond, I can't say.

In the US the USCG regulations are mandatory for Manufacturers. Not for boat owners or even repairers, and ABYC standards are voluntary. But there is a catch 22 called liability. Insurance companies, surveyors and civil courts all use ABYC as the standard for how it should be done. So simply from that point most everybody uses ABYC. (And so does the Canadian Coast Guard) But it is also the safe way to do it. As with most things there are some who prefer to do it their own way and claim it provides an equivalent level of safety. And there is a lot of argument over how electrical systems should be installed (especially on metal boats) but ABYC is a consensus standard that is put together by many people who spend many hours and days agonizing over how it should be done. I have sat on those committees and I can tell you first hand that some of the arguments get pretty heated. But, eventually they reach a consensus which is then put out to all of the members of ABYC (thousands) for comments. So the process starts again evaluating the comments and deciding whether or not to incorporate them. Everyone gets to have their say including any non member who cares to comment. Eventually a consensus is reached, voted on and published. Same thing happens at ISO.

So this is the consensus. If you don't agree well that's your right. Having an over 40 year background in electrical systems on boats and ships, I think it's right on. But then that's my opinion.
The liability issue is a non starter there are thousands of foreign boats in the US not built to voluntary ABYC standards. they seem to get insurance no problem.

Secondly there isnt a concensus, there are many NAs and others that argue the toss. There's a concensus within ABYC, buts that's different.

The European RCD with no dc interconnect and RCBs is only in force since the RCD was introduced., prior to that there were no RCBs and still no interconnect. ( RCD = recreational craft directive, RCB = Residual Current breaker. )

But my point was arguing the issue of connecting Ac earth to seawater. My understanding is ABYC doesn't need that.

Furthermore the zero potential point is nothing of the sort. Look up load dumping, transients, leakage resistance. Only on the level of " boat electrics for dummies" is that true at a proper electrical analysis the " ground " is all over the place and is a significant contribution to underwater galvanic and impressed corrosion. A fact that seems to trouble European boaters far less. ( or else you complain more !)
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Old 28-02-2012, 21:16   #26
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Re: How Important is this Ground Thingy ?

A few definitions may be in order to bring those on each side of the "pond" together.

The battery DC system has a "positive" and "negative" and as such does not have any "ground." If you stayed awake in high school science you will remember that the electrons actually flow backwards - battery negative to battery positive. But that makes no difference what-so-ever in a DC system. You only need a continuous circuit from one battery terminal out to the load and back to the other battery terminal.

If you are sufficiently old, you will remember that the early automobiles has battery positive connected to the automobile chassis. But now everybody connects the battery negative terminal to chassis or in the world of boats - the engine.

The battery negative is connected to the engine to provide the path from the battery to the starter (which is bolted to the engine); alternator; and other engine electrical systems and then back to the battery negative.

"Grounding" (like Ike explained - sort of) is the connection of the boat's negative battery terminal to the "earth" or "ocean/water." However, the boat's engine is not, in and of itself, "in the water."

The Propeller Shaft and Propeller are "in the water" and provide the "ground" or "earthing." (Ignore dedicated bronze grounding plates for now).

So - If the engine is "isolated" from the propeller shaft and propeller by a plastic vibration damper, then the boat is not "grounded" or "earthed." A jumper wire needs to cross the damper to establish a "ground."

Here's one for you, is a boat in jackstands in a boatyard "grounded?"

As to the OP, the suggestions to find out what is on the other side of the "mystery plate" are good. But if he is getting electrolysis eating away his zincs, then the place to look is first in the AC electrical system - if he has one connected. Then to see if there is any leakage across any loads in the boat of current when they are shut off. Also corrosion of wires and terminals throughout the boat can result in stray currents and disappearing zincs.

Also there may be two dissimilar metals on the outside of the boat (in the water) and they are connected together by internal wiring. That is a classical problem that results in rapidly disappearing zincs.

Sorting out and cleaning up a boat's electrical system(s) is a major endeavor by any "new" old-boat owner. As stated by others, there are almost an infinite number of "variations" in wiring practices that previous owners used and sorting them out takes time and work.
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Old 29-02-2012, 03:50   #27
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So - If the engine is "isolated" from the propeller shaft and propeller by a plastic vibration damper, then the boat is not "grounded" or "earthed." A jumper wire needs to cross the damper to establish a "ground."
Why in the same of god would you want to connect DC negative to seawater ground. It serves no purpose whatsoever and in fact promotes impressed corrosion. It is never done in European boats. The engine is connected for the reasons you give, but that's it.

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Old 29-02-2012, 09:42   #28
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Re: How Important is this Ground Thingy ?

To further muddy the waters, my Volvo 2020 with shaft drive has an insulating plate between the engine and transmission with a sticker cautioning against grounding.
The transmission has a raw water cooling line running through the aft end, does this have anything to do with it?

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Old 29-02-2012, 16:22   #29
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Re: How Important is this Ground Thingy ?

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Why in the same of god would you want to connect DC negative to seawater ground. It serves no purpose whatsoever and in fact promotes impressed corrosion. It is never done in European boats. The engine is connected for the reasons you give, but that's it.

Dave
See Post #5 - AND - you really do not have any choice in the matter!

Your battery negatives are connected to the engine to enable its DC equipment to function. AND, the engine is metallically connected to the Transmission AND the transmission is metallically connected to the Propeller Shaft and the propeller. And those items, shaft and propeller, are in the water! (unless you are on the hard). So your boat and its engine ARE "grounded" to the seawater around you - as it comes straight from the factory.

Except - very, very, very few boats have plastic vibration damper (a.k.a. "DriveSaver") which would electrically isolate the propeller shaft and propeller from the engine. Boats do not come from the manufacturer with "DriveSavers" installed.

I have a DriveSaver installed and the electrolysis was worse when the prop and shaft were isolated in real life experience on my boat. So I installed the "jumper" wire to reconnect the prop/shaft to the engine electrically.
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Old 29-02-2012, 16:41   #30
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Re: How Important is this Ground Thingy ?

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To further muddy the waters, my Volvo 2020 with shaft drive has an insulating plate between the engine and transmission with a sticker cautioning against grounding.
The transmission has a raw water cooling line running through the aft end, does this have anything to do with it?

Please explain that better. If the transmission is raw water cooled, then the transmission is "grounded" to the sea water - or at least to its heat exchanger.

For a transmission to be "electrically isolated" from the engine, the spline shaft from the transmission has to be received by something non-metallic that is attached to the engine flywheel assembly. And the bolts between the transmission and the engine have to be isolated by something that does not conduct electricity.

There should be something in the Volvo engine manual that describes what, how and why they did that. It seems like an awful lot of additional expense in "isolating" parts over just bolting the whole thing together like most all other marine engines. Easy way to find out, is to use a VOM meter and put one probe on the engine and the other probe on the prop shaft/lower unit and see if there is an electrical continuity.
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