Zinc Grounding

[Theis]

Interesting.

Stainless steel I understand will corrode - big time. That is why stays have to be replaced. It is iron, and, as my research has shown, corrodes just like iron, except it doesn't turn brown but turns greyish. It also depends on the stainless steel mix (304 v. 316)

There is no question that there is significant galvonic action, even in fresh water. I have had the bronze filter plate over the head water intake totally eaten away. That was when the water intake was the ground point for the Ariel electrical system (standard Pierson issue). There is no question that there is substantial corrosion occuring around my outboard (which has a generator and is connected to my electrical system), even with a zinc plate, which appears to be getting smaller at a significant rate. The prop and the lower unit are eaten away unless they are liberally covered with non-electolytic paint (Tri-X for example). These parts are all connected to the electrical system, and to the mast head, which is a major source of potential differential and, hence, electrical current.

Those are emperical pieces of evidence.

I don't appear to have experienced any corrosion on a) the copper grounding plate a couple feet under water, b) the rudder shoe or shaft or c) the head outlet valve.

I berth the boat at a slip but do not have slip power (except when charging the battery a couple times a season)

Crazy, eh?

[noeta-112]

Here is a link of some interest re this discussion



http://www.practical-sailor.com/news...ecorrosion.pdf

[noeta-112]

With all this new (to me) found knowledge re corrosion, and hot marinas etc., will there be any time left to sail after all that maintenance & inspection ???

www.practical-sailor.com/newspics/charts/9010corrosion.pdf

[noeta-112]

www.practical-sailor.com/newspics/charts/9010corrosion.pdf

[noeta-112]

Sorry, but can't get this to work.

Just type in the URL if you want a look..

[Scott Galloway]

I was indeed sailing, or actually raising the main sail when my Honda 7.5 hp four-stroke motor took its last gasp one afternoon a week or so ago. I posted a note of inquiry on the OB thread requesting advice on pros and cons of the Nissan 6 hp four-stroke motor. While I wait for responses on that thread, I now have some free time for maintenance.

I am thankful that my electric system is not grounded to the fresh water intake on my head. However, I have been staring into my bilge at an iron eyebolt to which a previous owner connected the green ground wire from the electrical system. The iron bolt runs into the lead ballast. I assume that the bolt's original purpose was related to lifting the lead ballast into the hull. I am not sure that grounding the electrical system to the ballast is a terribly great idea, or that it makes any sense at all, because the ballast, is not in contact with seawater (hopefully). Now maybe what I have here is a different sort of solid-state lead/iron battery in my bilge, and I just need to know how to harness the power.

In any case, grounding the electric system to the ballast makes no sense to me. Any thoughts from the electrical experts?

[commanderpete]

Is this the link? Just needed an http in front

http://www.practical-sailor.com/news...ecorrosion.pdf


I have the same question about grounding wires. My boat has white # 10 wires attached to the middle chainplates. There is also a # 10 wire that ends near the intake seacock, but is not attached to anything.

These wires are all original.

What purpose do they serve?

[Scott Galloway]

Pete,

Thanks for the corrected link Pete. I printed that .pdf file to read on the boat later today. The #10 wires from your chainplates probably served to ground your rigging to the original ground location. From the currently unconnected wire near your intake seacock, and from the comments made by Theis, that location appears to originally have been the fresh water thru-hull on the head intake.

As I recall, on my father's 35 foot cutter, the rig was grounded that way, but to zincs on the outside of the hull, and not to a thru hull. Grounding the rig should serve to slow crossion of the wire rigging, tangs, mast, boom etc.

My neighbor at the harbor recently had to replace the entire boom on her Coronado 25. When she removed the steel fittings on her aluminium boom, large corrosion holes were in evidence.The boom had to be replaced.

[Toby]

Tell me more about grounding plates – we don’t see lightning in the pacific NW. In fact, the risk of a lightning strike is so low that the Commander is the first boat I've ever seen with every hunk of above-water metal wired back to the battery's ground. And that's where it ends too: someone yanked the inboard (and all the extraneous hardware) long ago, so the grounding wires all end at the battery. Also, we replaced the bronze seacocks and thru-hulls with plastic, so we’re not grounded through that path. My question: If I don’t want to screw with copper plates on the bottom of the hull, what danger is posed leaving the battery connected to the ground terminal? It seems if I’m sleeping on a boat that's struck by lightning, an exploding battery might be the least of my problems. Any thoughts?

[mrgnstrn]

ok, i read though Nigel Calder's (Boatowner's mech. and electrical manual) discussion on grounding, corrosion, and lightening protection.

here is my condensed conversation:

why you want grounding:
1. if you have AC (shore power), you want a direct path to ground for your boat, in addition to the ground protection afforded by the shorepower connection. The reason for the redundant system is to make sure that there is no reason you should be electrocuted when playing with/using AC, so provide for your own ground, for your own safety.

2. for lightening, you want to bring the potential of all metal down to the potential of the water (in theory, making you no more of a target than the water around you). this should include, the rigging, the AC ground, and the negative of the battery.

3. your zincs should be grounded such that when connected to shorepower, they are the least noble/most anodic thing electrically connected to the common ground. if the zincs are not connected to the ground, but the bronze thru-hull is connected, the most anodic thing on the circuit electrically, are the bronze thru-hulls. bad.

why grounding is a pain:
1. if you are connected to shorepower, the ground from you and the ground from that aweful Hunter 38 next to you on the slip will create a galvanic cell (battery). the boat with the least noble/ most anodic stuff in the water will win out, and that might not be you. unless you have attached zincs to the ground and the water.

2. the obvious, its a pain to install a grounding plate. besides the new paranoia that there are more leaks, you have to make sure that the ground shoe is correctly connected to the gound, and that corrosion hasn't negated your electrical connections to it. and oh by the way, make sure that it isn't eaten away by ensuring zincs are electrically connected.


and by the way, most battery chargers connect the negative of the battery to the ground of the AC wires. so if they negative of the battery is connected to the thru-hull, you might have just also connected to the ground of that crappy Hunter and it's zincs, etc etc etc. so you might as well ground it correctly to begin with, lest you fool yourself.

so grounding to the thru-hull alone is just inviting corrosion.

and grounding to the lead ballast does nothing. (this was probably done because that PO thought that it was electrically connected to the water, or plain exposed to the water.


so, for you guys with OB's how did you electrically connect your zincs to the ground of the boat?
for those with nifty ground shoes, where did you put your zincs? and how much of a pain is it to install/maintain?

it would be really really cool if they made a zinc thru-hull strainer (to replace the bronze strainer on the head intake).

ok, i am continuing to plow through Calder's book, and will keep the populous posted to any more exceptions to the rules.

just adding to the confusion......

[Theis]

There is enough information in Morganstrn's comments to keep me busy for a while. This is not an easy subject, but the comments and article are enlightening. Bill, I can see you are doing as the Practical Sailor suggests. What troubles me is that I don't see that being done with other boats in our yard - excepting only the zincs on the propellor shaft.

There are two subjects now being discussed. The first is the corrosion caused by shore currents and galvonic corrosion. The second (at least so it seems to me) is the issue of gounding the mast, bow and stern pulpits to water ground - and a centrally grounded system.

The second one I can address, in as much as I have some confidence about my knowledge of the subject. The issue is not just lightning. Your mast head can be going through electrically charged air (even though the cloud is high above) and even though you may be at the dock. With a grounded mast, that cloud is being discharged through your grounding plate - and, voila, there is a current -and potentially a very large current. Without the grounding plate, the path of the current is unspecified, and the path taken may be dependent on the intensity of the voltage build up.

As to what can happen if everything internal is connected but not grounded? Your electronics and everything gets fried if the voltage build up is sudden and substantial. Better carry a hand held compass. Obviously, with an electrical storm, the problem can be acute, and the masthead can attract lightning if not adequately grounded with the ability to discharge immense amounts of current.

A zinc anode and a grounding plate are not synonomous, nor do they do the same thing. The zinc anode will not discharge enough current for a lightning/near lightning/charged cloud hit. It simply does not have the mandatory surface area.

The question was raised about the grounding plate on an OB. My OB is connected to the battery directly. It has an electric start so the ground is a solid #6ga wire. However, while pondering this, I realized that, with just the generator, as I had last year, the generator was likely isolated from the motor (Yamaha 8hp). With the electric start, the battery ground and the engine ground have to be commoned.

On the original Ariels, as I recall, the wire from the head inlet (There is a small #6 screw that fits into the fitting base) was commoned to wires from the battery/distribution panel and the chainplates (also the masthead) near the bottom front of the locker closet in the cabin. Note that for lightning protection purposes, the bow and stern pulpits should also be grounded. I use #6 guage wire for mast/bow pulpit grounding. Be careful not to have any sharp corners in any of these grounding wires (for lightning protection)

Back to corrosion caused by electrolysis and the sacrificial plates: I need to do further review the information mentioned above as to why multiple sacrificial plates are needed if the metal fittings on the boat are wired together to a single sacrificial plate. Why is not one plate adequate? Also, if there is a single plate system, from one end of the boat to another, with the totality being grounded, that should create a "shield" of a common voltage level, even in salt water.

For example, let us say that points A and C are 6 inches apart, underwarer, and bonded and grounded. An isolated metal point B, is between the two points and not bonded or connected to the other two. It is totally isolated. It would not develop a differential to cause corrosion according to my theory. Galvonic corrosion requires a current - no matter how you cut it. There is no way current could flow from either points A or C to B, even through the sea water is a conductor connecting all three because there is no path. Going further, assume there were a bunch of metal fittings, each being a point B between A&C, separated by a 1/64" gap. The only conductor connecting them was the seawater. Then lastly, assume A,B&C were points on a single copper plate where the points on the plate were connected both by the sea water, and the conductivity of the copper. I think all three situations, as for corrosion, are identical. But if that is the case, then every fitting need not have a zinc plate.

Unfortunately, at this time, for me, there are more questions raised than answered. Hope some of this makes sense.

[mrgnstrn]

i think there are now three aspects that we are now talking about:

1. galvanic corrsion caused by a perfectly functioning AC ground wire/ shorepower

2. grounding for the purposes of lightening protection/prevention

3. corrosion of metal parts that are not at all electrically connected to the boat. just grounded (that is, they are immersed in it.)

the first two make sense to me, but like someone else said, the third doesn't make intuitive sense. i am by no means denying that it happens, just trying to figure out the mechanism (so as to prevent it)

more confusion.....

[ebb]

This conversation here is trying to talk about four distinct electrical systems on a boat at the same time.
The DC system,
the bonding system,
the AC system,
the lightning shield.
If you are going to make any sway with an absolute dunce like me, we have to keep the terms straight. Confusion reigns.

Gut feeling and some evidense (eg Mr Amos in the aforementioned article - one of the experts disagreeing amongst themselves) suggests that each system should be independant, This does not seem possible at the moment.
1>Therefor, the batteries, motor and dc wiring have a single ground that is separate from the bonding system. Isn't this an 'active' system, while the bonding is a 'passive' one? So why would you ground the dynamic electric system to a thruhull?
2>The bonding circuit supposedly equalizes stray currents to protect metals from galvanic action. Why doesn't this circuit have its own ground or earth? It can't, I guess, because it'll get confused like the rest of us! So what they do on frp boats Now is Unbond and Isolate all important metal pieses from each other. Is this not so? 338 has all its bonding wires torn out!
3>Bringing shore power aboard is asking for trouble for many reasons. It must be isolated from the boats dc wiring, no? So why can't some real smart sparky create a little box that makes sure the charger Never can short over to the the dc ground. The AC grounds on shore, right? There has to be some kind of simple interuptor that will protect the ship. I really must be persuaded that shore power is necessary beyond an inconvenient extension cord!

4>Why connect the precious metals on the boat for lightniing protection? You want to create as unmistakable a path to the earth possible, No? So, don't you have a bottlebrush disapator up top as first defense and from there as straight a route down the shrouds to the water with fat copper as a hopeful dissuader? But the point is, isn't it, that you don't want to encourage a million volt hit to visit a boat that is an interconnected circuit?
(LATER EDIT): BB masttop disapators have lost favor. Maybe good for keeping gulls away!

Can't I have four separate systems?

Pretty soon there is going to be another nice little electronic box that will create a negative ion coating on inwater metals for OBs and propellers and thru hulls called a 'cathodic protection system.' It'll have a galvanic isolator chip for your ac and dc ground separation. It already exists but they haven't miniaturized it yet. Look for it at yer spring boat show.
__________________________________________________ __________________________________________________ ___________
LATER EDIT (3/2017): Seems to me that ole blowhard here did bring up some anomalies...

But here is a site with a great article on electrolyis for boats that live in the water. From a cruiser's standpoint.
"Never create a circuit unless you absolutely have to.' 'Zincs create electrolysis'. 2nd thoughts on ABYC common ground for DC/AC.
Electrolysis 101 http://yachtpals.com/how-to/electrolysis?page=1

[Theis]

This is getting complex - how about that for a comment on the obvious?

Going first to the lightning issue, keep in mind that the best minds I believe now agree that lightning does not "strike". What happens is a huge positive charge can accumulate on a high point (a person's head, a tree, or a masthead). The overhead negative charge from the clouds is attracted to the strong positive charge and shazamm. The electricity goes up, not down. The purpose of a bottle brush, and a large ground plate under water is to dissipate any positive charge buildup at the masthead. If the masthead is maintained at ground level electrically, it will not attract the negative tracers from the overhead cloud/passing air.

The issue of having a common connection for the internal electrical system ground and the hull ground is one I have mused about at length. However, my conclusion is that the experts opine that if you don't do that, a lightning hit will wipe out your entire electrical system - instruments, motor starter, everything. It will jump over to the second electrical system ground in other words. Very risky - at least.

Perhaps the worst alternative is to have multiple earth grounds (the seawater is effectively earth ground for a boat) because then you do have a loop, and electrical currents can flow. For example, if the system electrical ground is connected to the motor (which is then in the water), you have a loop with the masthead ground. That is not good, in my opinion. Everything has to be commoned to a common point closest to the ground dissipation point. In my boat the wire from the electrical system meets the ground from the masthead at the through hull plate.

When you hear about a boat that has been "hit" by lightning and winds up with areas of pin holes, that is because, lacking a clear low impedance path to the water, the current goes right through the fiberglass creating a myriad of pinholes and the boat can sink. Wood plugs don't work for those small pin holes. I have noticed that many west coast built boats do not have lightning protection/water ground, and it seems those are the ones that get hit and blown apart (I should mention that a laminated hull, which the Ariel/Commander does not have, is a big part of the problem).

Bill: I have been considering your concerns and putting a zinc on the rudder post(s). As I recall you have an outboard that you pull out of the well when you are not using it. In such case, the rudder post(s) may be the only metal connection to the water/ground. If that is the case, the posts are grounding posts and are subject to significant galvonic action (the shoe is part of the rudder post assembly for this discussion since it is electrically connected) In such event, a zinc sacrifical plate would be mandatory, but, based on my possibly flawed reasoning, one zinc plate should be adequate for the assembly - the preferable location being the shoe.

[Bill]

Peter,

Great theoretically, but maybe not empirically Owners around here have lost upper rudder shafts and had no problem with the shoe and vice versa. Some have had problems with both. The zincs on #76 have lasted about four years, both upper and lower, before needing replacement.

BTW - to my knowledge, none of the failed upper shafts have been on boats with shore power.