Best Ground Point

[walt]

My point is that even with an isolated prop shaft with a drive saver, and a sintered bronze ground plate as "ground", you still have two ground paths, the raw water intake is one and the ground plate the other.

Maine Sail, I also took this to mean that the sintered bronze ground plate must be in contact with the water - otherwise, it doesn’t really have much effect on corrosion. You can do all sorts of bad grounding inside the boat and as long as the grounds don’t contact the water at different voltage potentials, they don’t matter (regarding corrosion).

 

[Maine Sail]

Maine Sail, I also took this to mean that the sintered bronze ground plate must be in contact with the water - otherwise, it doesn’t really have much effect on corrosion. You can do all sorts of bad grounding inside the boat and as long as the grounds don’t contact the water at different voltage potentials, they don’t matter (regarding corrosion).

You understood that correctly and I was referring to a ground plate in the water. With a ground plate, sintered or not, and the engine you can still have potential for two ground points not just one as it is very difficult to totally isolate the engine from earth because of the raw water intake. Many assume a Drive Saver will isolate the engine to run everything to a ground palte but it may not do that at all when it comes to ground..

Both a ground plate and the engine would be contacting the water or earth at different points. This is why I raise the question. It has never made much sense to me to run everything to a ground plate, as Calder prefers, to have just "one ground" when the engine, in most situations, will be a second ground point causing the potential for multiple ground paths.

This is why I brought it up to open up a dialogue about this nagging question I have had for a long time. I am interested to hear other thoughts. The only solution I can think of is a closed Marelon seacock but I don't know if that would totally isolate the engine or not being submerged and wet and as the plastic still absorbs some moisture?

 

[Hermit Scott]

You understood that correctly and I was referring to a ground plate in the water. With a ground plate, sintered or not, and the engine you can still have potential for two ground points not just one as it is very difficult to totally isolate the engine from earth because of the raw water intake. Many assume a Drive Saver will isolate the engine to run everything to a ground palte but it may not do that at all when it comes to ground..

Both a ground plate and the engine would be contacting the water or earth at different points. This is why I raise the question. It has never made much sense to me to run everything to a ground plate, as Calder prefers, to have just "one ground" when the engine, in most situations, will be a second ground point causing the potential for multiple ground paths.

This is why I brought it up to open up a dialogue about this nagging question I have had for a long time. I am interested to hear other thoughts. The only solution I can think of is a closed Marelon seacock but I don't know if that would totally isolate the engine or not being submerged and wet and as the plastic still absorbs some moisture?

You are a very smart guy.
According to this document the problem is exacerbated by distance. So placing the bronze plate near the engine through hull may be the best solution. Unless you want to come up with some crazy contraption that causes a break in the continuity of the water, and I think even you wouldn't be that rediculously meticulous to achive 1 ground contact point.

 

[Ron20324]

The raw water intake hoses are filled with water (ground) all the way to the water pump or HX. No? The water pump and HX are grounded to the engine and filled with "ground". The only possible way I can see to possibly isolate the engine from ground would be to have a closed Marelon seacock. Unless you close the seacock and run the impeller dry? Perhaps I have missed something about water being ground or earth?

Having winterized my boat as it sits in the water, and also removed the impeller for the lay-up period, there is now no water between the impeller and seacock, so there went any "ground" via the water system. I think it would not be guranteed anyway that the raw water hose retaines water all the length of it anyway. Maybe it does, but I don't have clear plastic hose to test the theory.

 

[paulj]

[FONT=Arial, Helvetica, sans-serif]Summary[/FONT]
[FONT=Arial, Helvetica, sans-serif]By using capacitors to block DC connections in a few key areas, it is possible to have perfect ground systems for AC, DC, RF, lightning, and corrosion, and have a boat that is immune to stray DC currents that are traveling through the water in "hot marinas."[/FONT]
[FONT=Arial, Helvetica, sans-serif]In the old days, the technique of bonding everything together worked okay. In its defense, the "bond everything together" approach makes your boat less sensitive to electrolytic corrosion that can result from faulty wiring on your own boat. The problem is, the "bond everything" approach leaves your boat totally defenseless to wiring errors in nearby boats and nearby industry, that cause stray DC currents to run through the water. [/FONT]
[FONT=Arial, Helvetica, sans-serif]Today the technique of bonding everything together would still work fine if your boat spent all of its time on the high seas, in remote anchorages, or in marinas that were wired perfectly and in which all of the nearby yachts were wired perfectly. Having underwater metal bonded together in crowded marina's today, however, is asking for expensive trouble. It is possible, with careful wiring and a few capacitors, to have the best of all worlds, good RF and lightning grounds, ABYC approved DC and AC grounds, and security against electrolytic corrosion caused by hot marinas.[/FONT]
By Ben Franklin

Have you changed your zincs this year?


paulj :troll:

 

[walt]

I could be wrong but I have a real hard time with the concept of stray current in the water at marinas (ie, the reference Hermit posted a couple posts back). An example..

Let’s say that one boat has an electrode in the water which is at zero volts potential and another boat 100 foot away has an electrode at 100 volts.

The resistance of the water very close to the hot electrode is fairly high as the effective area of the water in contact with the electrode is small. So electric fields and current right at the hot electrode are also fairly high.

But as you move away from the electrode, the volume of the water increases by the cube of distance - so the resistance "seen by the electrode" also decreases by the cube of distance (current in water doesnt flow in a stream - in this case, it will "radiate" outwards from the electrode in
accordance with ohms law). This results in the electric field falling off very quickly with the cube of distance (actually likely between the square and cube since the water volume seen by the boat is a half sphere). So at even a fairly small distance away from the hot probe, the "local" current and electric field are very small and both fall of very rapidly with distance.. The boat at 100 foot away shares the entire volume of water in a 100 foot radius from the hot boat electrode. Its electrode is effectively a single point on the outside a large sphere of huge volume and if the current falls off at the square of distance, the current at 100 foot would be 1.4 million times smaller than at 1 inch. If the current falls off at the cube of distance, it would be 1.7 billion times smaller than at one inch. I.e., I can’t see the hot electrode having any influence on a second electrode 100 foot away.

Also to point out.. an outboard motor with AC on it would also have the electric field increase very rapidly with distance as you got close to it which is probably why they can be so dangerous.

On the other hand, AC green earth wires at a marina not being at earth potential is very believable. But you can solve this with a galvanic ground isolator.

 

[Hermit Scott]

I could be wrong but I have a real hard time with the concept of stray current in the water at marinas (ie, the reference Hermit posted a couple posts back). An example..

Let’s say that one boat has an electrode in the water which is at zero volts potential and another boat 100 foot away has an electrode at 100 volts.

The resistance of the water very close to the hot electrode is fairly high as the effective area of the water in contact with the electrode is small. So electric fields and current right at the hot electrode are also fairly high.

But as you move away from the electrode, the volume of the water increases by the cube of distance - so the resistance "seen by the electrode" also decreases by the cube of distance (current in water doesnt flow in a stream - in this case, it will "radiate" outwards from the electrode in
accordance with ohms law). This results in the electric field falling off very quickly with the cube of distance (actually likely between the square and cube since the water volume seen by the boat is a half sphere). So at even a fairly small distance away from the hot probe, the "local" current and electric field are very small and both fall of very rapidly with distance.. The boat at 100 foot away shares the entire volume of water in a 100 foot radius from the hot boat electrode. Its electrode is effectively a single point on the outside a large sphere of huge volume and if the current falls off at the square of distance, the current at 100 foot would be 1.4 million times smaller than at 1 inch. If the current falls off at the cube of distance, it would be 1.7 billion times smaller than at one inch. I.e., I can’t see the hot electrode having any influence on a second electrode 100 foot away.

Also to point out.. an outboard motor with AC on it would also have the electric field increase very rapidly with distance as you got close to it which is probably why they can be so dangerous.

On the other hand, AC green earth wires at a marina not being at earth potential is very believable. But you can solve this with a galvanic ground isolator.

I like you. But read the archive posts about people replacing zincs every two months that are 50% eaten away. Something did it and it wasn't a zinc fairy.

 

[walt]

Well, I really dont know and also have a trailered boat which is not even on the water most of the year so dont have any of these problems. But am interested in learing - mabe some day (hopefully) Ill need to really understand this stuff.

Zinc fairy.. please post some pictures of her...

 

[Maine Sail]

Zinc fairy.. please post some pictures of her...

She's hot !!

 

[Hermit Scott]

Well, I really dont know and also have a trailered boat which is not even on the water most of the year so dont have any of these problems. But am interested in learing - mabe some day (hopefully) Ill need to really understand this stuff.

Zinc fairy.. please post some pictures of her...

This is her. At Garner park Texas, stealing the zinc on my kayak.

 

[walt]

Picture of my wife this last Thanksgiving. Your zinc fairy looks like she is having more fun than mine.. (yup, its as steep and slippery as it looks)

 

[Hermit Scott]

Picture of my wife this last Thanksgiving. Your zinc fairy looks like she is having more fun than mine.. (yup, its as steep and slippery as it looks)

It looks as if you took her some place she didn't want to go.
I sometimes miss the snow. But then I remember how cold it is.

 

[jimford2158]

Hi again, Merry Christmas All! what i meant about the prop shaft is mine is a complete circuit from the engine to the shaft outside the boat(checked with an ohmmeter)so it is a path to ground thru the water. i haven't had any problem with the zincs but i just lately hooked the ac ground to the engine, i'm still not sure i like that though. I have a question on the lightning protection, on my 37 there is only a ground cable that is attached to the middle stay on the inside of the port hull. does anybody know where it should be attached in the keel? I had her drydocked and did not see any ground plate or where one would have been mounted. the cable was attached to one of the sea cocks at the front of the keel with a hose clamp. the book says to use a 12 inch square copper plate for a lightning ground on the outside of the hull. the info i have is mostly from the internet and caseys book but the way i have it wired now makes sense and is a lot better than what they had, with the black and white ac wires only going to the outlets. before i would get minor shocks if i touched the bilge water, fortunately i'm used to some of that from working on hei car ignition systems. anyways, the compression post is all wood and there is only the light wiring and radar cables coming from the mast. there is no other lightning protection that i am aware of. thanks.

 

[Hermit Scott]

Hi again, Merry Christmas All! what i meant about the prop shaft is mine is a complete circuit from the engine to the shaft outside the boat(checked with an ohmmeter)so it is a path to ground thru the water. i haven't had any problem with the zincs but i just lately hooked the ac ground to the engine, i'm still not sure i like that though. I have a question on the lightning protection, on my 37 there is only a ground cable that is attached to the middle stay on the inside of the port hull. does anybody know where it should be attached in the keel? I had her drydocked and did not see any ground plate or where one would have been mounted. the cable was attached to one of the sea cocks at the front of the keel with a hose clamp. the book says to use a 12 inch square copper plate for a lightning ground on the outside of the hull. the info i have is mostly from the internet and caseys book but the way i have it wired now makes sense and is a lot better than what they had, with the black and white ac wires only going to the outlets. before i would get minor shocks if i touched the bilge water, fortunately i'm used to some of that from working on hei car ignition systems. anyways, the compression post is all wood and there is only the light wiring and radar cables coming from the mast. there is no other lightning protection that i am aware of. thanks.

The lightning protection should go to a keel bolt. You don't need a copper plate. The lightning will completely ignore the bottom paint to get to the salt water. You are wise in removing it from a through hull. They have reportedly been blown out of the boat during a strike. If you are going to do lightning protection. You should run a line from the mast to the keel bolt, and all the stays to the keel bolt. Otherwise someone hanging onto a stay when struck will be fully, or attempted to be fully raised to the stays new potential.
Do you have sailbaot electrics simplified by Don Casey? Page 164 covers salt water.You are on the West coast of Fla in the salt yes?

 

[jimford2158]

Thank you Hermit, yes I just got the book so still reading it. He could have gone in to more detail on the 110 ac but definitely got me straightened out on the ac power circuit(really don't like being zapped, I now unplug the shore cord when working in the bilge especially). On the 37 Irwin the keel lead is glassed in and there are no bolts that I can see. I have been looking for a threaded stud in there but everything except for the very front of keel is below either the water tank or the fuel tank. I was thinking of maybe tapping into the keel lead at the point below the mast support post but I don't know how far forward the lead goes. I could then bolt a copper lead to the mast and run it straight down from the mast to the keel. But then I am not sure what to do about getting current from the keel lead outside to the water thru the fiberglas hull. Also I thought I read something that stated the 5000 pounds of lead would absorb the entire energy from the lightning strike but that sounds kind of iffy to me. I am waiting to figure this out before I hook up any real electronics since we are in the lightning capital of u.s. Other than this the boat is coming along fine and right now I am replacing all the plywood in the galley(rotted away from water leaks) and I am replacing the ac and 12v wiring and plumbing while I have it apart. Thanks again.

 

[Hermit Scott]

Thank you Hermit, yes I just got the book so still reading it. He could have gone in to more detail on the 110 ac but definitely got me straightened out on the ac power circuit(really don't like being zapped, I now unplug the shore cord when working in the bilge especially). On the 37 Irwin the keel lead is glassed in and there are no bolts that I can see. I have been looking for a threaded stud in there but everything except for the very front of keel is below either the water tank or the fuel tank. I was thinking of maybe tapping into the keel lead at the point below the mast support post but I don't know how far forward the lead goes. I could then bolt a copper lead to the mast and run it straight down from the mast to the keel. But then I am not sure what to do about getting current from the keel lead outside to the water thru the fiberglas hull. Also I thought I read something that stated the 5000 pounds of lead would absorb the entire energy from the lightning strike but that sounds kind of iffy to me. I am waiting to figure this out before I hook up any real electronics since we are in the lightning capital of u.s. Other than this the boat is coming along fine and right now I am replacing all the plywood in the galley(rotted away from water leaks) and I am replacing the ac and 12v wiring and plumbing while I have it apart. Thanks again.

Do not count on the lead keel to be a giant capacitor. Electricity only flows on the outside of metal. Capacitors are thin metal rolled up. Inside them is a very large area. Anyway that's not a sound way to think about the flow of lightning. Also I would skip the keel altogether. Since you have a sealed keel, you have a blessing. I would leave it that way. Go for the grounding plate.

 

[heart of gold]

As I understand it

I've been reading this thread with interest and posted a comment back near the beginning, "do not connect shore power ground and negative terminal of battery together". As this is my trade, I tend to think of things in terms of circuits, and if you think about it, tying shore power to your negative terminal at any point of your 12v system sets up a nice little battery when the boat is plugged into shore power. The circuit here is from any under water metal bonded to the negative teminal of the 12v system, through the ac ground to the main grounding point of the ac service for the marina, usually a large galvanized plate on the seabed as well as a grounding point on land at the point of feed. Of course the effects are much less the further you are from the main ac service. Althought the current will not be large it will be enough over time to eat valuable things like props, through hulls etc. as the metal flows from negative to positive through galvanic action. The only way that I can think of to stop current flow is to open the circuit , that is, by not tying the 2 systems together. The negative terminal on your battery is not "ground" it is merely negative and in conventional flow , current flows from the positive in the battery system through a load to the ngative terminal and should not go to the AC ground where it could actually add to the problem. I still believe that all under water metal parts of your boat should be bonded to negative and the engine to reduce current flow from these to each other. When they are all at the same potential, little or no current will flow. Where there is still a potential difference, sacrificial anodes(zincs) should be regularly changed as needed.
On the lightnening protection example of one boat taking the hit and one right beside it did not. I have found that high voltage including lightening will do exactly what it wants and is very unpredicable but one thing you can count on is that electricity in general will follow the path of least resistance to ground, mother earth' and will figure out the easiest way to get there. Having the lighting protecton installed on a boat may actually have attracted the bolt as it was a conductor to water and had fun getting there, while the other boat acted as an insulator and therefore no current flow! But who knows. I could tell you stories.....but I have to go, cheers

 

[wufibugs]

Heart, would that still be true if one had a galvanic isolator in the wire between shore power and boat ground?

 

[heart of gold]

I found this article on isolators. They will work to protect against galvanic action and AC faults as long as the galvanic voltage and/or ac voltage in the ground system do not rise above the conductive voltage of the diode pack or isolator, but in a fault situation rises to full voltage with enough current to trip the shore power breaker. If for any reason the voltage/current doesn't reach a high enough level to trip the breaker, then you could still have problems. The safest setup would include ground fault protection at the shore power point of service breaker but few places that I've seen have GFI's, especially older marina's. (I suppose you could buy an inline GFI and plug it in at shore supply first).
Before relying on this I would look carefully at both systems 12v and shore power on board and make absolutely sure that there is no chance that the hot conductors of each would ever make contact with each other or metal parts of the boat and are in good condition and all bonding points are metal on metal and tight.

"THE GALVANIC ISOLATOR EXPLAINED



NOTE: Recent boat wiring recommendations may specify that commercial galvanic isolators be constructed with indicating and testing electronics included. This article does not contemplate these devices but refers to the millions of units installed prior to these changes.
The purpose is to disconnect your wet metal parts from the dock supply in order to prevent electrolysis. The trouble is, however, you need them connected together so that if there is an electrical short on the boat, it doesn't make the boat alive at 120 volts or worse which can give you quite a kick when you step off an aluminum dock!!
The galvanic isolator relies on the fact that electrolysis voltages are quite low - usually less than one volt - whereas electrical failure voltages are quite high. Silicon diodes, which are used to conduct electricity in one direction but block it in the reverse direction, have a built in forward voltage drop of about 0.6 volts. It is not like a resistor voltage drop - no current has to flow to create the drop - so below 0.6 volts it is disconnected, above this it conducts with very little resistance to current flow.
Since we don't know the polarity of the fault voltage, and if it is an AC fault, it will be flowing both ways, two diodes are placed in parallel pointing opposite directions so there is always one available to conduct, but at low voltages, both are switched off and no electrolytic current can flow.
Since some electrolytic voltages are higher than 0.6 volts, a good galvanic isolator should have two diodes in series in each direction to give a 1.2 volt isolation. Some also add a capacitor to increase the ability to conduct AC current, however I personally think this is a mistake as it does allow low level AC currents to flow and cause electrolytic type activity, even if not true electrolysis. This activity can remove paint from the fitting and generate chlorine bubbles that damage surrounding antifouling paint. The diodes have to have enough capacity to pop a shore power circuit breaker if there is a short on your boat. This can require a capacity of more than 100 amps. Galvanic isolator diodes are designed to carry this current for a very short time - long enough to blow the circuit breaker plus a safety margin - but they cannot carry it for very long without overheating. They should be able to stand the shore power current rating indefinitely."

 

[Maine Sail]

On the 37 Irwin the keel lead is glassed in and there are no bolts that I can see. I have been looking for a threaded stud in there but everything except for the very front of keel is below either the water tank or the fuel tank.

With internal ballast you do not want to ground to the keel, especially for lightning.

Lightning likes to dissipate through long edges or large areas such as a keel but with internal ballast you may blow a hole right through the keel encasement by grounding to it for lightning.

Most boats with internal ballast, who are looking for lightning protection, install a ground strip or plate. For lightening the one with the longest "edge" is purported to be the best.

Here's what one may look like..