Zincs and the 'Hot' Marina

[Pura Vida]

Thanks Nate,
My tests were with the shore power unplugged but I can't recall of the battery switch was on or not. I suspect on. I was reading DC. I'll work with the testing methods you have outlined and review the ABYC and Fluke docs that Gord was so kind to link. Fortunately for me this is the shortest dock in the marina and most all of the boats get a lot of use. It is a good bunch of folks so getting them to cooperate should be easy if it comes to that.

thanks
pv

[EngNate]

I will try to keep up on this thread and walk through testing questions as they arise, but if I don't get to it, give me a reminder by private message or at engnate@midatlanticseatech.com

[hellosailor]

Where does one get these chloride test leads for the average multimeter? For how much??

Or, can you use standard leads and simply recalibrate to take the difference into account?

[EngNate]

Values I gave are for a zinc reference probe. For a silver probe, subtract the values given from 1. But, you don't want to use a silver probe, unless you are working with steel or aluminium boats. Silver(chloride) probes are expensive, and require extra hardware and steps to use, and are of no advantage for this purpose with bronze and SS parts.

The leads that came with your meter are fine.

[hellosailor]

"The leads that came with your meter are fine."
Thanks.

Now, about that upconverter to take the leakage in the marina and make it charge my batteries. Is there an MPPT controller that can work with power that low?<G>

[Therapy]

I had no idea that a zinc could be gone in a week or two.

Yikes!

I guess I will have to have solar - wanted it anyhow though.

Will the controller on the solar provide the stages the battery needs to stay charged and not be damaged by a constant trickle?

[MidLandOne]

Originally Posted by Pura Vida

Anyway I would like to hear the opinions of the group concerning the life of a zinc and your experiences with marinas hot or otherwise.

Returning to experiences with the life of zincs and marinas .

Our own sail boat is 40 foot steel construction (professional custom built and fitted out). We have one only 2.34 kg teardrop zinc anode (approx 170mm long) fitted to one side of the fin keel - there are no other anodes on the whole boat. Underwater metals are manganese bronze (prop), stainless steel (prop shaft and 2 standpipes thru hull for deck drains underwater discharge) and steel (hull plating, but is protected normally by the coating system).

Boat is on shorepower at least for 2 days per week, the DC systems are all isolated from AC and hull (engine is also isolated) and a galvanic isolator and earth leakage monitor (monitors any DC leakage from DC systems to hull/earth) is fitted.

In that environment the anode lasts easily the 2 years between our haulouts. When the boat was built 11 years ago we monitored it closely for about 6 months with several haulouts and use of silver/silver chloride half cell measurements. I suspect that we could do without the anode completely as all our underwater metals were originally selected as compatible, except for the steel hull plating if its coating system should be damaged.

My experience with marinas/docks has only been with well run ones and I have never come across a "hot" one. Have a number of times come across claims of them being so but in all cases has turned out to be an issue on the boat(s) concerned. I know that the electrical distribution in our own marina is regularly checked, although I suspect that is for personnel safety reasons rather than for any other.

My experience with other boats has been, in the main, with high quality build big aluminium ones whose particular requirements are probably not relevant to this thread. Suffice it to say that they have not experienced any particular problems or unusual rates of anode erosion.

John

[Boracay]

It sounds like it is sensible to not ground the DC system in a steel boat.

My engine is isolated by the flexible coupling and the engine mounts but there would be some connection through the raw water system.

Would an isolation transformer be essential when charging batteries?

[GordMay]

Originally Posted by Boracay

It sounds like it is sensible to not ground the DC system in a steel boat. (*1)

My engine is isolated by the flexible coupling and the engine mounts but there would be some connection through the raw water system. (*2)


Would an isolation transformer be essential when charging batteries? (*3)

*1. A steel or aluminum boat hull is conductive, and will require insulated two-wire (positive & negative return) DC wiring.

The senders (for water temperature, oil pressure, and so on) on almost all engines are grounded through the engine block. If these are connected to a gauge (as opposed to a warning device or alarm) a small current passes through the sending unit, and, therefore, the engine block, any time the ignition switch is turned on. Similarly, the alternator is almost always grounded to the block, which becomes a full, current-carrying conductor. Should there be a resistive connection between the engine block and the battery negative (not uncommon), this current, or a part of it, may be encouraged to find another path to the battery negative. If this should include the hull, or any underwater fittings, corrosion is likely.

For these reasons, engines on metal boats* should have insulated/isolated ground (2-wire) sending units; where the sending unit has a separate ground wire (not be grounded through the block**). It should also have an insulated ground alternator & starter.
* I prefer Two-wire (isolated) equipment on ALL boats.
** One-wire (Case Ground) equipment utilizes the connection between the device and the engine block to complete the negative return to the battery banks.

*2. If the engine is mounted on (electrically) insulated flexible vibration isolators, with a length of flexible hose in all fuel, water and exhaust lines, it will be, to a great extent, electrically isolated from the hull.

*3. The AC shore power supply (powering the charger) must be connected through either:
- A Galvanic Isolator*
- An Isolation Transformer (preferred, but heavier & more expensive)

* Galvanic isolators are solid-state devices that are part of a series connected in line to the boat's green safety ground lead ahead of all grounding connections on the boat. This device functions as a filter, blocking the flow of destructive low voltage galvanic (DC) currents but still maintaining the integrity of the safety grounding circuit.

Some applicable articles by Michael Kasten, NA (Metal Boats Quarterly)

“Corrosion Prevention For Metal Boats”
Corrosion Prevention

"Corrosion, Zincs & Bonding"
http://www.kastenmarine.com/mbqCref.pdf

"Marine Metals Reference"
http://www.kastenmarine.com/mbqMetRef.pdf

And:
“Galvanic Corrosion” ~ by Dr. Stephen C. Dexter
MAS Note-Galvanic Corrosion

[bobfnbw]

Enough to make my head spin....
2 weeks ago all the bronze mushrooms on the starboard side foreward were gone, and the one bronze sea cock eaten thru... boat to on more water than the bilge pump could handle, now its on the hard, a mess and waiting for insurance types to figure it out....
engine is wet thru, mold is growing, and wood swelling...

What a mess. Not sure why it happened. Could be from a slip change a week ago, but boat was NOT connected to shore power on the new slip. Could be from motoring to the new slip ~40 min total run time... haven't used the boat and engine since purchase except to move slips, been working on her.
Was going to rewire this spring put in new galvanic isolater, bonding system, panels, batteries etc. Now don't know where this is heading.

What I need to know now, from the people here that know, is how to prevent this from happening in the future.
Sure I could just install marelon seacocks and thru hulls, but there is still the prop, and other underwater metal, and there is a lot of debate over weather marelon is the best choice or not. I could replace all thru hulls with groco, or perko or spartan, and considerable cost... and still have this happen again, if I do not understand what caused it in the first place.
So, what is the best choice ?
Sounds like regularly checking stray current, which I have not done in the past.
Is there any device to install on our boats that will do this without removing bonding wires, undoing batteries, and the like ? Like a meter on a panel that says, theres a problem ?

Thanks,
Bob

[EngNate]

Galvanic monitor here:
Electro-Guard, corrosion and cathodic protection specialists for boats, yachts and small ships.

See my post in classifieds if you want to buy one.
Cheers!

[Boracay]

When I encountered a similar problem on Boracay (a steel boat) the apparent cause was that the paint on the below waterline part of the hull had partly broken down, the zincs had degraded at an accelerated rate and when they were consumed the hull metal was next in line.

I tested for stray currents and found some voltages that were larger than expected but they were the same whether I was in a marina or on a mooring and whether the engine was running or not.

I estimate that from the time the anodes were exhausted it took 4 months for noticeable damage to occur.

[chala]

Gord

“*1. A steel or aluminum boat hull is conductive, and will require insulated two-wire (positive & negative return) DC wiring.”
I agree.

“Should there be a resistive connection between the engine block and the battery negative (not uncommon), this current, or a part of it, may be encouraged to find another path to the battery negative.”
In a good installation this should never be the case.

“For these reasons, engines on metal boats* should have insulated/isolated ground (2-wire) sending units; where the sending unit has a separate ground wire (not be grounded through the block**). It should also have an insulated ground alternator & starter.”
Two wires or above ground equipment is very difficult to source.

“*2. If the engine is mounted on (electrically) insulated flexible vibration isolators, with a length of flexible hose in all fuel, water and exhaust lines, it will be, to a great extent, electrically isolated from the hull.”
It needs to be to a full extent and this is very hard to achieve. Cooling water, control cable, propeller shaft will require also to be fully insulated.

“*3. The AC shore power supply (powering the charger) must be connected through either:
- A Galvanic Isolator*
- An Isolation Transformer (preferred, but heavier & more expensive)”
A battery charger if it comply with serious Standards must be made of an Isolation Transformer. The problem arise when an Isolation Transformer or a battery charger is equipped with a earthed metal casing which in turn is in contact with the metallic hull.
I never was keen on Galvanic Isolator. A properly double insulated AC wiring on a boat should not require one and I go along with S/V JEDI in the Threads
Isolation Transformers post 42
http://www.cruisersforum.com/forums/...1&postcount=42

[GordMay]

Chala:
Thanks for taking the time to respond.
I’m kind of dense, and didn’t get the point you were trying to make. Where did we disagree?
Thanks,
Gord

[chala]

Gord
We do not have to disagree.
All the best.
Chala