Stray current in marina

[glcalahan]

I am doing a complete rebuild of a '72 Pearson 33. After being on the hard for 17 months and splashed May 18. The PO had no zinc's and lost 2 of 3 so I replaced both a new prop and shaft. Yesterday July 24th found my shaft end zinc totally gone in 2 months! I have not even wired the AC dock power yet!! The engine was connected to the battery. Okay....now, I realize there can only be serious stray current in the marina. I recall years ago a similar issue and took my DMM and connected the engine block and dropped the other probe into the water. Do I set on a low scale of AC or DC mode? Assuming I am reading current or voltage (which would it be??), can I determine the problem boat by disconnecting adjacent boats one at a time?? Of course with permission![emoji16]

[Neptune's Gear]

Nope. This is almost certainly an issue on/from your own vessel. You need a proper silver/silver chloride anode to measure it correctly. For the issue to be the marina, you MUST have a circuit to said marina - a shore power connection is the most common, but it could be a chain leading ashore etc. You have no circuit, only the water.
you need to find the electrical leak on your own boat. Bilge pumps in the water are a common source - is your bilge dry? Get the right gear to test, or employ someone to do it.

[glcalahan]

Originally Posted by Neptune's Gear

Nope. This is almost certainly an issue on/from your own vessel. You need a proper silver/silver chloride anode to measure it correctly. For the issue to be the marina, you MUST have a circuit to said marina - a shore power connection is the most common, but it could be a chain leading ashore etc. You have no circuit, only the water.
you need to find the electrical leak on your own boat. Bilge pumps in the water are a common source - is your bilge dry? Get the right gear to test, or employ someone to do it.

Thanks! Nothing is wired....not even the bilge pumps. Neither AC or DC , not even the 30 amp cord from dock. I manually hold wires on battery lugs for bilge! There is only the connection to the battery (remember no charger) connected to the Yanmar.

[boatpoker]

How are you charging the battery ?

Neptune has it right. If there is no electrical contact to the marina or another boat there is no circuit, therefore no stray current coming into your boat.

[glcalahan]

Originally Posted by boatpoker

How are you charging the battery ?

Neptune has it right. If there is no electrical contact to the marina or another boat there is no circuit, therefore no stray current coming into your boat.

The battery charger is not yet installed...so no, I am not charging the battery.

[boatpoker]

Originally Posted by glcalahan

The battery charger is not yet installed...so no, I am not charging the battery.

Forgive me for asking stupid questions but if you are not charging the battery how are you running a bilge pump ?

[S/V Illusion]

It's human nature to blame the other guy -in this case, blame the marina.

In fact, the vast majority of electrolysis problems are self-inflicted from the onboard D.C. circuit, usually a ground fault or multiple grounds.

[hellosailor]

gl-
If you have no AC connected, and no battery connected, then you cannot have a current flowing and you cannot having normal galvanic corrosion eating the zinc.

These leaves a few unlikely possibilities:
1-Your boat is docked in lemon juice, not water.
2-Your neighbors are stealing your zinc and leaving their used one in its place.
3-There's something hooked up, making a circuit on your boat!

Cable tv connection? Phone connection? SOMEthing the PO installed installed someplace that is on. A wind generator or solar panels that are supposed to be unplugged?

If you start with the shaft, trace that inside to the engine block. Now start chasing any cables that are bolted to the engine mounting rails, bolted to the motor mounts, anything attached to the block. Nothing there? OK, then the block still has at least one (sometimes more than one) ground wire that's going to the batteries. Uninterrupted? Anything else hooked into that?

Somewhere, you're probably going to find something really is hooked up, and making a circuit.

And you'd be using DC on your meter to search for this. Somewhere, there's got to be current floating, unless you're berthed in lemonade. (What, that never happened to you?)

[Diamond Life]

The isolation switch for the engine, is that being utilised (switched to off when not used) and if so does it isolate (switch) your positive or negative side of the battery.

[Paul Elliott]

Originally Posted by hellosailor

If you have no AC connected, and no battery connected, then you cannot have a current flowing and you cannot having normal galvanic corrosion eating the zinc.

You can certainly have current flowing through the salt water between the zinc and (say) a stainless steel propshaft or bronze propeller, if they are electrically connected in the boat. This connection can be direct (the zinc is clamped to the propshaft), or through the engine (if the zinc is wired to the engine ground).

However, the rate of zinc wasting caused by this type connection is typically pretty slow. On my boat, the zincs can easily last for a year. By the way, this slow zinc wasting is exactly what you want -- that's how the zinc protects the other underwater metals on your boat. You don't usually see fast zinc wasting without a shorepower connection.

[boatpoker]

Originally Posted by Paul Elliott

You can certainly have current flowing through the salt water between the zinc and (say) a stainless steel propshaft or bronze propeller, if they are electrically connected in the boat. This connection can be direct (the zinc is clamped to the propshaft), or through the engine (if the zinc is wired to the engine ground).

However, the rate of zinc wasting caused by this type connection is typically pretty slow. On my boat, the zincs can easily last for a year. By the way, this slow zinc wasting is exactly what you want -- that's how the zinc protects the other underwater metals on your boat. You don't usually see fast zinc wasting without a shorepower connection.

Correct ! this is where these threads typically go wrong, the lack of understanding of the difference between stray current and galvanic current and the ever present misuse of the word "electrolysis" which simply does not apply.

[glcalahan]

Originally Posted by hellosailor

gl-
If you have no AC connected, and no battery connected, then you cannot have a current flowing and you cannot having normal galvanic corrosion eating the zinc.

These leaves a few unlikely possibilities:
1-Your boat is docked in lemon juice, not water.
2-Your neighbors are stealing your zinc and leaving their used one in its place.
3-There's something hooked up, making a circuit on your boat!

Cable tv connection? Phone connection? SOMEthing the PO installed installed someplace that is on. A wind generator or solar panels that are supposed to be unplugged?

If you start with the shaft, trace that inside to the engine block. Now start chasing any cables that are bolted to the engine mounting rails, bolted to the motor mounts, anything attached to the block. Nothing there? OK, then the block still has at least one (sometimes more than one) ground wire that's going to the batteries. Uninterrupted? Anything else hooked into that?

Somewhere, you're probably going to find something really is hooked up, and making a circuit.

And you'd be using DC on your meter to search for this. Somewhere, there's got to be current floating, unless you're berthed in lemonade. (What, that never happened to you?)

In answer to you quiry...the only connections on the engine are B+ and ground of battery. There is not one other electrical connection on the boat. BTW...the battery has been disconnected for 2+ weeks.

Thanks again!

[glcalahan]

My previous 5 sailboats and in almost 50 years of being around sailboats only, this is a shock to me. Now...you mentioned something interesting. The prop and shaft have been replaced new because the PO sadly did not maintain the boat. 2 of the 14" bronze prop were lost to electrolysis. As a result, I replaced not only the prop but the 7/8" SS shaft. Point is.....dissimilar metals. ??????

[boatpoker]

Originally Posted by glcalahan

My previous 5 sailboats and in almost 50 years of being around sailboats only, this is a shock to me. Now...you mentioned something interesting. The prop and shaft have been replaced new because the PO sadly did not maintain the boat. 2 of the 14" bronze prop were lost to electrolysis. As a result, I replaced not only the prop but the 7/8" SS shaft. Point is.....dissimilar metals. ??????

You did not lose anything to "electrolysis".

As a retired Certified Corrosion Analyst I'd like to clear up the “ELECTROLYSIS”, issue. This term is frequently misused due to lack of understanding of the processes involved in corrosion.

There are many types of corrosion however, the two main issues on boats is either GALVANIC CORROSION or STRAY CURRENT CORROSION.

ELECTROLYSIS is actually the opposite action to galvanic corrosion so the distinction is not trivial as some people suggest.

ELECTROLYSIS is the forced introduction of a current in an electrolyte (water) to separate the components. In water this produces Hydrogen and Oxygen.

GALVANIC CORROSION
on the other hand is an electrochemical reaction that causes electrons to flow
from one metal to another metal. One of the metals is the anode and the other is the cathode. If you put the two in an electrolyte that conducts current, and connect them with a wire, they act pretty much the same way a battery does. A current flows between the two metals. The atoms from one are “sacrificed” and plated onto the other metal. This happens when you have dissimilar metals such as aluminum and bronze close to each other. The aluminum disappears.

STRAY CURRENT CORROSION is simply corrosion caused by stray (leaking) current from a bilge pump or a battery charger among other things.

Punch line do not take advice from or hire a marine electrician who uses the term electrolysis.

[Paul Elliott]

Originally Posted by boatpoker

GALVANIC CORROSION
on the other hand is an electrochemical reaction that causes electrons to flow
from one metal to another metal. One of the metals is the anode and the other is the cathode. If you put the two in an electrolyte that conducts current, and connect them with a wire, they act pretty much the same way a battery does. A current flows between the two metals. The atoms from one are “sacrificed” and plated onto the other metal. This happens when you have dissimilar metals such as aluminum and bronze close to each other. The aluminum disappears.

Battery cells were originally called "Galvanic Cells", after Luigi Galvani (or "Voltaic Cells", after Alessandro Volta), and this is exactly what you have when you put dissimilar metals in an electrolyte. On our boats, these metals are typically zinc and bronze, with the electrolyte being seawater. In a Lead-acid battery the electrodes are lead and lead-dioxide, the electrolyte sulphuric acid.

As an experiment, fill a glass with seawater (or tap water with salt added, seven tablespoons per gallon), and clip one of your DVM leads to a piece of copper wire and the other DVM lead to a galvanized nail. Immerse the wire and the nail in the salt water. You will measure about 0.9V. Set the DVM to measure current and you will see tens of milliamps (depending on electrode size and placement).

Congratulations! You have made a Galvanic Cell.