Eating through zincs - Need some ideas

[boatpoker]

Originally Posted by bletso

With the speed they are consumed it is obviously stray current. Further, as it seems to only happen whilst the engine is on it will be in a circuit energised with the ignition. You most probably have leakage from a positive wire through wet or moist conditions. This can be from frayed or broken insulation. It is very common with bilge pump wiring. (Not your case)

Very carefully check the condition of your charge circuitry wiring from the alternator / regulator to the battery.

This is the only post in this thread worth heeding.
PS. I'm a Certified Corrosion Analyst.

[fallingeggs]

Originally Posted by S/V Illusion

Sounds like you have multiple grounds exacerbated by having power to the engine/shaft. It's hard to imagine a different cause of what you describe.

Are all grounds at the same potential or have a common point?

The DC system and the bonding are ground to a single point on the engine block. It is this point where I attached the alternator negative jumper too. It is also this point to where I am performing the potential test from; although, attaching the negative lead elsewhere to the block or to the DC system negative busbar does not alter the results.

Originally Posted by Cavalier

Does the value change if you temporarily close the raw water intake for the engine? I.e. Does the introduction of constantly replenished electrolytes into the engine cooler alter the local potential.. Westerbeke 33 has zinc anodes in the heat exchanger (correct me if I'm mistaken), maybe be worth taking a look at their condition if the seawater cooling on/off changes the electrical values against the silver chloride anode.

Sent from mTalk

I haven't performed the test with the water off, but I will give it a try to see if the results change. I have changed the zincs in the heat exchanger and the water cooler for the SeaFrost. These zincs don't disappear nearly as quickly as the prop and shaft.

Originally Posted by smac999

Is that 500mv reading with the props spinning? Likly if they are spinning. The zincs are no longer making contact with the engine / rest of boat. Due to the gear fluid.

This wouldn't eat your zincs. It would make them last longer if they were no longer protecting the boat. But the boat would have issues.

I think I have only performed the test without the prop spinning (i.e., just sitting at anchor).

For what it is worth, none of my Spartan bronze seacocks show signs of electrolysis (thank Neptune).

[fallingeggs]

Originally Posted by Captsteve53

I would be looking firstly at the INSIDE condition of your Alternator especially for corrosion and or the winding's them selves and the varnish coatings etc, More than likely there's a situation here!!

On my steel built vessels we actually isolate the alternator all together with the use of fiber bearing sleeves and washers, but on GRP this would be extreme and basically never done- So - look for the cause in side first

Cheers Steve

Steve, can you explain how the condition of the alt could cause this problem?

With the alt 30+ years old, I have no doubt that it isn't in the greatest shape. According to my Victron battery monitory, I get about 30 amps max from it, and only for a short period of time. My charging system, obviously, doesn't reply on it. Replacement is not a simple swap because the foot of this alt is none standard (its a hair over 2 inches wide), which, I think, would require a bit of machine work to make most off-the-shelf alts fit.

If the condition of the alt really might cause my problem, I'll get more serious at replacing it.

[fallingeggs]

Originally Posted by bletso

With the speed they are consumed it is obviously stray current. Further, as it seems to only happen whilst the engine is on it will be in a circuit energised with the ignition. You most probably have leakage from a positive wire through wet or moist conditions. This can be from frayed or broken insulation. It is very common with bilge pump wiring. (Not your case)

Very carefully check the condition of your charge circuitry wiring from the alternator / regulator to the battery.

This is interesting and something I haven't considered before. I need to run the test with the ignition energized only and with the engine actually running. This might tell me if it is the alt or one of the wires. The wiring harness is original, so I wouldn't be surprised if there are some frayed wires.

Anyone have any tips for isolating which wire might be causing the problem? Or so I really just go around to each connection and see if it can be cleaned up, and then hope it solves the issue?

[fallingeggs]

Originally Posted by Mojadito

Try adding a shaft wiper, bonded to the ships bonding system

Haven't heard about these before. I'll look into them. Thanks!

[fallingeggs]

Originally Posted by Djarraluda

Try running the engine with the alternator drive belt disconnected. See if the same issue applies. If not, then you at least know it is the alternator. Easy step may reduce the problem, or you may solve it first step!
Roger

Will give this a try to help isolate where the issue is - alt vs other engine wiring.

Originally Posted by buzzstar

Are you motoring in place or going somewhere as your zincs are eaten?

Motoring at anchor in neutral. Not to keen on engaging the prop with the silver-chloride anode hanging in the water!

Originally Posted by Panacea2183

Possibly a bad diode in the alternator itself?
Put a load on your batteries and check alt output with a clamp meter?
Just thinking out loud

The alt isn't great, but it does pump out 30 amps for a while. It soon gets too hot and drops off, but that is a different issue and solution, I think.

Originally Posted by bluewatervet

RE: "Stray Electrical Currents vs. Corrosion".... Vessels and other structures (oil platforms, pipelines, powerline/antenna towers, etc.) sitting in salt water have significant corrosion caused by stray electrical currents. In the extreme, using active electronic devices to 'buck' this, some of this electrical 'difference' can be offset, if not totally 'nulled out' and then, electrically induced corrosion is slowed significantly, if not stopped totally. I would suggest "you have more unaccounted for metal objects in the water" that are aiding in this corrosion process. Is your rudder post &/or the rudder itself a metal (electrically conductive) material..? Or, how about any through-hull fittings under the water, typically naval bronze or Monel, somehow electrically interconnected with the internal metal objects & wiring system. The head may be an example; lots of metal there, connected on thru the hull. Is there a metal strip running the length of your keel..? Is your ballast iron or lead and somehow tied into the electrical system..? Sometimes this is intentionally done to create a 'radio ground plane' and/or lightening protection for metal masts. If not well isolated from seawater contact by hull coatings, which may have been intentionally removed on purpose to enhance seawater contact, you have a connection between that mass and your metal shaft/prop for example. In the simplest terms, electrically induced corrosion, which is a natural chemical/electrical process of two or more 'dissimilar' metals immersed in an electrolyte (...of which sea water is a very-very strong electrolyte....) can eat away an amazing amount of surface metal in short order, as you have seen. Throw in the charging (or battery bank) system 'stray' voltages, which can be very significant during recharging batteries, and this corrosion can really take off. Also, some vessels (steel/aluminum) may be surface preserved in such a way that no hull metal contacts the seawater. But heeled-over & wet, now a 'circuit' exists. some hull designs have steel underwater, yet all above deck structures are aluminum to reduce tip over moments...very tough to protect these designs from literally eating themselves to death. So thoroughly survey for ALL metal objects, including metal anchor chains & anchor immersed in the sea. Any and all can 'complete the circuit' needed to cause this corrosion in the first place....which may only occur "at anchor' for example. Ironically, interconnecting all these metal objects can literally be the very source of your problem(s). More is not necessarily better in this case. Sometimes 'isolation' is the simplest cure.....

The boat is fully bonded, that is, every bronze seacock it attached to the keel and engine block. The rudder post is stainless steel and not bonded. Neither is the anchor, which I understand is more common. I have also determined that the issue certainly accelerates while motoring versus sitting at anchor. Not saying the non-engine related corrosion isn't happening, but that it isn't currently the biggest issue.

[GordMay]

Originally Posted by Mojadito

Try adding a shaft wiper, bonded to the ships bonding system

See ➥ http://www.cruisersforum.com/forums/...haft-9124.html

[senormechanico]

What kind of alternator gets too hot after pumping out only 30 amps for awhile?
Imo, that ought to be a red flag.
Are you SURE it's really only putting out 30, or are you trusting a gauge?
Try a clamp ammeter on the positive and then ALSO the negative outputs.

[fallingeggs]

Question: is there any way to test for stray leaks in the ignition system or alternator while on the hard? My silver chloride won't be much of a help here...

[foggysail]

Originally Posted by Mojadito

Try adding a shaft wiper, bonded to the ships bonding system

Yes.....and eliminate the need for shaft anodes for galvanic corrosion protection although anodes will still be needed elsewhere such as a so called diver's plate.

[zeehag]

mine used to eat zincs---UNTIL i had a wonderful electrickery expert clean and straighten and add an external regulator to my alternator. now it is a 1.5 year adventure for replacement. beats 2 months or less, which was happening before the housecleaning in electrickery. mine does not eat zincs while under way or in a "hot basin" marina.

[Fuss]

Originally Posted by fallingeggs

I chew through a set of prop and shaft zincs in about 20 hours of motoring.

At first I blamed this on other boats in the marina, but I have come to the conclusion that it is me. I purchased a silver-chorine anode, and have used it to test every electrical component on my boat across various anchorages over the past month.

After flipping on and off every breaker and running each electrical component individually, the only thing that causes a voltage drop between the submerged anode and the engine block ground is running the engine itself.

With a fresh set of prop and shaft zincs, I read about -700mv with my silver-chlorine anodes, which is well within the "safe" range for my fiberglass boat according to the kit. Running the engine, I drop to -500mv or so, below the safe range for my bronze prop.

My engine is the original Westerbeke 33 from 1983, still with its original, case ground, 55amp alt. I figure the grounding among the alternator, the engine block and the DC system has a lot of corrosion, causing the voltage drop, with the leak through the shaft and prop.

Thinking I need to reduce the electrical resistance, I ran 8 awg wire from the bolt on the tensioner arm to the DC system's grounding point on the block. This grounding point is a tab bolted to the back of the engine block, in between the block and the transmission. (I also ran some 8 awg wire from the positive post on the alt to the positive post on the starter, to lower resistance into the battery bank, but I doubt this was the issue.) I also have new 0/2 awg cable between the block ground and the battery bank.

This additional wire didn't do much to solve my voltage drop issue. The boat is now on the hard till October, and I'm sitting here in my hurricane hole thinking of next steps.

I suppose I can remove the alternation and grounding tab in order to sand/grind it's connection points to lower the electrical resistance.

Anyone have additional ideas? Maybe my jumper wire needs to be attached between the alt and the block, rather than the tensioner arm?

You have to find the exact cause before attempting to fix it with some ideas.

Eating the anodes within 20 hours indicates a major problem. If you were not able to find it with the silver anode tester then you need to employ an expert as normally, with some connecting and disconnecting, it is possible to isolate the exact cause. This should have been possible when the boat was in the water and this exact cause you need to know. The job is now made more difficult by not being in the water.

I assume the problem has not been happening since 1983, so the cause is something that has been done or something that changed. wires immersed in water are a common cause.
My advice would be to get your silver silver chloride half cell meter tested and employ an expert. Ask the aluminium boat owners, some of them know this stuff.
ps... if the aluminium boat owner has anodes dangling over the side, do not ask them as they also don't know.

[jenniferoberoi]

See if the same issue applies. Try running the engine with the alternator drive belt disconnected.