Eating through zincs - Need some ideas

[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?

[AndyEss]

The forum suggested similar topics include "Eating fish", "Mussel eating mackerel" and "wood eating insects aboard".
Possibly there might be ideas in those threads that don't include the obvious first things to do - clean up corroded connection points.
Dribble hot sauce on wiring?
Spray insecticide on connections?

[Cavalier]

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?

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

[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?

[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.

[SailingFan]

[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

[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.

[Mojadito]

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

[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

[Cadence]

Originally Posted by AndyEss

The forum suggested similar topics include "Eating fish", "Mussel eating mackerel" and "wood eating insects aboard".
Possibly there might be ideas in those threads that don't include the obvious first things to do - clean up corroded connection points.
Dribble hot sauce on wiring?
Spray insecticide on connections?

Clean up corroded connection points. it's the place to start.

[jmschmidt]

Try a spring contact that rides on the prop shaft with a direct connection to the engine block ground point? Maybe?

[buzzstar]

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

[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

[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.....