Electrolysis

[ECGirlatHeart]

This is going to be strange, but I am posting this for my father, who is currently working on his sailboat out East and doesn't have the internet currently. He has asked if I could post to get some help to relay to him. His boat is a 41' DS hunter 2006.

His prop is needing replaced and was so bad that the surveyor could break a piece off. He is now concerned this was caused from Electrolysis. Thoughts?

The boat is currently out of the water getting repaired. Anyway for him to do some checks and make sure that his boat isn't causing the issue if it is Electrolysis in the water.

Last questions....if you had a 50hz transfer on a 60hz circuit would this cause the damage?

Thanks!

[GordMay]

Greetings and welcome aboard the CF, ECGirl.

Transformers rated at 60Hz should not be used on a 50Hz supply due to higher losses and core saturation, and the resultant higher temperature rise.
Transformers rated for 50Hz, however, can be safely operated on a 60Hz supply. In fact, a transformer designed to run at 50Hz will run cooler at 60Hz (at the same voltage).

[Sailmonkey]

You're suffering from stray current corrosion. Almost exclusively caused by D.C., not AC.

To locate the source you'll need a silver chloride half cell and a multimeter.

There's a simple write up here

http://www.frankshospitalworkshop.co...%20Systems.pdf

And a reference cell here

http://www.boatzincs.com/corrosion-r...ode-specs.html

[Badsanta]

When was the last time you replaced your zinc's?

[boatpoker]

Originally Posted by Sailmonkey

You're suffering from stray current corrosion. Almost exclusively caused by D.C., not AC.

To locate the source you'll need a silver chloride half cell and a multimeter.

There's a simple write up here

http://www.frankshospitalworkshop.co...%20Systems.pdf

And a reference cell here

Corrosion Reference Electrode Product Specifications

Sailmonkey is absolutely correct. You are dealing with stray current. Renewing anodes will not protect you from this issue.

Do NOT hire anyone to address this issue if he uses the term "Electrolysis", they clearly do not understand the issue.
.
I am a Certified Corrosion Analyst. The first thing they tell you in class is that use of that term is an automatic failure. It is the most misunderstood term in boating. That term relates to a chemical change in an electrolyte, not what is occurring at a cathode or anode.

[Captsteve53]

Above posts are all good input, how ever you didn't state what material the propeller was made from? as this can have a bearing on the longevity,

Also did the shaft have zinc's or not?

ALL PROPELLERS ARE NOT MANUFACTURED EQUAL:

Normal displacement vessels have one of the following

1) Manganese Bronze. This material is moderately heavy and moderately strong. It is the least expensive of the bronze materials and is quite repairable. It's main ingredients are copper and zinc. With a lack of protection, the zinc content in the material will act as an anode to protect other underwater metals on your boat leaving oxidized copper behind. This is indicated by a pink coloring to the propeller. After enough corrosion takes place, the propeller will be brittle and need to be replaced.
2) Nibral (nickel aluminum bronze). This material is lighter and stronger than manganese bronze. It is more expensive than manganese bronze, and is quite repairable. It's main ingredients are copper, aluminum, and a small amount of nickel. Due to it's higher copper content, it's more corrosion resistant than manganese bronze, but left unprotected the aluminum can act as an anode to protect other underwater metals on your boat. This is indicated by dark craters on the surface of the material ringed with a green color. Left long enough, these craters will go right through the propeller, and it will have to be replaced.

Cheers Steve

[jkindredpdx]

Originally Posted by boatpoker

Sailmonkey is absolutely correct. You are dealing with stray current. Renewing anodes will not protect you from this issue.

Do NOT hire anyone to address this issue if he uses the term "Electrolysis", they clearly do not understand the issue.
.
I am a Certified Corrosion Analyst. The first thing they tell you in class is that use of that term is an automatic failure. It is the most misunderstood term in boating. That term relates to a chemical change in an electrolyte, not what is occurring at a cathode or anode.

With destruction of the prop on a GRP boat would the stray current most likely be from the Engine? How can we tell if the problem is stray current or galvanic corrosion?

[Captsteve53]

Simply Galvanic corrosion Requires:
1) Two different metals (electrodes)
2) Immersed in current-carrying solution (electrolyte)
3) Interconnected by a current-carrying conductor
4)Expect corrosion with 0.25 V difference
5) Most negative electrodes will decompose
A) Magnesium @ - 1.50 V for freshwater
B) Zinc @ - 1.03 V for saltwater
C) Aluminum @ - 0.75 V will decompose if neither
D)magnesium or zinc are present
6) Zinc (or magnesium) will protect
A) Stainless steel shaft
B) Bronze propeller
C) Aluminum out-drive

Controlling Galvanic Corrosion
• Types of Metal
• Area of Metals
• Self-Destroying Metals
• Use of Sacrificial Anodes
• Indirect Cathodic Protection
• Resistance of an Electrical Path
• Between boats

STRAY CURRENT CORROSION
Requires
1)External source of electricity
2)From wetted metal surface (electrodes)
3)To return circuit of lower potential(ELECTROLYTE)

Stray current corrosion is more destructive

1) Hundreds of times stronger
2) Galvanic potential difference 0.25 to 1.5 volts
3) Stray current from 12 volt battery
• Sources of stray current
1) Internal from boat’s 12 volt battery and defective wiring
2) External to boat from another source of DC

FURTHER NOTES
Stronger than Galvanic current
 100 times more destructive
• Metals can be similar or dissimilar
 Current flow from positive through electrolyte
 Positive DC terminal will corrode
 Both AC terminals will corrode
• Electrolyte is any moist surface
 Bilge water
 Wet wood
 Wet or moist surface

Preventing Stray Current
• Wiring
• Bonding
• Battery charger
• Galvanic isolators
• Isolation transformers
Defective wiring is the most common cause
 Deteriorated insulation on hot wire
 Always use marine grade wires
• Run wires above water line
 Moist or wetted surfaces conduct current
 Moisture in loose connections will cause
corrosion
• Wires in bilge
 Waterproof terminals and butt spices
 Heat shrink tubing is 2nd choice
 Liquid electrical tape is also an option
 Electrical tape is inadequate

[Captsteve53]

After all that forgot about the testing: There are portable and built in corrosion meters available to monitor proper zinc protection. Or, learning how to use a good multi-meter (preferably digital)with a half-cell (zinc or silver/silver chloride are most common in the USA) is the key to solving current problems.

Many selling the half -cell provide a good reference guide on it's use

Cheers Steve

[boatpoker]

Originally Posted by jkindredpdx

With destruction of the prop on a GRP boat would the stray current most likely be from the Engine? How can we tell if the problem is stray current or galvanic corrosion?

One of the better layman's articles on how to do it from BoatUS