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Subject: Re: TWL: Bonding
From: Arild Jensen (elnav@XXX.XXX)
Date: Fri Mar 29 2002 - 18:04:57 EST
Michael Wilkie asked:
> Dancin' Dolphin was a fresh water boat until about 2 months ago and is now
> in salt water. While in the engine room the other day, I noticed new
> blue/green coloring on some of the metal work, especially the bronze and
> brass. Is this normal or a sign of poor bonding? Though all is wired bonded
> back to a large zinc on the transom.
REPLY
There is an easy way to check if your bonding system is intact.
You can check the millivolt reading at each of the fittings compared to a small zinc piece hung
in the seawater. Connect one lead of the digital voltmeter to this separate zinc piece while the
other lead is used with an extension lead to check each fitting.
All the fittings that are bonded will have a voltage reading very similar to the reading at the
connection to your zinc anode. If the bonding is not intact then you will see a difference.
If active galvanic corrosion is taking place then you will see a potential of more than a hundred
millivolts.
This is the same method as what is provided by Electro Guard. They supply a Fluke multi meter
and a small zinc "reference cell"; package the whole into a nice looking plastic case and
charge a LOT for it.
The normal galvanic test kit uses a silver/silver chloride half cell for a reference. The only
difference between the two is that the two reference cells are at opposite endss of the galvanic
series table.
What you are looking for is the "difference" between metallic fittings submerged in salt water.
The appearance of blue/green coloring is not a positive indication of galvanic corrosion.
This verdigris can also happen to isolated pieces that are merely reacting with the salt air.
Arild
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