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Bertram31.com General Bulletin Board
Re: Propeller Electrolysis
Posted By: Vic Roy In Response To: Re: Propeller Electrolysis (mike ohlstein)
Date: Tuesday, 22 November 2005, at 5:27 p.m.
Alright, guys, it's easy to tell when the weather gets bad in yankeeland, no need to watch the weather channel, just look at this site.
Prof - the reason the Nibrals are more subject to the galvanic action is nibral is an alloy of nickel, brass (an alloy of copper and tin itself) and aluminum. The aluminum in the allow is the least noble of the metals there, absent from brass or bronze, so more corrosion.
Now to the TefGel conductive debate. TefGel is non conductive to RF frequency currents such as the static electrcity type that causes galvanic corrosion between dissimilar metals. Which is why it works in the first place. It electrically isolates the two dissimilar metals and prevents the 'battery' effect that is the heart of galvanic corrosion and why your car starts when you turn the key.
I have a BK super duper VOM that will read ohms down to tenths. The leads themselves read 0.6 ohms. I just put some TefGel on some clean paper and could not get it to read any conductivity no matter how close it got the leads to each other. All that means it will not conduct 9VDC, which is what the internal battery puts out thru the leads to test the level of resistance between the leads.
Now, for some sense to all this. Dissimilar metals immersed in a conductive fluid, say your Nibral prop in salt water next to your stainless shaft - are going to create a battery effect that will attempt to erode the less noble metal and plate it on the more noble. We put zincs (a metal very low on the periodic table of nobility) in the mix to allow it to be eroded and plated on the more noble metals. That is why it is called a sacrificial zinc - we sacrifice the trhow away zine to save the Nibral and stainless or bronze.
It makes ZERO difference if the Nibral prop is electrically conductive to the stainless shaft as far as galvanic corrosion is concerned AS LONG AS BOTH are fully in electrical (thru the water) contact with the zincs. The zincs will go, not the good stuff. Now on the other hand, if no zincs are present, isloating the joint between the dissimilar metals with TefGel is critical, since the battery effect will take place at the dissimilar metals joint.
My view is that TefGel should always be the material of choice between any dissimilar metal anywhere on the boat, above or below the waterline. It is simple physics, right Prof?
UV
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