How much stray voltage is acceptable?

[nuru05]

It would seem I have about 0.2v DC of stray voltage when I test from my compression post to my keel bolts. I can’t seem to find my ground strap so I’m going to do some digging, but my question is; is this enough to be worried about? Or will my anodes just take care of it?

[GordMay]

IIRC; A typical rule of thumb, is that voltage differences of 0.2 Volts [200mV], or more, suggest a galvanic corrosion risk.
Generally speaking, the further apart the metals, in the galvanic series, the greater the risk of corrosion, with the metal being of least noble [Anodic] class, typically, corroding.

The voltage potential, between stainless steel [keel bolts?], and aluminum [compression post?], is in the range of 0.5 to 1.0 V, depending on the exact alloys involved, and can cause considerable corrosion. within months, under unfavorable conditions.

For example, suppose we have an aluminum alloy with a voltage range of -0.7 to -0.9 V (an average of -0.8 V) as shown on the series, coupled to a 300 series stainless steel with an average voltage of -0.07 V. The Galvanic Series predicts that aluminum will be the anode, and the voltage difference between the two alloys will be about 0.73 V (obtained by subtracting the two average voltages). It is this voltage difference that drives the current flow to accelerate corrosion of the anodic metal.

The two major factors, affecting the severity of galvanic corrosion are
1) the voltage difference between the two metals on the Galvanic Series,
2) the size of the exposed area of cathodic metal relative to that of the anodic metal.

BTW: CF member < boatpoker > is an expert in marine corrosion [ABYC Certified Corrosion Analyst], and more.