Galvanic Isolator Useful in Fresh Water?

[TejasSailer]

The question is to what extend would a galvanic isolator by useful in fresh water.

[ottos]

I'm no expert (they'll be along soon) but you need zincs in fresh water, don't you? (aluminum or magnesium - I forget which)

If the guy in the slip next to doesn't use/maintain them, you'll be losing your zincs twice as fast if you're connected to shore power....

There is another thread discussing this right now - do a search. It is very informative.

[mitiempo]

A galvanic isolator will prevent corrosion on YOUR underwater metal parts caused by stray current from YOUR boat. It does not solve problems from other boats nearby or those caused by marina power issues. I would install one wherever I tied up regularly, fresh or salt. As well as an anode or 2 on the shaft.

As far as which material the anode should be made of, it seems there is not a simple answer. Here are links to 2 charts. The first is for boats with shorepower and without a galvanic isolator here http://www.boatzincs.com/pdfs/Chart_...ould_I_Use.pdf Use column 1 for most boats.

For those without shorepower or with shorepower and a galvanic isolator the recommendations are here, again column 1. http://www.boatzincs.com/pdfs/Chart_...ould_I_Use.pdf

[fairbank56]

Originally Posted by mitiempo

A galvanic isolator will prevent corrosion on YOUR underwater metal parts caused by stray current from YOUR boat. It does not solve problems from other boats nearby or those caused by marina power issues.

A galvanic isolator is still useful in fresh water as fresh water has minerals which will conduct electricity. Galvanic currents are directly caused by the "weak battery" made by your boat's underwater bonded metal fittings, the shore power ground conductor, and other boats/structures connected to this common ground. Stray current is another issue entirely. The distinction between galvanic current and stray current has been skewed by mis-information.

From ABYC documentation:

"The electrical connection that occurs via shore power cables from the dock may result in a galvanic couple between the boat and dock structure or another boat. This can lead to excessive anode loss, or corrosion beyond the capacity of the boat's cathodic protection system. A galvanic isolator or isolation transformer can be used to break this couple."

"Stray Current Corrosion - Corrosion that results when a current from a battery or other external electrical (DC) source causes a metal in contact with an electrolyte to become anodic with respect to another metal in contact with the same electrolyte."

"Boats equipped to use dockside power are subject to galvanic corrosion because the boat ground is electrically connected to the shore ground via the grounding conductor. A galvanic isolator may be used to reduce this problem"

Eric

[ottos]

This was the thread I was referring to..link