Aluminium Hull protection

rick gray · Jun 13, 2017

CDK said: ↑

I see no reason why the hull should not be used as a return path for electrical circuits. Aluminum is an excellent conductor, more that 6 times better than steel, so the voltage drop for all usual DC loads (except starter motors) is virtually zero.
There is however another issue that needs to be addressed: any fasteners used must also be aluminum. Especially stainless bolts and nut must be avoided unless they are packed in grease and protected against moisture.
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WHAT?? no SS fasteners? I heard they were OK below W.L? Rick

IronPrice · Jul 23, 2017

CDK said: ↑

We were discussing zinc for hull protection.

On an outboard there is a shaft and sometimes a prop and ss bolts or nuts, each of them creating a galvanic element with the light alloy. Without zinc, the outboard body would be the sacrificial electrode as soon as the paint is scratched.
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The outboard is attached to the hull by metal fasteners ... so the hull, and the various metals in the outboard are electrically connected.

Cruisingsailor · Jun 13, 2024

CDK said: ↑

We were discussing zinc for hull protection.

On an outboard there is a shaft and sometimes a prop and ss bolts or nuts, each of them creating a galvanic element with the light alloy. Without zinc, the outboard body would be the sacrificial electrode as soon as the paint is scratched.
Zinc does not give 100% protection; in the 80's there have been Mercruiser drives that were eaten within a few years although they all had a zinc trim tab and a zinc plate. The alloy itself also contained a lot of zinc, so the electrical potential between the drive and the trim tab was too low to be effective.
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Hi, I know I am years late on this forum. I'm just really trying to get my head around your comment 'zinc's for aluminium hull protection are a waste of time' - I am very much interested in finding out more about this as I am currently looking at buying an aluminium boat which has no anodes and no fixtures for anodes.
You described above the scenario of an outboard engine with dissimilar metals. Are you saying that the anodes on an aluminium boat are not necessary because there are no other dissimilar metals electrically connected and also underwater?

If the boat is connected to shore power without a galvanic isolator or isolation transformer would this not also be a source of possibly eating the aluminium hull instead of a an anode fastened to the hull ?
Thank you

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Aluminium Hull protection

rick gray Junior Member

IronPrice Senior Member

Cruisingsailor New Member

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