Why do bronze fittings collect barnacles ?

[s/v Beth]

Bronze is a copper alloy , isn't copper toxic to the undersea critters? Why do I get barnacles on my thru hulls and prop then?

[Blue Stocking]

They are all addicts--can't say no

[Wotname]

Originally Posted by s/v Beth

Bronze is a copper alloy , isn't copper toxic to the undersea critters? Why do I get barnacles on my thru hulls and prop then?

As I understand it, the cooper itself isn't toxic to the critters, rather it is one of the compounds that copper degrades to in the presence of seawater that further degrades into "sumthink else" that is toxic to the little guys.

The copper in bronze is "locked" in there and so doesn't degrade as does pure copper.

You might notice that I don't recall my chemistry so well anymore .

FWIW, I had my bronze prop copper plated and had zero barnacles for about 18 months, after that they started appearing; slowly at first, then in droves.

[Stumble]

For copper to be toxic your really need two things. First you really need to have a specific form of copper, cupric ion ( cu++), this form is almost exclusively what you would find in anti-fouling paint. However it is mostly absent from coast copper and bronze parts, since the ions bond with other metals in the manufacturing process.

Secondly the copper needs to be freely available to react with the organism. In an alloy the copper is mostly bound to the other metals, there is no free copper to react. A cast part also has pretty minimal surface area compared to the small particles you would find in copper paint.

[s/v Beth]

Fair enough, then how come pure copper strips work then? I am sure only a small part of the metal is broken down into the cupric ion....

[Hudson Force]

I think the answer is that the surface of the copper is subject to oxidation. The active ingredient in the antifouling paints is cupric oxide. In this form it easily disassociates or ionizes.

[wsmurdoch]

I have a copper grounding plate on my sailboat which is perhaps 6"x16" and half an inch thick. The barnacles love it; maybe more than my bronze propeller and thru hulls. They cover it completely in a month or two. A sharp putty knife removes them with little trouble. That said, no shipworm has ever bored a hole in the plate.

Bill Murdoch
www.irish-eyes-to-the-bahamas.blogspot.com

[Wotname]

Originally Posted by wsmurdoch

I have a copper grounding plate on my sailboat which is perhaps 6"x16" and half an inch thick. The barnacles love it; maybe more than my bronze propeller and thru hulls. They cover it completely in a month or two. A sharp putty knife removes them with little trouble. That said, no shipworm has ever bored a hole in the plate.

Bill Murdoch
www.irish-eyes-to-the-bahamas.blogspot.com

Are you sure it is copper, most aren't?
At least most that I have seen aren't; maybe it's different in your part of the world.

[Wotname]

From the Coppercoat website:
"sea water attacks the exposed pure copper powder, causing the formation of cuprous oxide. This highly effective anti-fouling agent deters growth until the surface degrades further to become cupric hydrochloride. This final copper form is highly unstable, and is washed away by the movement of the yacht, thereby removing any accumulating silt or slime. This automatically reveals a fresh copper-rich surface whereby the process recommences"

As the powder in coppercoat is (almost) pure copper, then I would expect pure copper sheet to react in the same manner.

[wsmurdoch]

Yes, my grounding plate is copper -- nice red copper. The boat originally had a Dynaplate grounding plate. At survey in 2004 it was recommended that it be replaced due to corrosion. The Dynaplates were quite expensive, and I had some doubts about the effectiveness of their extended area. I bought a larger piece of copper, drilled and tapped holes in it for two pieces of bronze all thread that pass through the holes in the hull left from the Dynaplate, and connect to a copper grounding bus inside the hull. Wires from the mast, the under water fittings, and the enigne connect to that bus.

Bill Murdoch

[s/v Beth]

So the ships of antiquity were not getting rid of barnacles with their copper strips, they were just getting rid of the worms. That makes sense. Just looking for better ways to keep my keel clean. Thanks for the input.

[delmarrey]

Originally Posted by s/v Beth

So the ships of antiquity were not getting rid of barnacles with their copper strips, they were just getting rid of the worms. That makes sense. Just looking for better ways to keep my keel clean. Thanks for the input.

Hopefully the bottom paint industry will come up with something soon. The politicians are making it even harder to keep the keel clean.

[Astrid]

So the ships of antiquity were not getting rid of barnacles with their copper strips, they were just getting rid of the worms. That makes sense. Just looking for better ways to keep my keel clean. Thanks for the input.

Yes--coppering a ship's bottom back in the 1700s and 1800s was mostly to protect against shipworm. Any anti-fouling benefit was simply icing on the cake so to speak.

[Hudson Force]

'just to toss in a little more confusion. The shipworms are bivalve mollusks like clams and not worms at all.

[Cheechako]

Originally Posted by s/v Beth

Bronze is a copper alloy , isn't copper toxic to the undersea critters? Why do I get barnacles on my thru hulls and prop then?

Just like bottom paint, it takes a while to kill them. Sometimes they get quite big before they die! Regarding copper fittings, ....that would be If they die at all. I understand it's the Cuprous Oxide that kills... a fitting would have to create enough of that (green stuff) to do the job.
re: Copper strips: the copper strips used on ships of old kept the worms from eating into the wood, not so much by killing them as by creating a barrier.