Corrosion!!!

[Dan]

I kept my boat, covered, in the water this winter. I recently inspected some of the seacocks and found them to be TEAL colored! I'm anxious about the corrosion I didn't see. My shorepower cable, which I basically used just to charge the batteries, had corrosion as well. What did I do wrong? How worried should I be? What do I do?Any and all advice would be appreciated.

 

[Ross]

Were deicers deployed in the water around the boats?

Have you "picked" at the green to see what it looks like underneath? A nice mossy green doesn't hurt most copper alloys but high zinc content brasses turn green and then fall apart. If the insides appear to be ok then examine the outsides. Stray AC can erode metal under water at astonishing speeds.

 

[Joseph Shirley]

Some questions

Do you have your hull fittings grounded (should be)? and if so, do you use a Galvanic Isolator or some type of an AC Neutral disconnect on your shore power (should have)? If yes, and then no, there may have been a short, or current bleed over in the AC circuit on the dock, which could charge your through hulls, making them the plate part of a battery.

 

[RichH]

Couple of thing could have happened .....

The blue green that forms on bronze (verdigris) is a reaction of the copper with acetate (in the seawater) and in the wet ambient air. Copper acetates range in color from green to blue. Neutral verdigris is Cu(CH3COO)2· H2O, and basic verdigris contains more Cu(OH)2 and H2O ... and can be brownish. If you left an open bottle of vinegar on board the verdigris would have been 'stupendous'. That you were apparently charging the batteries all winter, may have caused the ambient atmosphere to become higher in 'acid' molecules to freely migrate throughout the boat. ... and the result 'may' be only cosmetic Another possibility could be that the battery tops became wetted, contained minute amounts of acid and the current began to leak across the 'wetness' across the batteries and other parts of the boat. Most 'bronzes' have a wee bit of zinc to aid 'machinability', zinc would be the sacrificial anode with galvanic corrosion .... so If you had a 'leak', had galvanic corrosion and your zincs are 'gone', the zinc IN the bronze will surely be gone ..... So, when you haul the boat, slightly sand the throughhulls and see what 'color' results. If visually the bronze sands to a yellowish color, you are probably OK; if it sands to a 'reddish' color, then suspect that somehow there was a galvanic reaction and the thoughhulls should be highly suspect. Most bronze will 'ring' when tapped with a hammer; if the sanded through hulls look reddish and when you tap them with a hammer if the sound is 'dull' you 'may' have extracted the zinc from the casting and the casting is now 'spongey'/weakened. Its a very subjective call. My personal read would be if the external portion of the throughhull can be sanded to show a 'brassy-yellowish look' then OK ... if not, make a decision.

 

[Joseph Shirley]

I haven't worked in a bronze foundry since about 1968 but

It seems to me that I recall Naval Bronze and Red Bronze were both reddish. Manganese and Aluminum bronzes were yellowish. The red Bronzes had more copper and almost no zinc if any. The yellow bronzes were harder and stronger, had less copper and more zinc. Through hulls used to be made from the red bronzes. The yellow were used for props an bells and such. They were the bronzes with the ring.The red bronze parts were expensive and fell into disfavor because of costs. Naval bronze had a tight surface but a slightly porous interior so were cast close to the finished size and machined only lightly. Just thought I'd let you know that all bronze that sands red is not damaged. Brass and Yellow bronze can look similar but brass is totally useless in salt water. It has high zinc which dissipates rapidly in solution.Good red bronze fittings for underwater are getting hard to findTry to clean the fittings first without sanding, and inspect them for pitting.Joe S

 

[Dan]

Thank you, everyone.

So . . . .1. I need to check the integrity and quality of the thruhull; the discoloration may be nothing to worry about, or it may be very unpleasant2. I need to check for AC current bleed (not sure how, but I'll look into it). I think this is too critical for me to learn on the job -- too much at stake. I'll bring in a pro to render an opinion.Thanks, all.

 

[Joseph Shirley]

Dan, you can't really check for AC current bleed.

It May have been caused by someone else's connection and might all be gone. The point is that you should have a Galvanic Isolator on the neutral lead to isolate your boat from those kind of problems. Without one a short on the dock could kill a diver working on your boat. You might not need one if you are not plugged in all the time, but they are something you should have.Joe S

 

[RichH]

Red Bronze

is a misnomer as its real name is Red Brass or Silicon Red Brass. It can have up to 20% zinc content. Beware of any 'bronze' for underwater service that is 'red'.

 

[Ross]

Everything you ever wanted to know about copper

alloys but were afraid someone would tell you.http://www.anchorbronze.com/products.htm

 

[Joseph Shirley]

Ross, Thanks for the link, I hoped someone would look it up

When I designed marine products for Merriman we had our own Bronze Foundry. We made Lubrite bearings for Bridges, Sintered metal products (like Textile Rings, Gears and the like) and Marine Hardware. Before that I had been a QC Engineer at General Dynamics Electric Boat, in the Foundry/machine shop areas. I'm a little rusty now but haven't fotgotten everything.Rich, you're right about the name of red brass, but I used the name Red Bronze deliberately. If you access Ross's link, you will see that Leaded Red Brass has a minimum of 84% copper and a maximum of 6% zinc and it is used for marine fittings. It has a good resistance to salt water corrosion so I called it bronze. High strength Manganise Bronze on the other hand which you might find in propellers, has only 60% copper and 22% zinc, and is not so good, as are many other of the yellow bronzes. So I'm sorry to say, your statement, though well intended, is incorrect, and the point I was trying to make, is that through hulls may properly be red. I hope you don't take offense.Joe S

 

[RichH]

Joe -- You're not going to believe this ....

In 1968, I was a chemist at Phila. Bronze and Brass (Ampco Metals) and we supplied EB with our 'famous' NiAlBronze for critical SALT WATER service !!!!! , ..... plus a 'shippot full' of CuNi and monel castings. ..... small world. I'll still stand by the 'red brass' as they are subject to severe 'dezincing' by galvanic action.