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Go Back   SailNet Community > On Board > Gear & Maintenance > zincs for lead.
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Thread: zincs for lead. Reply to Thread
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Topic Review (Newest First)
10-10-2006 11:36 AM
hellosailor Rockter, I appreciate your politeness. Try loosening the necktie, pouring a glass of recreational beverage, put on some soothing music (be it Grateful Dead or Beethoven, either will do) and read this again:

The correct kind of stainless is bronze.

I *know* that bronze is not stainless, that's what I'm saying. For some applications, the only correct type of stainless steel to use is (not stainless, it is) BRONZE.

You know, like when they say "The best man for the job is a woman" ?

I'll give you the doctor's note, it's time for a vacation!
10-10-2006 10:48 AM
Rockter I don't know what point you are trying to make here, but it looks very negative.

I was trying to be polite.

Bronze has never been a stainless steel, you see. Stainless is nprmally shiny (not always) and bright. Bronze has a coppery look about it. Bronze has lots of copper and tin in it, stainless steel does not... the chrome makes it shiny if you polish it. Indeed I have been on my boat and had a bonmze fitting in my right hand, and a stainless chainplate in my left. The bronze (to the right as I looked) kinda looked yellowy. The stainless (to the left as I looked) was all shiny like... you could see your face in it you see. I have witnesses too. Indeed there were three of us, and the other two nodded when I said that they looked different. Bronze it like that you see... the copper in it makes it look sort of yellow.

The prop shaft on my boat is all shiny like, and it's not yellowy. It's got a big pit in it too. That's where it was starved of oxygen in the presence of salt water (chlorides, like). It's not a crack... it a big pit. Keelbolts are like that, they tend to get wet and boats go out in the sea... salty, like. Keelbolts lile in bilges, bilges are wet, bilges often get oxygen starved.

I have a bolt that served for a while as a fastener for the sternplate. It's virtually eaten through, and still shiny. It's like 3/4" thick. It's stainless. It's not the stuff I'd dare use for keelbolts. Maybe duplex would work, but not that stuff.
10-09-2006 02:06 PM
hellosailor Rockter-
"Marine bronze is a bronze. I don't think it's a stainless steel."
My point exactly. (I have a good poker face online, don't I?)

Andrew-
Bear in mind that the lead used in "lead" keels is not 100% pure lead, it has substantial amounts of other materials, some by intent, some by accident. As I understand it, keels aren't considered a critical alloy and that means recycled lead, tire weights with antimony and other content, etc., may all be in there. I'd want to look into exactly what alloy was being tested/used before taking any test as "substantially" correct. (Perhaps you'd know?)

I know lead isn't totally inert, but who runs around with a bare lead keel anyhow? There's usually a heavy layer of old paint and more copper-bearing bottom paint over the lead, which essentially jackets it in sacrificial copper versus any stray current to other parts of the boat. And only a fool (or a prop saft salesman?) would be running a metal shaft and dissimilar metal prop without some zincs up there...wouldn't that make the lead keel a "distant" issue? Literally?

Keelbolts are theoretically embedded dry, solid, "bonded" by the lead cooling around them as they are cast in place. Galvanic corrosion in there shouldn't be a problem unless you like to keep a wet bilge. Heck, the classic way to build wrought iron fences was to pour molten lead into the ground (or masonry) and then stand the wrought iron in the lead, cast in place. When fencework is done that way it lasts hundreds of years, versus rusting out in a decade when the same ironwork is simply embedded in concrete or cement (the modern way). Lead and iron manage to live together very nicely.
10-09-2006 12:36 PM
Fstbttms
Quote:
Originally Posted by andrewburcham
Anyone else have thoughts on this?
Are SS keelbolts used in conjunction with a lead keel an unusual situation? I cannot remember ever seeing a lead keel suffering significant galvanic corrosion.
10-09-2006 07:02 AM
Rockter Marine bronze is a bronze. I don't think it's a stainless steel.

It's probably not a bad material for the keel bolts, but I am sure it will not be as stiff.... it will have a lower elastic constant.
10-09-2006 12:49 AM
andrewburcham
SS+Lead=Battery, No?

Based on my experience, and my understanding of the galvanic table, lead and stainless (or bronze, titanium, etc) creates a battery. In this situation your lead will be anodic, and will slowly eat away. I suppose an upside is that your SS will be safe . I would be very careful to have a well zinc'd underbody to prevent the degredation of your keel. Note: this will occur whether or not your SS and lead are bonded.

Lead has a galvanic potential of ~-0.2 and your other metals will be slightly above 0. This gives you a nominal potential of >0.2V.

See this link for more info:
http://www.corrosionsource.com/handbook/galv_series.htm

On a recent underwater experiment that I participated in, a series of lead pigs, secured with SS bolts were left in the marine environment for a month. When everything came out of the water, the lead pigs had about 10% of thier volume eaten away.

Anyone else have thoughts on this?
10-08-2006 09:25 PM
hellosailor AFAIK the correct grade of stainless for keel bolts is called "marine bronze". Like the stainless kitchen knives with horrible perpetually dual edges that were oh-the-rage after WW2...stainless just isn't always the right answer even if it sells well to the public. MARS Metals, the keel folks, probably could tell you where they obtain keel bolts from.

For prop shafts I think the trade name "Aquamet" is one of the known and proven shaft materials. Prop shafts are probably easier to obtain than similar size alloy rods, is there really any savings to trying to DIY on this?
10-08-2006 08:07 PM
waiatarua
bolts

One other possibility Titanium bolts?
10-08-2006 08:05 PM
waiatarua
bolts

I am new but if you use 303 stainless for bolts would this work?
10-08-2006 07:51 PM
Rockter Gosh Captain Dave, you really must have your eyes open much wider than mine.

As it is, I can see a big corrosion pit on the propshaft of my boat.

You see cracks where the motor is out of line or having run into something.

I remember lining it up with a feeler guage a while back, and I don't remember running into anything.

Hell, maybe it is all bent and haven't noticed and maybe that big corrosion pit really is a crack.
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