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Old 23-10-2013, 11:40   #16
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Re: What's the Best Way to Protect Keel Bolts ?

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Originally Posted by S/V Illusion View Post
It is the oxygen which renews the oxide layer protecting the steel; without it, you lose all protection. This isn't a generalization; it is a fact as is the fact the steel will corrode in the absence of air. These are fundamental
truths learned both theoretically and by experience as a chemical engineer for over 30 years.
Your boat, your rules but please don't imply I am misleading anyone.
The rest of the SS bolt is sealed all the way into the keel and into the fibreglass floor; in both cases completely absent of any oxygen.

Why is it any different than sealing the top section of the bolt and nut?
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Old 23-10-2013, 13:02   #17
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Re: What's the Best Way to Protect Keel Bolts ?

In my limited understanding of the chemistry, gained from numerous posted references online, it is NOT the absence of oxygen that makes stainless fail. That's a half-truth.

Stainless fails from crevice corrosion when it is kept damp AND deprived of oxygen. That is, submerged in stagnant water like that sitting in a bilge, unpumped and unchanged for months on end while sitting in a yard. Or buried under layers of electrical tape on a swaged fitting, allowing moisture to wick in and then keeping the moisture soaking the parts.

Covering the steel while it is dry, in such a way that it is KEPT dry, can do no harm and will provide total protection for stainless. This is analogous to the condition that stainless steel bolts are in, when someone has applied threadlock or other sealants and bolted them up in threaded assemblies. SEALED and DRY.

If they needed constant oxygenation under all conditions, you'd see tiny vent holes in every threaded part that stainless bolts went into. And, no threadlock or antiseize to gum them up and block the air flow.
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Old 23-10-2013, 15:26   #18
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Re: What's the Best Way to Protect Keel Bolts ?

When I had my keel rebedded last year, the yard installed the nuts with a ton of Tef-gel and liberally coated the exposes parts of the bolt head with it too. Not sure how fast this will wear off, but I was told this is common practice.

We have a keel stepped mast and get a lot of water down the mast sheave whenever it rains. Really wish the mast had a separate sump instead of draining into the bilge.


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Old 23-10-2013, 23:33   #19
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Re: What's the Best Way to Protect Keel Bolts ?

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Originally Posted by funjohnson View Post
When I had my keel rebedded last year, the yard installed the nuts with a ton of Tef-gel and liberally coated the exposes parts of the bolt head with it too. Not sure how fast this will wear off, but I was told this is common practice.

We have a keel stepped mast and get a lot of water down the mast sheave whenever it rains. Really wish the mast had a separate sump instead of draining into the bilge.


Matt
I have the same problem. But at least it's fresh water. Other then that it's a completely dry boat.

Back to bolts being submerged, it's the salt in the water, which has gone stagnant, from sitting, that does the damage.

My keel bolts are over 30 YO and still look new from the top. Of course, they are totally nonmagnetic no matter how strong the magnet.
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Old 24-10-2013, 06:51   #20
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Re: What's the Best Way to Protect Keel Bolts ?

Lars, We were having a problem at every insurance survey with corrosion on our keelbolt heads. We attacked the problem in two ways. First, when we installed the new keelbolts, we painted the heads with an epoxy paint. Second, we installed a garboard drain at the bottom of the bilge, whose fitting we remove when the boat is stored on the hard, thus allowing any internal water accumulation to drain out, keeping the bilge dry. Just completed a new survey - No problems! George
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Old 27-10-2013, 01:26   #21
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If you have a wooden boat, fresh water can be scary as it rots wood unlike salt water. as for the bolts put some fish oil rust preventor on it. Marine waterproof grease works well too. In my experience, if you decide to paint them, its very important that the humidity level is below 50%
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Old 27-10-2013, 06:54   #22
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Quote:
Originally Posted by S/V Illusion View Post
It is the oxygen which renews the oxide layer protecting the steel; without it, you lose all protection. This isn't a generalization; it is a fact as is the fact the steel will corrode in the absence of air. These are fundamental truths learned both theoretically and by experience as a chemical engineer for over 30 years. Your boat, your rules but please don't imply I am misleading anyone.
A simple lack of O2 does not in itself cause corrosion. If this were so SS could not be used in vacuum vessels. SS won't corrode unless there is something present that will oxidize the iron without first oxidizing the chromium. O2 will oxidize the chromium outer layer. Salt water with no O2 will oxidize the iron if it can get through the chromium oxide layer. Fresh rain water has O2 and almost no chlorides so it does not attack SS. In fact it's good because it dissolves salts. But if left for a long time then some dissolved salts might turn it into something that would attack the iron. A good periodic freshwater flush is a good thing for a bilge that cannot stay dry.
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