Keel stud chemistry

degas

degas

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Aug 14, 2023
71
Tanzer 29 Lake Ontario
So it's time to replace a few washers for some keel studs, and maybe a keel stud or two, on my Tanzer 29, which I sail on freshwater exclusively.

Stainless studs and nuts, galvanized steel washers, fiberglass hull, external cast iron keel. See my sketch below.

Some of the washers are rusting away. There's also some corrosion on the protruding parts of some of the studs.

There are plenty of discussions on SailboatOwners about keel bolts, so I won't bore you with that. But I am curious about the chemistry of it.

What are your thoughts or experience with these:
  • My understanding is that the galvanized washers are intentional sacrificial anodes, intended to be replaced periodically. That implies that the cast iron keel and stainless studs should be more chemically noble, right?
  • If that's the case, does it make sense to use anti-seize compound if I replace any keel studs? Would anti-seize compound interfere with the chemistry of favouring the washers as anodes?
  • If I remove or replace a few studs, is there a risk of galling threads with stainless & cast iron? If so, what's an alternative to anti-seizing compound that I can use to prevent galling while still allowing the washers to be the most anodic (is that a word)?
  • Am I overthinking this? Should I just expect corrosion no matter what I do and mitigate with proper, regular inspection and replacement? Frankly, I and POs haven't paid enough attention to the keel fastenings in the past.

keel stud.png
 
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dLj

dLj

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Mar 23, 2017
5,155
Belliure 41 Back in the Chesapeake
Your galvanized washers aren't really protecting much. An anode needs to be in the liquid medium. I hope your bilge is not constantly full of water.

When you do have water in the bilge and the galvanized washers are submerged, they will help to protect the nut and a small region of the stud functioning as a sacrificial anode, but they are not doing much of anything for your keel. They are simply too small and too far away electrically to have any effect on the keel. And they are connected to your keel through those stainless studs. Stainless is not overly conductive. There is a current thread about using stainless washers in your electrical system.

I wouldn't hesitate to use anti-galling on your bolts - or nuts as the case may be - and I would likely replace those galvanized washers with stainless washers but you can keep galvanized there also, doesn't hurt. Also doesn't do much.

Very little risk of galling between your cast keel and your stainless studs. But using an anti-galling compound won't be a bad thing.

dj
 
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Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
7,757
Hunter 310 West Vancouver, B.C.
dLj said:
I hope your bilge is not constantly full of water.
Click to expand
I think that's the big question here. Yes ? No ?

degas said:
If that's the case, does it make sense to use anti-seize compound if I replace any keel studs?
Click to expand
Just out of curiosity, have you removed/replaced any SS studs to date ? How long are they ? I've only dealt with lead keels.

Also, with my keenly developed sense of OCDism (we prefer to call it CDO) I'd be scared shirtless of any water being trapped at the bottom of the the threaded hole in the CI keel after removing a stud. That would be a recipe for trouble (loss of CI threads) with the SS stud and CI keel in contact with each other. But that's just the OCD in me speaking.

degas said:
Frankly, I and POs haven't paid enough attention to the keel fastenings in the past.
Click to expand
You can say that again. I've never seen/heard of the subject being broached before although I can see the concerns with a CI keel.

BTW nice drawing :thumbup:.
 
degas

degas

.
Aug 14, 2023
71
Tanzer 29 Lake Ontario
dLj said:
Your galvanized washers aren't really protecting much. An anode needs to be in the liquid medium. I hope your bilge is not constantly full of water.
Click to expand
The bilge is dry most of the time. Sometimes I'll mop up a cup or two of water that dripped from the stuffing box after running the engine for more than 30 minutes.
 
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Ralph Johnstone

Ralph Johnstone

.
Jan 4, 2006
7,757
Hunter 310 West Vancouver, B.C.
JamesG161 said:
activates the Chemistry!
Click to expand
Both good and bad chemistry.

I interested in learning more about SS keel studs in CI keels and the potential for damage to the internal theads.

Looks like the OP is not talking to me for some reason. Guess I pissed him off somehow.
 
degas

degas

.
Aug 14, 2023
71
Tanzer 29 Lake Ontario
Ralph Johnstone said:
Just out of curiosity, have you removed/replaced any SS studs to date ? How long are they ? I've only dealt with lead keels.


BTW nice drawing :thumbup:.
Click to expand
No, I haven't pulled out or replaced any studs. But I'm about to this fall after haul out, and that's why I'm asking these questions now.

I know another Tanzer 29 owner who did and the threads that were in the cast iron were fine. But like a few of mine, the exposed threads had some corrosion.

I'll keep this thread updated with the results.

Ralph Johnstone said:
BTW nice drawing :thumbup:.
Click to expand
Thanks. Professional hazard.

Ralph Johnstone said:
Looks like the OP is not talking to me for some reason. Guess I pissed him off somehow.
Click to expand
"Him"? How dare you assume that a sailboat owner is probably a middle aged man.

J/k. Sorry, I didn't see your question until now. Let me know if you have more questions.
 
dLj

dLj

.
Mar 23, 2017
5,155
Belliure 41 Back in the Chesapeake
degas said:
No, I haven't pulled out or replaced any studs. But I'm about to this fall after haul out, and that's why I'm asking these questions now.

I know another Tanzer 29 owner who did and the threads that were in the cast iron were fine. But like a few of mine, the exposed threads had some corrosion.
Click to expand
If you could take photos of your corroded keel bolts it would help.

dj
 
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Ralph Johnstone

Ralph Johnstone

.
Jan 4, 2006
7,757
Hunter 310 West Vancouver, B.C.
dlochner said:
I'm not sure the 3 oz of Mg will do much to protect the 2400lb cast iron keel.
Click to expand
It's allllllllllllllll about surface area, and the relative positions of the two metals in the galvanic series to some extent.

So maybe the Mg comes in a huge sheet which is few microns in thickness. BoatZincs.com sells the Mg, it's up to you to figure out how to apply it. And good luck with that :facepalm: .
 
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JamesG161

JamesG161

SBO Weather and Forecasting Forum Jim & John
Feb 14, 2014
8,078
Hunter 430 Waveland, MS
dlochner said:
I'm not sure the 3 oz of Mg will do much to protect the 2400lb cast iron keel.
Click to expand
He is not protecting the KEEL, but the wet bolts, nuts and washers

Is his Keel rusting off ?

Paint the keel for protection.

Jim...

PS: What is title of the Post?
 
Ralph Johnstone

Ralph Johnstone

.
Jan 4, 2006
7,757
Hunter 310 West Vancouver, B.C.
degas said:
"Him"? How dare you assume that a sailboat owner is probably a middle aged man.
Click to expand
After considerable time reading your post and looking at your avitar, I had an "Ahah" moment and concluded you were a middle aged man.

I will definintely be waiting for your pictures as you get into pulling the studs. I trust you will be working on the hard (an expensive process I admit) as there "could" be the danger of opening up a smile between the stub and the keel if done in the water. Not a pleasant thought at all.

My interest in your project is that I have never even though about the miriad possible "inconveniences" that a cast iron keel can experience along the numerous corrosion avenues. Be thankful that you're in fresh water. I certainly compliment you in taking your proactive approach. As you have previouisly mentioned, it's extrememly unlikely that anyone else is concerned with what is going on down there.

One other point, are you in Lake Ontario or Lake America right
now ? Do you know? Do you even care ?

I guess it's just about winter in your neighbourhood right now ? We're waiting for the second crop to come in just about now here on the Wet Coast.
 
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degas

degas

.
Aug 14, 2023
71
Tanzer 29 Lake Ontario
JamesG161 said:
He is not protecting the KEEL, but the wet bolts, nuts and washers

Is his Keel rusting off ?

Paint the keel for protection.
Click to expand
Yeah, shoulda mentioned that there is no evidence that concerns me about the cast iron keel.

Like I mentioned, the bilge is dry most of the time. The exterior hull-keel joint is gap-free, nothing weeping. Maybe every other season I'll sand down 2-3 small patches of surface rust which I'll then cover with some barrier coat and anti-fouling.

After haul out in a couple of weeks I plan to get started on this project and keep this thread updated.
 
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dLj

dLj

.
Mar 23, 2017
5,155
Belliure 41 Back in the Chesapeake
I was thinking about your keel bolts and the threaded connection into the iron keel. I'd have to see some serious corrosion issue with my keel bolts to consider changing them. And if I did have to, I would for sure use tefgel on them. Here's the galvanic series chart from ASTM G82 showing how your cast keel is likely more active than your stainless bolts irrespective of if the stainless is in it's active or or passive state.

dj

galvanic series with SS vs cast iron.jpg
 
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degas

degas

.
Aug 14, 2023
71
Tanzer 29 Lake Ontario
Ralph Johnstone said:
I trust you will be working on the hard (an expensive process I admit)...

I guess it's just about winter in your neighbourhood right now ?
Click to expand
Most definitely doing this on the hard after after haulout. Yeah, it's expensive, but fall haulout and spring splashing are practically necessary in this part of Canadia.

Still, winter isn't for another 3 months. I haul out earlier than most for reasons.
 
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