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Old 24-11-2015, 16:25   #1
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Replacing keel bolts: Which metal is best?

The boat is a Catalina 22, without the smile... yet. The existing bolts are pure rust and should be easy to drill out to a larger size and tap. What's the most appropriate metal for new studs/bolts to mate with the cast iron of the keel?
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Old 24-11-2015, 18:06   #2
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Re: Replacing keel bolts: Which metal is best?

Galvanized steel is recommended for cast iron keel. Stainless for lead keel.


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Old 24-11-2015, 18:45   #3
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Re: Replacing keel bolts: Which metal is best?

I agree... Just removed my stainless steel bolt and had to cut it out with a sawzall and then drill it out with a carbide bit .. The dissimilar corrosion pretty much welded the bolt to the keel... I'm still going to replace it with a 316 stainless for strength and corrosion resistance, but I will make sure that I either insert a sleeve that won't react, or epoxy the bore so there won't be metal to metal contact.
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Old 24-11-2015, 18:49   #4
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Re: Replacing keel bolts: Which metal is best?

I recently changed mine on a 43' Beneteau. Heads were a little corroded but the threads looked like new. Used a 3/4 inch impact wrench. Worked like a charm.


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Old 24-11-2015, 19:35   #5
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Re: Replacing keel bolts: Which metal is best?

Thanks for help, CHM and Curious. Galvanized it is then.
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Old 24-11-2015, 20:45   #6
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Re: Replacing keel bolts: Which metal is best?

I was involved in changing a few boats over to titanium bolts. As I remember it they added a few hundred dollars compared to stainless, but since they never corrode is a permanent fix.
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Old 24-11-2015, 20:57   #7
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Re: Replacing keel bolts: Which metal is best?

With a lead keel, silicon bronze keel bolts are preferred to stainless but stainless is commonly used these days. Ours had silicon bronze keel bolts and galvanized steel drifts (in a few places/deadwood) and we replaced all with silicon bronze. The bronze drifts we spiral cut to give them a little tooth to be more similar to a galvanized drift.

Cast iron, I don't know but it would seem to depend upon the alloy (unknown) of the cast iron to know whether it would fare better or worse than the keel bolt itself if galvanic corrosion took place. There's a galvanic series chart here.
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Old 24-11-2015, 21:04   #8
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Re: Replacing keel bolts: Which metal is best?

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Originally Posted by partingclouds View Post
Thanks for help, CHM and Curious. Galvanized it is then.
I would certainly try to back out the old ones if possible. A trick we use in the machine shop is to spin-on a nut and weld it to the stud so you can get a tool on it. If you break off a stud you can sometimes plug weld a nut on the exposed end from the ID of the nut. The heat from welding may also help you start the stud out. Spin it while its hot.
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Old 24-11-2015, 22:14   #9
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Re: Replacing keel bolts: Which metal is best?

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I was involved in changing a few boats over to titanium bolts. As I remember it they added a few hundred dollars compared to stainless, but since they never corrode is a permanent fix.
Aw, come on, Greg... it's a Catalina 22, not a Hinkley. A couple of your Ti bolts would cost more than the boat did. like as not.

And if dissimilar metals are worrying folks, use of anti seize or locktite or such will mitigate those problems. I think that the galvo bolts will work just fine, and if they start to corrode, they're cheap to replace once again.

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Old 24-11-2015, 23:08   #10
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Re: Replacing keel bolts: Which metal is best?

Thanks for mentioning the Locktite, Jim. Do you think that Satan's Glue would act as an insulator too? I'm tempted to use it to ensure a seal as well as grip the bolts. I'd like to sail knowing the keel has integrity. You know... 'Don't Worry, Be
Happy'!
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Old 25-11-2015, 00:16   #11
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Re: Replacing keel bolts: Which metal is best?

One of the things I learned on offshore oil rigs a few decades ago was that using just about any type of grease on bolts pretty well guaranteed that they would become corroded into the female thread as the grease biodegraded fairly rapidly. We solved the problem by lubricating the threads with paint which dried and excluded the salt water which caused the corrosion.
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Old 25-11-2015, 09:55   #12
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Re: Replacing keel bolts: Which metal is best?

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Originally Posted by partingclouds View Post
The boat is a Catalina 22, without the smile... yet. The existing bolts are pure rust and should be easy to drill out to a larger size and tap. What's the most appropriate metal for new studs/bolts to mate with the cast iron of the keel?
For a Catalina 22, you might be better off replacing the whole boat instead.
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Old 25-11-2015, 09:59   #13
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Re: Replacing keel bolts: Which metal is best?

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Originally Posted by partingclouds View Post
The boat is a Catalina 22, without the smile... yet. The existing bolts are pure rust and should be easy to drill out to a larger size and tap. What's the most appropriate metal for new studs/bolts to mate with the cast iron of the keel?
I'm using 2205 grade SS for my keel bolts. It is superior to 316. In my keel they are threaded into a mild steel frame as my keel is a composite construction. 2205 was specified by the naval architect who designed my keel. I don't know 2205 compatibility with cast iron but that is something you can check with a real expert. As its suitable for mild steel use I imagine it would be suitable for cast iron. They were machined for me out of round stock. Likewise the 2205 nuts were machined from hex stock. Quite a expensive but quite important. I also used a super strong red Loctite mainly to protect the threads. I can't remember the grade except it was the strongest.


I think 2205 would be much superior to galvanised MS but I would definately consult a metaloligst. You can google 2205 meanwhile.
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Old 25-11-2015, 10:19   #14
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Re: Replacing keel bolts: Which metal is best?

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For a Catalina 22, you might be better off replacing the whole boat instead.


I had a 22 footer and replaced the keel bolts, it was a Pearson P22. I recall we managed to get in touch with the designer, Bill Shaw, and he recommended an alloy. I'd contact the manufacturer and get their recommendation.

On that boat it was straightforward, really easy job actually, but partly because it was through-bolted. You /may/ consider tapping sisters rather than trying to drill out the existing ones.
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Old 25-11-2015, 10:32   #15
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Re: Replacing keel bolts: Which metal is best?

Depends on how long you want the bolts to last. Silicone bronze absolutely the best for any keel. Galvanized steel or monel with cast iron. Never use stainless steel with any keel if you want longevity. Stainless subject to stress corrosion and rots when no oxygen available. Not sure why folks use stainless anyways other than pure looks. Most grades of stainless have no use in stress situations.

But for disposable plastic boats that are not used too much, then go with whatever is cheapest.
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