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Old 12-17-2013
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TITANIUM Keel Bolts in cast iron?

I've been thinking that i will pull my keel bolts this winter for inspection and replace them as they have some corrosion. Please keep in mind that these are bolts screwed into the cast iron; not nuts on embedded keel bolts.

Any one have any thoughts about placing titanium keel bolts into a cast-iron keel?

What effect would titanium have on cast iron? It looks like the old keel bolts were galvanized steel.

Would the titanium have sufficient strength to match the old bolts of equivalent size? I believe (maybe wrong) that the tensile strength of ti is greater than stainless of the same equivalent size.

Please leave the price out of the discussion.
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Re: TITANIUM Keel Bolts in cast iron?

Interested in the answers too.... Stumble??
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Re: TITANIUM Keel Bolts in cast iron?

Lol why would you think I would jump it?

Bene,

I don't know of anyone who has done this, so you would be headed into the unknown. Assuming size for size replacement the titanium should be substantially stronger than most steel (it is alloy dependent to some degree), if the old bolts are stainless the titanium bolts would be 4-5 times the strength again depending on alloy.

Galvanic corrosion with titanium gets pretty complicated because while titanium is at the top of the galvanic chart (so the keel would be the anode) titanium also creates a ceramic film that makes it highly resistant to galvanic circuitry, which is why stainless-titanium materials are allowed for human implantation while stainless-stainless materials aren't.

I talked with MARS keels about this and they were fine with titanium keel bolts, but don't spec anything, it would be up to the NA to make the design changes.

As for cost. You would be looking at about 50% more than stainless for the bolts! but of course the labor and other costs are the same. So the project cost probably isn't effected much.


Btw. I no longer work for a titanium company, I got a job offer to go back into legal work I couldn't pass up, but still very much believe it is the way forward as prices are now competitive with 316L in many applications. And titanium prices are dropping quickly while other metals are getting more expensive.
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Re: TITANIUM Keel Bolts in cast iron?

titanium was developed for high temp enviourments and while the tensil strength is more than enough, I am not sure of the shear strength. I would stick with the stainless bolts. Titanium is good material, bot very expensive.
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Re: TITANIUM Keel Bolts in cast iron?

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Originally Posted by twelch View Post
titanium was developed for high temp enviourments and while the tensil strength is more than enough, I am not sure of the shear strength. I would stick with the stainless bolts. Titanium is good material, bot very expensive.
Shear modulus
G5 titanium - 44gpa
316 stainless - 77gpa

The meaning of this is really up to the engineers, and beyond my ability to discuss intelligently.

The cost of titanium is not what I would call very expensive. It's in the same price range as bronze.
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Re: TITANIUM Keel Bolts in cast iron?

I would stay with the stainless. Seems the concern is rust and the cast iron is going to rust. That rust will transpose to whatever is used. A good 316 stainless is a good choice. I am not sure of the type of cast iron is used but most all I have seen were a gray cast iron. White I think would be a bit to brittle for keels.
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Re: TITANIUM Keel Bolts in cast iron?

I think this is very interesting. It may be the modulus of Elasticity that becomes important. I like what Stumble said it is for an< Engineer > to work it out.
As I see it the 316 is able to bend more than titanium. TI is more like super high strength cast Iron and will not bend as easy. This could be good or bad. The 316 would be like chewing gum and bend. This could be good or bad. As the SS gets colder like gum it becomes more brittle. The water temps in the keys and BVI or the temp of the water in the higher Latitudes. You might get an advantage if both 316 ss and titanium are used every other hole ?
In the tables cast Iron and titanium are close in elasticity. Cast iron is rigid and will shatter before it bends very far. This can be a great quality.
As the OP said cost is not an issue and since he is not going to buy hundreds of bolts and will not be replacing them to many times I think he wants the best. I hope an Engineer will visit.
Maybe an odd number of engineers. If they do not agree we have a tie with even numbers.
good Day, Lou
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Re: TITANIUM Keel Bolts in cast iron?

Titanium, like aluminum also becomes very brittle with cold. The MOE of the metals concerned are close enough that that would not be a factor. Ti will bend before the stainless and would shear much sooner than the stainless. SS is the way to go here I think. When I get back to my computer I can get more into this and give more information.
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Old 12-18-2013
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Re: TITANIUM Keel Bolts in cast iron?

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Originally Posted by twelch View Post
Titanium, like aluminum also becomes very brittle with cold. The MOE of the metals concerned are close enough that that would not be a factor. Ti will bend before the stainless and would shear much sooner than the stainless. SS is the way to go here I think. When I get back to my computer I can get more into this and give more information.
how cold are you talking? the ocean water never gets below the freezing temp of water . that is not cold when talking about these metals
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Re: TITANIUM Keel Bolts in cast iron?

The yield strength (point of permanent distortion) of G5 titanium is massively higher than that for stainless.

-----Yield strength
G5 ---128,000psi
316L-- 42,000psi

Where titanium gets its reputation for brittleness is because engineers use it in the technical sense, which is the DIFFERENCE between the yield strength and the tensile strength as a percentage. So titanium with a yield of 128ksi and a tensile of 138ksi is very brittle because the delta is only 128/138=.927. But note that the absolute difference is 10ksi.

Compare this to 6061 aluminum with a yield of 8ksi and a tensile strength of 18ksi. With a delta of 8/18=.44. But also not this is the exact same absolute delta of 10ksi.


In short titanium is a very intriguing material with its own strengths and weaknesses. It is extraordinarily strong, relatively light, and immune to corrosion in the marine environment. But it does have limitations, and only an engineer or NA is really able to make recommendations.
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