# TITANIUM Keel Bolts in cast iron?



## benesailor (Dec 27, 2012)

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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## Faster (Sep 13, 2005)

Interested in the answers too.... Stumble??


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## Stumble (Feb 2, 2012)

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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## twelch (Mar 19, 2013)

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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## Stumble (Feb 2, 2012)

twelch said:


> 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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## twelch (Mar 19, 2013)

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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## Lou452 (Mar 2, 2012)

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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## twelch (Mar 19, 2013)

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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## overbored (Oct 8, 2010)

twelch said:


> 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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## Stumble (Feb 2, 2012)

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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## bobperry (Apr 29, 2011)

Go monel or similar alloy if you want the best.
Titanium is for when you want light weight. Why would anybody want light weight keel bolts?


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## Alex W (Nov 1, 2012)

benesailor said:


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


Everyone keeps comparing the strength of Ti to stainless steel, but your original bolts aren't stainless.

Are there grade markings on the bolt that are readable? Grade 8 bolts have a tensile strength of 150kpsi and a yield of 120kpsi, which is higher than the grade 5 Ti bolts (138kpsi tensile/128kpsi yield) being considered and a lot higher than 316 or 304 stainless (around 75kpsi tensile, 40kpsi yield).

You will want to have engineering input if you switch to a bolt that is weaker than the original bolt.


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## benesailor (Dec 27, 2012)

The original bolts have no markings and i have not contacted Beneteau for the original specs. I couldn't even say that the bolts are original. I have some problem ones but most are in good shape. I have an unusually dry bilge. But, if i'm going to pull two i'm pulling them all. 

I'm watching the price drop on Ti and it appears that it's not much of an up charge to go to Ti VS stainless. If its a $50 up charge for Ti, why not go with Ti if it possesses the proper strength? 

I'm more worried about the different types of corrosion with the cast Iron. 

Monel; i really nothing about.

What do the use in the high end boats? 

Then again, i could put stainless or monel (?) in the boat and probably die before i change them again. (One way or the other!  )


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## SloopJonB (Jun 6, 2011)

They built the SR71 primarily out of Titanium and it is the fastest, highest flying aircraft ever built. Since it routinely flew at 80,000 feet, I doubt cold embrittlement will be a factor in some keel bolts.

I think titanium hasn't been used in boats simply because it has always been so enormously expensive and hard to machine.


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## Faster (Sep 13, 2005)

SloopJonB said:


> I think titanium hasn't been used in boats simply because it has always been so enormously expensive and hard to machine.


I know some of the high end race boats used Ti in stanchions and other deck fittings, perhaps rudder stocks?, as a weight saving measure.

When I was still working in industry a machinist buddy made a new furling drum for our M242... a thing of beauty, out of titianium!..


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## twelch (Mar 19, 2013)

A G5 temper would be much to hard to be of any use on a keel boat. 316 stainless has a Tensile Strength that varies with temper, like all metals and cover a range from 80000 to 120,000 psi. I have never worked with a 316 stainless that was less than 80000 tensile. Not sure where you get your information, but after more than 40 years of working with metals, I never encountered a 42000 psi 316 stainless. 6061 aluminun with a T6 temper has a Ultimate Tensile Strength of 45000 and a Tensile Yield Strength of 40000, and in an "as welded" condition, a strength of about 18000 to 24000. Temper can be either chemical or heat treat.

The temp ranges in question here are not enough to worry about. What one needs is the strength and ductility and corrosion resistance. And for that, nothing beats 316 stainless for this application.


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## benesailor (Dec 27, 2012)

twelch, thanks. That helped answer my overall question. I guess Ti is out unless engineered for the specific application.



> I know some of the high end race boats used Ti in stanchions and other deck fittings, perhaps rudder stocks?, as a weight saving measure.


I believe it was a New Oyster 80 at the boat show that had all the Titanium on board.


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## twelch (Mar 19, 2013)

SloopJonB said:


> They built the SR71 primarily out of Titanium and it is the fastest, highest flying aircraft ever built. Since it routinely flew at 80,000 feet, I doubt cold embrittlement will be a factor in some keel bolts.
> 
> I think titanium hasn't been used in boats simply because it has always been so enormously expensive and hard to machine.


Only certin parts of the skin of the SR71 were titanium. The SR71 leaked fuel while it was on the ground. Fuel just ran out of every seam and it had to refuel right after take off. At altitude and speed, the SR71 skin temp was right at 600 degrees F. The metal heated up, expanded and sealed. Ti was developed for high temp applications.

Titanium retains its strength at higher tempertatures than steels or aluminums. Crome steel retains its rigidity up to 600 degrees F, but it is softer at that point. Ti in the same tempertature would also retain its strength.


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## benesailor (Dec 27, 2012)

I remember what a high maintenance plane the SR71 was . (I'm starting to date my self.) I started at Edward's AFB during the best times.... the memories, F-22,F-23,B-2..... the experimental plane. 
There's a whole lot of Titanium in Military jets. Light and bulletproof!


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## twelch (Mar 19, 2013)

benesailor said:


> I remember what a high maintenance plane the SR71 was . (I'm starting to date my self.) I started at Edward's AFB during the best times.... the memories, F-22,F-23,B-2..... the experimental plane.
> There's a whole lot of Titanium in Military jets. Light and bulletproof!


I would say something, but that would date me back even more if I did. A new bomber was just being talked about to replace the B52.


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## Stumble (Feb 2, 2012)

Twelch,

My numbers come from matweb.com


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## Lou452 (Mar 2, 2012)

So here we sit waiting for a PE. to show up and not charge $ for good advice.
maybe one might send a little bird to chirp so no liability is incurred . This is a post I like. Hope the OP stays with it and informs us what happens. 

I would like to add, correct or clear up a statement I made about TI being like cast Iron. TI is bent and formed with care. I did not mean to imply TI can not bend at all. I also do not think anyone of you will think 316 SS is as soft as chewing gum. I am just trying to use imagination to compare how I might try to explain. 
Good day, Lou


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## twelch (Mar 19, 2013)

Stumble said:


> Twelch,
> 
> My numbers come from matweb.com


Ahh...heard of it, but never used it. I use ASTM, ASME and AWS for metals. Much more information in the grades and types.

And if I were replacing keel bolts, I think I would go back with the same type bolt that came out. Or maybe an A325 grade 8, and if worried about corrision, I would just replace them every year.


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## Foxy (Sep 14, 2013)

If your original bolts were steel, then 316 SS would probably not be as strong although they would be more corrosion resistant. Without knowing the parameters of the keel, I could not tell you what would the required number and diameter would need to be for the bolt material.

You got the best advice from Bob Perry when he told you to go with Monel. Either Monel 400 or Monel 500 would be stronger than any of the steel alloys likely to have been used and also stronger and more corrosion resistant than 316.


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## benesailor (Dec 27, 2012)

I was looking at the fact that Ti is very corrosion resistant. Not sure how cast iron would react with TI. To many uncertainties. 

At this time i'll probably go with original spec from Bene or stainless. Just check them in 5 years.


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## hellosailor (Apr 11, 2006)

Ignoring that four-letter word (B**K) and concentrating on the materials aspects...I can't see why bother. Machining titanium, threading it, creates a lot of global warming and tends to make machinists curse almost as badly as sailors. Then there's the question of whether this is to any net gain, as you could just order the new old iron OEM parts, from BendyToy, slather 'em up in NeverSeize or a good protectant of your choice, and screw 'em in.

Surely, a generous coating of "good stuff" is all that is necessary to prevent rust from ever happening there again?


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## RichH (Jul 10, 2000)

bobperry said:


> Go monel or similar alloy if you want the best.
> Titanium is for when you want light weight. Why would anybody want light weight keel bolts?


Monel, forged cupro-nickel, or Nickel-Aluminum Bronze are proven 'marine' metals that have stood up to nearly 100+ years of acceptable saltwater service. If possible if such is your choice, get "mill certifications" for any materials that you use for such *critical items* as a LOT of 'counterfeiting' and sub-standard metals are being passed along these days. Of course, 'certs' will add greatly to your cost.

More important than material strength values from a 'cookbook' is the 'factor of safety' (FS) that you should apply to any such application. What I mean by 'safety factor' is that for especially critical/important service you need to 'overbuild' by a factor of at least three (for open ocean stuff) - to cover unexpected/unforeseen stress, material faults, inherent design errors. 
FS=4 is better than FS=3


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## SloopJonB (Jun 6, 2011)

For keel bolts I'd go a lot higher than a 3 or 4 to 1 safety factor.

My old Columbia 43 had a 10K Lb iron keel held on by 10 X 3/4" bolts (studs actually).

I thought they looked rather skimpy so I did some research and found that was a 13 to 1 safety margin. Most boats I've seen have considerably larger bolts, even for less weight.


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## Faster (Sep 13, 2005)

I think for most bolt-on keels a single bolt (or maybe two) would be adequately strong to lift the entire boat on, so with 8 - 10 bolts/studs pretty common that FS is pretty well built in when you consider the weight of the ballast alone.

I'll be getting into this in the spring - cast iron keel with SS bolts. May look into the cost of Monel for interest's sake.. Jon do you think Pacific Fasteners or Metal Superstore would carry it?


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## RichH (Jul 10, 2000)

SloopJonB said:


> For keel bolts I'd go a lot higher than a 3 or 4 to 1 safety factor.
> 
> My old Columbia 43 had a 10K Lb iron keel held on by 10 X 3/4" bolts (studs actually).
> 
> I thought they looked rather skimpy so I did some research and found that was a 13 to 1 safety margin. Most boats I've seen have considerably larger bolts, even for less weight.


F3 or F4 is for SINGLE BOLT, no matter how many bolts are used. This would be in compliance to standard engineering practices for severe/critical service applications .... and why someone else mentioned that a NA or engineer should be the one doing the approval/analysis for such a retrofit, ..... and then give you his 'stamped' certs on the dwgs, etc.

Severe/critical/lethal service is not a place for 'guesswork'. 
A keel join is a structural 'dynamic cantilever' one of the most difficult structures to 'get right'. Its either meets or exceeds accepted standard compliance or its simply not valid. 
Imagine deposing before a judge or litigator from your insurance carrier etc. ... and you dont have the foggiest clue of what your talking about. ;-)


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## SloopJonB (Jun 6, 2011)

Faster said:


> I think for most bolt-on keels a single bolt (or maybe two) would be adequately strong to lift the entire boat on, so with 8 - 10 bolts/studs pretty common that FS is pretty well built in when you consider the weight of the ballast alone.
> 
> I'll be getting into this in the spring - cast iron keel with SS bolts. May look into the cost of Monel for interest's sake.. Jon do you think Pacific Fasteners or Metal Superstore would carry it?


Pacific might have it or be able to get it. If they can't, no-one can around here.

I haven't dealt with MS for fasteners so I can't say.

Edit: I just checked PF's catalogue - they have Monel all thread rod available - Ti too if you want.

That place is great - they have never turned me away.


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## Foxy (Sep 14, 2013)

Faster said:


> I think for most bolt-on keels a single bolt (or maybe two) would be adequately strong to lift the entire boat on, so with 8 - 10 bolts/studs pretty common that FS is pretty well built in when you consider the weight of the ballast alone.
> 
> I'll be getting into this in the spring - cast iron keel with SS bolts. May look into the cost of Monel for interest's sake.. Jon do you think Pacific Fasteners or Metal Superstore would carry it?


Safety Factor is not a meaningful term unless you know what the forces are and the limits of the materials you are using. If you are simply using the weight of the keel and applying a SF in your bolts, you would be fooling yourself.

The force on keel bolts is not the weight of the keel alone. Consider the boat when heeled, the force (really moment) is the weight of the keel X the distance of center of gravity from the root. That force is levered against the hull by the root of the keel and the bolts must resist the levered force. Note too that only bolts on the high side of the keel are effectively working for you. Obviously the further the center of gravity is from the root, the higher the force. Consider for example a torpedo bulb weighing more than the hull, suspended 2-3 meters below the root of the fin VS the trapezoidal fins of the late 70's / early 80's with no bulb.

Also one needs to consider grounding force which depends on how far the bolts are from the center of rotation about the floors. Only bolts forward of that point are loaded. Once again keel configuration comes into play. The longer the root is fore & aft, the lower the grounding force on the bolts.

Rather than the term Safety Factor, we generally now use "allowable design stress" as the basis for calculations. In the case of boats it is.
stD=stLIM X kMAT X kDC X kLC.

stLIM for metals is the lower of Yield or 0.5 Ultimate strength. For wood or composites it is Ultimate Tensile or compressive as relevant.

kMAT is a coefficient dependent on elongation at break or ductility for metals. For most bolt materials it would be .75 For Wood or composites kMAT is .33

kLC is a coefficient dependent on Load Case or usage. For keel bolts it is .67

kDC is a coefficient based on use and would typically be 1.0

So for 316 SS keel bolts we should not stress the bolts more than. 195 Mpa X .75 X .67 X 1 = 98 Mpa or about 14,214 PSI in their maximum load condition. Maximum load condition would be the boat broached at 90 degrees or a grounding hit at approximately hull speed.


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## bobperry (Apr 29, 2011)

Allow me to poke the dog with a stick here for a moment.

I approach keel bolts from a totally different angle than you guys. I like Monel or a similart alloy and I pick a bolt dimeter from one of the scantling rules knowing they are conservative and we know they work. Period! But in almost every case it just takes two of three bolts to hold the keel on by the math that you guys think is valid. Great, do it that way. I pick a bolt diameter then I uses as many bolts as I can comfortable fit into the structure so I can SPREAD THE LOADS OUT. It sure as hell is not about the strength of one bolt. I want 12 of them, maybe 16 of them on a smaller boat maybe 8 keel bolts. I wnat the keel loads to be sporead out over as much of the bottom as I can manage.

The way Foxy lays it out it's all about bolt strength. I think it all about the stress on the bottom of the boat.


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## Foxy (Sep 14, 2013)

Bob,

Of course stress on the bottom is a factor, you have to satisfy all parts of the scantling rules, but we were only discussing bolt stress. You can have more smaller bolts or fewer larger ones and satisfy the scantling rules, none that I know of tell you to use XX diameter without knowing the number and spacing. When you look at FEA simulations you can see that bolts in the widest part of the keel get loaded up first. This happens even with keels that have top plates to spread the bolt pattern out over a wider area. It makes sense to use more bolts in the higher stress area or bolts of a larger diameter so none are over stressed. And what floors you can fit in also plays a part in the decision. 

I'm with you on Monel. Stronger and more corrosion resistant than 316, relatively easy to machine, nuts are not going to gall. Well worth the difference in initial cost.


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## christian.hess (Sep 18, 2013)

im with BOB on this one...



people get too damned involved and worried with getting the best "something" whatever that may be...

its not the bolt per se, but how they are installed, how they are torqued and spread out, how the bilge stub, or glassing is, etc...no point buying unobtanium bolts at $200-300 a peice if you have a flexi flier thin bilge...right? or an attachment point with certain parameters factored in for example...

on my motorcyle I regularily used to replace all crappy stainless bolts, especially those on footpegs and subframes etc with regular old steel 12.9 grade bolts...allens that I would simply grease up and thread them, with anti seize coatings...

the heads I would paint if I felt like it.. I rode saltwater covered beaches all the time at high speeds drenching the whole bike...

the savings in COST and the improved strength made me a happy camper...AND the looks on peoples faces was always PRICELESS!





anywhoo

back to scheduled programming

x2 on monel

I had a h28with twin monel fuel tanks and water tanks...


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## RichH (Jul 10, 2000)

Please take note of Bob's reference to the 'scantling rules'. Scantling rules are the successive and continual evolving history of what 'works' and what fails; its totally independent of finite element strengths of components, .... its the WHOLE entire structure or assembly that survives for a long time the service intended. Experience !!!!!!!!! not glossy brochures of 'future-isms'.

One must consider exactly what a 'bolt' is and what a bolt is NOT. What a bolt or similar fastener is - is a small mechanical element that provides / generates FRICTION between SURFACES, and NOTHING ELSE!!!!! 
Think of a bolt as anything else and youre merely FOOLING yourself !!!!!!!!

The generation of sufficient FRICTION (via 'normal forces', in the mathematical sense) that keeps the surfaces together and functional without displacement or 'slip' is the primary function of a 'bolt' - it 'drives' surfaces together so that there is sufficient FRICTION to keep the two surfaces positioned and the 'assembly' functionally intact. Such is applicable for cylinder heads of engines and pumps, flanges on the 'core' of a nuclear power plant, the root interface of airplane wing attachments, containment of lethal chemicals, .... ad nauseum - a bolt induces FRICTION of two surfaces ..... and nothing else. 
An advanced designer would NEVER EVER 'hang a load' on a bolt or fastener - its just plane STUPID to do so. An advanced designer, using the knowledge passed along by hundreds of previous designers and engineers (scantling rules !!!) uses a 'bolt' to draw things together so that FRICTION is what holds the 'joint', etc. together. Those hundreds of previous designers have created 'scantling rules' - "this will 'work' over time, and this will fail ... based on my 'experience'".

Bob states that he will use so many bolts for such and such a design, etc. and when you back-calculate his and other high level boat designs you'll find his generated friction in the assembly is exactly what engineers and designers of other critical disciplines use (called safety factor of the whole assembly) ---- this 'works' and this does not work and scantling history is usually 99.9% correct ... and no finite element computer program will be able to tell him otherwise. When engineers and designers 'chintz' on the scantling rules (under pressure for cost etc. savings, or unclear and unrefined finite element design programs), wings and vertical stabilizers are ripped off of aircraft (Airbus), keels get ripped off of sailboats (Bavaria), spade rudders fall off (Jeanneau), etc. etc. etc. .... their faulty design evolution usually found to exceed the limits of the 'scantling rules'.

The lesson and advice that Bob is giving you is: its not the bolts nor bolt strength capability that is important, its the friction forces that are generated by the torquing of the bolts that causes the proper FRICTION that holds an *entire assembly* together, even under 'unforseen' and 'unexpected' events. The bolts are just a miniscule minor part of that assembly.

Do yourself a favor with keel bolts .... take only very small evolutional steps in such an 'upgrade' as the OEM designer/engineer probably was 99.99% correct with the original selection. Stay away entirely from 'cookbooks', etc. unless you know how to 'tread water' for extended periods of time. Titanium? ... not enough scantling history over long term sailboat history for me to use it.

A keelbolt upgrade or change is the domain of a Naval architect or structural/mechanical engineer. Only they have the basic understanding and knowledge of specific 'scantling rules' that has been passed along for well over 200 years. 
For a DIY change of keel bolts or other critical boat structure based on engineer's handbooks/cookbooks and glossy marketing brochures, Id add, that you should then also learn to be able to physically 'tread water' for indefinite periods.

Bob is totally correct about 'scantling rules' and the experience to know and use them. Listen very carefully what Bob is implying here. ;-)


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## christian.hess (Sep 18, 2013)

^^^^thats that

Im about to clean my keel hull joint and paying attention to if and what flex happens...if so I will take precautionary measures but not "improving" on the design...


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## hellosailor (Apr 11, 2006)

I suppose that if one really wanted to spread out the loads on the keel bolts, one would not simply install bolts and washers, but one would install a ring (or plate) that ran under all the bolts, connected them all, spread the load evenly over a large area and sandwiched the hull between the ring and the keel.

I think the two extreme incidents that might reflect maximum keel bolt load would be striking a submerged object (in which case one might want the bolts to deform somewhat rather than tear out the hull bottom with them) and a capsize during a storm, when the entire mass of the hull might be rotating off the top of a wave and then striking the "solid" water as the keel rotated back down into it again. 

How do the historical scantlings account for extremes like that? Or don't they?


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## RichH (Jul 10, 2000)

My impression is that a boat heeled over to a max. of 45° over will develop its max. forces for keel, rigging, etc.; beyond that heel angle value, the forces become 'self relieving' due to simple trigonometry and the loss of keel force against the water/fluid (CLR forces being at or approaching their relative minimum). A keel at 90° to the vertical will have essentially zilch water resistance pressure (load) against it ... as the boat simply skids off to leeward. 

Impact however is a horse of a different color and the shape of the structure is important, as all the 'lines of force' (tensors) do not necessary arrive at the same places in-phase and in equal alignment with each other ... something like how bones work - a severely impacted bone will take much much more force before shattering than a bone subjected to a slow agonizing twist. Such is the mystery and wonder of 'composite construction'. When all the individual 'lines of force' arrive at a single point and become concentrated (know as a stress riser, a momentary artificial 'magnitude' increase in applied stress) and where all the cookbook values of material strength go out the window. Thats what Bob Perry is describing with his statement of 'as many bolts as possible' - spreading all those forces out as much as possible to prevent 'stress risers' and not letting those forces 'concentrate' in a single area. 

Those folks who use the historical 'scantling rules' have the advantage here, as all those 'anomalies' are well included in those those rules of what works and what doesnt. 
In industry such shapes and assemblies are physically multi-tested to destruction -- not something that a boat construction yard with a limited budget can afford to do and the only alternative is to follow the well established historical 'scantling rules' ... at least thats the way that I perceive how its done with boat design.


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## SloopJonB (Jun 6, 2011)

The only problem with relying on historical success (scantling rules), largely gained through trial & error, is when you are into something previously untried - witness the problems with current type extreme blade/bulb keels that are so far outside historical norms.

Prior to Drum in the 80's I had never heard of a boat losing its keel. I'm sure it happened but it was basically unheard of. Even then, Drum was due to an improperly cast keel - the bolts weren't J'd and the lead simply slid off them. 

However, in the last 15 or so years keel attachment problems have become almost commonplace, certainly far from unheard of.

Time for some new calculations to update those old scantling rules I'd say.


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## Foxy (Sep 14, 2013)

If we relied totally on historical scantlings, we might be back to Nevin's which allowed only bronze bolts at 1 in^2 per 1500 lbs of ballast. Very safe and worked well for the keel designs of that era. Designs and construction methods changed and so have scanning rules. We went through ABS which became obsolete and now we are into ISO 12215.

Not sure how or why Rich thinks keels are held on by friction, but that is his issue. I happen to comply with ISO 12215, but also make use of FEA to show me where the stress concentrations are and make sure that following the scantlings is enough.

You can evenly space bolts, but the only time those bolts are evenly loaded is at the dock. Upwind, the windward half are loaded and the leeward half are not. The top of the keel is compressed against the hull. When you run aground, the aft end of the keel gets pushed into the hull and the forward bolts are loaded. In all cases you need adequate structure within the boat which includes backup plates thick enough to not bend so that the force is spread out over a wide enough area.

As to the 90 degree heel, the laws of gravity do not stop at 45 degrees and 90 you have the maximum moment on the keel itself. Time has proven that this will work for the sailing forces and that's why the scantlings rules still use it.

Sent from my iPhone using Tapatalk


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## casey1999 (Oct 18, 2010)

RichH said:


> Please take note of Bob's reference to the 'scantling rules'. Scantling rules are the successive and continual evolving history of what 'works' and what fails; its totally independent of finite element strengths of components, .... its the WHOLE entire structure or assembly that survives for a long time the service intended. Experience !!!!!!!!! not glossy brochures of 'future-isms'.
> 
> One must consider exactly what a 'bolt' is and what a bolt is NOT. What a bolt or similar fastener is - is a small mechanical element that provides / generates FRICTION between SURFACES, and NOTHING ELSE!!!!!
> Think of a bolt as anything else and youre merely FOOLING yourself !!!!!!!!
> ...


Rich,
I do hold a Professional Engineer (Mechanical) License in Maryland and Hawaii. This thread is interesting and did some reading last night on the subject of bolt connected structures. A bolted connection that relies soley on friction is called a Friction Critical Joint. I do not believe a keel hull joint is considered such- as specific things are critical in the design and installation of a frictional critical joint such as roughness between the members and torques requirements of the bolts, and also the type of bolt used. Also, if only friction were holding a keel hull joint- what happens when the boat is sitting at the dock? A friction critical joint is only used to prevent members from sliding apart- not pulling apart as a keel would be trying to do when at rest. Also, as others have posted- the most stress a keel sees is a grounding, or duing a 90 degree knock-down. During the knock down, the keel is a cantilevered member. This is why two rows of keel bolts are much preferred over a single center row. The single center row will work loose as during any heeling of the boat, the bolts are at a poor location to resist keel movement. If the keel/hull joint were a friction critical joint, a signal row of bolts would be ok, but this is not the case.

No doubt friction between the bolted keel and the hull plays an important and probably large part in keeping the keel and hull together, but it is not the only factor. And even if your keel bolts were loose, your keel should not fall off. Additionally, the bedding compound probably plays an important part too. Keels generally have to be wedge free of the hull even when all the keel bolts are removed. This is done by lifting the hull and letting the keel hang free while driving wedges to break the bond of the keel bedding compound.

From Wikipedia:
http://en.wikipedia.org/wiki/Slip-critical_joint

And here is more information:
http://www.fastenal.com/web/en/69/bolted-joint-design


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## RichH (Jul 10, 2000)

Casey, think of the elemental enhancement of using 'pre stressed' structures. In the case of a bolted on keel, done properly with the correct amount of 'prestress' via bolting, the transfer of stress across that keel join is more uniform, more equally distributed, the interface of the surface can bear MORE stress because of the initial prestress as applied by the bolting, etc. Further, when bolts are used to COMPRESS surfaces together to enhance the interface, frictional forces the bolts and their threaded bores are no longer as subject to plastic deformation of the shapes and surfaces ... ie. ductile 'bearing saddle' deformation (projected stress on 1/2 the length of the circumference of a 'bolt hole', etc.) due to side/shear loads .... the friction of the 'join' transmits those stresses/forces, not the BOLT whose only job its to apply compression to the interface. 
Plus, the bolt(s) (a terrible element in pure shear due to the thread profile as an immense stress riser) if it/they lose(s) its torque becomes a last chance vs. 'shear' (as a 'pin') .... a 'natural' inbuilt factor of safety due to the stress configuration of the joint. 

In any such analysis, simply replace a bolt with a pin and see the resultant stress transmission differences, especially where the 'lines of stress' become concentrated. The friction joint transmits stress due to the induced FRICTION caused by the bolt compressing the join together, not due to the elemental strength of material of the bolt or its mating/joint surfaces. 

Scantling rules apply not only to maritime construction but to civil, mechanical, nuclear (code 3) and chemical engineering; and it works, plus continues the constant slow evolution/progression of 'the art' .... and much better than a finite analysis program that only considers the strength of elements and not 'the whole'.
Think of 'prestressed' materials of the structure and their response to dynamic forces.


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## casey1999 (Oct 18, 2010)

RichH said:


> Casey, think of the elemental enhancement of using 'pre stressed' structures. In the case of a bolted on keel, done properly with the correct amount of 'prestress' via bolting, the transfer of stress across that keel join is more uniform, more equally distributed, the interface of the surface can bear MORE stress because of the initial prestress as applied by the bolting, etc. Further, when bolts are used to COMPRESS surfaces together to enhance the interface, frictional forces the bolts and their threaded bores are no longer as subject to plastic deformation of the shapes and surfaces ... ie. ductile 'bearing saddle' deformation (projected stress on 1/2 the length of the circumference of a 'bolt hole', etc.) due to side/shear loads and shear .... the friction of the 'join' transmits those stresses/forces, not the BOLT whose only job its to apply compression to the interface.
> Plus, the bolt(s) (a terrible element in pure shear due to the thread profile as an immense stress riser) if it/they lose(s) its torque becomes a last chance vs. 'shear' (as a 'pin') .... a 'natural' inbuilt factor of safety due to the stress configuration of the joint.
> 
> In any such analysis, simply replace a bolt with a pin and see the resultant stress transmission differences. The friction joint transmits stress due to the induced FRICTION caused by the bolt compressing the join together, not due to the elemental strength of material of the bolt or its mating/joint surfaces.
> ...


Not quite sure I follow.

Fully agree the friction forces created by keel bolts most certainly contribute to the strength of the joint. However, when the keel is hanging vertical, like at a dock, the keel bolts themselves are supporting the keel (unless one would like to assume the bonding sealant between the keel and hull is doing the supporting). The bolts may be pre stressed and not see any additional loading until the load exceeds the prestress- which it will not if the bolts are tightened. But if the bolts were completely loose, the bolt would support the keel.

In design of buildings and structures, the design is based on engineering calculations, not scantling rules. The structure may not be able to be completely analyzed, however that is the reason for the use of safety factor and "belts and suspenders" design, as well as complete and adequate analysis of the structure. Airplanes and space vehicles are not designed using scantling rules.


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## bobperry (Apr 29, 2011)

On the FRANCIS LEE we were dealing with a very deep fin and bulb and a red cedar hull. We needed to keep the potential keel loads off the hull skin and spread out over the entire floor and longitudinal system. Tim Nolan designed this gridwork in s.s. to do the job. The red cedar strip planking was removed in way of the fein and replaced with a solid grp "pan".


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## RichH (Jul 10, 2000)

Buildings and other static structures do not experience the _dynamic_ stresses (to the same degree/magnitude) as do aircraft, vehicles, machinery .... boats, etc. Dynamic structures are quite 'different'. ;-)

Most certainly civil/architectural engineering has its own 'secret handshakes' of its very own scantling rules .... eg. deflection of beams is limited to 1/60" per ft. of span --- keeps the plaster/concrete from cracking when the floor space reaches full occupied design load. I think youll find that (or similar) inbuilt to most building codes .... deflection under load and not 'plain vanilla' strength. ;-)


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## SloopJonB (Jun 6, 2011)

Here are some pics of a real world example. I dropped the 10,000 Lb. keel on my Col. 43 due to the corrosion of the mild steel studs and backers. I thought the studs (3/4") looked awfully skimpy compared to what I had seen on smaller boats, let alone one as big as this.

I did some research and found they were very adequate - a single bolt had enough tensile strength to hold the keel at 90 degrees. When the yard was moving the keel around they had a bracket bolted on with two "grade nothing" bolts that only threaded part way in and it was no problem to sling it on a forklift. I guess the fact that the bilge was dusty dry, even with that wasted mess holding it on should have told me something.

First pic is the rusted crap that held it on. Second pic shows the wide flange top to the keel. Third pic shows what I replaced the wasted hardware with.

The flange fitted into a moulded recess in the bottom of the hull. The flange was a foot wide with two rows of 5 studs paired 10" O.C.


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## SloopJonB (Jun 6, 2011)

bobperry said:


> On the FRANCIS LEE we were dealing with a very deep fin and bulb and a red cedar hull. We needed to keep the potential keel loads off the hull skin and spread out over the entire floor and longitudinal system. Tim Nolan designed this gridwork in s.s. to do the job. The red cedar strip planking was removed in way of the fein and replaced with a solid grp "pan".


Looks good enough for government work.

I hope you polished them like I did mine.


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## bobperry (Apr 29, 2011)

Casey:
Please keep in mind that this is the world of yacht design.
"Airplanes and space vehicles" enjoy a far greater design budget than does the yacht.

If you expect FEA to be used on a typical yacht design project you are dreaming. Scantling rules have been around far longer than I have and they work. You could think of the current Euro certification system as just another scantling rule.


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## RichH (Jul 10, 2000)

Nice design. I especially admire those 'compression tube ferrules' and the bottom curved beam shapes ... nice 'optimization'. ;-)


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## SloopJonB (Jun 6, 2011)

RichH said:


> Buildings and other static structures do not experience the _dynamic_ stresses (to the same degree/magnitude) as do aircraft, vehicles, machinery .... boats, etc. Dynamic structures are quite 'different'. ;-)


I'd say hurricane force winds and earthquake forces put some pretty severe dynamic loading on a 1000' skyscraper.

There's a relatively short (12 storey) highrise in Vancouver that is "hung" from the central core (The old WestCoast Transmission building to locals). In extreme winds - low hurricane force, it sways so much that people have trouble maintaining their footing on the top floors.

I'd say that is pretty severe dynamic loading.


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## SloopJonB (Jun 6, 2011)

bobperry said:


> If you expect FEA to be used on a typical yacht design project you are dreaming.


You bring up an interesting point there Bob. Are the big BeneHuntaLina manufacturers big enough to use FEA when developing their designs?


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## casey1999 (Oct 18, 2010)

RichH said:


> Buildings and other static structures do not experience the _dynamic_ stresses (to the same degree/magnitude) as do aircraft, vehicles, machinery .... boats, etc. Dynamic structures are quite 'different'. ;-)
> 
> Most certainly civil/architectural engineering has its own 'secret handshakes' of its very own scantling rules .... eg. deflection of beams is limited to 1/60" per ft. of span --- keeps the plaster/concrete from cracking when the floor space reaches full occupied design load. I think youll find that (or similar) inbuilt to most building codes .... deflection under load and not 'plain vanilla' strength. ;-)


We could look at suspension bridge design if you would like. Scantling rules are not used there. The bridge is engineered. Some not so well:
http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)
From above:
"A lesson for history[edit]Othmar Ammann, a leading bridge designer and member of the Federal Works Agency Commission investigating the collapse of the Tacoma Narrows Bridge, wrote:

The Tacoma Narrows bridge failure has given us invaluable information...It has shown [that] every new structure [that] projects into new fields of magnitude involves new problems for the solution of which neither theory nor practical experience furnish an adequate guide. It is then that we must rely largely on judgement and if, as a result, errors, or failures occur, we must accept them as a price for human progress.[26]"


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## casey1999 (Oct 18, 2010)

RichH said:


> Most certainly civil/architectural engineering has its own 'secret handshakes' of its very own scantling rules .... eg. deflection of beams is limited to 1/60" per ft. of span --- keeps the plaster/concrete from cracking when the floor space reaches full occupied design load. I think youll find that (or similar) inbuilt to most building codes .... deflection under load and not 'plain vanilla' strength. ;-)


Building codes will not tell you how to build the structure, only how much load psf and amount of allowable deflection. The Engineer of Record is responsible for the design.


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## casey1999 (Oct 18, 2010)

bobperry said:


> Casey:
> Please keep in mind that this is the world of yacht design.
> "Airplanes and space vehicles" enjoy a far greater design budget than does the yacht.
> 
> If you expect FEA to be used on a typical yacht design project you are dreaming. Scantling rules have been around far longer than I have and they work. You could think of the current Euro certification system as just another scantling rule.


Bob,
Not saying FEA is required, only a few basic engineering calculations using very conservative keel loading assumptions and very conservative SF.


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## Lou452 (Mar 2, 2012)

A chance to reflect. Looking back at history " Good enough for government work " AT the time of WW II This was said with the meaning it was meant to imply. A large % of the "boys" were off in the fight. Rosie the riveter and many other unlikely workers found themselves working in the war effort. Their work and work quality was what could make the difference between the life or death of a son, spouse or the kid next door. " Good enough for government work " Say this to someone that was part of NASA . Most of the men on the missions lived to tell about them because the work was " good enough'' 
I am not trying to pick and nit pick. I just wanted highlight how view points about something can start to become totally different.
This thread has become very interesting. At first I thought it was going to bomb. Now we are exploring what level is good enough. How cost and safety factor in. 
Merry Christmas All, Lou


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## casey1999 (Oct 18, 2010)

Lou452 said:


> A chance to reflect. Looking back at history " Good enough for government work " AT the time of WW II This was said with the meaning it was meant to imply. A large % of the "boys" were off in the fight. Rosie the riveter and many other unlikely workers found themselves working in the war effort. Their work and work quality was what could make the difference between the life or death of a son, spouse or the kid next door. " Good enough for government work " Say this to someone that was part of NASA . Most of the men on the missions lived to tell about them because the work was " good enough''
> I am not trying to pick and nit pick. I just wanted highlight how view points about something can start to become totally different.
> This thread has become very interesting. At first I thought it was going to bomb. Now we are exploring what level is good enough. How cost and safety factor in.
> Merry Christmas All, Lou


Good point of view.

A lot off topic (but since we are talking boat design), I got a question for Mr. Perry:
One thing I do not understand about sailboats. Why is the rig not better designed with more SF. The loss of one stay (forestay, back stay or a shroud) could bring the entire rig down. One failed connection and pow.. Is there not a better way to design the rig? Especially since we use stainless steel which some have major issues with its performance.

Merry Christmas to all...


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## Faster (Sep 13, 2005)

casey1999 said:


> Why is the rig not better designed with more SF. The loss of one stay (forestay, back stay or a shroud) could bring the entire rig down. One failed connection and pow.. Is there not a better way to design the rig? .


I'll let Bob address the essential question here, but wanted to make a observation on the point..

Hi tech - edge-of-limits racing machines aside, I think rig failures are exceedingly rare - and usually due to lack of maintenance, upkeep and due diligence, possibly/occasionally coupled with an extreme event of some sort.

I think the SF is probably quite good when new, esp on 'cruising boats'..


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## RichH (Jul 10, 2000)

casey1999 said:


> We could look at suspension bridge design if you would like. Scantling rules are not used there. The bridge is engineered. Some not so well:
> http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)
> From above:
> "A lesson for history[edit]Othmar Ammann, a leading bridge designer and member of the Federal Works Agency Commission investigating the collapse of the Tacoma Narrows Bridge, wrote:
> ...


Well if you want to look at bridge collapse/failure based on very similar circumstances to that we're discussing here, just look into the details of the Mianus Bridge Interstate-95 collapse in 1983 in Connecticut. That bridge mainspan dropped into the water catastrophically when one of the 4 PINS, the sole support links of that bridge and stunningly similar in construction to a keel held on solely by 'bolt strength' fails. 
Of course the real culprit was lack of maintenance and lack of adequate inspection to visualize that these pins, _the sole support of the bridge_, were failing. 
And, the Interstate 90 (Albany) collapse in 1987 (?) ... another pin set / pin hung bridge that went down when one of the bridge supports was weakened by flooding. 
And, then again another 'pin set / pin hung' bridge collapse on Interstate 35 in Minnesota in 2007.

You can bet your assets that the current implied civil engineering 'scantling rules' for such bridges no longer include 'pin set / pin hung' bridge design. The historical record now shows 'they dont always work', and no matter how a finite element analysis will show them to be an advantage.

Tacoma Narrows was a failure (lack of) of aerodynamics investigation; aerodynamics setting up the generation of the induced harmonics that brought it down. Even worse, it was a failure of the local government officials who diverted the bridge insurance money - Tacoma Narrows wasn't insured, a 'double' loss.

Say what you want, not many FRG 'encapsulated keels' have fallen off in comparison to bolted on keels where the bolts have failed.

;-)


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## Lou452 (Mar 2, 2012)

Going back to the OP .. Cost is not an issue. From what I have seen posted I am going to vote for 316 SS. and a heavy dose of nickel anti-seize good work on the installation. I am a shade tree mechanic with zero keel jobs on record. so I just get one vote :laugher You get two votes if you have expertise that can be applied  Time to take a stand or at least x out the TI 
Would the mating surfaces have an adhesive or an anti-adhesive ? 
The op has a bolt on keel so no point in the fin vs full keel or other options of why a keel comes off
Having fun, Lou


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## RichH (Jul 10, 2000)

Faster said:


> ....... I think rig failures are exceedingly rare - and usually due to lack of maintenance, upkeep and due diligence, possibly/occasionally coupled with an extreme event of some sort.
> 
> I think the SF is probably quite good when new, esp on 'cruising boats'..


I dont agree. 
I sail the east coast and down into the caribbean where the trade winds are quite constant. My observed average sighting of boats with failed rigs per season in 'de islans, mon' is usually 2-3, mostly coastal production boats and usually in the range of ~20 years of age and with OEM rigging failures.

Stainless 300 series is a funky material as it has a quite low endurance limit (30Kpsi) which when exceeded will quickly and quite predictably fatigue fail after 1 million load cycles at above that limit. 1 million cycles above 30ksi, I equate/estimate to approx. one circumnavigation or ~10 years of 'hard' recreational sailing. 
So-called blue water boat rigs seem to have a FS=3 or more which equates to approx. 90Ksi/3 = 30ksi at or below the endurance limit ... so the intention seems to be a rig thats close enough as pertains to rig fatigue for one circumnavigation. 
Coastal design boats being seemingly at FS=2 for their rigs ... are the ones I see without masts, etc. 
In the 'trade winds' more often than not youre going to be 'well over' and 'working that wire'.

Being a belt and suspenders plus velcro person, I change out one of my 'majors' (back, cap, headstay, etc.) every 2 years for a total change every ~10 yrs. I proof-load to ~60+% any wire thats apparently changed from my basic tension setting (Im not going to explain how I proof-load as its damn dangerous). Proof-loading usually finds 'the errors' etc. I replace the (mirror polished) chainplates every time I change a wire. I use oversized toggle straps - the thicker the better. 
To lessen crevice corrosion, I yearly heavily spray the rig terminals and plates with "Boeshield" - an aircraft structure 'wax'. If I find any 'rust' on any rig component, I replace -- I dont know if this really works but it makes me feel better.

;-)


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## Foxy (Sep 14, 2013)

bobperry said:


> Casey:
> 
> Please keep in mind that this is the world of yacht design.
> 
> ...


I use both the ISO 12215 scantling rule and FEA in my office for critical structures like keels, rudders, and chainplates. Ten years ago FEA was cost prohibitive, but not any more. The software is inexpensive and will run on a widows desktop.

I also believe in testing to make sure the builder is producing what I spec. Learned that the hard way a few years ago when a Brazilian foundry poured a keel in gray iron when the spec was 80-55-06 ductile. The US foundries I know would have verified what they poured automatically so I did not make a special point of it.

Sent from my iPhone using Tapatalk


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## christian.hess (Sep 18, 2013)

RichH said:


> I dont agree.
> I sail the east coast and down into the caribbean where the trade winds are quite constant. My observed average sighting of boats with failed rigs per season in 'de islans, mon' is usually 2-3, mostly coastal production boats and usually in the range of ~20 years of age and with OEM rigging failures.
> 
> Stainless 300 series is a funky material as it has a quite low endurance limit (30Kpsi) which when exceeded will quickly and quite predictably fatigue fail after 1 million load cycles at above that limit. 1 million cycles above 30ksi, I equate/estimate to approx. one circumnavigation or ~10 years of 'hard' recreational sailing.
> ...


very nice info

I just boucht some new intermediate stays from rigging only and they look awesome...Im basically doing what you do...since my forestay is way oversized and uses mechanical terminals I will simply check them...my cap shrouds or uppers are also oversized and use norsemans so I bought some cones to check and or replace

my back stay and lowers are next on my list but in the meantime I made new 304 mirror polished plates that have been lengthened a bit, on new bulkheads...

My thoughts are to start with a good solid base and work your way up...

good info and thanks


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## christian.hess (Sep 18, 2013)

now back to keel bolts

Ill hopefully be torquing mine a bit since I have a leak at the keel hull joint, I will be redoing that too....hopefully the 5200 fast cures fast enough in 1 and a half tide changes...

heres hoping!


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## Foxy (Sep 14, 2013)

christian.hess said:


> now back to keel bolts
> 
> Ill hopefully be torquing mine a bit since I have a leak at the keel hull joint, I will be redoing that too....hopefully the 5200 fast cures fast enough in 1 and a half tide changes...
> 
> heres hoping!


One note here. If your bolts have threads through the fiberglass, there is a possibility that the lingering water could cause or accelerate crevice corrosion. It would be far safer to haul the boat, drop the keel and re-bed it all properly. I would pull a nut and add bedding around the bolt only as a stop gap measure.

5200 is moisture accelerated and there are some fast drying versions available to use if you are in a hurry.


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## christian.hess (Sep 18, 2013)

I will be in a huge hurry I already have 1 tube of fast cure 5200, but would like at least one more or just standard 5200

unfortunately I will only have 1 or 2 tide changes to work on the boat, it will be careened in sand bags and hopfeully the pressure on the keel upwards will help me source the leaks better(I already have dove the boat and sourced one area that has a crack) and HOPEFULLY be able to tighten a few nuts

i understand this is not ideal but most things arent where Im at...I cant sail to any major marina yet as they are 5-7 days away.

the nuts are j bolts cast into iron or lead depending what year islander 36 you have...I still dont know if Im iron keel or not till I haulout really so a lot will depend on that

My initial idea was to sister in some bolts but I heard its really hard to do on iron keeled boats so considering the condition of the nuts and bolts themselves despite being in water a while I think I can be safe till I get to a proper marina

Ill do an update after the careening for sure

thanks though!


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## Foxy (Sep 14, 2013)

Christian,

Good luck with your leak.

A lead keel would likely have J-bolts, but in a cast iron keel, the bolts would most likely be drilled and tapped. Lead is a fairly low temperature casting (usually poured vertically into a permanent mold) and bolts are usually hung in place with a jig.

An iron casting is usually poured into a sand mold and poured on it's side. While I have cast flange bolts into a fin, it requires a separate core piece to hold the bolts and some very careful gating. Since the bolts act as a heat sink, you can get premature freezing of the iron and porosity around the bolts if all is not right. Not so good!

So if it is an iron casting, chances are the bolts can be backed out and new ones threaded in.


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## casey1999 (Oct 18, 2010)

Faster said:


> I'll let Bob address the essential question here, but wanted to make a observation on the point..
> 
> Hi tech - edge-of-limits racing machines aside, I think rig failures are exceedingly rare - and usually due to lack of maintenance, upkeep and due diligence, possibly/occasionally coupled with an extreme event of some sort.
> 
> I think the SF is probably quite good when new, esp on 'cruising boats'..


I was talking with my boat insurace agent here in Hawaii. He insures a lot of world cruising boats. I said to him I am surprised there are not a lot of demasting due to rig failures. His comment was "there are a lot more than you think" and went on to describe several that happened mid ocean (boats that he insures). Not sure if demasting was due to lack of maintenance or poor design.


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## Faster (Sep 13, 2005)

RichH said:


> I dont agree.
> I sail the east coast and down into the caribbean where the trade winds are quite constant. My observed average sighting of boats with failed rigs per season in 'de islans, mon' is usually 2-3, mostly coastal production boats and usually in the range of ~20 years of age and with OEM rigging failures. ......


OK, perhaps 'exceedingly rare' was an mis-statement, but boats losing their rigs to 20 yr old OEM failures would fall into line with what I meant when I said rig failures were often down to lack of maintenance, upkeep and due diligence.

The practice you went on to describe would be the polar opposite of that approach, is laudable to be sure, but likely not adhered to by the majority.

But.. thread drift... back to keels and bolts!!


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## casey1999 (Oct 18, 2010)

RichH said:


> Well if you want to look at bridge collapse/failure based on very similar circumstances to that we're discussing here, just look into the details of the Mianus Bridge Interstate-95 collapse in 1983 in Connecticut. That bridge mainspan dropped into the water catastrophically when one of the 4 PINS, the sole support links of that bridge and stunningly similar in construction to a keel held on solely by 'bolt strength' fails.
> Of course the real culprit was lack of maintenance and lack of adequate inspection to visualize that these pins, _the sole support of the bridge_, were failing.
> And, the Interstate 90 (Albany) collapse in 1987 (?) ... another pin set / pin hung bridge that went down when one of the bridge supports was weakened by flooding.
> And, then again another 'pin set / pin hung' bridge collapse on Interstate 35 in Minnesota in 2007.
> ...


First, I am not a civil engineer and do not design bridges. I have taken bridge design engineering courses however.

Here is some information on pin set/ pin hung bridges from:




(go to wikipedia for a pic of what they are talking about)

"A Pin and Hanger assembly is used to connect two plate girders of bridges. These assemblies are used when the space between two bridge piers is too wide to be spanned by a single set of girders. To overcome this, steel beams are set with one end resting on a bridge pier, while the other end is connected to adjacent steel beams that are cantilevered from the next pier. The two steel beams are connected using a pair of connecting plates (one on each side of the bridge joint). A pair of bolts are inserted through the plates and girder webbing: one through the cantilevered beam and one through the suspended beam. Exceptionally long spans may have two sets of girders cantilevered from opposite bridge piers with a third set of girders suspended by pin and hanger assemblies from both cantilevers.

Safety concerns[edit]Pin and hanger assemblies are considered fracture critical bridge components, meaning that the assemblies are non-redundant and failure of these systems could cause part or all of the bridge to collapse. The collapse of the Mianus River Bridge in Connecticut exposed potential flaws with pin and hanger bridges that could lead to catastrophic failures, if left unchecked. Because of this, state departments of transportation incur costly expenses on bridges with pin and hanger assemblies, as they require constant inspection and maintenance. As a result of these safety concerns, and advances in bridge design to allow longer spans, pin and hanger assemblies are no longer used on new bridges in the United States.

Retrofitting[edit]Attempts have been made to increase the safety of bridges with pin and hanger assemblies by adding some form of redundancy to the assembly. Retrofits that add redundancy to pin and hanger assemblies include adding a "catcher's mitt"--a short steel beam attached to the bottom of the cantilevered girder that extends out beneath the suspended girder to "catch" the suspended girder should the pin and hanger assembly fail. Another redundancy is connecting the cantilevered and suspended girders at the pin and hanger assembly with welded blocks and tie rods. Finally, a bridge may be retrofitted by replacing the pin and hanger assembly with a pair of gusset plates that are much larger and thicker than the pre-existing hanger plates."

Second, this design is totally different from a bolted on keel. A bolted on keel has somthing like a 10 to 1 safety factor. You can loose quite a few keel bolts before your keel falls off. and you can loose quite a few before the keel even comes loose.

Third, comparing a encapsulated keel to a bolt on is comparing two different designs, one not necessarily better than the other. An encapsulated keel relies on the fiberglass skin to support the keel ballast. If the boat is at dock, the fiberglass skin will only see tension. When the boat is heeled, the keel skin near the surface will be in tension and other side will be in compression- just like a cantilerverd beam would see.


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## christian.hess (Sep 18, 2013)

Foxy said:


> Christian,
> 
> Good luck with your leak.
> 
> ...


thanks man! Im quite familiar with iron in motorcycles, and the sandcasting process

if indeed my bolts are threaded into iron I think I will be in the sistering keel bolts camp but I need a nice big drill have to have the boat on a lift I think...it would be a bit too much to do this while careened really DONT want to risk it

heres hoping all goes well

I think your advice of backing of te nuts and rebedding that with a new washer is a good one and might be someting that can be done in the water...at least one at a time...however there is the IF IT AINT BROKE dont fix it camp...and honestly fixing a keel hull joint leak is pretty commonplace on fin keelers and I THINK I can pull this off with what I have available

again I appreciate youre help

now back to bolts...if I do sister in and my keel is in fact iron and I cant BUY titanium what would the crowd be happy with?

Im guessing whatever steel bolts the originals are...but what thread? coarse right?

would you epoxy the holes? then redrill?

my islander has a steel backing plate where all the bolts go though so that helps...a new one would be ideal but that is too much to chew at this point

thanks guys


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## casey1999 (Oct 18, 2010)

Here is some interesting reading about keels, keel bolts, and the keel hull connection:
http://www.tamus.edu/assets/files/c...woods/Cynthia-Woods-Report-SIAD-OGC-FINAL.pdf


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## SloopJonB (Jun 6, 2011)

christian.hess said:


> if indeed my bolts are threaded into iron I think I will be in the sistering keel bolts camp but I need a nice big drill have to have the boat on a lift I think...it would be a bit too much to do this while careened really DONT want to risk it
> 
> heres hoping all goes well
> 
> ...


I wouldn't sister keel bolts. If the existing threads in the keel are worn or otherwise iffy, I'd overdrill them for the next thread size and re-tap them. Using the existing holes as a drill guide makes it much easier than starting from scratch alongside them.

Coarse threads are the way to go. As to material for the new studs, I used S/S when I did mine but galvanized worked fine for 30 years. One nice thing about iron keels is the studs can easily be pulled for inspection. Use anti-seize on the threads (for the future).

I also cut my studs long enough to double nut or jam nut them - just a little more peace of mind.

Don't forget to use a torque wrench - far too many people use a breaker bar and a piece of pipe and just pull on it as hard as they can.


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## benesailor (Dec 27, 2012)

This is getting better and better. Love the engineering aspects of the conversation.


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## Foxy (Sep 14, 2013)

You know it is funny how some people expect boats to last forever with the original equipment in a very corrosive environment. Cars and bridges require maintenance. Aircraft have very rigid maintenance schedules to stay airworthy. 

As far as I can see, Rich is one of the few that routinely replaces things before they are worn out. I know a couple whose 30 year old boat sunk because they never thought to replace the hoses to the seacocks they took apart and greased every few years.

But back to keel bolts. One can go to the other extreme as well. Last year I was called on a case where the owner wanted to drop his keel and check it out before going on long cruise. Only problem was that the bolts passed through a deep sump that was filled in and tabbed over. For good measure, the builder had poured epoxy around the bolts to make sure they were well "protected". The yard welded a hole saw to the end of a pipe so they could cut around the bolts. Of course they managed to mangle the bolts in the process. They would have been better off to leave things alone because the boat was only about 6 years old and the only thing wrong with the bolts was caused by the yard.

It wasn't my design, but I got called in because I have done other work for the builder. Needless to say it became a very expensive fix for something that wasn't broken.


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## SloopJonB (Jun 6, 2011)

Personally, I would never buy a boat that had buried keel bolts, chainplates or any other critical structures or components.

Living the majority of my life in a rain forest has taught me that you can never entirely keep water out, you can only trap it in.

Every single part of a boat should be accessible for service.


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## manatee (Feb 27, 2013)

christian.hess said:


> {snip}
> 
> the nuts are j bolts cast into iron or lead depending what year islander 36 you have...I still dont know if Im iron keel or not till I haulout really so a lot will depend on that


Got a magnet, or diver's compass? --
Magnet sticks to keel --> keel=iron
Compass swings near keel --> keel=iron

Good luck.


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## christian.hess (Sep 18, 2013)

you know I have a small compass...Ill try that as I dont have a big rear earth magnet

of course it could also be the backing plate that sends a "signal" so I wont be completely sure until halout but thanks

I really dont know but on the islander 36 site they dont mention the iron keel as having studs...they mention all islander 36 have j bolts cast into the keel be it iron or lead so the saga continues I guess

I really DONT want to break a stud or not for "peace of mind" hence the adding bolts scenario...

anywhoo well see!

peace


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## manatee (Feb 27, 2013)

christian.hess said:


> you know I have a small compass...Ill try that as I dont have a big rear earth magnet
> 
> of course it could also be the backing plate that sends a "signal" so I wont be completely sure until halout but thanks
> 
> ...


 Wouldn't the lead keel be smaller for the same weight? I found 3 Islander 36 on sailboatdata. Does your boat draw 4.8'/1.46m or 6.08'/1.85m? They weigh within 150 lbs of each other, so my guess is the shoal-draft has lead. Only one listing had drawings, so I had nothing to compare the different models to.


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## christian.hess (Sep 18, 2013)

not necessarily on the islanders, apparently there is a way to tell, the bilges are shallower on some models

the shoal drafts were only on later model boats, and yes I do beleive they were only lead...

my bilges are shallow...BUT I cant remember what that meant keel material wise or not...

anywhoo thanks for the help


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## svHyLyte (Nov 13, 2008)

benesailor said:


> 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?
> 
> ...


For the sake of the exercise, I assume you're sailing a Beneteau Oceanis 400 (40' LOA). That yacht commonly has a ballast keel of Cast Iron weighing in at approximately 5300 lbs. Typically, Beneteau uses Type 8.8, M20, Dacrotized Steel Bolt on Cast Iron keels of this size. (Dacrotizing is a method of corrosion protection utilizing Zinc-Aluminum flakes in a chrome/polymer matrix-one step up from common galvanizing in the opinion of some). A Type 8.8, M20, bolt is equivalent to a ¾" diameter ASTM A-325 bolt with a yield strength of 36,000 psi.

For what it's worth, designing a ballast keel/hull connection is akin to designing a column/base-plate connection for a column intended to have a fixed end connection. When the column is subjected to a lateral load, the base plate must secure the foot of the column to the foundation pad as if the column were embedded in the foundation/earth-i.e. the base of the column cannot rotate with respect to the foundation. Likewise on a yacht, the top of the keel (in its normal upright configuration) cannot be allowed to rotate with respect to the hull but must act as if the ballast keel and hull were a single homogeneous structure.

Assuming your yacht is an Oceanis 400 with a bulb/fin keel, the "base plate" or point of connection of the fin to the underside of the hull is about 6.83 feet long with the bottom of the ballast keel being about 4.3 feet from the underside of the hull. For a keel of that size and weight, I guestimate that you are fitted with 10 keel bolts. A single bolt, each, foremost and aftermost, along the centerline of the yacht and then 4 pairs of bolts relatively evenly spaced between them. The root of the fin at the bottom of the hull will likely have an average overall width of about 8 inches with each pair of bolts roughly 6 inches apart from side to side. Based on the shape of the keel, I'd guess that about 60% of the ballast (3180 lbs) is centered in the bulb and the remaining 40% (2120 lbs) distributed over the fin. Within the fin, based upon its shape I'm guessing that the center of mass would be roughly 40% of its "span" below the hull (or about 1.37 feet) while the center of mass of the bulb would be at the centroid of the bulb, about 3.85 feet below the hull.

Based upon the foregoing, with the yacht fully knocked down to 90º, with her keel extended horizontally and unsupported by the water, the bending moment of the keel weight about the top of the keel at the hull would be on the order of 15,147 foot lbs. Assuming the keel surface at the hull joint is a foil, I will ignore the forward most 10% of the keel and after most 20% leaving a "working" root of approximately 70% or about 4.78'. Accordingly, the bending moment about the keel base at the hull is approximately 3,168.2 Ft-lbs per foot or 264 ft-lbs per inch. This is carried by compression on the hull as the ballast keel attempts to rotate about the joint and, tension in the upper-most row of keel bolts (the bolts along the center-line of the keel fore'n aft ignored although, as a practical matter, they do contribute resistance as well).

For the sake of analysis, I assume the bolt pairs are spaced to ensure that each pair carries roughly the same loading so that the moment carried by each of the four bolt pairs is approximately 3787 ft-lbs. Because the face of the ballast keel at the hull is, relatively, infinitely rigid compared with the hull, the compression load on the hull is triangular with a maximum at the bottom edge and, effectively zero at the top edge (ignoring for a moment the pre-compression in the keel bolts induced by the torque applied at installation, typically between 94 ft-lbs minimum and 195 ft-lbs maximum for M20 bolts). Given that, the line of action of the compression load will be at 2/3rd of the assumed width of the keel root or about 5.33" below the top of the keel. With 6" between the bolts in each pair, the resisting bolt will be 1" below the top edge such that the "couple" formed by the bolt in tension and the compression load will be about 4.33 inches or .36 feet. The resisting load will then be 3787/.36 or 10,487 lbs in each of the uppermost bolts and 731.2 lbs per inch of compression on keel/hull joint. Remembering that the total compression load is the maximum compression (in PSI) x 2 divided by the base, the maximum compressive load applied to the hull by the keel would be on the order of 183 PSI which is easily within the compressive strength of the GRP used in the Beneteau keelson.

As for the loading on each of the assumed bolt pairs, an ¾ inch diameter ASTM A325 bolt has an allowable tensile load of 17,670 lbs. While the combination of tensile loading and shear loading induced by carrying the weight of the keel in the bolts as a bearing connection (not friction as some have suggested although friction would contribute some load bearing capacity), could be assumed to reduce the tensile capacity of the bolts somewhat, the actual shear loading, 5300/10=530 lbs, is negligible when compared with the bolts shear strength (9720 lbs) and can be safely ignored.

I realize the foregoing is a somewhat "dumbed-down" explanation of a fairly esoteric subject (for the sake of the lay person) but getting into the esoterica really wouldn't add much to the discussion and would likely make even the eyes of those that have gotten this far glaze over.

In summary, the Type 8.8 M20 bolts normally used by Beneteau for a keel of the type used on the Oceanis 400 are more than adequate for the job and there is little to be gained by going to a more exotic bolt at fantastically greater cost. For what it's worth, this past year I pulled and replaced a number of 26 year old keel bolts on our yacht as they were showing some rusting about the heads. The bolts all came out clean and dry and other than little more than a bit of heavy wire brushing and new cut washers, were good to go with a couple of coatings in Pettit RustLok for protection. Keep in mind that the amount of "rust" one sees about a fastener is about 600% of the amount of steel consumed in the process of being oxidized into "rust" so the process often looks far worse than it is in reality.

Of course, if you wanted to have titanium bolts machined up of a matching size, they would certainly work but why bother?


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## benesailor (Dec 27, 2012)

Thanks svhylyte, Great explanation, my brain just turned to mush. I feel so much better that you dumbed it down. Do you have friends that are on Big Bang Theory 

I'll order up some original equipment bolts for my Oceanis 400. Now i know what the coating is anyway. The aft ones have more than surface rust.


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## benesailor (Dec 27, 2012)

> Typically, Beneteau uses Type 8.8, M20, Dacrotized Steel Bolt on Cast Iron keels of this size.


For future reference: This model uses 4 M20 x 90's and 6 M30 x 130's. A little bit stronger. 
This conversation definitely makes me feel better about the Bene and the strength of the hull/keel connection.

Thanks again


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## casey1999 (Oct 18, 2010)

Great write up by SvHyLyte.

From a book called "Metal Corrosion in Boats" by Nigel Warren (page 139-144) has a good discussion of keel bolts:
Iron Keel Nigel recommends #316 Stainless with plently bedding compound. Also recommends monel and titanium, but states good electrical insulation is necessary to reduce galvianic corrosion. Seems to indicate mild steel is a good solution.

Nigel also notes for iron keels, Lloyds recommend galvanized iron or steel or stainless steel for keel bolts. For a lead keel use bronze (gunmetal, silicon bronze or aluminum bronze or monel.

Looks like you existing bolts are a good choice.

Here is book if interested:
Metal Corrosion in Boats by Nigel Warren - New, Rare & Used Books Online at Alibris Marketplace


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## hellosailor (Apr 11, 2006)

There are often good reasons to follow convention. For instance, you won't find many silicon bronze keel bolts, or nuts. Silicon bronze is a great metal, but also known as "bell metal" and known to be brittle. As in the twice-cracked Liberty Bell.


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## casey1999 (Oct 18, 2010)

RichH said:


> I dont agree.
> I sail the east coast and down into the caribbean where the trade winds are quite constant. My observed average sighting of boats with failed rigs per season in 'de islans, mon' is usually 2-3, mostly coastal production boats and usually in the range of ~20 years of age and with OEM rigging failures.
> 
> Stainless 300 series is a funky material as it has a quite low endurance limit (30Kpsi) which when exceeded will quickly and quite predictably fatigue fail after 1 million load cycles at above that limit. 1 million cycles above 30ksi, I equate/estimate to approx. one circumnavigation or ~10 years of 'hard' recreational sailing.
> ...


Rich,
You state you proof load to 60% any wire that has changed from your tension setting:

"I proof-load to ~60+% any wire thats apparently changed from my basic tension setting (Im not going to explain how I proof-load as its damn dangerous). Proof-loading usually finds 'the errors' etc."

Looking at both 304 and 316 stainless (most common type for wire rigging) the yield strength is about 50% of the breaking strength of the wire (breaking strength is the wire at Ultimate Tensile Strength, UTS).

Therefore, I would think by going to 60% of UTS you are yielding your wire rigging during your proof load. Once the yield point of a wire is exceeded, the wire is now trash. If you want to proof load, I would not exceed 30% of you wires breaking strength. Maybe this is why you see your wire changing its tension setting (if your boat is not deforming)- you have yielded your wire.

I annually test rigging gear and cranes. We proof load to test the gear and hoists. During proof load we inspect for breaks and metal deformation. We never exceed 105% of the gears rated capacity (rated capacity is in the order of 5x break strength of the gear). So for our equipment, we test at 21% of break stength- far less than 60%. If we exceed 105% of rated capacity, we consider the gear to be damaged- maybe a little extreme for a boat, but I would never go above 30% break stength.


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## Stumble (Feb 2, 2012)

The one thing I would add, is that while there are many good reasons to stick with convention, the cost of titanium is not one of them.I know its reputation, but it no longer is true as the cost keeps going down while the cost of other materials is going up. 

In practice, when I was selling titanium fasteners, we were selling titanium G5 bolts to major distributors for roughly 15% more than they were paying for 316L stainless of the same size. Exact same size, length, head, ect.. But the titanium was 15% more expensive at roughly 5 times the strength.


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## RichH (Jul 10, 2000)

casey1999 said:


> Rich,
> You state you proof load to 60% any wire that has changed from your tension setting:
> 
> "I proof-load to ~60+% any wire thats apparently changed from my basic tension setting (Im not going to explain how I proof-load as its damn dangerous). Proof-loading usually finds 'the errors' etc."
> ...


I must have had a brain fart when posting and missed the 'edit'. Yes indeed ~30ksi is yield str. (.2% offset) for non-annealed ~300 series. I do routinely bring my rigging up to the approach of below that 30% value when proof loading (perpendicularly loading the wire). When my mast is down, I always carefully check the length for just that reason - yield. Mea Culpa.


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