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  #1  
Old 06-26-2012
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Chain Plate Material

Looking at replacing my chain plates. Bronze (Silicon) seems to be the best choice so far. Should basically last forever. Also, seeing my new turnbucles are bronze (with male threaded studs 316 ss) seems like the material should be compatiable.

Do you see any disadvantages?

Should I use bronze bolts or stainless to hold the chain plates (bolts will be located in side the boat, out of weather)?

Regards
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Old 06-26-2012
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Re: Chain Plate Material

Casey,

I am prejudiced, but I would recommend titanium chainplates, with titanium bolts. Lighter, stronger, and more corrosion resistant than any other option, and while they are more expensive, not tremendously so. And when you think about the fact that the titanium chainplates will effectively last forever (likely longer than the boat), it means you will never have to go through the process of repair again.

If you go with siliconized bronze be aware that it is a range of alloys, and you need to know exacally which one you are dealing with. Depending on the alloy it's tensile strength can range from half that of 316L to twice that of 316L. It is a fine metal for chainplates, but you need to know exacally which grade you are buying.

If you decide to go titanium from me or someone else, I would recommend Grade 5 instead of grade 2 or 9 (the other common alloys). Grade 5 is much stronger than the other alloys, and since it is the most common grade used in structual materials the cost is a little less. As compared to bronze the part will be significantly stronger, lighter, and even more corrosion resistant than bronze. I would need to know exacally what your chainplates dimensions are to price them, but we have some that range from $20 (strait 2 hole small boat chainplates) to $1,200 (60' bowstay plus integral bow roller Chainplate, and bobstay fitting).
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Old 06-27-2012
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Chain Plate Material

Stumble

What's your company?

This is what I have done so far.
http://theincrediblehull.blogspot.com/search/label/chainplates

Gerry
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Old 06-27-2012
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Re: Chain Plate Material

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Originally Posted by gtod25 View Post
Stumble

What's your company?

This is what I have done so far.
The Incredible Hull: chainplates

Gerry
Enjoyed your blog. Ok, now I am leaning towards Titanium. I also used to work "underwater" and think things (at least on marine transport devices) should be done right the first time, overdesigned, overbuilt, and built to last.
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Re: Chain Plate Material

I liked the blog.

The one thing I would add though is that because of titaniums resistance to corrosion, it's like buying insurance. You hope you never need it, but it gives you a good feeling to know that it's there. Similarly every sailor hopes their chainplates never fail, but knowing that they won't rust away gives me a nice feeling inside.

I am working with some of the production builders to try and get them to switch to titanium as OEM parts, which should drive the prices down a lot. Sadly some of the push back has been that it isn't something that will ever be covered under a warranty repair, so why should they bother.

Ignoring my financial interest for a moment, I have sailed thousands of miles on boats with spotty chainplates (once to deliver a boat to a yard to have them replaced), and there is nothing so unnerving as doubting the structual reliability of them. It's try a good 316 Chainplate will last for years likely decades, but when they go, they go with a band.
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Re: Chain Plate Material

OK, I suggest 3/8" G10, no corrosion and stronger than steel or Ti or bronze.
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Re: Chain Plate Material

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OK, I suggest 3/8" G10, no corrosion and stronger than steel or Ti or bronze.
I don't think it would hold up well to the fatigue the chain plates will see.
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Re: Chain Plate Material

G10, like bronze, aluminium, and all fiberglass has fatigue issues. There is a definite life cycle number that will eventually break the part. The stronger the part is from inception, the higher the number, but it is still a definite number.

Steel including stainless varieties eventually have a logarithmic flattening of the fatigue cycles needed to break the part. As the loads go below some % of tensile strength of the part, it takes progressively more cycles to fail. For steel (including stainless) this occurs around 30 and 40% MBL though it is alloy specific, so to know exacally what the failure point is will require knowing exacally what alloy you have.

Like steel titanium has a flat lined fatigue cycle curve, but generally titanium flatlined earlier than steel does (40-50%) MBL. Again it is alloy specific, and the actual calculations are pretty complicated (beyond my abilities certainly).

In practice what happens is that a designer will spec a stainless chainplate of X size, which is chosen to get the fatigue limit into the flatline, and assumes some amount of corrosion degrading over time. By switching to titanium you acomplish a few things.

1) the part itself is roughly twice as strong for the same size (most replacements are done size for size, not strength for strength).

2) the fatigue limit is higher for the titanium

3) the corrosion allowance used for the 316 can be ignored in the Ti.

So the result is a part that is honestly massively overbuilt for the expected loads. Because in the ways that matter the titanium is actually stronger across the board than the steel. Effectively this gives a titanium replacement a nearly infinite fatigue cycle as compared to a 316 replacement.


Bronze on the other hand does not have a logarithmic flattening of the fatigue cycle curve, which means as the loads go down, the number of cycles it can endure do go up, but at a roughly linear rate. By sizing bronze for a definite life cycle, and making a number of assumptions about how many cycles it will see in a given period it is possible (and has been done for years) to design a part that will last for some given time. But it has to be larger and stronger than a comparable part out of steel or Ti.

Fiberglass including G10 has a very steep fatigue cycle life, and while it can be used for chainplates, the number of cycles it can absorb is like bronze much lower. This requires the part to either be replaced more often, or to be build significantly oversized. G10, is also prone to fracturing and shattering from impact loads, like carbon fiber it has massive physical properties, but these are offset by real limitations. Again, it is doable, but it really isn't the best material for the job. Though like titanium it is effectively immune to corrosion and is very light.

Honestly if you design it right you could make chainplates from just about anything. But there are certain materials that are more suited than others. Stainless of course has been the go to for a long time, and will be used a lot in the future as well, with very good results. New fiberglass/composite chainplates are showing interesting promise, but are held together with titanium or stainless pins and bushings.

Titanium is coming on the market is a big way, and it's easy to see why. Sadly the price is still quite high compared to stainless, though we are working on getting the prices down to comparable with stainless. Honestly it isn't even the material price difference, it is the cost of fabrication. People don't buy it because it is expensive, which keeps the price up, when things go into mass production, our cost is only about 20% more than a stainless part. This is why we are trying so hard to get manufacturers to install them OEM. Figure it would add $100-$300 to the purchase price of a boat for them to install titanium as opposed to stainless, and effectively remove them as an issue to worry about.
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Last edited by Stumble; 07-13-2012 at 08:40 PM.
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Old 06-27-2012
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Re: Chain Plate Material

I replaced the chainplates on my Alberg over the winter and upgraded the size of the stock from 3/16" x1 1/4" to 1/4" x 1 1/2", as well as the fasteners. I stayed with 316L stainless for ease of availablity and price. I ordered a 6ft piece to my door for 70 bux and that did all of them. I am not saying its the best choice but orginal stainless units lasted 40yrs, these should go at least half that. Silicone bronze was gonna be around 300 and availabilty was not so easy, I think the only place i could find it was in Colorado. I can build 4 sets of 316L for what bronze ones cost. They will have to be inspected no matter what material is used. Alberg 30 units are not very hard to duplicate either. Check onlinemetals.com, great selection and pricing.

good luck!
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Re: Chain Plate Material

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Originally Posted by Stumble View Post
Like steel titanium has a flat lined fatigue cycle curve.
Greg,
to get an cost comparison, what would the budget price be for Grade 5 Ti chainplate 1/4" thick X 1-1/2 X 16" long? sand blast finish.
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