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Old 11-04-2012, 09:21   #1
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Can I trust my new chainplates??

This season I figured it would be a good idea to replace the chainplates and bolts. I had a local steel shop fabricate two plates out of 316 Stainless steel plating to match the size, thickness, and bolt pattern of the old plates. They came out nice, but were a little rough to the touch, so I brought them to an electropolishing shop and had them smoothed out for long term corrosion prevention.

I ordered new matching bolts out of 316 steel from a company I found online called Marsh Fasteners. They claim to specialize in "high quality, marine grade" bolts. They seemed legit enough to me, although it doesn't say where their parts are made on the website.

When I actually installed the new plates and put the bolts in, I came across a problem. The threading on the bolts was getting messed up as it passed through the chainplates, I guess because the holes were a little too small.

But here is the part that really bothers me. After the nut got stuck on a bolt with bad threading, I figured we had to cut the bolt to get it off. Since this was taking forever, I just tried torquing it off instead. The bolt snapped in the middle without too much force. I tested the others, and I was able to break them all myself with nothing more than two socket wrenches, one in each hand. What is going on? I ended up using the original bolts to put the new chainplates in, which are solid as a rock compared to the new ones.

So basically now I'm concerned about the strength of my new chainplates. Is it just that Marsh fasteners is using bad steel, or is steel generally low quality these days (as my father is insisting). I can get back in touch with the steel shop to see where the plates came from, but there is no way of actually testing their strength. The old chainplates still look fine (304 steel, I believe). I was replacing them as a precaution, but now I'm not sure if I've done more to weaken my boat than protect it.

And where can I get high quality stainless hardware? I've had parts easily break now from two marine supply stores and from Marsh fasteners.

Any guidance is much appreciated...
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Old 11-04-2012, 10:08   #2
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Re: Can I trust my new chainplates??

Quote:
Originally Posted by OrangeCrush View Post
I ordered new matching bolts out of 316 steel from a company I found online called Marsh Fasteners. They claim to specialize in "high quality, marine grade" bolts. They seemed legit enough to me, although it doesn't say where their parts are made on the website.

When I actually installed the new plates and put the bolts in, I came across a problem. The threading on the bolts was getting messed up as it passed through the chainplates, I guess because the holes were a little too small.

But here is the part that really bothers me. After the nut got stuck on a bolt with bad threading, I figured we had to cut the bolt to get it off. Since this was taking forever, I just tried torquing it off instead. The bolt snapped in the middle without too much force. I tested the others, and I was able to break them all myself with nothing more than two socket wrenches, one in each hand. What is going on? I ended up using the original bolts to put the new chainplates in, which are solid as a rock compared to the new ones.

So basically now I'm concerned about the strength of my new chainplates. Is it just that Marsh fasteners is using bad steel, or is steel generally low quality these days (as my father is insisting). I can get back in touch with the steel shop to see where the plates came from, but there is no way of actually testing their strength. The old chainplates still look fine (304 steel, I believe). I was replacing them as a precaution, but now I'm not sure if I've done more to weaken my boat than protect it.

And where can I get high quality stainless hardware? I've had parts easily break now from two marine supply stores and from Marsh fasteners.

Any guidance is much appreciated...
OrangeCrush,

I see from you profile photo that you're located somewhere in the US, so we'll talk imperial rather than metric moving forward.

Firstly, you should be able to ask for the actual material certificate (with Heat number) for the plates. It'll be hard, now that they've been polished, to verify whether the plates you have came from the material certs. If they can't produce any material certs or don't know what you're talking about, or just give you a standard material specification - then you may want to ask yourself how they know it was AISI316.
If you get the material certificate, the bits you're interested in are as follows:
Rp 0.2% offset yield should be above 260MPa (37.7ksi) the standard is 260MPa but typically you'll find it testing above 300MPa.
The material certificate should also show a Brinnel hardness of 180max - higher than this and the material is out of spec.

Your fasteners are the biggest problem. You could have a chainplate made out of Kryptonite, but if it's fastened to your hull with shiny-poo then they're only going to act as pendulums at the lower end of your shrouds!

Bolts:
This is a tough one. It's actually very common for sub-standard bolts to be sold stating that they're of "A4" or "A2" quality stainless when they're not. If they came in a bag without any form of certificate or paperwork with them then they cannot be relied upon.
Apart from a magnetic test (which really proves little), i'd check to see how much torque you're applying to the bolts when you tighten them. It very easy to over-torque bolts using socket-wrenches.. especially if they're small.

Your bolts may not be 316, but rather something like 18-8 Stainless which has a slightly lower yield than 316.

Below is a small table of maximum torque values for various bolt sizes versus applied torque in inch-pounds: whereby 1 inch pound is 1 pound of force applied tangentially at a distance of 1 inch from center of rotation. With a socket-set with a length of around 12' you're probably producing over 500 inch-lbs when you give a good firm tug on the spanner! Bolts are devilish creatures when it comes to torque failure. The material tends to self-anneal once it's started to fail and gone into 'plastic mode' temporarily stiffening before it fails completely.

Remember that if you 'pre-stress' a bolt too much by over-tightening then there'll be less 'headroom' available for the shear-loads which will be introduced into the bolts from the loads on the chainplates.

Hope this helps,

Phil
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Old 11-04-2012, 10:33   #3
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Re: Can I trust my new chainplates??

What size are the bolts? If they are 1/4" then I can see them snapping pretty easy, but they are more likely 3/8 or larger and it should take a heck of a breaker bar to snap those. I'd scrap them. I wouldnt worry about the bolts being 316, but you do want quality bolts. In a perfect world I would want bolts with unthreaded portion where it goes thru the chainplate/hull. If the total thickness isnt enough this might require buying longer bolts and cutting some of the bolt off.
Are you saying your chainplates were made from Plate not bar? Not a show stopper I suppose, but the edge of cut plate is going to have a lot of stress rissers in it unless very well ground back and polished. Also, bar stock usually has some cold work in it making it stronger. I always like the idea of square holes in the chainplate and carriage bolts....
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Old 11-04-2012, 10:39   #4
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Re: Can I trust my new chainplates??

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Originally Posted by Cheechako View Post
I'd scrap them. I wouldnt worry about the bolts being 316, but you do want quality bolts. In a perfect world I would want bolts with unthreaded portion where it goes thru the chainplate/hull. ..
+1 completely agree
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Old 11-04-2012, 11:42   #5
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The bolts are 3/8" in diameter and each one is stamped with "316" on it. It took most of my strength to snap them, but all of them snapped promptly on the first try.

As for the plates, yes they were made from plate stock, not bar. What is the difference exactly? This is all rather new to me.

What would you guys suggest for now? Since I'm running out of time to get the boat in the water, I've got two options the way I see it: Leave the new plates in with the old bolts, put the old plates back in with the old bolts. Either way, I could get new plates for next year's season and do it right. It's just frustrating because that's what I thought I was doing in the first place.

Yes I am located in the US, in New York. Any suggestion on who to go to for acceptable bolts or chainplates?
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Old 11-04-2012, 11:54   #6
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Re: Can I trust my new chainplates??

If your chainplates are new, appropriate size, and polished nicely on the edges I wouldnt worry about them. threads systems exert amazing force. Your screws are not subjected to the same force when holding your chainplates on as they are when a nut is cranked down. They are in shear from your rigging and in tension from the nut. Go to a hardware store and buy another 3/8 stainless bolt and try breaking it. If it's similar to what you are experiencing, then your screws are likely fine and you are overtightening them. You may start making stress cracks in your hull from that. The trouble is if you've overtightened all of them, you have no idea if they are starting to crack. You'll have to use your judgement on whether you have done that. If you have several 3/8 bolts on each chainplate, I doubt if the rigging on a 26 footer is that strong.....
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Old 11-04-2012, 12:00   #7
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Re: Can I trust my new chainplates??

Proper torque for a 3/8-16 (coarse thread) 316 SS bolt is 18-20 ft lbs.
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Old 11-04-2012, 12:09   #8
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Re: Can I trust my new chainplates??

Thanks for all the help so far, guys.

There was another problem with the bolts, which was that they didn't have quite enough threading on them, so even on the ones that didn't strip from the chain plate I ended up running out of thread before the bulkhead was getting much of a squeeze. This would have been reason enough to get different bolts, but when I found that the easiest way to get them out was to break them, I started getting nervous about all the new stainless.

The old bolts had a little more thread, so when I put them back in and cranked them down it squeezed the plate against the bulkhead as it should (which is clearly visible on the inside of the cabin). When I could see the clear coat flexing under the washer, but before any stress cracks started appearing, that's when I judged it "tight enough".

Yes I agree that my relatively small sail plan will not tax the metals as much as they would be on a larger rig, but I'm still anxious about getting this right.

Would you advocate a new set of bolts from the local marine supply store rather than the original ones, which are time tested but also old.

Thanks again,

Jack
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Old 11-04-2012, 12:12   #9
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Re: Can I trust my new chainplates??

I suggest buying your new fasteners from McMasterCarr. I trust them to sell what they say they are selling.
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Old 11-04-2012, 12:17   #10
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Re: Can I trust my new chainplates??

I, personally, get almost all of my hardware from McMaster-Carr.

McMaster-Carr

Depending on your location, it is usually overnight shipping and they have an incredible assortment.

Try this link:

McMaster-Carr
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Old 11-04-2012, 12:23   #11
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Re: Can I trust my new chainplates??

+1 on MMCarr. Not sure if the marine store will be any better than your local Ace Hardware.... which both MIGHT be fine... but hard to tell... It sounds like your chainplates go through the deck to bulkheads rather outside the hull.... I missed that.
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Old 11-04-2012, 12:29   #12
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Re: Can I trust my new chainplates??

A316 is a bit weaker than A304, but is more corrosion resistant.

Stainless Steel Information Knowledge alloys 316 304
Grade 304 Stainless Steel Technical Data

It sounds like the holes the plates were drilled the same size as the bolts, they should have been oversized 1/16" or 1/32".
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Old 11-04-2012, 12:42   #13
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Re: Can I trust my new chainplates??

Yes, chain plates go through the deck and bolted to the bulkheads.

So, are we reaching a consensus that the new plates will be "good enough" if they are made from new 316 plate stock and polished smooth? I trust the steel shop and if they said it was 316 I'm confident that they're not being dishonest.

Thanks for the tip about McMaster-Carr. I guess what I'd be looking for is Grade 9 "Extreme strength" bolts? After a quick look at their site, it seems like these only come "fully threaded" so this may not be perfect for the bulkead connection. Is there another variety I'm not seeing?

Thanks a lot!
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Old 11-04-2012, 13:03   #14
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Re: Can I trust my new chainplates??

beware of graded bolts--if not stainless, they do rust...mexican loctite only lasts so long before snapping....

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Old 11-04-2012, 13:25   #15
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Re: Can I trust my new chainplates??

chesapeake marine fasteners at fawcetts Annapolis has good quality fasteners. no question about where they came from. mcmaster carr will anything you want and on your doorstep tomorrow but youll pay a touch more.
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