Help me understand how chainplate loads work?

[Cheechako]

Originally Posted by a64pilot

I think you do polish the whole thing don't you? Isn't the purpose of polishing to remove stress risers, not to make it pretty?

They break at the holes likely because that is where they are weakest, especially if the hole is not de-burred, back to stress risers

Yep, but in order for the holes to be stressed to be the weak point, the plate has to move. Thus, the friction isn't holding!
Looking at the pics mentioned, it may be the corrosion at the hole that is more a detriment than the hole itself ... Probably water getting in there over time and trapped next to the stainless...

[ur2slo]

Originally Posted by a64pilot

I think that is way more common than we realize, its professional judgement, and more often than not I am more comfortable with a known designer with decades of experience than I am with a wiz kid and a computer

A great discussion going on here, but as we are seeing, the emphasis I make is at what point to call good enough good enough.

THATS the part lacking today. I sat in many meetings over the years discussing the work I was about to do with high level types and the common thread in a lot of my frustrations nowaday's is that no one will stand up, say I will take responsibility for my calculations and leave it at that.

NO we now spend millions to engineer our way out of making decisions. So all can say I didn't do it, well guess what? The cost is killing us, get off ur butt and make a decision and stick to it.

2 rules we need in mechanical engineering...

1. If it moves & shouldn't....Duct tape it.
2. If it doesn't move & should........wd 40 it.


there done.

DUCT TAPE & gorilla glue, ( I just googled it!) the polished stainless chain plate to the base material .

[DumnMad]

Originally Posted by Cheechako

Yep, but in order for the holes to be stressed to be the weak point, the plate has to move. Thus, the friction isn't holding!
Looking at the pics mentioned, it may be the corrosion at the hole that is more a detriment than the hole itself ... Probably water getting in there over time and trapped next to the stainless...

Heck of a difference between slipping and stretching.

Coefficient of friction dry steel on glass is 0.5 to 0.7 so its easy to get the friction value needed.
If bolts get loose and water gets between then the bolts are in shear/bearing and significant movement must take place.(And corrosion will follow.)

How many of those failures were caused by poor maintenance? - water getting in - timber getting soft - clamping force fading away and bolts getting loose.

[Cheechako]

Originally Posted by DumnMad

Heck of a difference between slipping and stretching.

Coefficient of friction dry steel on glass is 0.5 to 0.7 so its easy to get the friction value needed.
If bolts get loose and water gets between then the bolts are in shear/bearing and significant movement must take place.(And corrosion will follow.)

How many of those failures were caused by poor maintenance? - water getting in - timber getting soft - clamping force fading away and bolts getting loose.

My guess is most were caused by corrosion/IGC. (must slip in order to stretch right? Maybe not ....if the fiberglass stretches too)

[DumnMad]

Originally Posted by Cheechako

My guess is most were caused by corrosion/IGC. (must slip in order to stretch right? Maybe not ....if the fiberglass stretches too)

Right, fibreglass stretches too so no slippage for a shear friction joint. Stretch must happen for all bolts to share the load.

If due to poor design or poor maintenance there is slippage the bolts take the shear load in the same way a shackle bolt does. In this case significant slippage must happen for all bolts to share the load.(I suspect some of those photos show the result of very little slippage and some bolts taking more than their share of load while others are yet to be properly loaded.)

[Stumble]

Originally Posted by a64pilot

I think you do polish the whole thing don't you? Isn't the purpose of polishing to remove stress risers, not to make it pretty?

They break at the holes likely because that is where they are weakest, especially if the hole is not de-burred, back to stress risers

You do polish the whole thing, but that's because stainless is a stupid metal to make chainplates out of. The reason they are polished is to try and reduce the likelyhood of tensile stress crack corrosion... this on a metal that is know to suffer from stress crack corrosion, then put in service in a place where the likelyhood of salt water intrusion just has to be assumed.

Frankly after hocking titanium chainplates for a while it amazes me that we put up with it at all. Stainless chainplates are about the stupidest metal selection for the job you could have chosen.

For not much more than the cost of the stainless used boats could switch to composite plates tied into the hull during layup, or titanium plates. Composites would be my preference, but titanium is a direct replacement, costs about double, but will outlive the rest of the boat. Because it's completely non-corrosive you donthave to design a way to replace them. Heck you could use titanium chainplates as the core of the hull where they are pretty easily.

[ur2slo]

Originally Posted by Stumble

You do polish the whole thing, but that's because stainless is a stupid metal to make chainplates out of. The reason they are polished is to try and reduce the likelyhood of tensile stress crack corrosion... this on a metal that is know to suffer from stress crack corrosion, then put in service in a place where the likelyhood of salt water intrusion just has to be assumed.

Frankly after hocking titanium chainplates for a while it amazes me that we put up with it at all. Stainless chainplates are about the stupidest metal selection for the job you could have chosen.

For not much more than the cost of the stainless used boats could switch to composite plates tied into the hull during layup, or titanium plates. Composites would be my preference, but titanium is a direct replacement, costs about double, but will outlive the rest of the boat. Because it's completely non-corrosive you donthave to design a way to replace them. Heck you could use titanium chainplates as the core of the hull where they are pretty easily.

This thread is getting off the hook!

It's headed to discussing the cost effectiveness of boiling water thread.

Your designing a boat that will be so prohibitively expensive, just to enforce the personnel goals of your knowledge, then build it.

Stop talking about it and do it.. Show me, don't tell me is the words I live by.

It brings to mind a laughable picture from life.......So overburdened with others making them safe or profitable.

https://www.beatonindustrial.com/wp-...after-OSHA.jpg

[ur2slo]

Originally Posted by Cheechako

(how can the metal pull apart if the plate doesn't move?)

Intergranular corrosion, stress fractures caused at forging, various other issues that can compromise the integrity of the plate.

Once a stress riser occurs at that particular point, stress's are concentrated there, when it reach's the failure point it fails at highest concentration.

Same principal why safety glass wont fail when hitting it with a baseball bat, but a spring loaded center punch will explode it.

[a64pilot]

No, he is right, if you have found the boat for life, Ti plates make,a whole lot of sense and the expense is not nearly as high as you might think

[tankersteve]

So I have learned a bit from this thread about chainplates. My concern is that I had chainplates bolted to an interior bulkhead. Water intrusion resulted in rot in the bulkhead - chainplate is fine and even better now after some polishing.

My question is, after my bulkhead is replaced (and tabbed in much stronger than the original), how do I know how hard to tighten the bolts on the chainplate to achieve acceptable/optimal clamping action? The boat is a Cal 31, so not a huge rig, but I certainly want this to be the last bulkhead replacement that I do.

Is there a good reference for calculating clamping strength requirements? The bulkhead is 3/4 marine ply.

Tankersteve

[ur2slo]

Originally Posted by tankersteve

So I have learned a bit from this thread about chainplates. My concern is that I had chainplates bolted to an interior bulkhead. Water intrusion resulted in rot in the bulkhead - chainplate is fine and even better now after some polishing.

My question is, after my bulkhead is replaced (and tabbed in much stronger than the original), how do I know how hard to tighten the bolts on the chainplate to achieve acceptable/optimal clamping action? The boat is a Cal 31, so not a huge rig, but I certainly want this to be the last bulkhead replacement that I do.

Is there a good reference for calculating clamping strength requirements? The bulkhead is 3/4 marine ply.

Tankersteve

1/2 inch pound before stripping .........

[ur2slo]

I'd say SAE standard torque or Manuf torque limits for type and grade of fastener used..

(disclaimer: Above is subject to conjecture,innuendo and internet googling)

Pm from now on............

[Stumble]

Originally Posted by ur2slo

Intergranular corrosion, stress fractures caused at forging, various other issues that can compromise the integrity of the plate.

Once a stress riser occurs at that particular point, stress's are concentrated there, when it reach's the failure point it fails at highest concentration.

Same principal why safety glass wont fail when hitting it with a baseball bat, but a spring loaded center punch will explode it.

The premium for titanium chainplates for an Island Packet 41 came out to be about $750 per boat. This was a size for size replacement with G5 Ti which worked out to be about five times stronger than the stainless that was stock. The 41 used the same chainplates grid as the IP 380, which has an anecdotal 50% replacement expectation after 15 years.

The replacement cost in labor alone to swap out the chainplates was about five times the new chainplates.