G10 for chainplates?

In a new build of a small daysailer, I’m contemplating using G10 for chainplates and other anchors for rigging loads.  

The published tensile strength is about 40,000 PSI, about half that of stainless, so they’d be bulkier, but bonding into structure could be cleaner.

Ideas?  Alternatives?

 

SloopJonB

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IIRC the Carbon Cutters had carbon chains so I can't see glass being a problem on a small boat.

I think I'd want some sort of sleeving for the pins to ride in though.

 

kevinjones16

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I used 1/4 inch G10 as backing plates. It's pretty stout. I'm no engineer, but I'd guess a properly designed and installed G10 fitting would be fine. Just like those parts on Perry's carbon cutters. 

 
The holes in the g10 would certainly be abrasive.  Can’t think of what material for sleeves would be good.  Periodically replacing pins would do, but be inelegant.

 

ExOmo

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G10 is probably not the best choice for tensile applications with small edge distances.  Standard rigging etc. sort of assumes a standard metallic thickness/hole edge distance.   It might mean that adapters (probably metallic) would be needed to connect your beefed up G10 chainplates to off the shelf standing rigging hardware.   Have fun.

 

12 metre

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If you want cheap, quick, and simple, stainless is hard to beat, but if you want composite then I would definitely fab up some carbon ones instead of using G10.
Even cheaper use regular UD E Glass.  Carbon is probably overkill for a daysailor.

The section itself doesn't have to be very large in cross sectional area, even for E Glass.  Tensile strength isn't typically the limiting factor for composite chainplates.  Lap shear is usually more important, and I think there was a thread on Boatdesign.net about this and someone with far more knowledge than I suggested to assume a lap shear strength of 15 MPa (2,200 psi) for epoxy.

Use the breaking strength of the shrouds as your guide  to calculate the required bonding area.  It will likely be much less than you would think.  Same thing with the required cross sectional area.

You could use G10 if you need to construct a bulkhead to attach the composite chainplates to.  In fact here is an article where someone constructed a replacement G10 bulkhead for an Evelyn 32-2  https://www.jamestowndistributors.com/userportal/document.do?docId=396

But for the chainplate itself forget the G10.

 
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A couple questions...

1) Why are you considering composite chainplates rather than stainless? What problem are you trying to solve by using G10?  Leaking? Cost? Corrosion avoidance?

2) What problems are going to be created by using G10? The upfront costs seem like they may be higher to install. What about repairability? If a chainplate on a daysailor is damaged, typically its a pretty straightforward operation to rip out the old/damaged one, stick a new one in there, and re-glass/bolt to hull/bulkhead or however the solution may be.

What size boat are you working with here? Hull mounted or bulkhead mounted (inboard) chainplates? I would be concerned about creating other issues that are already known qualities with solutions with SS chainplates, and it doesn't seem like it would be a cost saving measure when one considers the extra time designing and figuring out how to make the G10 work. 

 
A couple questions...

1) Why are you considering composite chainplates rather than stainless? What problem are you trying to solve by using G10?  Leaking? Cost? Corrosion avoidance?

2) What problems are going to be created by using G10? The upfront costs seem like they may be higher to install. What about repairability? If a chainplate on a daysailor is damaged, typically its a pretty straightforward operation to rip out the old/damaged one, stick a new one in there, and re-glass/bolt to hull/bulkhead or however the solution may be.

What size boat are you working with here? Hull mounted or bulkhead mounted (inboard) chainplates? I would be concerned about creating other issues that are already known qualities with solutions with SS chainplates, and it doesn't seem like it would be a cost saving measure when one considers the extra time designing and figuring out how to make the G10 work. 
It’s a wood composite monohull.  Displacement 2,000 lbs.  
SS chainplates require creating a hard point in structure to bolt to.  That’s a point of movement and leaking.  I figure it’s simpler and cleaner to bond a slab of G10 and maybe strap it in with some uni glass.

 

cavelamb

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Consider - do the G10 attachment to the structure - bring it above deck as a stub.
Then attach stainless to that so that normal hardware (turnbuckles, clevis, whatever) will fit with normal steel edge margins for holes. 
The stub could even be slotted so the attachment is in double sheer.
No holes through the deck. No leaks.
Normal hardware attachment.
 

 

DDW

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If you thing the Carbon Cutter chainplates where made by cutting up some carbon plate think again. Uni carbon tows are wrapped around the holes, then splayed and bonded to hull and bulkheads. Holes are lined with titanium sleeves. Really not that hard to do on a light daysailer using uni glass, but not as simple as cutting up some G10 plate as a replacement for stainless. The yield for stainless is about the same as G10, but it is a malleable and work hardening material, ending up about 2x the strength of G10 at failure. On many daysailers, you can see this in the distortion of the holes in SS chainplates. G10 (and all composites) rather fail suddenly and without warning. The modest crush resistance of epoxy (< 20Ksi) is why you line the holes with something harder (and, in the case of carbon, the probability of galvanic corrosion). 

 

Zonker

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You could do it but it wouldn't be ideal. Bearing stress in the hole would be important, rather than tensile.

See if there is published bearing strength for G-10. But let's say bearing = tensile = 40,000 psi = 274 MPa    

(That might be very optimistic by the way - just saw DDW post)

So say 1/8" or 5/32" wire? 1/4" or 6mm pin. Let's pick 5/32" wire since I don't really know how much about the boat. 1x19 302 s.s. = 3300 lbs =1500 kg = 14715 N

I picked a turnbuckle to suit that wire and it had a 6mm gap in the eye. So say your G-10 is 4mm (3/16") thick to fit and have 1mm either side.

Bearing stress, assuming you are working on B.S. of wire = F / (dia x thickness) = 14,715 N / (6mm x 4mm) = 613 MPa

Boo.  Fails spectularly. 1/8" wire? It would still fail.  So... bad idea.

            I should set up a paypal tip jar for free engineering. Just like the Delos folks. Buy me a beer etc. MiddayGun owes me one

 

Zonker

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There is a reason that even metal lifting lugs often have cheek plates welded on either side of the hole. It's not the tensile strength of the material - it's local bearing stress and shear tearout of the hole that often governs. Amel yachts have these sort of welded cheeks on their chainplates. Everybody else just uses a thicker piece of flat bar or plate. It's more inefficient but cheaper.

 
That’s very helpful, Z.  

It explains a failure I had in a composite sheave box in another project.  
I conclude that I can’t use a part that ends in 3/8” G10 as a substitute for stainless.  
Lemme see what I can work up with glass uni.

 

DDW

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This is one of the reasons you sleeve composite with something harder at localized loads. With the 1/4 or 6mm pin from above, and 1/4" thick G10, the bearing strength may be (optimistically) 1/4 x 1/4 x 20K or 1250 lbs. Put a 1/4 x 1/2 bushing of SS in there and you are up to 2500 lbs. You can go bigger but the G10 section loses. A bit of a balancing act. If you double the thickness locally with 2 cheeks of 1/8 material bonded on, now you've got 5000 lbs. 

There is also the stress riser of the hole in 0-90 composite material. In SS, this will deform and harden up. In composite, it needs to be thicker (like 50% thicker) to mitigate the riser. Uni wrapped around a bushing changes the whole equation. Almost no stress riser, bushing bearing more or less directly on fiber not frozen snot. 

 

Zonker

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Is G-10 just 0/90? I would have thought some +/- 45...Sheesh.

Yes, I built some carbon chain plates for my boat. Mostly because I was attaching them to the transverse mast beam that was a long way below the cabin front face where they penetrated. They would have had to be 4' long s.s. which would have been very heavy! Well the beam was also glass and carbon so I could just bond them to the beam which made life easier too.

They are easy to make but much more time consuming than just bolting on some s.s.!

 

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