Composite Chainplates or External Stainless Chainplates?

[Redreuben]

P.S Someone said carbon is a compression strong material, that is totally wrong it’s a tensile strong material it would be ideal but is not necessary.

[tamicatana]

Look,
Online isn’t the only source for Ti, and local fabrication houses have water jetting. And you will only buy them once, regardless. Maybe y’all need to make friends with a fab shop or a mech.eng.

https://www.mcmaster.com/titanium/hi...eets-and-bars/

My main point is: think laterally.

[BigBeakie]

Originally Posted by Redreuben

P.S Someone said carbon is a compression strong material, that is totally wrong it’s a tensile strong material it would be ideal but is not necessary.

That is correct, carbon has several advantages over either S or E glass, not the least of which is its much higher modulus, both tensile and specific modulus, which is what matters. And in a chainplate application, carbon's stiffness prevents the "working" of the composite matrix. Glass chainplates can fail from repeated stretch cycles ( from its low modulus) , which create micro fractures in the resin. They multiply over time.....not good.

We have 10 carbon chainplates ( 2 shrouds, 2 intermediates, staysail & baby stay, 2 for JSD & 2 for parachute anchor) and I would say that technique is everything. With good technique and job preparation it is pretty quick and immensely strong with very little weight. You'll save material handling headaches by using unidirectional carbon stitched tapes instead of cut cloth. Layup and wetout on acetate sheets and then peel it off and install the flaired out tapes on the boat. Be sure to have a smooth transition from the stainless tube core to the carbon straps by using a foam triangle "filler" next to the stainless tube to avoid the uni fibers being "kinked". Be sure to grind the surface glass first and clean for best mechanical adhesion.

They spread the load so effectively you don't necessarily have to use bulkhead surface attachment.

[Chotu]

Originally Posted by BigBeakie

That is correct, carbon has several advantages over either S or E glass, not the least of which is its much higher modulus, both tensile and specific modulus, which is what matters. And in a chainplate application, carbon's stiffness prevents the "working" of the composite matrix. Glass chainplates can fail from repeated stretch cycles ( from its low modulus) , which create micro fractures in the resin. They multiply over time.....not good.

We have 10 carbon chainplates ( 2 shrouds, 2 intermediates, staysail & baby stay, 2 for JSD & 2 for parachute anchor) and I would say that technique is everything. With good technique and job preparation it is pretty quick and immensely strong with very little weight. You'll save material handling headaches by using unidirectional carbon stitched tapes instead of cut cloth. Layup and wetout on acetate sheets and then peel it off and install the flaired out tapes on the boat. Be sure to have a smooth transition from the stainless tube core to the carbon straps by using a foam triangle "filler" next to the stainless tube to avoid the uni fibers being "kinked". Be sure to grind the surface glass first and clean for best mechanical adhesion.

They spread the load so effectively you don't necessarily have to use bulkhead surface attachment.

Just out of curiosity, can you share your laminate schedule and geometric layout patterns/fiber orientation for the main shroud chainplates for your 50fter? That would give me a good comparison to consider these for my 50fter. With those, I could compare the laminate schedules and consider a carbon solution. Not to save weight, but to compare the advantages of carbon over glass looking at laminate schedules for very similar boats side by side.

[BigBeakie]

Chotu,

I can't freely share the drawings with you, especially on an open forum. That IP is owned by the designer and composites engineer. I hope you won't think I'm being churlish, it's because I have come to understand just a little bit about composite engineering in this process for commissioning and building this cat. Things like composite carbon chainplates are not just something you can cobble together as a DIY project, unless you are willing to suffer the consequences of a catastrophic rig failure.

And I'm reluctant to share the composite layup schedule, because that was designed to handle the loads for our boat with our displacement with our rig plan and sail plan and in the bluewater conditions we expect on a bad day sailing southern Oz & NZ waters. I would strongly encourage you to find someone with composite engineering knowledge and experience in the multihull industry. Your life and that of your crew may depend on it. They must be experienced with carbon layups, and any "designer" who says using all glass is "just as good", doesn't understand composites engineering, IMHO.

Having said all that as a proviso, and frankly, a clear warning , I'll share just the foundation info as a guidance. I hope that will suffice.

The chainplate area of the hull inside is prepared with a foundation of 3 layers of 600gsm double bias glass, overlapping 50mm all around and extending well beyond the area of the carbon straps themselves on all sides. This is applied "green" so to get full chemical bonding. Our shrouds are near a structural bulkhead, as they should be, and the 3 layers of DB go on the inside hull surface & under deck BEFORE the bulkhead is installed. That bulkhead shares load of course, as does the deck, so the bulkhead-inside hull junction has 4 layers of 600DB over the high density coving extending 200mm on both the bulkhead and hull side and layers are tapered 50mm. ie. 200mm first lay, then 150mm, 100,50. Both sides of bulkhead are the same, and also done layer on layer "green".

Our carbon straps are 300mm wide of 500gsm carbon unidirectional stitched tapes and each wrap over the stainless tube is 1,000mm long down the inside hull surface with each layer overlapping 50mm per layer. There are 8 layers. So where it wraps over the SS tube bushing is 8 layers but 16 layers as it wraps back over itself. Each layer is interleaved with a layer of 600gsm DB because we used high modulus 18K carbon that was densely laid and the interleaving assures resin penetration through the carbon.

The carbon chainplate is then over layed with the same 3 layer DB schedule to encapsulate it, and on the outside hull it is encapsulated with 3 layers of same 600gsm DB.

Use a solids glass wedge under the SS bushing to transition the carbon uni straps around the bushing and then a high density foam tapered wedge just short of 1 meter long under the solids wedge so the carbon unis are not kinked but lay in a straight line to carry the loads the way they should, avoiding stress concentrations.

Please go find a composite engineer to design the chainplates for YOUR boat with YOUR loads.

[Chotu]

BigBeakie: thanks for sharing that. I thought maybe you would just share it over private message or something. So I could compare the two laminate schedules. Carbon and glass.

It really doesn’t look all that different from my plans with the glass ones. I just have a few more layers than you do. Either way, this isn’t a job I can give to someone else. It’s too vital to the boat’s structural integrity and it’s a very difficult glassing job. Wet on wet all day long.

Doing this job would probably land me right in the graveyard with epoxy and it can’t be done with polyester.

I think this really leaves me with metal chain plates. Unfortunately. As much as I want the nice composite ones, I have no way to achieve that.

I may have learned a thing or two about composite engineering myself having built a boat the exact same size and type you did. Lol the disclaimers weren’t really necessary. But I appreciate your sharing the laminate schedule so I could make an educated choice between the two types of composite chainplates available.

The sad truth of the matter is, my health (destroyed by amount of epoxy it takes to make a boat this size) doesn’t allow me to make these chain plates. The only way for me to farm this out is to use metal.

[TeddyDiver]

Not that anyone should follow my reasoning but uni carbon is stronger than steel so dimensioning the carbon to have equal cross-sectional area as SS chainplates is adequate.. And if in doupt make a test piece with one strand of CF and measure the tensile strength.. anything more you are propably not able to break it

[Redreuben]

@Chotu Is the boat built with an epoxy laminate?

[Cheechako]

Originally Posted by tamicatana

Look,
Online isn’t the only source for Ti, and local fabrication houses have water jetting. And you will only buy them once, regardless. Maybe y’all need to make friends with a fab shop or a mech.eng.

https://www.mcmaster.com/titanium/hi...eets-and-bars/

My main point is: think laterally.

That site, Bar: 1/2" thick x 3" wide by 3 ft long is $890!
Plate cheaper than bar until you pay for the waterjet....

[Chotu]

Originally Posted by Redreuben

@Chotu Is the boat built with an epoxy laminate?

Unfortunately. I wish I had used polyester in hindsight.

Epoxy severely altered my life.

It seems so innocuous. Polyester stinks so you know you can’t breathe it or go near it until it’s well cured. Epoxy has nearly no odor so you end up being overexposed to it more easily. It seems like nothing, but make no mistake. It’s every bit as dangerous as MEK and all that.

[Redreuben]

Vinyl Ester would have been the call but too late now.
I don’t have epoxy issues myself but work colleagues did. In their cases they only had problems with the raw resin fully cured materials were no issue, in fact I’ve heard cured epoxy described as being “inert” I guess there are degrees and you drew a short straw.
My sympathies for your inconvenient situation !

[Chotu]

Originally Posted by Redreuben

Vinyl Ester would have been the call but too late now.
I don’t have epoxy issues myself but work colleagues did. In their cases they only had problems with the raw resin fully cured materials were no issue, in fact I’ve heard cured epoxy described as being “inert” I guess there are degrees and you drew a short straw.
My sympathies for your inconvenient situation !

Or yeah... vinylester. Right. I used that for everything after the boat was launched. No more epoxy.

Fully cured epoxy is inert (that takes months in the 90 degree Florida sunshine), however, once you machine it, you break the bonds of the polymer, leaving some amines floating around. It’s no longer completely inert after sanding, drilling, etc.

[JD-MDR]

I had mine done like this with 1/2 g-10. I have bronze padeyes on the deck. The g-10 is used for backing plates and knee braces at each point. It cost alot about $1000 each. Also a pic of the rust I removed

[BigBeakie]

Apologies Chotu, I forgot you were a boatbuilder. I didn't mean to tell the fox how to suck eggs

I was also going to suggest using a good high solids vinylester resin, something like Scott Bader Chrystal. Although you have to be careful with the catalyst on bare skin, it would solve your epoxy allergy issue. And by using a slow catalyst ratio you can keep working on a job the next day, there is enough cross linking left to keep going wet on wet, and no amine blush issues. We did adhesion tests on fully cured VE with rough grinding using 40 grit, and it was pretty good. You could try a test patch on your hull to make sure it sticks.

I have a mild epoxy skin allergy myself after helping build a Simpson cat with System 3 and West. I still have it and that's over 30 years ago!

[Chotu]

Originally Posted by BigBeakie

Apologies Chotu, I forgot you were a boatbuilder. I didn't mean to tell the fox how to suck eggs

I was also going to suggest using a good high solids vinylester resin, something like Scott Bader Chrystal. Although you have to be careful with the catalyst on bare skin, it would solve your epoxy allergy issue. And by using a slow catalyst ratio you can keep working on a job the next day, there is enough cross linking left to keep going wet on wet, and no amine blush issues. We did adhesion tests on fully cured VE with rough grinding using 40 grit, and it was pretty good. You could try a test patch on your hull to make sure it sticks.

I have a mild epoxy skin allergy myself after helping build a Simpson cat with System 3 and West. I still have it and that's over 30 years ago!

Yes, it’s a lifetime thing once epoxy gets to you.

I am not sure I’d trust the VE to epoxy bond. Is that what you’re suggesting? That I use VE to make the composite chain plates and do the secondary bond to my hull using vinylester?

I thought that absolutely, positively needed to be an epoxy to epoxy bond?