composite chainplates

[Stumble]

Scott,

The only composite chainplates I have seen are built integral to the hull. Where the carbon uno was interlaced with the carbon that makes up the hull itself. I have never seen anyone try to replace stainless chainplates with fiberglass like G-10.

[Mudita]

Stumble - fair enough. It does surprise me that we're not seeing it more, though.

Ben - thank you for the response. Another question, if you have the patience:

You mentioned "a lot thicker" for the fiberglass than stainless steel. This rapidly gets outside of my comfort zone for calculations but here goes:
[list=1][*]The G10 (or FR4) is a continuous fiber sheet with a tensile strength of ~35k psi.[*]E-Glass Tensile strength is often shown at ~500k psi. I'm guessing the difference between this and the G10 spec is that the G10 is when the glass is actually laid up? Like a real world application?[*]316 Stainless Steel is also in the 500k psi range


But of course, the actual strength is all about the layup schedule and quality control. Can you give a idea of how much thicker I should go than the original chainplate? I'm guessing somewhere between 2x and 10x. But I'd like to get within an order of magnitude!

[Brion Toss]

Hi,
I do like this thread, in particular that paper, with its information on hybrid joints. Chainplates are a transition point for rig loads, having to accommodate the needs of both the standing rigging and the hull (as well as the requirements for humans living in the hull), so it is not surprising that, since the dawn of rigging, so many chainplate configurations and materials have been tried. But basically there is a concentrated load where the piece of rigging attaches, shifting to a distributed load into the relatively tender, fragile hull. Built-in carbon fiber "fan" chainplates take this to an extreme, but glassed-in steel chainplates approximate the same thing. And both suffer from difficulty of examination, and of difficulty of maintenance and repair. Bolted-in chainplates can achieve acceptable levels of load distribution and accessibility, along with minimal intrusion into crew space. Tie rod chainplates can be at least as good at all these considerations, plus they feature a modular construction, plus they offer an opportunity to bring HM materials into the mix; picture a rope chainplate, readily inspectable and replaceable, wedded to deck hardware that carries the load to a strong point on the hull, via a metal or HM tie rod. This type of thing is already being done, with varying degrees of success.
While waiting for designs to improve, it is still most practicable to optimize existing configurations, polishing and sealing stainless better than we did in the past, or using titanium or bronze, etc.
Fair leads,
Brion Toss

[benz]

Hi,

Sorry, no photos of the chainplates. We glued them on with thickened resin, filleted the edges and put large patches of glass over the whole thing, thus getting massive surface area. It was not a cosmetically important area, or it might have been impossible to make attractive. Chainplates through a deck would be a different set of engineering, and I personally would not venture to use G10 or any composite chainplate in that application without consulting a competent structural engineer.
I'm afraid that I can't think of a really good way to do inboard chainplates--I dislike holes in the deck of any nature or purpose, and those especially seem to be prone to leaking. Several folks I know have simply moved their chainplates outboard to the outside of the hull, where they belong--a re-rig is a good time to see whether that's a good option for your boat.
Again, certainly don't rule out using alternate materials and thinking outside the box, but by all means proceed with extreme caution when making alterations to location or materials.
Ben

[Mudita]

Well, you've all convinced me that my situation isn't a great candidate for a composite through-deck chainplate retrofit. All of your points are good ones, and a truly appreciate the advice.

It's either bronze or stainless in my future, much as in my past.

Thank you, gentlemen, for the voices of experience and reason.

[Stumble]

I would recommend titanium instead of bronze or stainless. Do it one right and never think about them again. Plus you can fill the slot between the hull and chainplates with epoxy to permanently seal up the hole.

[Mudita]

That's a good point about Titanium - I'm just catching up on reading previous threads on that option. Is it reasonable to say that using G5 Ti, I could reduce the chainplate cross section to about 35% of the current 316 Stainless, and save me both money and corrosion issues? That sounds like magic.

Regarding sealing up the deck hole permanently, what does experience show how well that would hold up given the temperature expansion issues with two dissimilar materials, plus flexing at the deck level? Would something like G-Flex work? Is there too much movement for that? Does it make more sense to leave a larger hole and fill with a highly elastic goop, acknowledging that the deck will never provide enough stiffness to keep the wiggling down?

[Stumble]

G5's UTS is 160 ksi vs 90ksi for 316 stainless so yes you can reduce size somewhat. The tricky bit is that it still needs to match the rigging hardware so you have to retain a large enough size to allow for proper fitting.

I was think of GFlex epoxy to fill the void. I know of one person who has done this without issues, but it has only been about two years so I can't say for certain that it will work long term. No matter how much flex there is in the GFlex, it's still less than the slot holes that were there from the old chainplates.