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Old 07-07-2010, 13:23   #1
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Dynnex Dux Chainplates ?

Please try to be skeptical and inform me if I am missing something.

I have decided it would be much stronger, simpler, and cheaper to use the same synthetic line (dynnex dux) for standing rigging to replace the chainplates as well.

The fiberglass bulkheads the current stainless chainplates bolt to are more than an inch thick which would give sufficient turn radius for 6mm lanyards, so instead of bolting a chainplate, I could instead run lashings through these holes. The lashings then would go up through the deck to a deadeye-deadeye connector.

I included a 3d animation (click to see it moving) of my idea for a deadeye-deadeye connector. Entirely made out of delrin (with 18,000psi crush strength) It would eliminate metal completely from the standing rigging. The lanyards are run so that the delrin is only in compression, not tension (same as normal deadeye)

The only reason to use the deadeye-deadeye connector is to reduce friction and allow the use of sealant on the lower lanyards to eliminate any leaks in the deck. It would be possible to bypass in an emergency. I would like to rig the lanyards for redundancy somehow but I can't figure out how I would distribute the load equally.

Anyone see faults with this?
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Old 07-07-2010, 14:14   #2
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I can only see three problems with this.

1. my gut tells me you'll never get a lasting seal at the deck level
2. the fiberglass knees won't tolerate the point loads from the lashings
3. the delrin won't tolerate the loads from the lashings

I sail on a cat that has dux rigging using the colligo alu eyes, i can tell you that the load placed on the small contact point the lashing is supplied on the eye would destroy in a short time any plastic. The only other problem i see with your proposed deadeye is the shape of the leads, they would cause a hard turn at the line's entry and exit. I'll assume you'd lace this in a failsafe manner (loop within loop?)
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Old 07-07-2010, 16:16   #3
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Senator,

It would be very difficult to seal the lines at the deck as water would travel down the inner fibers. It would be easier and cheaper to use your stainless chainplates with off-the-shelf deadeyes from Colligo or Precourt. They are well engineered and relatively cheap. If you are set against stainless you could attach a composite chainplate to your bulkheads. This could be a simple eye made of fiberglass, kevlar or carbon uni with the fibers fanned out across the bulkhead. A good epoxy has a peel strength of something like 1000lbs/square inch.

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Old 07-07-2010, 18:20   #4
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Thanks for the replies, but I am not entirely convinced it won't be a good solution.

As for water traveling down the inner fibers... the amount of leakage may actually be acceptable to me, but It may also be possible to shrink wrap the entire lashing beforehand which would allow me to completely seal it.

Why would the fiberglass knees not tollerate the load of the lashings? It would be at the same load points as the bolts. The only thing I can think of is because the lashing diameter is smaller than the current bolt diameter, so it could in theory cut the fiberglass, but I doubt this would be possible. In the worst case, it only needs to support 2000lbs per 6mm lashing going through an inch of fiberglass, I don't think that would tear but maybe. I want to be able to put lashings through fiberglass, so I would like to figure out what is possible here.

I don't see how using a premade deadeye terminator would be cheaper. Those terminators cost something like $60 which is a huge cost since you need 2 per stay. If you buy the terminators, they end up costing more than the synthetic line itself per stay, so the cost is more than double which is too high.

My thinking is, Delrin plastic is roughly half the strength of aluminum for compression, so if I oversized the connector and made sure the area of contact of the delrin and dux roughly twice as much it should be just as strong as an aluminum one right? That means I might have a turn radius of 10:1 instead of 5:1 for everything, and kind of large terminators, but they would be strong, light, low friction.. and I could carve them myself. As for making terminators that can connect to conventional chainplates.. this seems trickier and I am not sure how to get the strength needed since I cannot mill almuminum.

Also my leads would be filed out and rounded to avoid any sharp turn, this is not shown in the image.
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Old 07-07-2010, 18:28   #5
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my chainplates have backing plates, which means that they reinforce the hull at an area of high stress. Your design does not include any such reinforcement. While it may be lighter, there's no way it could be as strong.
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Old 07-07-2010, 20:08   #6
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If your fiberglass knees are like mine they're plywood in the middle.
Other than that I would worry about a little thing called plastic deformation, in the very short term the lashings would be ok, but in the long term (could be days to months) the lashings would tend to displace the plastic and make their way through.

I think you'd be better off using your existing turnbuckles and chainplates and just do a jaw/jaw arrangement on the turnbuckle and splicing a heavy duty stainless thimble on the dux.
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Old 08-07-2010, 08:34   #7
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Plastic deformation. Doesn't sound good. I think I'll get some delrin anyway and play around with it, but I don't think I'll be using it for deadeyes right away.

I'm hoping I can get some used bronze oversized turnbuckles for cheap, but in the worst case I could get galvanized ones.

For chainplates, if I switch to carbon fiber, which is better, rigid or flexible carbon fiber? For flexible we have:
  • Flexural Strength: 60,000 psi
  • Compressive Strength: 60,000 psi
For Rigid:
  • Flexural Strength: 110,000 psi
  • Compressive Strength: 16,000 psi
I'm guessing both are strong enough, but the rigid ones would be more likely to crack.
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Old 09-07-2010, 08:26   #8
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FWIW i was able to purchase 12' of stainless flatbar for $70 ,a drill press for $60 and a bit set for $40. it took me two evenings but I have made all new chainplates on the cheap!
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Old 10-07-2010, 06:35   #9
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See ➥ http://www.equiplite.com/2009/Frames...hainplates.pdf

And ➥ http://www.precourt.ca/images/pdf/ar...ris_kinzel.pdf
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Old 10-07-2010, 06:56   #10
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I remember reading years ago in Multihull Mag of someone who fabricated chainplates with synthetic (kevlar I thought, but whatever) line of small diameter. He spread a ss thimble, and cut off the bottom legs to give him a saddle to lay multiple loops of the line in, and then thru the deck and around whatever structure is available, tightly so there won't be any movement. Saturate with epoxy.

You could probably do something like this. Lace the line thru the several (I assume) chainplate holes you already have, plus more if you want. I think it would work fine, if done carefully.
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