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Old 16-06-2014, 14:24   #1
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Dyneema Cord/Poly Webbing Jacklines Questions

I have been reading Evans Starzingers otherwise excellent article about jacklines and I am unfortunately left somewhat uncertain about a detail with making loops at the end.

When knotting he suggests -

"Knotting works and is easy . . .
just bring the cord out the end of the webbing and tie it into around the webbing loop.
However, sewing is preferred, because it keeps the cord inside the webbing and protected
from chafe and UV and it is neater with less to snag on deck."

My question, what kind of knot should you use and why don't you just leave the cord inside the webbing? Presumably the presence of the webbing over the cord reduces the strength of the knot, but I don't understand how or why.

If you are using 1/4" Dyneema with about 8,600lbs breaking, strength plus the strength of the webbing, I would think that a simple bowline with 70% strength would keep you well above the desired 5,000lbs number.

But maybe not?

http://www.bethandevans.com/pdf/jackline.pdf
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Old 16-06-2014, 14:35   #2
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

It's very slippery stuff. If you were to leave it inside the webbing it might pull out unless you sew it in. On the last jack line I rigged on the boat, I was in a hurry so tied the webbing in a water not and the spectra in a bowline. Not the best knot by far but with a little messing around it worked.
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Old 16-06-2014, 14:48   #3
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

I guess here's another question, given the core is providing the strength and the webbing is for chaff and roll-resistance, can you just stop the webbing short of the overall length and lock-stitch and whip the webbing ends to the core?

Yes, still leaves the rope exposed at the knotted ends, but you are providing chaff protection for ninety percent of the run. Or is this basically what he is saying?

Not really understanding what he means when he says "tie it into around the webbing loop"

If you are taking the cord out of the webbing, how? By cutting a hole?

It's not like you can pick apart the webbing like you are extracting the core from double braid, or can you? Seems like that would be difficult. Then you're tying separate loops in the end of the core and the webbing? Seems messy.
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Old 16-06-2014, 15:23   #4
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

Forget I asked what kind of knot. Locked Brummel splice for loops, duh! But still what to do with the webbing ends? Sew em and whip em I guess.
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Old 16-06-2014, 15:35   #5
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

Delancey,

Here's what I think they mean: The webbing is hollow to begin with. You thread into it the spectra or dyneema line, of longer length than the webbing, so that the webbing will take up and stretch that little bit that you need. Therefore, sewing it in (incorporating the slack) leaves the ends sewn - and the dyneema UV protected - and the slack incorporated.

If you tie bowlines in the ends, you can still attach with soft shackles, or secure over a cleat. If you want to do bowlines, allow the extra length of both webbing and line to accomodate the knots, it seems an easy way to have the chafe and UV resistance throughout.

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Old 16-06-2014, 15:59   #6
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

Isn't hollow webbing like 5K#??? My jacklines are just the tubular webbing... I get all the safety factor stuff, but what are you securing the jackline to???? and what is IT'S rating.
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Old 16-06-2014, 16:32   #7
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

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Originally Posted by capngeo View Post
Isn't hollow webbing like 5K#??? My jacklines are just the tubular webbing... I get all the safety factor stuff, but what are you securing the jackline to???? and what is IT'S rating.
The heavy duty Nylon webbing is 5K but it rots in no time and is to stretchy. The polyester webbing is only 2700 lb but lasts for a good while so you need the spectra inside for strength and no stretch.
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Old 16-06-2014, 16:43   #8
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

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The heavy duty Nylon webbing is 5K but it rots in no time. The polyester webbing is only 2700 lb but lasts for a good while so you need the spectra inside for strength.
No.

1. Tubular webbing is 17.8 KN or 4000 pounds.

2. I defy you to make a connection over 85% efficiency, 3404 pounds, or 68% of the standard. This stuff is very hard to sew to high efficiency because of the stretch (there is a long discussion, with testing on SA gear). It is NOT UIAA approved for climbing unless used as a loop, which greatly increases strength.

3. It stretches too much, particularly when wet. Try slack lining on it and see what I mean.

4. Yes, the end fittings need to be 5000 pounds. That is not difficult.

Add sun deterioration, and nylon webbing is only suitable for boats under ~ 25 feet for occasional use. Because of the shorter lines, and because only one sailor will be on the line, the stress is less and it is safe. The ISAF rules really should spec strength based upon length, as they do for lifelines; that is how the math works. The correlary is that 5000 pounds is not enough when a boat exceeds about 50 feet, just in case that isn't obvious. If you take 2 men and throw them against the line at ~ 8 knots, considering the tight rope effect, there is ZERO safety factor. look up your high school physics and do the math. Given wear and tear and the sun, you NEED the safety factor and should be wary of scrimping if you have not done the math. Please check my math.

http://sail-delmarva.blogspot.com/20...jack-line.html

Actually, the loads on a Dyneema system, with little stretch, can get really high. I'd probably go up a size and build some burly anchors. But do your own math.
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Old 16-06-2014, 16:50   #9
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

I wrote this before I did my load testing, and there are some things that should be changed.

The whole section on sewing webbing is pretty much wrong. It is MUCH harder to sew high strength loops than I thought. There are some very specific procedures that need to be followed (stitching patterns and reinforcing material).

Knots weaken dyneema cord more than I thought (only 40-55%) strength, and splices should definitely be used instead. The dyneema also UV weakens more than I expected and the webbing should be used as a cover for the whole splice loop - this requires a specific (but not hard) splice technique.

Thin (7.7 - 8.5mm) climbing line is a more interesting tether material than I thought.
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Old 16-06-2014, 17:00   #10
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

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Originally Posted by thinwater View Post
No.

1. Tubular webbing is 17.8 KN or 4000 pounds.

2. I defy you to make a connection over 85% efficiency, 3404 pounds, or 68% of the standard. This stuff is very hard to sew to high efficiency because of the stretch (there is a long discussion, with testing on SA gear). It is NOT UIAA approved for climbing unless used as a loop, which greatly increases strength.

3. It stretches too much, particularly when wet. Try slack lining on it and see what I mean.

4. Yes, the end fittings need to be 5000 pounds. That is not difficult.

Add sun deterioration, and nylon webbing is only suitable for boats under ~ 25 feet for occasional use. Because of the shorter lines, and because only one sailor will be on the line, the stress is less and it is safe. The ISAF rules really should spec strength based upon length, as they do for lifelines; that is how the math works. The correlary is that 5000 pounds is not enough when a boat exceeds about 50 feet, just in case that isn't obvious. If you take 2 men and throw them against the line at ~ 8 knots, considering the tight rope effect, there is ZERO safety factor. look up your high school physics and do the math. Given wear and tear and the sun, you NEED the safety factor and should be wary of scrimping if you have not done the math. Please check my math.

Sail Delmarva: Sample Calculations for Jackline Stress and Energy Absorption

Actually, the loads on a Dyneema system, with little stretch, can get really high. I'd probably go up a size and build some burly anchors. But do your own math.
From the Sailrite Catalog, pn #4532 blue nylon 1" webbing, avg strengthh 5300lbs. White tubular Polyester webbing pn#82300 avg strength 2700 lbs.
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Old 16-06-2014, 18:08   #11
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

^^ True... and not.

He said hollow, and the HD webbing is not hollow. What I quoted was the tubular webbing I believe he was referencing and that most posters reference. One big different is price: $1.10 vs $0.27/foot.

And the other statements are still true. It is VERY difficult to sew nylon to high efficiency, so you are still under, and it still stretches far too much. Also, you really need 6000 pound webbing to get 5000 pound fabricated strength.

But yes, there are stronger products. And it really takes a serious worst case to get to these limits. For most of us, that are only trying to catch easy slides and slips, there is a lot of overkill. You need a knock-down to get there... or 2-3 men on the line.
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Old 16-06-2014, 18:16   #12
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

Hi Evans,

Thanks for chiming in. For our purposes the jacklines are for a delivery and will not likely be permanently rigged. I am at a bit of a loss to imagine the type of webbing cover/ single braid core splice you allude to except where the cover isn't actually spliced, but maybe hand sewn over the top of the loop?

Maybe our needs would be met with exposed loops and the webbing covering the remainder, sewn in place as I suggested? Or maybe the simplest approach of extending the webbing the full length of the core and knotting would work?

Your feedback is always appreciated. Thanks!
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Old 16-06-2014, 18:44   #13
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

I bought a set of custom made spectra jack lines from the guys at Sailing Gear: Clothing, Equipment, Hardware, Shoes, Line, Sailboat Parts | Annapolis Performance Sailing
They eye splice the spectra at each end and cover it with the tubular Polyester webbing. There is a layer or heat shrink over the ends of the poly webbing, but I'm not sure if they provided an additional attachment mechanism to the spectra. Check them out, they can custom make them to any length.
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Old 16-06-2014, 18:52   #14
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

Here's a photo of the APS jacklines. Should be easy enough. Can't tell from the photo but doesn't look like the cover is sewn to the core except where is is made fast at the ends.
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Old 17-06-2014, 03:24   #15
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Re: Dyneema Cord/Poly Webbing Jacklines Questions

Quote:
Originally Posted by Delancey View Post
Hi Evans,

For our purposes the jacklines are for a delivery and will not likely be permanently rigged. I am at a bit of a loss to imagine the type of webbing cover/ single braid core splice you allude to except where the cover isn't actually spliced, but maybe hand sewn over the top of the loop?

It is essentially just like a 'core to core' splice, where the loop is covered but the cover is (usually) not buried (it is sewn/whipped down). To make it happen with webbing . . . . #1 you pull the tail out of a small hole in the webbing about 2" from the end of the webbing, #2 you pull a loop of the cord out of another small hole in the webbing where you want the base of the final loop, #3 you bury the end of the cord into the loop you have pulled out, #4 you pull the loop of cord back into the webbing. This pulls the two pieces of webbing together, forming the end loop you wanted. #5 you sew the webbing together for about 3" (2" after the splice/join and 1" before)

Maybe our needs would be met with exposed loops and the webbing covering the remainder, sewn in place as I suggested? Or maybe the simplest approach of extending the webbing the full length of the core and knotting would work?

The webbing around the loop is for UV and wear protection. If the jackline is not going to see months of UV/use then you can simply have the dyneema loops extend out the ends of the webbing and be uncovered. Because the loops are 'double strength' they can in fact loose a lot of strength without effecting the system strength. But if they are going to see a lot of UV or wear then covering them is just good practice and not that difficult.

Your feedback is always appreciated. Thanks!

I will be losing my internet this afternoon. Not sure when I will get a connection back.
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