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-   -   Jack Lines (https://www.sailnet.com/forums/general-discussion-sailing-related/329536-jack-lines.html)

Jeff_H 05-08-2019 04:22 PM

Re: Jack Lines
 
Quote:

Originally Posted by Jeff_H (Post 2051600716)
I would assume that you add an eye to the 1" webbing by having the eye professionally sown by a company who is certified to do that kind of structural sewing....
Jeff

Quote:

Originally Posted by pdqaltair (Post 2051600788)
Does this exist? In a practical sense, not really.

In a former life I manufactured climbing gear, and generally, we are talking self-certifications though ISO (6 sigma break testing program). That's it and many are not. Realistically, a sailmaker will do it. You will also need to source the correct webbing, which is a problem.

You are right that the Dyneema approach is probably best for DIYs. Fewer question marks and a solid finished product.

I don't know whether its true that companies that are certified to do that kind of structural sewing exists, but I see 'OSHA' certified safety harnesses and tethers and so I have always assumed that there are companies that are certified to do structural stitching. That said, I have no idea if that is actually the case.

Jeff

SanderO 05-08-2019 04:35 PM

Re: Jack Lines
 
With all due respect... I do not need a system designed to 5000# load... static or dynamic. This WAY more than the force of a 200# human be tossed my boat motion from a wave.

Stretch? I how much stretch will a 25' line loaded when a person is tossed by a wave? Another nonsense concept. Actually a little shock absorption is not a bad idea!

I will keep the vinyl coated wire jack lines as back up.... so I am not concerned about being with no jack lines.

pdqaltair 05-08-2019 06:29 PM

Re: Jack Lines
 
Quote:

Originally Posted by SanderO (Post 2051600800)
With all due respect... I do not need a system designed to 5000# load... static or dynamic. This WAY more than the force of a 200# human be tossed my boat motion from a wave.

Stretch? I how much stretch will a 25' line loaded when a person is tossed by a wave? Another nonsense concept. Actually a little shock absorption is not a bad idea!

I will keep the vinyl coated wire jack lines as back up.... so I am not concerned about being with no jack lines.

* Safety Factor. Your anchor chain has a safety factor. Your shrouds have a safety factor. For safety critical applications a 10:1 safety factor is common, depending on the materials.
* Wear.
* Dynamic forces. If you cannot calculate it or measure, then you guess, I assume.
* Humans HAVE broken tethers on boats. You can google this. That is the reason the standards were updated to include a drop test. People died. And they weren't 200-pound humans. Most recently a skinny guy died on one of the Clipper Race boats (CV30--google it) because his tether parted; I believe new standards will result, since a clip meeting the last standard failed.

You have declared disrespect for ANSI, ISO, OSHA, ISAF/WS, and UIAA. OK.

I don't always or even often use tethers. But I would not want to have safety gear that was unreliable. That's worse than none, if you have fooled yourself into believing that it is good.

SanderO 05-08-2019 06:40 PM

Re: Jack Lines
 
I have Lirakis harnesses and they are very robust.

I am not contemplating any offshore work in the foreseeable future. And I don't know whether I will do new jack lines or not... but for the use contemplated... 1" dacron will suffice.

Thank you for your concern!

colemj 05-08-2019 08:00 PM

Re: Jack Lines
 
Quote:

Originally Posted by SanderO (Post 2051600800)
Stretch? I how much stretch will a 25' line loaded when a person is tossed by a wave? Another nonsense concept. Actually a little shock absorption is not a bad idea!

Actually, stretch is one of the things I dislike about our current polyester webbing lines. When they are wet, they get very loose, and when they are in the sun, they get like guitar strings.

On our recent trip from Antigua to Georgia, I just rigged some old dyneema halyards as jacklines and liked that much better. I think I will be replacing the webbing with 1/4" dyneema in the future.

As for shock absorption, there will be enough of that just in the bowstring effect from the unsupported run, as well as the stretchy tether. In addition, one won't be coming up dead short on the jackline, they will also be sliding along it for some distance, which reduces the shock force. But personally, I think the less stretch in the static system the better - the dynamics will be providing the force reduction.

Mark

RegisteredUser 05-08-2019 08:12 PM

Sure.
Tether onto a mast..padeye or side rail and you arent asking how much 'give' that hardware allows.

Good discussion...but north is still north.

pdqaltair 05-08-2019 08:32 PM

Re: Jack Lines
 
Quote:

Originally Posted by SanderO (Post 2051600800)
...Stretch? I how much stretch will a 25' line loaded when a person is tossed by a wave? Another nonsense concept. Actually a little shock absorption is not a bad ....

In testing, as much as 2 feet (PS Magazine). Or you could place a 25' section between two trees, without pretension, and step onto it. The static load will be on the order of 500 pounds and it will sag about 2 feet, depending on the product. Certainly body weight is reasonable. Try it. I have. Any slackliner or tight rope walker know of this. and look how many sailors, like ColeMj, have simply noticed it. Any engineer can check my math; it's high school physics and trig. Nothing complex in the static case.

Why belittle a concept you have not studied and have no personal knowledge of? You can test this for yourself.

RegisteredUser 05-08-2019 08:37 PM

How bout dem Braves?

Springs wound tight....


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