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Old 25-02-2013, 10:36   #16
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Re: Homemade Jacklines

There is a lot more engineering in this than folks realize. As a 30-year engineer, 25-year sailor, and 30-year rock and ice climber that has logged more air time than most would like to consider (thousands of falls), I think I have a few thoughts of value. Fortunatly, I've posted most of this elsewhere so I don't need to retype it.

Yes, I agree there is money to be saved, but it must be done intelegently. I have helped scrape the remains of 2 climbers (separate events) from the ground that were using good equiment they used improperly; that's how serious it is.

The forces involved? Here are some calculations. Some is catamaran specific.
Sail Delmarva: Sample Calculations for Jackline Stress and Energy Absorption

Ideas in general. Some is catamaran specific.
Sail Delmarva: Climbing Gear for Sailors--Jacklines and Harnesses for the Unemployed

And this about shock absorbing tethers. Shock absorbers are required by OSHA and the military and I believe most of the tether failures we have read about were the result of unsustainable impact forces. If you don't think this matters, secure a conventional tether to a rigid point, get about 6 feet of slack and a good running start as though you were thrown by a wave, and then call us from the hospital (broken ribs).
Sail Delmarva: The Case for Softer Tethers

There are dozens of factors to consider, and each boat is different:
* Can you get back on if you fall of?
* Will the jackline be perminant? Mine are. Then consider UV very seriously.
* How wide are your side decks? What is the worst case fall?
* One leg or 2? Most people are going to 2-leg tethers as that is the only way to stay on the boat in all cases.
* What is the proper length? 6'/3' is standard, but shorter may be required on some boats.
* Where to run the jacklines?
* Will you also use hard-points?
* How does the harness fit? With clothes?
* Where do you sail and how do you sail? The requirements of a relaxed coastal sailor (me), solo ocean racer, and fully-crewed racer are different.
* What sort of boat?

______________

I do not mean to be harsh, really, but the OP's tethers scare me silly in several ways. They need to be trashed. Homemade tethers can be economical and safe, but these are not.

* The slides are of unknown strength and may cut the webbing. A water knot is a better known quanity and can be tied in a few seconds. It is a much safer choise for home-built, the safe choise of climbers for many decades.
* The carabiners are a complete unknown. About all I would trust them with is a fender. Climbing carabiners are quite inexpensive, the wire gate sort quite corrosion proof, and they are of know strength. However...
* Carabiners without a locking function and a quick-open function are scary. It is easy to unclip a regular biner from a u-bolt, almost a party trick. Just take the tether and rotate it with the gate facing the bolt. It is acceptable to use a locking biner at the jackline end, but the harness ned must quick release.
* These carbiners are not so easy to use in the dark or with gloves.
* Webbing. Can't say for certain, but I would be more comfortable buying webbing that was rated for climbing and of known stregth (4,000-pound plus).
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Old 25-02-2013, 11:24   #17
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Re: Homemade Jacklines

Tut! Tut! 67! Tut! Tut!
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Old 25-02-2013, 13:14   #18
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Re: Homemade Jacklines

There may be an argument for Nylon tethers but not for a jack line. If anything you should use Spectra. Clipping on in the middle of a 30' length of Nylon is like hooking up to a rubber band.
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Old 25-02-2013, 13:44   #19
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Re: Homemade Jacklines

Quote:
Originally Posted by Guy View Post
There may be an argument for Nylon tethers but not for a jack line. If anything you should use Spectra. Clipping on in the middle of a 30' length of Nylon is like hooking up to a rubber band.
And spectra could dislocate your shoulder.
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Old 25-02-2013, 13:58   #20
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Re: Homemade Jacklines

Mark; Are you up to speed on Jack Lines vs a tether? A jack line goes from stem to stern. Even if it were a steel cable it would have lots of give.
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Old 25-02-2013, 14:16   #21
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Re: Homemade Jacklines

Quote:
Originally Posted by Guy View Post
Even if it were a steel cable it would have lots of give.

No, not factual. The amount of stretch in a steel line that would fit on the size boat of the OP would not absorb significant energy; I've demonstrated this by breaking (shackle failure) a tight and straight 5000-pound jackline with my hands. If you feel differently, show the math. Likewise, Spectra does not stretch enough on a 35-foot boat to meet a worst case fall as defined by the sailing rules. If you have calculations that demonstrate otherwise, please share them. Caviate: as boats get longer, stretch increases, and both Spectra and steel become good choices at some length. One size cannot fit all since the stretch on impact must be calibrated.

Unfortunately, the people writing the rules don't understand all of the engineering, or much more likely they simplify the rules to fit typical 35- to 50-foot monohulls. With polyester webbing, the calculations work.

Nylon for jacklines is not proper for monohulls. If you read that on my post there was a big caviate stating that calculations were for catamarans only, which perhaps you missed. Wide decks change the rules in several important ways (longer falls and more room to cover). The length of the jackline is also a major factor; on my 32-foot center cockpit cat the jacklines are only 15 feet long. Different horses for different courses, my friend.
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Old 25-02-2013, 14:22   #22
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Re: Homemade Jacklines

Quote:
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And spectra could dislocate your shoulder.
This is a good point. While we generally clip to a jackline, nearly as often we clip to a hard point in the cockpit, in which case Mark is absolutely correct. I've been pulled up short on Spectra tethers while climbing (forgot I was still on) and it is exactly like hitting a steel beam. At speed it could kill someone, and climbers have died from using Spectra tethers.

Spectra versus Nylon

Clipping to a hard point in wild conditions without a shock absorber is tempting fate, and a few have lost.

"1998 Sydney-Hobart Race Accident. Glyn Charles was never found, after his tether parted. But the force of dragging his body through the water could not have generated that kind of force, only a sudden impact. The inquest stated that he was attached to a "fixed point" and thus would not have benefited from jack line shock absorption. The lanyard may have also been defective, though I can't locate the testing information. Sydney To Hobart Yacht Race Coroner's Inquest - 07/03/2001 - QWN - NSW Parliament. Yachting: Charles died after safety harness failed - Telegraph.
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Old 25-02-2013, 15:01   #23
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Re: Homemade Jacklines

I've seen two references to a "water knot." What is a water knot?
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Old 25-02-2013, 15:18   #24
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Re: Homemade Jacklines

So we seem to have two conflicting camps here: one says that stretchy jack lines are bad in that they allow you to perhaps go overboard, the other says that stretchy jack lines are necessary or your body will break.

Seems to me that having non-stretch jack lines coupled with tethers with controlled stretch would be the best compromise. There is some hope of engineering the tether in such a way. However, doing the same for the jack lines seems difficult in that you don't know just where the load will be applied.

And FWIW, on our previous boat we made jack lines from the old lower shrouds that were surplus when we re-rigged. Being 5/16 inch 1x19 their strength was more than adequate in this application even though we didn't want them as rigging. No worries about UV damage with them! An inexpensive and permanent solution IMO.

Cheers,

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Old 25-02-2013, 15:20   #25
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Re: Homemade Jacklines

Quote:
Originally Posted by Triton318 View Post
I've seen two references to a "water knot." What is a water knot?
Water knot - Wikipedia, the free encyclopedia
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Old 25-02-2013, 15:23   #26
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Re: Homemade Jacklines

Quote:
Originally Posted by Guy View Post
There may be an argument for Nylon tethers but not for a jack line. If anything you should use Spectra. Clipping on in the middle of a 30' length of Nylon is like hooking up to a rubber band.
I'm guessing that at least 99% of all sailboats are using nylon webbing for jacklines. How is that suddenly wrong?
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Old 25-02-2013, 15:30   #27
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Re: Homemade Jacklines

I guess they don't know any better and they are too cheap. Spectra costs $4 a foot. Any body ever really pulled the middle of a length of Nylon? You might as well be wearing water skis.
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Old 25-02-2013, 15:43   #28
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Re: Homemade Jacklines

Quote:
Originally Posted by Bash View Post
and from that same source:

Quote:
Although used in climbing, the water knot is considered unsafe. According to Walter Siebert, several deaths have been reported due to failure of this knot. In Germany the knot is also named knot of death.
Hmm...
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Old 25-02-2013, 15:56   #29
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Re: Homemade Jacklines

And the reason why is also given:

Quote:
Testing has shown the water knot to slip very slightly, but very consistently, with each load and unload cycle.
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Old 25-02-2013, 16:08   #30
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Re: Homemade Jacklines

Has anyone heard the story about a woman who spent 8 days being drug along overboard with her boat while sailing alone? Eventually a wave kicked her back on deck. Sounds pretty far fetched but still not impossible. She was reported as a big woman... Guess that means she had a reserve of stuff...
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