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Old 26-03-2017, 07:03   #16
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Re: alternative to tether

I tend to question internet wisdom.

At the risk of sounding arrogant, I will share my logic. The role of a jackline and tether is to keep me alive. If the center of mass of my body mass goes over the rail, it becomes difficult to get myself back on board. This increases the odds of mortality. The only way to keep the core of my body on deck is to have a jack/tether length short enough to keep my ass (literally) out of the water. My legs may go over, I may hit parts of my body on a stanchion, but I can self-rescue and get back to the cockpit.

ASA and others recommend jack lines down the sides of the boat. I respectfully suggest that these people are lacking in experience in workplace safety. Double jacklines is a guarantee that your center of mass will go over the rail. Windward, leeward- it don't matter. One rarely plans when and where they mess up. Assuming you do not drown, once you are in the water the countdown to hypothermia starts.
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Old 26-03-2017, 07:12   #17
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pirate Re: alternative to tether

An alternative to a tether..??
Develop your sense of balance, speed up your reaction times and learn to work with one hand for you and one for the boat..
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Old 26-03-2017, 07:18   #18
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Re: alternative to tether

Quote:
Originally Posted by UNCIVILIZED View Post
I've taken a few falls on Kevlar, amongst other materials, so I'm familiar with many of the issues. Though it would be interesting to read the current standards. The thing is though, many of the current standards are actually based on information which is quite ancient, & or that is flat out wrong, as well as dangerous.
Not true. The offshore OSR/SER, as followed by USSailing and World Sailing are updated every two years and change regularly based on testing of various products and techniques. I've served as the safety officer on a number of boats racing offshore in the past few years, and a safety inspector for one of them. If there is a safety-related incident in a race you can pretty much guarantee that there will be a post-mortem review of the situation and the gear, like the San Clemente incident in '13 that led to a review of inflatable PFDs. Also, testing from various groups, like the USCG and Navy, filters down in the form of revised requirements (along the lines of dyneema lifelines).

All that said, I don't think any of the safety regulations specify anything about tethers other than minimum breaking strength, so your suggestion would meet the requirements.
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Old 28-03-2017, 23:28   #19
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Re: alternative to tether

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Originally Posted by Paul Elliott View Post
I don't have a centerline jackline, but we've seen and had wild "death roll" spinnaker wipeouts where windward and leeward trade sides several times before the eventual crash.

This.

Plus, a member of the crew could go overboard while the boat is not heeled (e.g. While taking a piss of the stern).
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Old 29-03-2017, 02:38   #20
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Re: alternative to tether

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Originally Posted by Steady Hand View Post


1. That thing costs a lot of money ($276) and that almost $200 more than a very good safety tether made for ocean sailing), which can be purchased for as little as $79.

I hope you find this helpful. If you want my suggestion for an appropriate safety tether I do recommend, and why, I will post that upon request.
Steady, I would be interested in your suggestion as I am looking to add a safety tether in June. $79 sounds good.

Thanks

Larry
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Old 29-03-2017, 08:43   #21
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Re: alternative to tether

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Originally Posted by UNCIVILIZED View Post
[...]Though it would be interesting to read the current standards. The thing is though, many of the current standards are actually based on information which is quite ancient, & or that is flat out wrong, as well as dangerous.
I believe it is more physics related than standards. Compare Nylon tether to Dyneema, quick math with simple numbers:

Nylon elongation at break: 28%
Dyneema elongation at break: 4%
tether length: 1.5 m
body speed: 1 m/s

assume final elongation at full stop: 2/3 of elongation at break (very low safety margin for a tether)

2/3 of 28% =~ 18%
2/3 of 4% =~ 2.7%

stretch - Nylon : 0.18 * 1.5m = 0.27m
stretch - Dyneema: 0.027 * 1.5m = 0.04m

time to full stop - Nylon: 0.27[m] / 1[m/s] = 0.27s
time to full stop - Dyneema: 0.04[m] / 1 [m/s] = 0.04s

deceleration - Nylon: (0[m/s] - 1[m/s]) / 0.27s = -3.7 [m/s2]
deceleration - Dynema: (0 - 1) / 0.04 = -25 [m/s2]

Both will stop you, one will damage you.
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Old 29-03-2017, 09:48   #22
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Re: alternative to tether

The item that the OP posted about is a fall arrestor and is required to be worn by all construction workers, working within 10 feet of the edge of a highrise building or tower under construction in the USA and other countries. It has a brake that slows the webbing as it spools out, that slows the fall very quickly but not suddenly. The intent is to not have that sudden stop at the end that might snap a back.

However the amount of line/webbing on the spool would put a person wearing it on the boat well underwater. The spool is NOT retractable under load, nor is it salt water rated. It would help in all the wrong ways on a boat.

As others stated, A good standard tether is the way to go.
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Old 29-03-2017, 14:58   #23
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Re: alternative to tether

Sailorchic good catch!

I have purchased fall arrestors for my (former) staff and used them. They are not "salt water friendly" way too many do-dads to get rusty.

They definitely do NOT belong on a boat
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Old 30-03-2017, 10:28   #24
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Re: alternative to tether

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Originally Posted by thinwater View Post
No. Very dangerous and forbidden by sailing standards.

Try this. Splice a Dyneema tether, attach it to a tree, attach the other end to your harness, and then take a run at it, backwards, as though stumbled down the deck or got hit by a wave. If you give it a good try you have an excellent chance of ending up in the hospital with a cracked rib or spine injury. Try it slowly, and report back. I have tried this test.
Just curious if you have tried the same test with webbing? Honest question - I totally agree about dyneema but although webbing (commonly used in safety attachments) is somewhat more forgiving, I wonder if it would feel similar if you ran away from it?

There is a new attachment system on the market for climbers that uses dynamic rope, in an adjustable length system. Haven't read the material to know if it is rated for short falls yet.

https://www.rei.com/product/890387/p...adjust-lanyard

I have not tried running from it either!
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Old 01-04-2017, 04:56   #25
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Re: alternative to tether

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Originally Posted by boatman61 View Post
An alternative to a tether..??
Develop your sense of balance, speed up your reaction times and learn to work with one hand for you and one for the boat..
You will still get knocked overboard if the wave is big enough. Balance has nothing to do with it.
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Old 01-04-2017, 05:02   #26
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Re: alternative to tether

Quote:
Originally Posted by mrm View Post
I believe it is more physics related than standards. Compare Nylon tether to Dyneema, quick math with simple numbers:

Nylon elongation at break: 28%
Dyneema elongation at break: 4%
tether length: 1.5 m
body speed: 1 m/s

assume final elongation at full stop: 2/3 of elongation at break (very low safety margin for a tether)

2/3 of 28% =~ 18%
2/3 of 4% =~ 2.7%

stretch - Nylon : 0.18 * 1.5m = 0.27m
stretch - Dyneema: 0.027 * 1.5m = 0.04m

time to full stop - Nylon: 0.27[m] / 1[m/s] = 0.27s
time to full stop - Dyneema: 0.04[m] / 1 [m/s] = 0.04s

deceleration - Nylon: (0[m/s] - 1[m/s]) / 0.27s = -3.7 [m/s2]
deceleration - Dynema: (0 - 1) / 0.04 = -25 [m/s2]

Both will stop you, one will damage you.
Practical Sailor did some testing of different jacklines. From what I remember boats larger than 45' need very low stretch lines, smaller boats need stretchy lines to limit shock. The small amount of stretch in a 6' nylon line tether will not help much, that is why many tethers have built in elasticity.

Kong Double Line ORC Tether
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Old 01-04-2017, 05:16   #27
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pirate Re: alternative to tether

Quote:
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You will still get knocked overboard if the wave is big enough. Balance has nothing to do with it.
You do your thing and I'll stick with mine.. its served me well over the years in 4 oceans and a few sea's..
I don't use a PFD either.. its all down to personal choices.
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Old 01-04-2017, 05:28   #28
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Re: alternative to tether

Safety tethers have been studied to death. The international standards are not based on old outdated thinking, They are based on thousands of tests that were well instrumented. Many "common sense" based ideas turned out to be wrong when subjected to rigorous fall testing. For example, the less stretchy materials actually put a higher stress on the tether and the person. When you see the actual tests where a weaker material survives the fall test and the stronger material breaks it makes sense. But it is not intuitive at first. So in this area it's not a good idea to trust your instincts unless you have really studied and tested the materials First instincts are usually wrong when it comes to safety tethers.

Best advice is to follow the international standards created by the sailing organizations. They are based on real world testing. It is not "easy" to make a proper tether that works.
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Old 01-04-2017, 05:41   #29
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Re: alternative to tether

Quote:
Originally Posted by UNCIVILIZED View Post
I've taken a few falls on Kevlar, amongst other materials, so I'm familiar with many of the issues. Though it would be interesting to read the current standards. The thing is though, many of the current standards are actually based on information which is quite ancient, & or that is flat out wrong, as well as dangerous.

(My) personal opinions aside, there's a lot of gear & training out there which is flat out wrong, based on ancient precepts, & or, dangerous. As, for example, there's plenty of approved safety gear which falls into conflict with concepts & testing which was known & accepted decades ago. Yet the agendas still get pushed. Much of the time by personell who've never tried out the gear or concepts personally. And I say these things based on a fair amouont of professional experience in these areas.

May I be wrong about the tethers issue? Certainly. But I'd surely like to know exactly why. Including the testing involved in reaching said conclusions. Done by whom. How. Real world reports on same. Etcetera, etcetera.
Yup, ISO stuff is copyrighted. I forget where I found it, but it's out there somewhere.

The current drop test is less than 5 years old, I believe. It is based on current research and commonplace mechanical engineering. It is not outdated.

World Sailing does not require harness-end release because not all people agree on the desirability. I'll just leave that there, since it is a separate issue.

You can find drop tests of Dyneema by climbing gear manufacturers--the failures are glaring and the forces terrific. I think the simplest answer is to say that engineers familiar with drop testing are satisfied that non-stretch materials always fail by a wide margin and thus they no longer pursue it. We also no longer try to demonstrate that the world is round; it isn't worth the testing resources, even though it is very easily done. Try the test (very carefully) I suggested at 4 feet. Start with less than 4 feet of slack, since that might injure you. However, obviously, as the tether becomes very short, the material matters less and less.

As a general rule, harnesses and tethers don't break because they are too weak, they break because they are too stiff. By the time they break (>4000 pounds), you have a broken back and punctured lung.
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Old 01-04-2017, 05:47   #30
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Re: alternative to tether

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... All that said, I don't think any of the safety regulations specify anything about tethers other than minimum breaking strength, so your suggestion would meet the requirements.
Correction. The ISO (12401) and World Sailing standard includes a drop test (200 kg 2 meters, on a 2 meter lanyard). Only materials with some elasticity can pass.
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