# Dyneema (or similar) jacklines



## killarney_sailor (May 4, 2006)

I need to replace my Wichard polyester webbing jacklines and the replacement price is ridiculous. Anyone using hi-tech line instead? Would be cheaper and probably would stand up better. Only shortcomings would be that it would roll if you stepped on them (the webbing slides) and it might be a problem to get a good tension on them.


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## aeventyr60 (Jun 29, 2011)

I used tubular webbing from REI. Was surprised how much the commercial jacklines cost too.


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## JonEisberg (Dec 3, 2010)

killarney_sailor said:


> I need to replace by Wichard polyester webbing jacklines and the replacement price is ridiculous. Anyone using hi-tech line instead? Would be cheaper and probably would stand up better. Only shortcomings would be that it would roll if you stepped on them (the webbing slides) and it might be a problem to get a good tension on them.


I'm using 1/4" Amsteel for jacklines, it's the orange rope in the pic below...

It's held up well, and I haven't had any problems with the possibility of it 'rolling' underfoot, as Amsteel really tends to 'flatten out' after it gets stepped on after awhile...

Other advantages are the lack of stretch, obviously, and the 'slippery' nature of Dyneema, and how easily a tether will slide along it, without getting hung up...

Then again, I'm not necessarily the best one to ask about jacklines, as I virtually never use them aboard my own boat I've come to prefer fixed tethers instead... But I have brought mine along on a delivery of a boat that was not equipped with jacklines, that's another advantage of Dyneema, how light and easy to stow it is, and how quickly it will dry...


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## pdqaltair (Nov 14, 2008)

You did no mention the size of the boat (any poster). I am working on an article for Practical Sailor, and one thing that has become apparent is the one size does NOT fit all.

a. Nylon webbing (REI) is very safe from the strength standpoint (even though below ISAF minimums, because of stretch it operates at a VERY high safety factor); HOWEVER, if the boat is over 25 feet (20 foot jackline) the stretch will be dangerous (several feet, up to 4-8 feet on larger boats). Not acceptable for most sailors.
b. High modulus lines MUST be above ISAF minimum strength, and in fact the 1/4 Amsteel the Jon is using (8600 pounds) is the minimum, with very little allowance for wear. Because it cannot stretch, it does not absorb stretch and the safety factor even in that size is lower than polyester lines. There is a reason climbers do not use Dyneema for anything that must absorb impact.
c. High modulous lines require very strong deck fittings. The shackle that Jon has will not hold the 8600-pound force that a tight Amsteel line can generate in a high speed fall.
d. I think you will find that HMPE, done right, is not a lot cheaper than the WM webbing lines. It depends on the details (lashings, anchor points), diameter, and whether you elect to cover them.
e. HMPE lines are lower in stretch, which certainly makes up for some down side. The ease of sliding if not covered is sweet too. But some folks find them slippery naked.

Personally, I like to see jacklines that can be left rigged and used regularly. I don't know the layout of Jon's boat, but that location seems awkward (a lot going on an a lot to snag on). I would probably go a little inboard, but ADMITTEDLY, I do not know the layout. And sometimes you have to go with the anchor points you have, so long as they are strong. I like them inside and under all sheet lines so that there are no crosses (tacking with a tether over a genoa sheet track does not go well--you can get ejected).


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## RichH (Jul 10, 2000)

(As one involved high angle mountain rescue and who once did a lot of dynamic structural engineering) I *disagree* with MOST of what has been previously posted !!!!!!!

If youve ever watched (or did) bungee jumping .... ask yourself which type of 'line' would you use (and all at the same common tensile strengths, etc.)? .... Twisted stainless steel, a polymer equivalent of 'wire', dacron, nylon or rubber filled nylon (bungee)? 
Why am I asking this question, as one who would NEVER use stainless or a high strength/low stretch polymer? .... and for 'engineering safety' reasons when impacting human bodies are involved???

Two very very *very* important reasons:
• *IMPACT* and its time interval of that impact which can be an exponential force MULTIPLIER
• Good old 'Archimedes' (and Aristarchus, the 'father' of trigonometry) - "levers".

1. Dynamic developed Force is MULTIPLIED in relation of HOW LONG/SHORT IS THAT _IMPACT INTERVAL_. The shorter the impact time the higher the developed force. Why bungee jumpers are relatively safe is because the 'stretchy-ness' also stretches out that impact TIME interval and as such VASTLY lessens the shock load due impact, that shock load being 'magnitudes' greater than the weight/mass that is 'stopping' due to the impact ..... and possibly the strength of the 'connections' and the gear. 
Simple speak: if you use low stretch line/wire for your deck-run jack line runners the impact 'may' cause the CONNECTIONS to which that jackline is connected to see 5 or 10 or more TIMES the force generated by that weight/mass against that line if that line had a bit slack that allowed a noticeable (10+°) angle to form during full load. The 'longer' that impact interval becomes the less IMPACT there will be; hence 'safer' using nylon, as less impact forces are generated. If the impact forces exceeds the ultimate strength (at 5 or 10 or more times than inherent strength of the gear .... guess what happens? Ans.: MOB drill
"Stretchy" / elastic line (such as nylon tubular webbing or braided nylon line) greatly extends the impact TIME and thus reduces the impact LOAD.

2. One of the FIRST things any engineer involved in a static or dynamic structures course of instruction is "& beat about the head and face" is: #1 ---- NEVER EVER EVER design a structure that "divides by the sin (sin = trigonometric function) of the angle, especially when the deflection angle is a very 'small angle'. The reason is that calculation of the resultant forces generated by 'small angles' of deflection (applied perpendicularly) can be develop VERY LARGE forces, including 'infinity' in the item that is perpendicular .... such as a jackline. The smaller the deflection angle under load, the GREATER the forces generated at ~90° to the applied force (ie. moving body going towards overboard). This would be a parallel example of Archimedes being able to lift the weight of the entire world ... if he only had a lever that was large enough. 
The exact SAME analogy apples to 'rope, etc.' that is stretched between two 'immovable' points; and then, force is applied perpendicularly to the long axis of the rope ---- can possibly generate INFINITE forces along the long axis of that rope.

Mountain and Rescue climbers would NEVER EVER EVER EVER stretch a _*TIGHT*_ line horizontally across two 'mountains', peaks, crevasses, open spaces and apply a 'hanging' load at perpendicular to the axis of the rope. To do so, which would prevent any 'sag' (thus generating 'small' angles of sag) in the rope --- aka: dividing by the sin of the deflection angle) and would generate (the possibility) of infinite forces in the 'rope' or the connections, or the rock, other gear, etc that 'connections' are affixed. Any time such a 'Tyrollean Traverse' (horizontal line with a hanging perpendicular load) between two fixed object the rope is ALWAYS set to that it has 'lots of sag' (larger trigonometric angles by which to divide into that load, the larger the 'angles' the less the load into the terminal connection of the rope AND the rope itself).

Calculated Trigonometry Examples ( one horizontal rope between two immovable connections and a *200lb.* person hanging from the middle of the horizontal rope and pulling on the rope 'perpendicularly')

Calculation Formula: weight ÷ sin (sag angle) = resultant force
'sag' angle Resultant force (by 200 lb. person)
30° 400 lb. (force)
20° 584 lb. (force)
10° 1151 lb. (force)
5° 2194 lb. (force)
2° 5730 lb. (force)
1° 11460 lb. (force)
0° 'infinite' (force)
....... and these are only 'static' forces without impact. 
For (guestimate) impact MULTIPLY those resultant forces by 5X. 
With a gorilla tight jackline of stainless steel or amsteel that 200lb. body with 5X added (guess)magnification force IMPACT factor could 'theoretically' approach 60,000 lb.(!!!!!!) into that TIGHT (1° deflection) line AND its connections to the boat! ...... But only 6,000 if that deflection angle is 10°. Even LESS for larger deflection angles at full impact load.

*Rx:* SLACK jacklines and 'short' tethers and 'stretchy rope/webbing'. 
1. Use 'stretchy' line for jacklines and DO NOT use low stretch materials such as wire rope, dyneema, etc. - otherwise you risk pulling the jackline connection OUT of the boat during FULL high impact scenarios. Reason: With non-stretch - higher impact values and LESS deflection angle (dividing by a very small number). 
2. Do NOT pull the jackline to '_real taught_', leave 'some slack' so that a relatively large angle is formed between your tether connection and the line when the weight of the falling body is 'at the end of his her rope' - otherwise you risk pulling the jackline connection OUT of the boat during FULL high impact scenarios. Reason: LARGER deflection angle (dividing by a very larger number yields smaller results/forces).
This will prevent breaking the cleats and other fasteners to the Boat 'off' the boat, will vastly increase the impact time; hence DECREASE the impact (total load induced).

Do 'proof load' your tether and jacklines ..... example: with your harness on, your tether attached to the jackline and to your harness ...... start from the centerline of your boat, "run like hell" towards an open lifeline gate .... 
1. see if you are kept reasonably on board with the now at full extension & tight tether/harness. If now overboard, shorten your tether, and then repeat. but go faster across next time. 
2. make sure the 'connections' from the boat TO the jackline are still intact - not bent, pulled out, deformed, etc. etc. If so, make 'stronger', much stronger (includes 'cleats')
3. have an assistant estimate the angle that the rope (from the tether connection to one of the boat connections) makes with your centerline .... should be 10-12° or more. If less than 10-12° shorten the tether and slightly loosen/lengthen the jackline. 
If you want to proof load 'less dynamically' get three to four buddies and all of you - stand near the rail and try to force yourself over the side ... everyone pushing 'hard' against that jackline system.

hope this helps .... helps you to stay onboard. 
Slightly SLACK jacklines made of tubular ('slightly' stretchy _mountain climbing grade_) webbing & short tethers are to be preferred; in comparison, ............... to being 'accompanied' overboard by silly looking broken fiberglass boat fragments firmly attached to broken tether/wire or amsteel rope/jackline terminal connectors, etc. 
My tubular webbing jacklines run 'mostly' along the centerline of the boat.

Anyone ever see someone using a stainless wire rope or dyneema 'bungee cord'? .... now you know why you haven't. ;-)


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## pdqaltair (Nov 14, 2008)

^^ Yes, I am an engineer, understand the trig, statics, and dynamics very well, and my statements were based upon rigorous calculations that will be published, not guesswork. As you point out, impact is important. However, there are a few things you have not considered.

1. The falls are more like slides and are equivalent to a short (2-4') fall.

2. The tether has some stretch (ISO requires a drop test similar to a UIAA fall factor 1).

3. Volvo and similar boats have been using Dyneema for years in wild conditions. No broken jacklines. Actual experience must be considered. In fact, I consulted with sailors involved in US Sailing rulemaking, and to our knowledge, there is no record of a jackline failure causing MOB. The tether failures have all been associated with tethers clipped to fixed points.

4. Both Dyneema and SS do stretch. In fact, the models and practice show deflection to be about 2-3 feet on large boats in hard falls, assuming an initial straight line and zero preload.

5. If the jackline stretched, as you suggest and as nylon webbing will, the sailor will be over the railing, alongside the boat, and at very high risk of drowning in the bow wave. Models predict deflection could be over 6 feet on larger boats. I've seen slacklines that were not pre-loaded deflect that far. On boats deflection MUST be limited to 2-3 feet. Additionally, this is the reason most jacklines are near the windward rail, not down the centerline.

6. There is also energy absorption due to harness slip, body deformation, and the sliding of the tether along the jackline (falls are generally at an angle).

Yes, the forces on the jackline are VERY high and proper engineering is vital. This is the reason that ISAF 4500# Dyneema is not safe (1/4" is common practice). While I appreciate your enthusiasm for the forces involved, please consider that no racing authority or experienced rigging contractor will accept nylon webbing as valid beyond about 20 feet, and that all jacklines in actual racing use are either polyester or high modulus. I think a spread sheet would confirm my calculations, and encourage you to explore the calculations. Yes, the anchors will need to hold over a ton during a moderate fall and nearly 1.5 tons in a good whipper. They need to be strong. The impact on the sailor, however, will not exceed 500 pounds.

Regarding industry, I have install a number of high-line systems over the years for fall protection. There is little stretch or sag and they do work, if the stresses are considered and engineered for.


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## JonEisberg (Dec 3, 2010)

Damn, I _KNEW_ there was some reason I've come to rely upon fixed tethers made from climbing rope and employing a snubber...










...and consider my Amsteel jacklines to be only a backup/secondary means of additional security, and in fact never _ONCE_ clipped onto them in the course of 4K miles of sailing last summer...

)










Evans Starzinger's take on all this is worth a look, another interesting viewpoint...

http://www.bethandevans.com/pdf/jackline.pdf


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## RichH (Jul 10, 2000)

1. one can easily 'get catapulted' across a deck, no slide required. 
2. A tether would be in tension. No deflection angles (force multipliers) etc. involved to its connections. 
3. Volvo could used bananas for all I care, ... if the bundle of bananas had the correct strength and elasticity characteristics. 
4. All solids are 'elastic' ... your point? My point is when there is insufficient elasticity, that ~perpendicularly applied load keeps that deflection angle small ..... in free-body analysis, dividing by the trigonometric SIN of small angles results in BIG forces ... in the 'rope' and its reaction points.


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## RichH (Jul 10, 2000)

JonEisberg said:


> Damn, I _KNEW_ there was some reason I've come to rely upon fixed tethers made from climbing rope and employing a snubber...
> 
> Evans Starzinger's take on all this is worth a look, another interesting viewpoint...
> 
> http://www.bethandevans.com/pdf/jackline.pdf


I agree almost totally with Evans Starzinger... 'not too tight', but just enough slack [to keep that damn deflection angle 'noticeable' when at near max. load]. I vaguely remember to have had such an online SSCA discussion with him about 12-15 years ago.

WOW! 'short lines' !!!!
When I was doing 'high angled rescue', we used 'short lines' (aka: 'jumpers') whenever possible to 'independently tie in', to double-secure clip-on's, knots, etc. .... very similar to your set up. I use the 'short leg' on my tether to tie in direct to the mast; Stupid of me, I should be using a 'short line' from the mast.
I have to get back to that philosophy on the boat. Thanks for 'rekindle'.


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## pdqaltair (Nov 14, 2008)

RichH said:


> 1. one can easily 'get catapulted' across a deck, no slide required.
> 2. A tether would be in tension. No deflection angles (force multipliers) etc. involved to its connections.
> 3. Volvo could used bananas for all I care, ... if the bundle of bananas had the correct strength and elasticity characteristics.
> 4. All solids are 'elastic' ... your point? My point is when there is insufficient elasticity, that ~perpendicularly applied load keeps that deflection angle small ..... in free-body analysis, dividing by the trigonometric SIN of small angles results in BIG forces ... in the 'rope' and its reaction points.


Please, do the math. The results may not be so bad as you may fear. I also thought it would be worse when I began my investigation, but there are more minor absorption factors than you first realize.

1. Yes. When I did the calculations I used variable velocities up to 15 ft/s normal to the jackline, which is really the practical upper limit.
2. Obviously.
3. That statement is just plain funny. In fact, the jackline requirements are in the boat construction scantlings, right down to the pad eye and deck requirement. So yes, engineering matters. 
4. The point was quite obvious. Even Amteel cable can be quite springy when deflected sideways, absorbing significant energy. Not nearly as much energy as webbing or rope per foot, but there are enough feet involved.

And you can't ignore the requirement for low stretch. It is NOT acceptable to have enough stretch that you can go over the side. The obvious corollary is that energy absorption will be a challenge and that forces will be high. There is no trick for getting around this corollary. As you correctly pointed out, the quicker you shot, the higher the forces involved. But most (all?) jackline related deaths have involved drowning in the bow wave to leeward; thus, it is falls to leeward we must protect against.

I think we all agree that work station tethers are a good idea. My tethers are 7.8 mm ice climbing rope which nicely match high stretch, light weight, and sufficient strength. Splicing is a *****. They do a wonderful job of reducing impact on both me and the fittings when I take a long stumble on my cat. I understand that the Volvo guys prefer Amsteel for its sheer compactness, though energy absorption is nil. They keep them short, so it works for them.


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## JonEisberg (Dec 3, 2010)

RichH said:


> WOW! 'short lines' !!!!
> When I was doing 'high angled rescue', we used 'short lines' (aka: 'jumpers') whenever possible to 'independently tie in', to double-secure clip-on's, knots, etc. .... very similar to your set up. I use the 'short leg' on my tether to tie in direct to the mast; Stupid of me, I should be using a 'short line' from the mast.
> I have to get back to that philosophy on the boat. Thanks for 'rekindle'.


I find that one of the most useful components of my setup is the sliding Schaefer cleat I have mounted on my spinnaker pole track. I usually have it parked right at chest level, so when I get to the mast I can create a short leash with the tether, and have both hands free...

Even better than granny bars, at least on my boat... Of course, if the rig goes over the side, I suppose I could be in a bit of trouble, although the tether is ultimately fixed at points at the base of the mast that aren't going anywhere....


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## MarkofSeaLife (Nov 7, 2010)

killarney_sailor said:


> Only shortcomings would be that it would roll if you stepped on them (the webbing slides) and it might be a problem to get a good tension on them.


Tension with a truckers hitch. Oooops, can I say truckers hitch on a sailing forum?
Better do some maths and physics and getter a better knot 

If tensioned Dyneema could it be up off the deck? Or is that a tripping hazzard?


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## pdqaltair (Nov 14, 2008)

MarkofSeaLife said:


> Tension with a truckers hitch. Oooops, can I say truckers hitch on a sailing forum?
> Better do some maths and physics and getter a better knot
> 
> If tensioned Dyneema could it be up off the deck? Or is that a tripping hazzard?


I would not try to pre-tension Dyneema. On the other hand, it does not stretch when wet, so you won't need to.

My jacklines are NOT on the deck; they run along the cabin chime and thus are not under foot or a tripping hazard. They intentionally end ~ 5 feet short of the bow (on a cat getting thrown forward is more probable than sideways).

Just call it a lashing and no one will yell at you. The problem with a truckers hitch, BTW, is that the knot will probably slip at peak load, though I don't know of anyone who has tested it specifically. Lashing through an eye is easy and is standard practice.


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## RichH (Jul 10, 2000)

A Truckers hitch is great way to snug up any looped rope system. A bombproof way to keep the 'looped knot' portion from slipping or capsizing is to use an 'alpine butterfly' knot .... a 'go to' knot for mountaineers. The 'butterfly' is a fast, quite strong, non-jamming, very easy and secure way to tie-in a loop 
on any long length of line.

Alpine Butterfly Loop | How to tie the Alpine Butterfly Loop | Climbing Knots


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## aeventyr60 (Jun 29, 2011)

I think some folks have been watching too much reality TV and maybe a bit much of the on air/internet of the Southern ocean racing drama of wide open decks deck with deck sweeping waves. Reality is your going to be on your hands and knees when it gets a bit sporty, a long slow slide is more like it, with you digging in your fingernails and big toe for a grip. Not like your going to be doing a peeler of 50 feet and on the crappy pro you put in with your little bitty "friend".


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## killarney_sailor (May 4, 2006)

Damn. this turned into a much more interesting discussion than I expected.


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## Capt Len (Oct 9, 2011)

Sailing is usually more interesting than you expect.


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## Zanshin (Aug 27, 2006)

While everyone has been concentrating on the jackline's dynamic loading the fact that a fall or loading will put loads on both the jackline and the harness/tether. An ISAF approved hardness/tether has built-in elasticity as part of the certification process and it is assumed that the tether is attached to a hard point which will have no give (like a taut overspec'd dyneema line). The tether has the "give" and will usually also have appropriate colored threads showing that the tethered loads have been exceeded. The jackline will not usually not see the full forces described above.


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## pdqaltair (Nov 14, 2008)

Zanshin said:


> While everyone has been concentrating on the jackline's dynamic loading the fact that a fall or loading will put loads on both the jackline and the harness/tether. An ISAF approved hardness/tether has built-in elasticity as part of the certification process and it is assumed that the tether is attached to a hard point which will have no give (like a taut overspec'd dyneema line). The tether has the "give" and will usually also have appropriate colored threads showing that the tethered loads have been exceeded. The jackline will not usually not see the full forces described above.


Yes and no. Tether stretch was included in the calculations, it is important, and it can be the difference between a failed design and an acceptable design.

The tether only accounts for about 20% of the energy absorption in a Dyneema system (most of the stretch is not activated until much higher loads--the certification is based upon a more severe drop, basically 100kg 6' on 6' of tether). Even before the 500-pound tether indicator triggers, the jackline will have seen 1500-2000 pounds of force.

It is also exceptionally difficult for a sliding sailor to hit the tether squarely, like a falling climber hits the end of a rope; normally the body is not in line with the fall and thus only a part of the mass acts on the tether/jackline instantaneously.

Yes, it all counts.

A fixed point and a taut Dyneema line are really almost nothing alike; the Dyneema will move 1-2 feet.


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## MarkofSeaLife (Nov 7, 2010)

Killarney_Sailor, I have some spare dynema, mostly 14 mm and you are welcome to borrow it and see how it works in practice.




Mark
PS I expect you to make measurements with your thumb and calculate with a slide rule.


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## aeventyr60 (Jun 29, 2011)

Anybody have a full body weight fall, slip, trip, monster wave experience while using your own jackline/tether/harness set up? If so, how did your system work? I can't ever remember having one myself. Wondering if your/our deck prowess and experience gives a leg up on preventing those kinds of experiences? I think a fall or event will be more out of not paying attention to the conditions. Your thoughts?


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## JonEisberg (Dec 3, 2010)

aeventyr60 said:


> Anybody have a full body weight fall, slip, trip, monster wave experience while using your own jackline/tether/harness set up? If so, how did your system work? I can't ever remember having one myself. Wondering if your/our deck prowess and experience gives a leg up on preventing those kinds of experiences? I think a fall or event will be more out of not paying attention to the conditions. Your thoughts?


Sorry, I can help you there... I have never, _ever_ been brought up short by, or had a tether stretched sharply to it's limit... The closest I've come is having one snag on some bit of deck clutter aboard someone else's boat...

Clearly, I'm doing something wrong, here... 

I think the Pardeys have the best answer to your question, from their comments on "You Can't Buy Safety"



> The harness you may or may not use on deck is just that, a harness to back up your hands. It does not insure safety, nor is it a substitute for learning to move around on deck using the old fashioned sounding seaman's adage; one hand for you, one hand for the ship...
> 
> ...
> 
> ...


Evans Starzinger has also written about this, and commented how often many experienced sailors they know move about their boats without the use of harnesses, when they don't feel they're warranted... I'll admit I've always been of a similar mind, I'm certainly not one of those solo sailors who claim that I NEVER venture out on deck without clipping on, but rather generally have done so whenever the mood strikes, or I really thought it was a good idea  As I've aged and become less agile, and recently began having a bit of knee problems, however, I definitely find myself using a harness more often. And, one of the things I like best about a fixed tether/workstation arrangement in lieu of jacklines, is that I find them so much easier to use, at least on my boat, therefore I'm more likely to use them...

This is definitely one of those subjects we love to obsess over, and I rarely fail to learn something new every time it comes up... But I think it also helps to keep the risks in perspective, and I'm pretty sure more sailors fall off their boats at the dock, or getting in and out of dinghies at anchor or whatever, than they do while underway, or offshore...


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## aeventyr60 (Jun 29, 2011)

^ Yes, I feel that I will more likely be run over by a bus or fall into one of the many open sewer system drain systems on land then by all the hazards I've faced in offshore sailing to date.


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## outbound (Dec 3, 2012)

Would note:
It's not uncommon in weather to have one person at the helm and another sleeping ( wearing full kit) on the leeward settee in the cockpit. That allows some one immediately present to assist if necessary. I prefer to have both clipped in. I have a short jack line running on the side of the cockpit seat to allow this. Also have hard points at either side of helm station as hard point shown in above picture will interfere with wheel movement. 
Although seen logic in moving jack lines to centerline find on many boats shrouds,sheets,stays, lines will be interfered with when movement required. Find if you use both the one and two meter lengths of tether it seems more secure to up on windward side and drop down to leeward if required.
Find it unfortunate designers don't incorporate a track and car system for tethers. This could be recessed, be always present and circumvent the issues of jack lines.


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## pdqaltair (Nov 14, 2008)

outbound said:


> Find it unfortunate designers don't incorporate a track and car system for tethers. This could be recessed, be always present and circumvent the issues of jack lines.


a. If seatbelts come standard with cars, why aren't jacklines and related anchors factory equipment? Certainly they could make more sense if designed in.

b. Tracks sound good, but have proven to be a very bad idea. This has been done, and one down side is that the sailor can be washed aft that much faster. It makes passing by 2 sailors that much more difficult. What if you are not clipped in and suddenly chose to (where is the damn car!), wish to transfer from windward to leeward, or need to unclip to clear something (a loaded sheet got under your tether!!) They were subsequently removed. Apparently a certain amount of friction is a good thing. Some of the big boats have been known to splice small loops (the clips can slide over them) at key locations so that a sailor can limit this.

What about Dyneema vs webbing friction? That certain carabiners are more prone to snagging on deck hardware than others (I've found aluminum biners snag less because they are lighter, although they do require more maintenance attention)? Discussion?

This is a tricky subject area, often full of compromise.


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## ccriders (Jul 8, 2006)

Ah, safety engineering. What a subject. Just think you could reduce boating fatalities by 50% just by making pants without zippers. But then what unintended consequences would that spawn? I would think my jack line requirements at 28 feet would be significantly different than yours at 40 feet and bay vs big blue. Also cats tris and monos would just drive the safety spec writer crazy.
I'm still thinking I don't need a lot of shock absorption on a centerline system for my boat as I certainly will be down on all fours transiting from cockpit to mast or bow. 
Of course when you see pictures of a capsize, they beg the question of what Jack line design is going to work in that situation?
John


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## RichH (Jul 10, 2000)

ccriders said:


> Of course when you see pictures of a capsize, they beg the question of what Jack line design is going to work in that situation?
> John


In those situations, you want to choose (beforehand) a carabiner, safety snap clip, etc. that can be opened while under tension. In my past 'rescue life' I had the sad experience of recovering a young teenage Hobie-18 sailor who was attached to her trapeze wire, the boat 'snap' pitchpoled and then turtled, ... and she was unable to release the trapeze wire 'hook' connector while being held underwater.


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## pdqaltair (Nov 14, 2008)

^^ Another thing. In the Windnuts capsize, I believe there was one fatality because the sailor had clipped his second leg (2 leg tether) back to the harness ring when not in use (there was no other place provided). This effective eliminates the quick release feature. Oops. 

Something to be mindful of. I added "storage loops" to my tethers.


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## pdqaltair (Nov 14, 2008)

ccriders said:


> ... I would think my jack line requirements at 28 feet would be significantly different than yours at 40 feet and bay vs big blue. Also cats tris and monos would just drive the safety spec writer crazy.
> I'm still thinking I don't need a lot of shock absorption on a centerline system for my boat as I certainly will be down on all fours transiting from cockpit to mast or bow....
> 
> John


Absolutely. But all of that can be addressed in a few sentences, once the broad strokes of the engineering are formalized. The challenge is functional layout.
* Stretch is a minor factor on a smaller boat, and reducing deck loads is more important.
* Cats worry as much about getting thrown forward when stuffing a wave at 15 knots as sliding sideways.
* Tether lengths vary. I use one 10' and one 2'. Wide foredeck, narrow side decks (the 10' tether doesn't reach all the way to leeward as it is, even with the jackline inboard). And for that reason, shock absorption matters more.


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## aeventyr60 (Jun 29, 2011)

* Something to be mindful of. I added "storage loops" to my tethers. *

Tell me about these? I just clip the short tether back onto my harness, it's also about three feet long.


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## zz4gta (Aug 15, 2007)

Do NOT do this. Put a short loop of line through the bail of the snap shackle. Connect the other tether to that. That way, when you release the snap shackle, the tether stays with the boat, and you are completely detached.


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## pdqaltair (Nov 14, 2008)

^^ What he said. If you clip the spare end back to your harness, then you no longer have a quick release (the spare will still be attached, and now it will be under load).

What is astounding is that most of the "quick release" tethers do not provide this loop, and thus are not quick release at all! They just never thought about it.

For me, I like for the loop to be a hard ring (easier to clip).


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## RichH (Jul 10, 2000)

Storage loops on climbing harnesses (can be applied to tethers too) are simple 'plastic' or rubber tubes (hose) sewn as a loop and onto which you can temporarily place other gear. Their purpose is to temporarily 'hang' gear that isnt being used. The connection stitching of these loops is minimal, so that in an 'emergency', if the loop or the attached gear becomes trapped, etc. the entire loop and its attached gear can be ripped off or broken free.


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## JonEisberg (Dec 3, 2010)

pdqaltair said:


> ^^ What he said. If you clip the spare end back to your harness, then you no longer have a quick release (the spare will still be attached, and now it will be under load).
> 
> What is astounding is that most of the "quick release" tethers do not provide this loop, and thus are not quick release at all! They just never thought about it.
> 
> For me, I like for the loop to be a hard ring (easier to clip).


On the other hand, many who do a lot of solo sailing don't believe in the use of snap shackles or quick release terminations...

If worse comes to worst, I'd rather drown quickly still attached to my boat, than slowly after watching it sail over the horizon...


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## aeventyr60 (Jun 29, 2011)

aeventyr60 said:


> * Something to be mindful of. I added "storage loops" to my tethers. *
> 
> Tell me about these? I just clip the short tether back onto my harness, it's also about three feet long.


Let , me be a bit clearer on this..the short tether is not attached to the jacklines, simply climped back on my harness so as not to get in the way of my moving about on deck.

Back in the old days we had racks with our gear on them, nothing attached to the old sawmi belt except the bitter end. No friends either..or juicy fruit gums shoes.


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## zz4gta (Aug 15, 2007)

RichH said:


> Storage loops on climbing harnesses (can be applied to tethers too) are simple 'plastic' or rubber tubes (hose) sewn as a loop and onto which you can temporarily place other gear. Their purpose is to temporarily 'hang' gear that isnt being used. The connection stitching of these loops is minimal, so that in an 'emergency', if the loop or the attached gear becomes trapped, etc. the entire loop and its attached gear can be ripped off or broken free.


And what is the industry standard for this? At what load do the loops break away? I do agree with you that the loops are not meant to be load bearing. But I haven't seen many "storage" loops on a sailing chest harness. And a climbers fall is far greater than that of a sailor falling off a boat.


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## aeventyr60 (Jun 29, 2011)

zz4gta said:


> And what is the industry standard for this? At what load do the loops break away? I do agree with you that the loops are not meant to be load bearing. But I haven't seen many "storage" loops on a sailing chest harness. And a climbers fall is far greater than that of a sailor falling off a boat.


I customized mine to accomodate a knife, strobe light and a whistle. Nothing i saw commercially available fit the bill, so little time with needle and thread and a bit of webbing solved some of those shortcomings out of the WM catalog...


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## RichH (Jul 10, 2000)

JonEisberg said:


> On the other hand, many who do a lot of solo sailing don't believe in the use of snap shackles or quick release terminations...


that goes for climbers and especially rescue climbers .... and where only a locking carabiner will do. Its too easy for quick release devices to become twisted or inverted and then errantly ('surprise') opened. Even with locking carabiners we always look to see what would happen IF the carabiner would become inverted and always arrange how the rope engages the carabiner so if it does become inverted the action of the rope doesnt 'unlock' the locking device of the carabiner.

In rescue climbing we mostly put a 'safety jumper' (short tied, short length safety line) across a locking carabiner and its harness connection as an adjunct for extra safety when ascending/descending with extreme loads ... such as with 'victims', loaded rescue baskets, ... and body bags, etc. 
I still always tie in a 'safety jumper' across my harness connection when going up a mast; and, would NEVER trust a 'splice' or a snap shackle .... only a doubled fig. of eight tied-in to that halyard and then free-climb/'shinny' up the mast (usually barefooted) with someone belaying for 'just in case'. Increasingly, I see riggers are doing this belayed (barefooted) free-climbing - smart and safer!


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## aeventyr60 (Jun 29, 2011)

Nope no quick release or snap shackles for me either. Won't be dragged through the water either.


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## RichH (Jul 10, 2000)

zz4gta said:


> And a climbers fall is far greater than that of a sailor falling off a boat.


Doesnt matter as in most places in the USA, any (non-rock climbing) 'fall' from more than a 20 ft. height (or equivalent) gets you an automatic immediate entry into a 'trauma center', including a helo ride. 
A climber usually falls attached to a 'stretchy' rope, which greatly lessens that terminal impact.


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## pdqaltair (Nov 14, 2008)

JonEisberg said:


> On the other hand, many who do a lot of solo sailing don't believe in the use of snap shackles or quick release terminations...
> 
> If worse comes to worst, I'd rather drown quickly still attached to my boat, than slowly after watching it sail over the horizon...


That's a whole different topic... and by the way, I agree. I can think of few cases where being released would be better. I use Kong Tangos on the harness end. I wouldn't use a quick release climbing! But a different topic.


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## pdqaltair (Nov 14, 2008)

RichH said:


> Storage loops on climbing harnesses (can be applied to tethers too) are simple 'plastic' or rubber tubes (hose) sewn as a loop and onto which you can temporarily place other gear. Their purpose is to temporarily 'hang' gear that isnt being used. The connection stitching of these loops is minimal, so that in an 'emergency', if the loop or the attached gear becomes trapped, etc. the entire loop and its attached gear can be ripped off or broken free.


a. Some are near full strength (2000 pounds, Metolious). They did this because some folks would use them to clip belay anchors .
b. If an ill informed rescuer clips a weak loop in the recover process and it rips out, loosing the sailor, someone gets mad.

http://www.metoliusclimbing.com/harnesses.html

And I'm not so certain gear loops release in any controlled manner; they are not designed for any calibrated failure, so I think any assumption is just guesswork. And it is a very rare fall that approaches 2000-pound impact (fall factor 2 is closer to 1200-1600 pounds with real world ropes and belays).


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## RichH (Jul 10, 2000)

pdqaltair said:


> b. If an ill informed rescuer clips a weak loop in the recover process and it rips out, loosing the sailor, someone gets mad.


Oh come on now, thats just 'schadenfreude'. Ever participate in a high angle rescue/recovery?


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## pdqaltair (Nov 14, 2008)

RichH said:


> Oh come on now, thats just 'schadenfreude'. Ever participate in a high angle rescue/recovery?


a. Yes, several. We've covered this.

b. I was not referring to high-angle rescue teams or the gear loops on climbing harnesses; I should have been more clear. Those guys are very well trained and not stupid. I was speaking of sailing MOB situations. I don't believe weak loops are a valid option on sailing tethers. Whether they are a valid option on deck harness is a more interesting discussion; could be the right answer, but would some knuckle head clip the tether there?

Schadenfreude? My current rock harness was subject to a safety recall after some putz clipped the elastic loop that restrained webbing from the waist loop and decked-out. The recall involved cutting the elastic away, nothing more.


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## RichH (Jul 10, 2000)

'Putzes' have indeed decimated the climbing and 'outdoor' supply industries. 
Ask Yvon Chouinard (Chouinard Equipment and founder of Patagonia) what happens when you dont 'putz-proof' and wussy-proof mountain, etc. gear. 
Probably its the very exact same reason boat builders dont OEM install safety gear: shysters and liability risk. 
;-)


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## zz4gta (Aug 15, 2007)

RichH said:


> Doesnt matter as in most places in the USA, any (non-rock climbing) 'fall' from more than a 20 ft. height (or equivalent) gets you an automatic immediate entry into a 'trauma center', including a helo ride.
> A climber usually falls attached to a 'stretchy' rope, which greatly lessens that terminal impact.


I'm confused, I thought we were talking about falling off a boat? 
Not a dead drop 20+ feet.


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## RichH (Jul 10, 2000)

The fall of 20ft. establishes determines the amount of deceleration forces that can cause 'significant' injury - based on volumes of statistical / historical evidence. If that same force/speed results in deceleration from any other non-vertical trajectory, the same rules apply .... injury involving two or more proximal long bone fractures, auto crash at over 35 mph (potential), etc. etc. etc. Every state EMS system has its published 'absolute trauma referral protocols' for EMS/rescue, etc. personnel .. and all based on statistics of outcome when those estimated forces are encountered ..... and which can be determined / estimated by an educated rescuer alone or by on-line consult with an ER Doc or Trauma Specialist, etc.

The simple speak here is that any force that can equate to that 20ft. fall (in some places a fall from twice the patient's height) is grounds for fairly strict adherence to those preset protocols ..... and it works as it gets the injured to the precise place of best care available for the potential injury, faster; even bypassing hospitals that are not set up for such care. It works and with much much better patient survivability and outcome.
;-)


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## pdqaltair (Nov 14, 2008)

zz4gta said:


> I'm confused, I thought we were talking about falling off a boat?
> Not a dead drop 20+ feet.


A common misconception. Horizontal velocity and a vertical fall are the same thing.

In fact, ISO added a very severe drop test for deck tethers after a few of them broke due to severe impact loading (~ 5000 pounds). For racing, all tethers must be drop-rated. In fact, a 6-foot throw across the cockpit on a non-stretch tether to a fixed anchor point is many times more severe than a 20-foot fall climbing on a dynamic rope.

Try this simple test rather than trusting the internet. Put on your deck harness, connect a non-stretch tether to a solid object (strong tree?) and run away as fast as you can (no faster than a wave hit, I am certain). Actually, don't do this, as there is a very good chance of an emergency room visit. start with only 2 feet of slack and work your way up. I doubt you will get past 3 feet of slack without at least minor injury, if you really throw yourself at it.

As a contrast, if you used a climbing rope all you would suffer is a bounce and 6 inches of stretch.


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## zz4gta (Aug 15, 2007)

Do either of you have any evidence that injury from a 6'/2m tether while sailing? Besides just being sore? And documentation at all? Seems that the Volvo ocean racers or Vende racers or any IMOCA class at all would have sailors with broken ribs all over the place. 

I understand physics and how the climbing rope helps slow the body down and is safer. But I'm interested in the probability of the sailor seeing these types of loads. 

Assuming the sailor gets hit by a wave and imposes the same load their tether as a dead drop (extremely unlikely in actual use), clipped into a hard point. What load is seen by the sailor? 

It seems that more people are going in the direction of installing hard point work stations instead of using the jackline. Removing the 'stretch' of the jackline deflection. Wouldn't this impose greater loads on the sailor? 

My point being, in actual use, sailing doesn't see the loads a climber does. Even at 6'. Is the possibility there? Yes, but in practice this is rarely the case. Otherwise, why would ISAF allow non shock absorbing tethers if they are so inherently unsafe?


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## smackdaddy (Aug 13, 2008)

zz4gta said:


> I'm confused, I thought we were talking about falling off a boat?
> Not a dead drop 20+ feet.


Yeah - we've covered it in the past:

http://www.sailnet.com/forums/gear-maintenance/146602-request-comments-diy-tether.html

The fear is a bit over the top.


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## RichH (Jul 10, 2000)

zz4gta said:


> Do either of you have any evidence that injury from a 6'/2m tether while sailing? <snip>
> 
> It seems that more people are going in the direction of installing hard point work stations instead of using the jackline. Removing the 'stretch' of the jackline deflection. Wouldn't this impose greater loads on the sailor?
> 
> My point being, in actual use, sailing doesn't see the loads a climber does. Even at 6'. Is the possibility there? Yes, but in practice this is rarely the case. Otherwise, why would ISAF allow non shock absorbing tethers if they are so inherently unsafe?


An in-depth response, including apparent state-of-the-art 'philosophies'.

Actually the trend in ISAF, etc. seems to be indicating just the opposite in that the inherent strength recommendations of boat tethers and harnesses, etc. seem to be approaching double of the strength of that normally used in mountain equipment. This is probably/possibly because within 'boat motion' the acceleration forces can be in simultaneously _opposing_ directions, thus doubling the resultant forces (rocks and other anchor points usually dont move thus a fall on a mountain only results in one, not two accelerations).

Sailors overboard, etc.
Anecdotal evidence or anecdotal supposition doesnt apply in such situations, only maximum 'potentials' that can lead to catastrophic failure should be considered. One cant predict the forces generated in a class 5 hurricane nor an F5 tornado but you can come close in approximating based on historical evidence. In boats, such is usually derived from scantling history or insurance records of what survived or what didn't survive such episodes.

Consider.
The way to evaluate (and 'test'/verify) to see if your safety gear is functional at the upper ranges of extreme stress and in accordance to simple 'physics' ... and which would be consistent with the inbuilt safety factors already incorporated in your boat's design; applying those historical safety factors and applying the same to new 'additions', etc. and then 'test'. Such verification estimates is called "proof loading" and is usually regularly applied to all 'hazardous' applications, including conveyances for carrying people or where if failure risks a high potential of death or injury: - cranes, tram systems, ski area chairlifts, pressure vessels, gondolas and cable cars, elevators, airplanes, etc. etc. etc. All these devices are built to 'hazardous' safety factors, typically 3 to 4 times the inbuilt strength of the expected maximum 'load rating' for 'normal' usage. 
Sailboats are generally designed with such safety factors included - coastal design @ FS=2, offshore @ FS=3 (or more) which implies that the forces generated (by 'accelerations') can be 2 to 4 times that for 'normal' sailing. These safety factors are based on a long historical record based on what 'survived' and what didnt; and, are used to _attempt_ to safely cover '_* unforeseen and unpredicted*_' events. Im one who believes that added/attached safety gear should be selected based upon 'equal strength' of the safety factors already inbuilt to a boat, as the designer already worked this out in his/her head, and kind of lets one know what forces (or accelerations) can be expected as a relative maximum to the overall design (not how many 'successfully' fell overboard, etc.).

If your sailboat is an 'offshore' design, we can ASSUME that at a minimum it was designed to handle at least 3 (or 4) times the normal 'stress' than when sailing 'normally' -Factor of Safety = 3 or 4. That would equate to 3*Gs acceleration,* or the 3 to 4 times the acceleration (potential forces) for just about everything of and ON the boat. (an extreme example - fighter aircraft are designed to at least 9 or more"*Gs*" and have the appropriate safety factors applied so they dont 'come apart' when they do encounter forces at greater than 9*Gs*).

Following Newton's Law of F=MA .... "force is equal to mass times its _acceleration_", a 'blue water boat' would be designed to not come apart in 4G (accelerations due to gravity) &#8230;&#8230;&#8230;&#8230;. A 200 pound sailor at 4G would apparently 'weigh' at least 800 lbs if he/she free-fell that length of 6ft tether when he/she came to the abrupt 'snap' at the end of that travel. Considering just the tether and applying that at least FS=4, one would want that tether to be able to 'hold' at least 200 lbs 'times' (FS=4) = 800 lb. Since the boat may be accelerating in the opposite direction of the 'body' &#8230;. then, 800lb times TWO = 1600lb.; then multiply by the safety factor of 3 (or 4) = a tether that can withstand 4800 lb.). Most 'offshore' tethers and harness are designed in the range of 4800 to 5000lb. maximum load .... so it seems that the safety equipment manufacturers are possibly following the maximum Safety Factors of the offshore boat .... times TWO, because of the possibility of two opposing accelerations to their equipment - quite reasonable. 
Since I dont take anyone's word for anything (especially for 'crap' made in asia), for a 4*G* or FS=4 situation, I'll take that ~4800lb. rated 'tether', load a pallet of cinderblocks, etc. to ~4800lb., tie in that 'tether' between the pallet and lift it off the ground (with a come-along, etc.) .... if the tether breaks or the connectors begin to deform, ..... or more usually the stitching starts to break, the 'proof test' *condemns* the tether and its 'connectors'. I do the same thing with my 'harnesses'. 
For a 'coastal' design (FS~2) for jacklines and tethers, etc. I would use at least a FS=4 which is the middle value of accepted normal lower limit of safety factors for '_hazardous_' applications. I prefer FS=4 for 'hazardous service' even that the 'elasticity under shock/impact load' is less.

The same applies to the jacklines, being careful to allow that certain amount of 'slack' so that you dont unduly generate (mathematically) 'order(s) of magnitudes' more force in the jackline line or its connectors because of 'inelasticity' and lack of deflection by a 'side load' - as inferred in a previous post.

But all this doesn't always result in a utopian anecdotal perfection &#8230;. as in the real world airplanes do come part, ball joints and other steering components fail on automobiles, ski lift chairs do become 'detached', cable cars do drop &#8230;. but happen very rarely because of the inbuilt factors of safety &#8230;&#8230; and constant 'proof testing'.

IMO - Anecdotal evidence / supposition is for 'literary' or courtroom _fiction_, not the potentials of the real world - as one shouldn't care how many sailors went overboard because of faulty or undersized or oversized equipment. All one should care about is that sailor (him/herself) and or his/her crew stays aboard during the maximum projected and perhaps a few 'overwhelming' unforeseen and unpredicted events ..... AND it appears that the current perceived newer industry standards of boat safety gear by manufacturers (for offshore) is currently at this 4800 to 5000 lb. max. load (it used to be at ~3600lb.) and which is consistent with the scantling design history of applied safety factors for 'offshore' boats. Very 'clever', huh?

Subjective conclusion.
So, if youre going offshore you should buy your tethers and harness, etc. based on a ~4800 to 5000 max. load capacity .... as those values would be able to handle those 'possible' double diametrically opposed accelerations that is 'possible' to tether/harness/jackline on a boat during 'maximum' sea-state conditions; plus, such would be consistent with the normal 'factors of safety' of the boat's 'offshore design' parameters. Very 'clever', huh?

BTW, .... since these 'stand up' hardpoints / mast base pulpits, etc. are essentially 'cantilevers' which due to 'their shape' and attachment support structure require a LOT more 'safety factor' .... Id keep my tether and harness attached to some 'strong point' even when being supported by a 'hardpoint' (granny railing) all due to the vulnerability of Mr. Archimedes and his infernal 'law of levers'.

;-)


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## FloridaBoy (May 4, 2014)

You Guys!!! Take all the fun out of jacklines and tethers! Well, not for you engineers, anyways. Guess it keeps you all out of the bar....Kevin


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## zz4gta (Aug 15, 2007)

Thanks Rich. I understand the reasoning behind the breaking loads. But not so much the reasoning behind the "worst possible scenario". Lets say you have a sailor on a tether and the worst does happen as you describe above. Huge shock loads, 6' tether, etc. Getting dangerously close to that max number. He/she is saved and kept on the boat and survives, albeit with broken ribs or back, but alive. This, thanks to taking in consideration the dooms day approach to worst possible loading. 

Now add another sailor on the same jackline. How about 3 sailors? Are we now required to carry a system that holes 9600 lbs or 14,400? And that's assuming sailors of 200 lbs. I don't have a ton of experience, but some of the sailors I've seen frequently tip in above 200 lbs. And with the safety factors involved, a 230 lbs person would generate a lot more force than a 200 lbs person. 

I'm sure you can see the rabbit hole this is going down. But that's why I asked about anecdotal evidence.


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## RichH (Jul 10, 2000)

Keep "Shamu the Whale" on a shorter tether ... less time to accelerate; therefore, less impact forces, ...... as he goes down the rabbit hole. :-o


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## Leftbrainstuff (Apr 26, 2011)

*good engineering debate*

Airplane wings flex so they can absorb energy. There is a dynamic fatigue limit based on peak load and number of cycles that we design for.

Bungee cords stretch to avoid subjecting the heart to excessive acceleration and jerk (rate of change of acceleration). That is the limiting load we design for. They are also lifed.

In both cases miners law, and the yield strength of the material, is the engineering tool we use to design and manage these systems so that catastrophic failure is avoided. We want elastic deformation but never plastic deformation throughout their useful life.

Jack lines and safety lines are typically designed for one time use. Safety systems like these are typically only rated or certified for one time use. This equates to a very high peak load of just one cycle. Maximum tensile strength is the material property limit that is of interest here. Good designs will permanently deform giving visual evidence that the system has now done its job. Here we want plastic deformation but not fracture.

For these safety systems we typically have a flexible and a rigid element because we want to limit deflection. Either to avoid a MOB situation or to avoid hitting the ground in a highline system. Both the rigid and elastic elements need to indicate by plastic deformation when they have been loaded (used).

The real issue is do users replace them at sea when they have done their job.


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## Waltthesalt (Sep 22, 2009)

I opted to put in fixed attachment points and tracks instead of jacklines. Attachment points are in the cockpit, at the mast, and on the foredeck. There are port and stbd tracks with cars mounted several feet inboard for going forward. There’s also a track in the cockpit to move fore and aft. The tether is adjustable. This arrangement comes from observations of the arrangements on the USCG rescue craft at the Columbia River Museum and arrangements on navy ships. The idea is not allowing enough slack, flex/stretch to go over the lifelines. As pointed out a jackline that is tight enough for limited deflection has a lot of stress when loaded especially dynamically


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## pdqaltair (Nov 14, 2008)

*Re: good engineering debate*



Leftbrainstuff said:


> Airplane wings flex so they can absorb energy. There is a dynamic fatigue limit based on peak load and number of cycles that we design for.
> 
> Bungee cords stretch to avoid subjecting the heart to excessive acceleration and jerk (rate of change of acceleration). That is the limiting load we design for. They are also lifed.
> 
> ...


Certified for one time use?

What? This is flatly absurd, and you even explained why; a sailor is not going to replace the system mid-storm (he might need it several times within minutes), and a climber is not going to replace a rope mid-wall just because he took a whipper (he may take dozens in one climb). Frankly, that would be a useless design, and the market will tell you as much. The fact that it is only suitable for one use suggests very little safety factor, testing, or fatigue allowance in the design.

Bold statements like that require back-up. This is simply not true of rock climbing, OSHA, or sailing gear. Yes, user inspections after use are required (not re-certification unless and over load indicator has triggered), but not use it once and pitch it.

Is there such a fall that the equipment will need replacement after one cycle? Not if properly designed. Of course, there are substandard designs out there.

Highline systems with load indicators? I have seen them designed that way, but in many cases this is rendered quite unnecessary by insuring that all possible falls are within the elastic fatigue limits. This is the way to approach jacklines, and it is quite practical.

---

I can only guess this is outside of your practical experience.


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