[killarney_sailor]

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.

 

[aeventyr60]

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

 

[JonEisberg]

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...

 

[pdqaltair]

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).

 

[RichH]

(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. ;-)

 

[pdqaltair]

^^ 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.

 

[JonEisberg]

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

 

[RichH]

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.

 

[RichH]

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'.

 

[pdqaltair]

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.

 

[JonEisberg]

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....

 

[MarkofSeaLife]

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?

 

[pdqaltair]

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.

 

[RichH]

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

 

[aeventyr60]

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".

 

[killarney_sailor]

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

 

[Capt Len]

Sailing is usually more interesting than you expect.

 

[Zanshin]

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.

 

[pdqaltair]

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.

 

[MarkofSeaLife]

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.