Dyneema for lifelines

[wingssail]

Originally Posted by Jolly Roger

To all members who got
involved with my original post—there is an article in
this month’s Cruising World, about how I finally
renewed my lifelines with Dyneema, along with the
accessories used. They look dynamite! and I have
every confidence they will be just as effective as
wire, but with other advantages as well.

There will also be another one in next month’s
magazine, about how I spliced the lines. JR

We changed to Dyneema for the lifelines about 4 years
ago, 6mm Robline, same as what we used for our 3
forward halyards, they were tapered. We used eye
splices on the ends of both the lifelines and the
halyards and luggage tagged the them to the shackles
(halyard) and the railing loops (lifelines). We used
lashing on the other ends to tension the lifelines.

The boat is in Mexico full time, ion the hot, direct
sun.

After three years all three halyards failed within a
month of each other. All failed at the eye splice.

The Dyneema broke exactly at the end of the buried
part. There was no chafing or other sign of wear.
Just a sudden "Bang" and the sail came down.

I replaced the halyards with 6mm Dyneema and have
started running them up when the boat is not in use
to get the dyneema out of the sun.

This year, in the fourth season, one of my lifelines
broke at the dock while was leaning on it. Same type
of failure: right at the end of the buried part of

the eye splice, which was only tapered down to about
1/2 the rope's original diameter. I replace that
lifeline and will do the other side soon. (I have
bought a spool of the 6mm Dyneema).

In all cases the Dyneema looked good just prior to
the failure. My friend David who was head rigger for
West Marine San Diego for several years thought they
looked OK but he said the end must be tapered down to
nothing when making an eye splice.

So the take aways from this are:
Be very careful when making eyesplices in Dyneema and

DO NOT neglect to use a safety line when going aloft
on a dyneema halyard.

[Jolly Roger]

That’s very interesting Wingssail. Do take a look at my article in next month's Cruising World which shows how to splice Dyneema. I will be interested in your observations.
Just one thing, when you speak of “right at the end of the buried part of the eye splice” do you mean the actual end of the buried part, (i.e. about 8” inches along the splice), or where it enters the standing part?
I advocate that the splice should be lock-stitched, for about one-quarter the depth of the bury, mainly to prevent it sliding back out when under light load. I also used CS Johnson’s special end fittings for my lifelines, which present a very smooth eye in the splice.
I also give a warning proviso: never to use any spliced line, (by whatever method or rope), to go aloft, because the splices cannot be inspected internally. A knot is a much more secure method for attachment to a bosun’s chair.

[jo_sail]

5mm Dyneema can work for Jackstays, too:

https://www.skipperguide.de/mediawik...Strecktaue.pdf (in German, but pictures tell the message)

Meanwhile I prefer them for:
+ minimum stretch of the jackstay line
+ very simple to clip on with your tether compared to completely flat jackstay band
+ dyneema hollow braid is flat enough to not show any rolling effect under your shoe
+ strong and still light weight for carrying in air plane luggage, if you like to have your own primary safety gear on charter yachts

Note, the requiered stretch to not break your spine shall come 1st from the tether material, only 2nd from the hopefully very low stretch remaining in the geometry of lines, when a tether pulls at about right angle at the straight jackstay (see red lines in pictures) . The 2nd is problematic with more elasticity in the jackstay rope material and/or „slack“ installation by curving the jackstay close to the board edges (see bottom left pictures, where the old dirty-yellow jackstay is still laying).

It is in my view important to:
! carefully taper at the ends in the dyneema splices (avoiding a weekpoint there) and
! find strong fix points with significant radius (or alternatively do a very thick lashing, like suggested in this thread for the lifelines, which becomes thick enough in the eye of your dyneema splice, thereby providing for a good radius)
! avoid sand under your shoes for sailing

See also two articles, related to this topic:

https://www.ussailing.org/wp-content...n-Jan-2014.pdf

https://www.yachtingmonthly.com/sail...void-mob-51411

Jo

[thomm225]

My lifelines have been Polyester/Dyneema for years.

No splicing required just tie with your favorite knot.

Redo/retighten as needed.

[Benz]

Originally Posted by jo_sail

5mm Dyneema can work for Jackstays, too:

https://www.skipperguide.de/mediawik...Strecktaue.pdf (in German, but pictures tell the message)

Meanwhile I prefer them for:
+ minimum stretch of the jackstay line
+ very simple to clip on with your tether compared to completely flat jackstay band
+ dyneema hollow braid is flat enough to not show any rolling effect under your shoe
+ strong and still light weight for carrying in air plane luggage, if you like to have your own primary safety gear on charter yachts

Note, the requiered stretch to not break your spine shall come 1st from the tether material, only 2nd from the hopefully very low stretch remaining in the geometry of lines, when a tether pulls at about right angle at the straight jackstay (see red lines in pictures) . The 2nd is problematic with more elasticity in the jackstay rope material and/or „slack“ installation by curving the jackstay close to the board edges (see bottom left pictures, where the old dirty-yellow jackstay is still laying).

It is in my view important to:
! carefully taper at the ends in the dyneema splices (avoiding a weekpoint there) and
! find strong fix points with significant radius (or alternatively do a very thick lashing, like suggested in this thread for the lifelines, which becomes thick enough in the eye of your dyneema splice, thereby providing for a good radius)
! avoid sand under your shoes for sailing

See also two articles, related to this topic:

https://www.ussailing.org/wp-content...n-Jan-2014.pdf

https://www.yachtingmonthly.com/sail...void-mob-51411

Jo

This might derail the thread, but it's probably gone as far as it's going to.
Jo: do you really think anyone can generate enough force to break their backs by falling the length of a tether onto a jackline? It's not like you can free-fall even that far on a deck.
And if the dyneema jackline is tight enough that you're worried about shock-loading a body, it certainly won't lie flat: that rope will be nice and round, unless you have some special sort of braid most of us don't know about.

[Ween]

Originally Posted by Jolly Roger

...when you speak of “right at the end of the buried part of the eye splice” do you mean the actual end of the buried part, (i.e. about 8” inches along the splice), or where it enters the standing part?

Dyneema doesn't like stress risers and he commented that his splices only tapered to 1/2 dia on the bury. Thus there is a pronounced spot in the line where the dia drops drastically from ~ 1.5 to 1.0 dia. This is bad. Make a nice long taper since you have plenty if bury (>60 dia) if you are doing it right. Do a full taper one strand at a time all the way down to one. You should not be able to identify where the bury ends, visual or tactile.

Cannot find but I "believe" I've seen data that the double brummel lock area is weaker than a straight long bury done correctly. It is what I do anyway.

[thinwater]

Originally Posted by wingssail

We changed to Dyneema for the lifelines about 4 years
ago, 6mm Robline, same as what we used for our 3
forward halyards, they were tapered. We used eye
splices on the ends of both the lifelines and the
halyards and luggage tagged the them to the shackles
(halyard) and the railing loops (lifelines). We used
lashing on the other ends to tension the lifelines.

The boat is in Mexico full time, ion the hot, direct
sun.

After three years all three halyards failed within a
month of each other. All failed at the eye splice.

The Dyneema broke exactly at the end of the buried
part. There was no chafing or other sign of wear.
Just a sudden "Bang" and the sail came down.

I replaced the halyards with 6mm Dyneema and have
started running them up when the boat is not in use
to get the dyneema out of the sun.

This year, in the fourth season, one of my lifelines
broke at the dock while was leaning on it. Same type
of failure: right at the end of the buried part of

the eye splice, which was only tapered down to about
1/2 the rope's original diameter. I replace that
lifeline and will do the other side soon. (I have
bought a spool of the 6mm Dyneema).

In all cases the Dyneema looked good just prior to
the failure. My friend David who was head rigger for
West Marine San Diego for several years thought they
looked OK but he said the end must be tapered down to
nothing when making an eye splice.

So the take aways from this are:
Be very careful when making eyesplices in Dyneema and

DO NOT neglect to use a safety line when going aloft
on a dyneema halyard.

How were the ends cut? Knife? Scissors? Hot knife?


How long were the buries?


Brummel or lock stitch?



To fail that that light load is not just the sharp bend. There must have been internal chafe from load/unload across something like an edge. Or perhaps there is something to do with a combination of little taper and short bury.

[thinwater]

Originally Posted by Benz

This might derail the thread, but it's probably gone as far as it's going to.
Jo: do you really think anyone can generate enough force to break their backs by falling the length of a tether onto a jackline? It's not like you can free-fall even that far on a deck.
And if the dyneema jackline is tight enough that you're worried about shock-loading a body, it certainly won't lie flat: that rope will be nice and round, unless you have some special sort of braid most of us don't know about.

It's not the impact force on your body, it is the impact force on the non-stretch jackline. Remember, it is stretched like a guitar string, and I bet you have broken those.


The maximum impact would be a sort of running stumbler down hill with a wave pushing you. That is about as severe as a free fall, if you do the energy calculation.


A fun winter exercise. Attach your tether to something that will not move (telephone pole) and then run (back up fast) at the end of it with progressively increasing slack. You won't get to more than a few feet before it hurts. I would not suggest this exercise with 5-6 feet of slack, and 12 feet could land you in the hospital.


Tethers don't have to stretch enough to protect you, only enough to not break in a test drop with a wooden dummy. A person would not survive the drop. They are NOT tested like climbing equipment, where a max impact force is specified. Look up the test standards.


Also note that the strength requirement for jacklines was developed for polyester webbing and never amended. The force is higher with Dyneema, so the jackline should be stronger. Attachments too. Just sayin'.

[Seman]

My 4mm lifelines with chafe protection.

[jo_sail]

Originally Posted by Benz

Jo: do you really think anyone can generate enough force to break their backs by falling the length of a tether onto a jackline?

Yes, I think so and thinwater has correctly pointed to the safety discussion and experience with climbing gear. In climbing a length of 30 cm Dyneema from you to a fixpoint is already seen as a risk, as it could allow a vertical fall of maximum of 60 cm into a non-elastic line. The dyneema will not stretch and transfer nearly the full energy of the fall to the weakest point in the system consisting of fixpoint-tether-belt-body. And here the weakest point lies between fixed belt and falling body, i.e. your spine.

Alternatively more elastic polyamide/nylon webbing is suggested for connection to fix points in climbing and this is good for tethers in sailing. It will absorb part of the shock (energy) and thereby reduce peak stress at the spine. Kong offers a nice example for sailing which also has robust and safe hooks used for climbing gear. When it comes to safety gear, sailors can make good use of fundamental experiences in climbing.

And length of the tether has to be considered. Keep it as short as practical for safe movement on board, is my idea. Acceleration of your body will be stopped sooner (at lower speed, less energy absorption needed to stop the movement, E=m*v^2) and it will limit the chance of hanging over the lifeline or even overboard. Two good reasons in my view.

A length of close to 2 m offered by many tethers (also the long one on the Kong) can become very dangerous, when you involuntarily start running and falling into it. So in my opinion, something like 1.5 m max for the long leg would be better.

[Benz]

Originally Posted by thinwater

It's not the impact force on your body, it is the impact force on the non-stretch jackline. Remember, it is stretched like a guitar string, and I bet you have broken those.


The maximum impact would be a sort of running stumbler down hill with a wave pushing you. That is about as severe as a free fall, if you do the energy calculation.


A fun winter exercise. Attach your tether to something that will not move (telephone pole) and then run (back up fast) at the end of it with progressively increasing slack. You won't get to more than a few feet before it hurts. I would not suggest this exercise with 5-6 feet of slack, and 12 feet could land you in the hospital.


Tethers don't have to stretch enough to protect you, only enough to not break in a test drop with a wooden dummy. A person would not survive the drop. They are NOT tested like climbing equipment, where a max impact force is specified. Look up the test standards.


Also note that the strength requirement for jacklines was developed for polyester webbing and never amended. The force is higher with Dyneema, so the jackline should be stronger. Attachments too. Just sayin'.

If you stretch a dyneema jackline as tight as you can without busting the fittings out of the deck, then fall against it (assuming a 30-ish-foot length) there will be some give. I can stretch a piece of 8mm dyneema to 30% of break load on a hydraulic test bench and still yank it sideways.
I think this notion of breaking a spine by being caught by a jackline is a bit silly: you'd have to catch serious air, have a badly-designed harness (we can talk about sailing harnesses later), be fetching up to a leash that's way too long (anything longer than arm's length is kinda stupid; why would anyone have even as much as five feet?), and have a spine so weak you probably shouldn't be at sea anyway. Bigwall climbers take "daisy whippers" all the time: a static fall to the end of their daisy chain. The stop is abrupt and uncomfortable, but no one I know has broken a spine doing that.

[fxykty]

Originally Posted by Ween

…



Cannot find but I "believe" I've seen data that the double brummel lock area is weaker than a straight long bury done correctly. It is what I do anyway.

I’ve dealt with a number of yacht riggers since we decided to switch our wire shrouds for Dyneema. Even very experienced synthetic riggers (15+ years) disagree on whether double brummel lock eye splices are significantly weaker than (properly) lock stitched straight eye splices, assuming both have long 72x tapered buries.

Using Dyneema DUX one sizes for creep, not strength, resulting in 5x or so more strength than wire. Even if a double brummel lock were to lose 50% strength, so what?

And I have been told that by John Franta of Colligo that with 72x bury a double brummel lock doesn’t lose anywhere close to that. Certainly Colligo recommend and use them for their rigging. But a rigger who was recommended to me by the local Hampidjan distributor refused to work on my rig unless I removed the Colligo Cheeky Tangs and double brummel lock splices and replaced with tang and terminal and straight eye splices.

I hate competing ‘experts’.

Does anyone have actual data comparing the strengths of the two eye splices?

[Benz]

^^ I wonder what he had against cheeky tangs? Can't they be used with a straight-bury eye splice?

[Breaking Waves]

Originally Posted by fxykty

Does anyone have actual data comparing the strengths of the two eye splices?

I tested them rather extensively. The brummel (well done) loses you about 10% vs well-done lock stitching long straight splice. So, it is not huge . . . . but the Brummel adds complication and possibility for error and that is mostly why the commercial lifting riggers essentially never use it. There are in fact some 50% failure modes for the brummel, with brummels which look ok' externally but either did not split the strands evenly or did not tension the bury to carry the load (and allowed the load to come on the brummel).

The length of the bury really has very little to do with static strength (beyond about 45x).

Poorly done you can f&*k-up any of these solutions, a Brummel can lose you more than 10% (as I said above up to like 50% loss even with an 'ok looking' one), and poorly done lock stitching (often pulled too tight) can also lose you more.

bottom line . . .the brummel is really not used any place other than 'yachting', and is generally considered 'not best practice' by riggers with experiences beyond yachting.

[thinwater]

Originally Posted by Benz

... you'd have to catch serious air, have a badly-designed harness (we can talk about sailing harnesses later), be fetching up to a leash that's way too long (anything longer than arm's length is kinda stupid; why would anyone have even as much as five feet?)...

It's common to think based on only personal experience.


Own a multihull. Even on my PDQ, the bow jacklines are 12-14 feet apart and many use tethers longer than the stock 6' (if you don't you can't reach the mast or most of the deck). A running "fall" of 8 feet is easy. I've done it.


It's not the sailor impact that is the concern, it is the tight rope force, and I HAVE tested this. A hard fall across the deck can easily have an impact force of 500-1000 pounds. That doesn't feel like a lot, just a few Gs. As you say climbers do that all the time. But it is multiplied by the shallow angle and lack of stretch of the Dymeema many times, to well past the safe working load of the Dyneema and the anchor points.


Do the math. You probably took high school physics and trig. It's all there.


I am NOT against Dyneema lifelines. You just need to do the math, which is different from the old polyester math.