Jacklines and tethers
- Thread starter Mark48
- Start date
I'm a big believer in DIY, but this is a tricky subject and deserves some expansion. I've done a fair amount of testing, some of which has been published.
a. Climbing webbing, while very strong stuff, is slightly below the ISAF strength requirement (small issue), stretches when wet (bigger issue), and is weaker and stretchier yet when wet (big issue). I doubt it is suitable for any boat >30 feet. For boats > 40 feet, Dyneema or SS inside webbing is required to control stretch. Remember that climbers use this webbing doubled (loops) from applications exposed to fall impact; it is NOT USED SINGLE because it is not strong enough.
b. Nylon webbing is VERY difficult to sew to strength without a commercial bar tacking machine. No amount of long x-patterns will get you much past 50%. The reason has to do with differencial stretch between the 2 parts preventing equal load distribution. Reinforcement with a 3rd layer helps (it stiffens the webbing, reducing stretch), but this is all beyond the abilities of a DIY that will not be test breaking samples. This is all very different from sewing polyester and more like sewing Lycra. Bottom line: you are very unlikely to sew something stronger than 2000 pounds.
c. While locking climbing biners can be used, most are quite subject to seawater corrosion and will need to be careful maintained and greased. On the other hand, their light weight is an advantage (won't ding the gel coat and they glide more smoothly) that can be worth it. For light users, this can work. The Kong Tango is very nice and does not seem very prone to corrosion.
(Yes, these are sewn, but I pulled many samples to failure before settling on a method. Before I developed the sewing method, I used scaffold knots, which are about 80% strength in this application and much better than most sewing. This is 8.2mm dynamic rope which is UIAA fall-tested with knots as part of the rigging.) These will also exceed the drop test requirements of the new CE standard for tethers.)
The nice thing about DIY tethers is the ability to customize the length; the standard 3/6 split is all wrong for many boats. My recommendation, given the problems with sewing, is either knot the slings and recognize they are lower strength, or use dynamic climbing rope (8mm is best). For jacklines over 30', run Amsteel inside them.
And a lot more discussion:
http://sail-delmarva.blogspot.com/2013/12/dynamic-tethers.html
a. Climbing webbing, while very strong stuff, is slightly below the ISAF strength requirement (small issue), stretches when wet (bigger issue), and is weaker and stretchier yet when wet (big issue). I doubt it is suitable for any boat >30 feet. For boats > 40 feet, Dyneema or SS inside webbing is required to control stretch. Remember that climbers use this webbing doubled (loops) from applications exposed to fall impact; it is NOT USED SINGLE because it is not strong enough.
b. Nylon webbing is VERY difficult to sew to strength without a commercial bar tacking machine. No amount of long x-patterns will get you much past 50%. The reason has to do with differencial stretch between the 2 parts preventing equal load distribution. Reinforcement with a 3rd layer helps (it stiffens the webbing, reducing stretch), but this is all beyond the abilities of a DIY that will not be test breaking samples. This is all very different from sewing polyester and more like sewing Lycra. Bottom line: you are very unlikely to sew something stronger than 2000 pounds.
c. While locking climbing biners can be used, most are quite subject to seawater corrosion and will need to be careful maintained and greased. On the other hand, their light weight is an advantage (won't ding the gel coat and they glide more smoothly) that can be worth it. For light users, this can work. The Kong Tango is very nice and does not seem very prone to corrosion.
(Yes, these are sewn, but I pulled many samples to failure before settling on a method. Before I developed the sewing method, I used scaffold knots, which are about 80% strength in this application and much better than most sewing. This is 8.2mm dynamic rope which is UIAA fall-tested with knots as part of the rigging.) These will also exceed the drop test requirements of the new CE standard for tethers.)
The nice thing about DIY tethers is the ability to customize the length; the standard 3/6 split is all wrong for many boats. My recommendation, given the problems with sewing, is either knot the slings and recognize they are lower strength, or use dynamic climbing rope (8mm is best). For jacklines over 30', run Amsteel inside them.
And a lot more discussion:
http://sail-delmarva.blogspot.com/2013/12/dynamic-tethers.html
Isn't the strength an issue when the Jackline must not break when dragging a man through the water? If the Jackline is designed to keep the man inside the safety lines it need not be nearly as strong. 300lb strength would be plenty for me. So if it runs down the centerline and is designed to keep the man on deck almost any rope would do.
For jacklines, what about the webbing the truckers use to cinch down massive loads in all kinds of weather [not talking about the hardware on them]? Or the towing straps the repo jockeys sometimes use?
Too wide (2"). Biners/snaps won't fit. If you find 1" versions they might be just the ticket.
The critical load is NOT dragging but flying across the deck. Consider a body moving at 7-8 knots; this is the same as a 6' fall. Stopping a 200# man within feet will require about 3 Gs, depending on the specifics, or 600#. Reasonable.
Then consider the tight rope factor. The rope will feel a tension about 3-6 times greater because it is strung tight, even allowing for stretch. 1800-3600 pounds. Given any imperfections in stitching, wear, knots, UV, and weakening due to water (strength is rated dry) you are very close to failure. The ISAF-rated straps are known to hold, climbing webbing may not in a worst case.
Even worse if there are 2 men on the jackline.
Thus, climbing webbing should be OK for boats under 30' (shorter fall distance), but no larger.
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As for the center line theory, in my experience on heeling boats it makes little sense. No one ever falls off to windward, or at least I have never heard of it (stupid rail meat excepted--that is a different case and they aren't tethered anyway). On a small boat it makes even less sense, since the leeward side is that much closer. But much depends on exactly where the lines can be run. I like the top edge of the cabin, if possible, rather than the deck.
Nice post.I'm a big believer in DIY, but this is a tricky subject and deserves some expansion. I've done a fair amount of testing, some of which has been published.
a. Climbing webbing, while very strong stuff, is slightly below the ISAF strength requirement (small issue), stretches when wet (bigger issue), and is weaker and stretchier yet when wet (big issue). I doubt it is suitable for any boat >30 feet. For boats > 40 feet, Dyneema or SS inside webbing is required to control stretch. Remember that climbers use this webbing doubled (loops) from applications exposed to fall impact; it is NOT USED SINGLE because it is not strong enough.
b. Nylon webbing is VERY difficult to sew to strength without a commercial bar tacking machine. No amount of long x-patterns will get you much past 50%. The reason has to do with differencial stretch between the 2 parts preventing equal load distribution. Reinforcement with a 3rd layer helps (it stiffens the webbing, reducing stretch), but this is all beyond the abilities of a DIY that will not be test breaking samples. This is all very different from sewing polyester and more like sewing Lycra. Bottom line: you are very unlikely to sew something stronger than 2000 pounds.
c. While locking climbing biners can be used, most are quite subject to seawater corrosion and will need to be careful maintained and greased. On the other hand, their light weight is an advantage (won't ding the gel coat and they glide more smoothly) that can be worth it. For light users, this can work. The Kong Tango is very nice and does not seem very prone to corrosion.
(Yes, these are sewn, but I pulled many samples to failure before settling on a method. Before I developed the sewing method, I used scaffold knots, which are about 80% strength in this application and much better than most sewing. This is 8.2mm dynamic rope which is UIAA fall-tested with knots as part of the rigging.) These will also exceed the drop test requirements of the new CE standard for tethers.)
The nice thing about DIY tethers is the ability to customize the length; the standard 3/6 split is all wrong for many boats. My recommendation, given the problems with sewing, is either knot the slings and recognize they are lower strength, or use dynamic climbing rope (8mm is best). For jacklines over 30', run Amsteel inside them.
And a lot more discussion:
http://sail-delmarva.blogspot.com/2013/12/dynamic-tethers.html
4500 pounds.
ISAF special regs 4.04D
But the 6000# stuff look OK. Too bad it is nylon (high stretch).
Also, all hand holds are required to hold 1.5KN (330 pounds). I wonder about many wooden handholds.
Because those that know how to make them and proof-load them, 'tailor' the length so that they dont go overboard and get dragged along the side of the boat.
Another 'why': Just reflect for a second or two on where 'most' of such 'boat stuff' is now being made.
Ditto with 'perfect fit' harnesses, too. I prefer a Liakiris type self-adjusting harness w/ crotch straps.
I've always thought that the desired strength of a jack line was based on the force of solid water propelled by gravity/momentum hitting someone and potentially knocking that person off the boat, rather than by the force generated from potentially falling over the lifelines.
if you are my size.
I bought webbed tubing of sufficient strength for jacklines. had a canvas maker who did my dodger stitch a loop in one end. I attach them to the forward cleats, run them along the deck and tie them off at the stern cleats. I always use them when going offshore, even coastal. I require everyone to clip in at night if they go forward. we have PFDs with integrated harnesses. I bought tethers primarily due to the specialized clips that are safest to use.
Supposed to be 4500# rated for anchors. Would you hang an SUV from it? At deck level, maybe, any higher, no.