The Offshore Voyaging Reference Site

The Right Tethers To Keep Us Aboard—Part 1, A Mix

As those of you who have been reading here for a while know, we—Phyllis and I with the help of the smart people that comment—have been working for over three years on better crew overboard prevention systems and practices. A project inspired by our realization that current common practice is deeply flawed and may even be worse than no tethering system at all.

If that statement comes as a surprise to you, you will need to read through the rest of this Crew Overboard Prevention Online Book before going any further.

Let’s finish this project by looking at tethers:


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Dick Stevenson

Hi John,
A great series of articles. I appreciate all the work this took to put together.
In your discussion of the material to make tethers from, you rejected nylon, but it sounds like you may have been considering nylon braid and not 3 strand nylon. In casual research in years past, I thought 3 strand nylon and dynamic climbing rope to be similar in stretch characteristics. I can see nylon braid being 3 times less stretch as 3 strand stretches far more than braid. I am not sure that I would want any more stretch than my (homemade) ½ inch 3 strand nylon tethers already have, but I am looking forward to hearing and learning more.
On another note, I know 3 strand nylon to vary widely in quality: does to same go for dynamic climbing ropes and can you flag some of the manufacturers whose reputation is good.
Thanks again, Dick Stevenson, s/v Alchemy

Marc Dacey

Articles like this are hugely useful and, arguably, are even ground-breaking in terms of drilling down to what can really save you and kill you on a lurching deck. It has occurred to me that shorter lengths of round “rope” terminating at strongly backed padeyes might make sense for places like the cockpit where one is a) partially protected; b) tends not to move around a lot; and c) if you do move, you will tend to slide toward the gunwhales, rather than get tossed. This happened to me offshore: it made a strong impression.

Yours is the first mention of the topic where a mix of stretchy tethers and short tethers on jacklines has been suggested.

Erik Williams

Hi John. I’m an old climber. I’ve been adapting climbing practices to the “staying on the boat” issue for years., as well as a few others for years. A lot of climbing practices are optimal for sailing solutions.
I have a couple questions: typically, DCR is not available except in standard lengths (50 or 60 meters being standard). Have you been able to source it by the foot/meter? if so, please share. An even more significant question is securing the line to the biner/shackle. What does the research indicate? I’ve used either a ring bend (with secure secondary tail) or a figure 8 on a bight, as one would tie into the rope when climbing. The choice was dictated by these factors: size of the eye in the hardware (if only room for one pass of the line, then the 8, if room for two, ring bend. This is because I understand the ring bend preserves the highest % of the original line strength. I’ve used 8 mm “double rope” ( intended to be used as a pair, not alone) and so the rated strength is lower, and I don’t have the redundancy/safety factor, or at least I want to keep as much as possible.
interesting thoughts in this bit!
Thanks

Eivind Haugan

Hi John
I was a bit surprised to read that the Spinlock tethers should be made of dyneema, which I agree would be unsuitable.
I checked with Spinlock and they told me that they use a mix of polyester and nylon.
Otherwise an interesting article on a very important issue where we will always have trade offs, where it’s difficult to know if we are right or wrong before we are in trouble.
Regards Eivind / Abraxas 3

Drew Frye

I would never have thought of a mix of tether materials, though I see no flaw in the reasoning. This is definitely a choice for sailors who know their gear, something World Sailing can’t be sure of. For jackline locations, stretch is not needed and polyester has many advantages. The primary places the shock absorption is of value on my boat are the bow (catamaran–wide and totally different from monos) and the transom area, because there I am clipped to hard points, it can be a real jolt, and the tethers cannot easily be shortened without compromising movement. However, even though they have a long leg (9′), they do not violate the “edge of the deck” priniciple.

I like to leave my tethers on the line, but I do stash them below when not sailing for a few days. I also might think differently about this with a different layout.

3-strand nylon is is nice to splice, but it has a few weaknesses. The primary problem is that to achieve equivalent toughness (force times stretch) it must be much large in diameter, and thus a hazard under foot. The catch will also be more firm. The reasons are that it does not stretch as much ( about 12% at 20% BS vs 19% at 20% BS) and is not quite as strong. My recollection is that you need 7/16″ (11mm) 3-strand to meet the toughness requirement. That could be a good answer for some people, and certainly would be acceptable for work station tethers, like one that is left at the mast, for example.

Quality of climbing ropes is very tightly controlled by UIAA standards. There simply is no market for a climbing rope that is not well tested and with an impeccable reputation. Just look for the stamp (they are required to be labeled on the end).

Rope by the foot. UIAA 1/2 rope (the 8mm that John speaks of) is available in 30M lengths for glacier travel. Since I also use 8mm dynamic rope for my main traveler (another place shock absorption is very nice), this is not an excessive amount. Also, http://www.MEC.ca sells 8.3 mm rope by the foot. Just sort by “lowest price first” and look for a UIAA 1/2 rope.

UIAA ropes are drop tested using a figure 8 as the baseline knot. First, this means that some loss in strength is assumed in the test procedure. Second, there are other knots that are just as strong and are far more compact. The halyard has tested well, as has the double overhand noose. The main advantages of the figure 8 it that absorbs more energy in the tightening process, and that if tied with a Yosemite finish (extra tuck), you have a good chance on untying it after a good drop; other knots will seize, but does that really matter? A figure 8 with a tuck back really is quite bulky; excellent for a climber’s tie-in, but not for tethers, I think.

John’s main point, as I read it, is that the jacklines and tethers must fit the boat. That is the point.

Dick Stevenson

Hi Drew,
Thanks very much for your thoughts and information. As John said, they are well put.
It appears that 3 strand nylon checks many of the boxes for a shock absorbing tether (when of large enough diameter for your toughness caveat), although not as shock absorbing as DCR, and I agree that they are handy to make (any length) as splicing is so easy.
I have been using ½ inch (12mm) 3 strand nylon for decades as my tethers and have not found rolling underfoot a problem, I believe because their size is immediately apparent when you happen to get the rope underfoot. The worst I have experienced was a boat where wire was used as a jackline: small enough to not feel quickly and hard enough to roll like ball bearings. I turned to 3 strand nylon decades ago when the only other alternative was Dacron at a far greater expense. That and I could choose my end fittings.
A word to the European readers: for whatever reason, I found good quality 3 strand nylon very hard, even impossible, to find in the Med and also in Northern Europe (the lay was very soft and I found the strands not continuous). Also, few boats use it for dock line so it is far from common. I suspect that I might have succeeded if I looked harder, but I just bought from venders in the US and brought the rope back in my luggage. Bottom line, I would not use any of the 3 strand nylon I found for tethers.
My best, Dick Stevenson, s/v Alchemy