[Will Hunt]

When I tie my ropes together for an abseil, I've always used a double overhand knot. Tie an overhand, tighten it up and make it nicely dressed, then repeat with another tight overhand tied as close to the first as possible. My prussiks are tied together with a double fishermans, but because I've only tied this knot a few times I'm not very adept at tying it quickly and neatly.

Questions:
1. When placing a thread on a trad route or in a belay, is it acceptable to use a double overhand? Or is a double fishermans the only acceptable thing to use?

2. I've got some skinny cord that I sometimes use in trad belays and I often wonder whether a double overhand is advisable with this skinny cord. Might be more prone to rolling.

3. If placing a thread for use on a trad route, what's the minimum diameter cord/rope that you'd use?

[petejh]

Careful using your skinny cord, especially on belays, unless you're using dyneema cord.

Depending on the diameter the breaking strength can be much lower than you might expect.
5mm cord: 5.8kN
6mm cord: 7.5kN
7mm cord: 10.5kN

Admittedly higher in a closed loop with fishermans knot, but still a much lower strength than more typical belaying material such as sewn slings (22kN), and breakable in a factor 2.


Minimum for runners on routes is up to you, but know its strength. For belays I'd use dyneema cord, if any.

[Muenchener]

1. When placing a thread on a trad route or in a belay, is it acceptable to use a double overhand? Or is a double fishermans the only acceptable thing to use?


2. I've got some skinny cord that I sometimes use in trad belays and I often wonder whether a double overhand is advisable with this skinny cord. Might be more prone to rolling.

Double overhand in skinny black kevlar cord is what the Frankenjura locals use a lot. Doesn't look very confidence inspiring but I assume they've done their homework with Germanic thoroughness. There have been a couple of thread breakage related accidents lately, but from what I've read they were the rock breaking rather than knots coming undone. Skinny kevlar cord seems to cut through soft Frankenjura limestone quite easily.

Personally if I were placing on ab and not on the lead I'd go for double fisherman's in nylon, triple in kevlar/aramid/dyneema (whatever the correct name for the stuff is this week)

3. If placing a thread for use on a trad route, what's the minimum diameter cord/rope that you'd use?

5.5mm kevlar is plenty strong enough but not visually super inspiring - but also not visually obtrusive. Nice fat 10mm+ rope looks more confidence inspiring - but is also more of an eyesore for passing civilians, landowners, park rangers etc.

[Paul B]

3. If placing a thread for use on a trad route, what's the minimum diameter cord/rope that you'd use?

Depends on the size hole you're threading (runners)? At High Tor there's some optimistic threads that look to have used shoe laces (/exaggeration)! Also, at the big thread on limelight there's always so much tat that you can barely fit anything other than a thin sling through (I've got a Beal 6mm thread that's ace for this but a PITA to un-knot).

[Johnny Brown]

Short answer:

Personally if I were placing on ab and not on the lead I'd go for double fisherman's in nylon, triple in kevlar/aramid/dyneema

I'd do the same on lead unless in extremis, in which case I'd use my thinnest sling (Beal 5mm dyneeema). In fact why not just use thin slings and minimise decaying in situ tat blocking the placements?

Long answer: personally I treat the double overhand/ EDK as a special knot for a special use - abseiling - where the avoidance of jams is more important than strength. For this reason I don't back them up with a second knot either. If it's a clean pull use a stronger knot (reef knot plus double fisherman stoppers or double fisherman's inside alpine butterfly).

In Nylon, a loop tied with a double fisherman's will be roughly double the strength of a single strand (i.e. unusually, the rule that knots weaken rope does not apply).

Kevlar/ aramid I've only ever used for non-safety applications (pale brown core that does not melt - the sheath is nylon). It is stronger than nylon for a given diameter, but is brittle, so strength reduces rapidly when bent over and edge or in a knot. I think the official guidance is triple fisherman's only.

Dyneema/ spectra (always white, may be mixed with dyed nylon for colour) is again stronger than nylon but is much more slippery, so will pull much tighter in a knot, again reducing radiuses and strength more than nylon. The whiter a sling is the higher the dyneema content, as a rule - don't knot dyneema slings. Dyneema cord, like kevlar typically has a nylon sheath. This mitigates the low-friction effect so a triple fisherman's is acceptably strong - but no other knots are usually recommended.

Real world answer: the strength of the placement and any sharp edges therein may often make the above irrelevant.

[Muenchener]

Real world answer: the strength of the placement and any sharp edges therein may often make the above irrelevant.

There were two serious accidents caused the thread failures in the Frankenjura last Autumn; the second one at least was definitely caused by the rock breaking. Report (in German) with pictures of the breakages on frankenjura.com

For those who can read German or know how to use google translate, here's another comment thread on fj.com in which Martin Grulich talks about replacing a broken thread with a bolt on one of his own FA's from the 80s. Martin is a Frankenjura legend, who put up basically most of the mid-grade ultra-classics in the area in the 80s, and is now going around diligently cleaning up and intelligently re-bolting many of them. Apparently it's ok to retrobolt your own routes. The key point in this discussion is where he describes threads in Jura limestone as basically untrustworthy pseudo-protection.