/ Abseiling on two different diameter ropes (9mm dry - 9.8mm not)

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BoulderyDave - on 16 Nov 2012
I can only find a couple of articles which recommend either 'Double fishermans' or 'Double figure 8 fishermans' for joining to ropes of unequal diameter together for an ab.

The ropes in question are 9mm and 9.8mm, it is for rapping off mainly bolts (and some in-situ). What would you recommend?

Does it matter that one is dry treated and the other isn't?

Thanks

BoulderyDave - on 16 Nov 2012
In reply to BoulderyDave: btw, I am fine with double fishermans but some sites suggest it isn't sufficient? Just wanted to check

Much appreciated
BoulderyDave - on 16 Nov 2012
In reply to BoulderyDave: Sorry, I will stop replying to myself in a second...

On the black diamond website it says overhand knot is fine for unequal diameter? This would obviously be a lot easier but on UKC it says to use the double fishermans

http://www.blackdiamondequipment.com/en-us/journal/climb/all/qc-lab-what-is-the-best-rappel-knot
http://www.ukclimbing.com/articles/page.php?id=167

Confused
The Pylon King on 16 Nov 2012
In reply to BoulderyDave:

I use overhand on different diameters and seems alright.
Jon Stewart - on 16 Nov 2012
In reply to BoulderyDave:

What's the worst that could happen?
BoulderyDave - on 16 Nov 2012
In reply to Jon Stewart: I have to pack 3 ropes and I don't have enough space in my rucksack... followed by death
BoulderyDave - on 16 Nov 2012
In reply to Mr Mark Stephen Davies: Found two very recent sites which are saying the overhand is safest

http://vikingalpinism.blogspot.co.uk/2012/08/using-overhand-knot-with-ropes-of.html
http://www.needlesports.com/catalogue/content.aspx?con_id=75b7be92-45dd-474a-9229-9c9e00a60c7f

I know it, I use it normally, unless too much doom arrives, I will be using it from this weekend on enequal ropes ;-)
Ben Sharp - on 17 Nov 2012
In reply to BoulderyDave: It's only .8mm difference so i wouldn't have thought it would cause any trouble with either knot but obviously the overhand is better for other reasons as well, as long as your tails are long enough.
FWIW I've failed to be able to roll an overhand knot made with a single rope and 6mm accessory cord so doubt you'd have any trouble with 9 and 9.8.
a lakeland climber on 17 Nov 2012
In reply to BoulderyDave:

0.8mm is hardly a big difference. Usually advice about unequal diameters refers to say 11mm and 8mm. There's no absolute formula, also a lot of the old advice referred to hawser laid rather than kernmantle ropes.

In your case, overhand (with long tails) is fine. If you are really unsure/paranoid then double fishermans.

ALC
martinph78 on 17 Nov 2012
In reply to BoulderyDave: If there's not much chance of it getting snagged on the pull-down why not tie a fig 8 and stopper in each end and join them with a screwgate?
jkarran - on 17 Nov 2012
In reply to Martin1978:

> If there's not much chance of it getting snagged on the pull-down why not tie a fig 8 and stopper in each end and join them with a screwgate?

Why? All the joining knots mentioned so far are fine, what do you gain by overcomplicating matters?

jk
Scott Kirkhope - on 17 Nov 2012
In reply to BoulderyDave: I'd just use two overhand knots. Tie the first one as normal and the second is tied on the tails and butted up against the first to stop it rolling.
Bruce Hooker - on 17 Nov 2012
In reply to BoulderyDave:

The double fisherman's knot is the safest option, some people prefer the overhand knot as they say it snags less easily, but as they always insist on leaving long tails as the knot slips a bit it has never inspired me with confidence :-)

The choice is yours, I know what mine is.
BoulderyDave - on 17 Nov 2012
In reply to BoulderyDave: Cheers everyone, do to the risk of the rope snagging I will stick with an overhand. Really appreciate the replies, I have no internet access where I am going.

Thanks very muchly
nniff - on 17 Nov 2012
In reply to Scott Kirkhope:

Overhands don't roll. If they did, no-one would use them
Scott Kirkhope - on 17 Nov 2012
In reply to nniff: You are right, they shouldn't roll if tied properly. It just adds a bit more security with two different diameters of rope to have the second overhand.
wivanov - on 17 Nov 2012
In reply to BoulderyDave:

With same diameter ropes, I usually tie just a flat overhand like everyone else does with 30cm tails.

With different diameter ropes, I sometime use the "Doppelter T-Spierenstich" (Double T-Fischerman's Knot) shown here http://www.gudelius.de/spst.htm (you have to scroll down a bit)

Basically it's a double fisherman's knot but is not tied "inline". It's tied as a "flat knot". It's more complicated than the overhand knot but non more complicated than the regular double fisherman's. It's not much more bulky than two overhand knots. I've found it to be relatively easy to untie after loading. I've never seen or heard of it capsizing.

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