Joining ropes of differing diameters for rapping

When rapping on two ropes, is there a point where the difference in diameter of the ropes is great enough that the EDK is no longer the preferred knot?

For example, are you comfortable with joining a 10mm and an 8mm with an EDK for rapping?

Ive never done tests on say 4mm joined with a 10.2, 11mm, etc BUT I have experienced more than a few times joining a 6mm tag line to a 10.2 and have had zero issues. My experience says for simple, straight forward situations (which was my experience, cant speak for abnormal conditions) a 6mm and a 10+ is accecptable.

I've done this using a 7mm tag line to a 10mm rope. I usually tie a keeper knot with the smaller line around the larger to guard against the knot inverting.

Never had any issues, providing (obvious it would seem) they are the same length. We done it with 10.2, and either 9, or an 11. We've always used the double-grapevine, just use the smaller diameter as your "pull" side.

The Cowardly Noob wrote:When rapping on two ropes, is there a point where the difference in diameter of the ropes is great enough that the EDK is no longer the preferred knot? For example, are you comfortable with joining a 10mm and an 8mm with an EDK for rapping?

A couple old threads on the topic.

mountainproject.com/v/skinn…

mountainproject.com/v/joini…

I normally use dynamic ropes ranging from 9.4 - 10.5mm with 6mm cordelette and an EDK. I pull-tested 6mm with 11mm before, a few years back, but I cant find the exact testing data so I will do it again today since this seems to be a reoccurring question.

We made at least 15 rappels at red rock a couple weekends ago using a 60mm 10.2 and one of a pair of 8mm BD doubles. Used the EDK every time without any noticeable movement (rolling) in the knot. After having the thin rope snag a few times on the first day, we pulled the double every time when rapping Crimson Chrysalis. This required untying and re-tying the knot at each rap, but that's part of the beauty of the EDK...it's easy to tie and untie. And it doesn't snag. Go for it. Just tie it tight and dress it pretty and put a stopper in each tail.

Chris D said: put a stopper in each tail.

+1. I, not to rely on assumptions should have noted this. longer than usual tails + overhand "stopper" knots = always for me and the edk/flat overhand regardless of rope diameter.

Make sure to back it up with a overhand on a bight with a Biner through it if you're rapping on the fat strand only. There was a tragic accident where the two edk's pulled through the rap rings that were much smaller than the knots. Oh found it
rockandice.com/lates-news/r…

http://blackdiamondequipment.com/en/qc-lab-what-is-the-best-rappel-knot.html

thats all there is to it folks

;)

bearbreeder wrote:http://blackdiamondequipment.com/en/qc-lab-what-is-the-best-rappel-knot.html thats all there is to it folks ;)

It appears that chart is in reference to ropes of the same diameter. The OP was asking about ropes of different diameters.

bear has data for everything. I'm sure he'll pull through.

Edit: We all have bad reading comprehension. Bearbreader did understand the question. Look at the chart again...different diameters are listed.

20 kN wrote: It appears that chart is in reference to ropes of the same diameter. The OP was asking about ropes of different diameters.

MPers needs glasses ... as an AZN it fortunate that my coke bottle spectacles are top notch to compensate for you folks

;)

Thanks for the responses.

Regarding bearbreader's chart, there might be a difference between strength of the knot and "creepability" of the knot. And there might not.

The Cowardly Noob wrote:Thanks for the responses. Regarding bearbreader's chart, there might be a difference between strength of the knot and "creepability" of the knot. And there might not.

the last point on the chart i posted lists the slip values for the 10.2/8mm ... roughly 8-9 KN

here what the DAV says ... basically its not the knot strength on 8mm->10mm you need to worry about

Der Knoten wird an allen vier Strängen
festgezogen. Die Seilenden sollten mindestens
20-25 cm betragen (ca. Handlänge).
Deutlich längere Seilenden bergen die Gefahr,
dass man sich mit dem Abseilgerät
versehentlich in die Enden einhängt.
Beim Verbinden ungleich dicker Seilstücke
(z.B. 5 mm und 10 mm i) zum Abseilen
bestehen keine Bedenken bezüglich der
Knotenfestigkeit. Erstaunlicherweise
rutschten die dünnen Reepschnüre (5
und 6 mm) bei den durchgeführten Reißversuchen
nicht aus dem Knoten. Die
Bruchwerte lagen über denen der dünnen
Reepschnur mit demselben Knoten (vgl.
2.4), da der Kantenradius beim Verbinden
mit einem Einfachseil wesentlich
günstiger ist. Die ermittelten Festigkeiten
liegen weit über den beim Abseilen auftretenden
Kräften. Viel bedenklicher ist
das Pendeln über scharfe Kanten für den
dünnen Reepschnurstrang. Solche Pendelbelastungen
sollten vermieden werden.

------

The knot is connected to all four strands
tightened. The cable ends should be at least
20-25 cm (approx. hand length).
Significantly longer rope ends run the risk of
that you are with the descender
accidentally hangs in the ends.
When connecting different pieces of thick rope
(e.g., 5 mm and 10 mm i) for rappelling
There are no concerns regarding the
Knot strength. Astonishingly,
slipped the thin cords (5
and 6 mm) in the conducted tensile tests
not from the knot. the
Break values ​​were higher than those of the thin
Cord with the same knot (see
2.4), as the radius of the joining edge
significantly with a single rope
is less. The strengths identified
occurring far above the abseiling
Forces. Is much concern
commuting over sharp edges for
thin Reepschnurstrang. Such oscillating loads
should be avoided.

;)

As promised, the testing. 11mm and 6mm joined via an EDK: mountainproject.com/v/edk-d…

20 kN wrote:As promised, the testing. 11mm and 6mm joined via an EDK

Thanks