Moderator: Tim White
Ralph E. Powers wrote:However; if there were to be a rescue load then certianly to prevent possible slippage a back up of a half-sheetbend/fisherman's knot would be a good idea at the base of the 8 knot...
GoHighGoDeep wrote: Oh... someone mentioned backing up a fig-8... and i'd have to agree that backing up an 8 is not always necessary... if you can't tie the 8 right, what makes you think you'll tie the backup knot right?
Tubo Longo wrote:Sorry, may be my English is at fault, but I don't understand: back up a knot...??
Adam Byrd wrote:Tubo Longo wrote:Sorry, may be my English is at fault, but I don't understand: back up a knot...??
Think about the bowline, which is usually tied with a backup. In fact, let's look at a diagram.
In b we have a bowline knot, plain and simple. In c, the bowline has been "backed up" with an overhand knot.
It's done to prevent knot from coming undone, should the tail slip.
Think about the bowline, which is usually tied with a backup. In fact, let's look at a diagram.
In b we have a bowline knot, plain and simple. In c, the bowline has been "backed up" with an overhand knot.
It's done to prevent knot from coming undone, should the tail slip.
... I have been told that a figure 8 used to join a rope but with the two tails upstream of the knot
(no I don't know why you'd do it either) can let the figure 8 roll off the end of the rope.
That said I have never seen it do it and probably never will because I won't rig that way
and if someone else rigs that way I a) won't get on the rope and
b) will suggest they use a double fisherman's or a back-fed 8 as a rope join.
Where it does become an issue is at rebelays for instance if you ...
In the end a 9 (so I am told) is stronger than an 8 in all loadings so I use a 9
the extra rope it uses and the extra size of the knot are marginal.
with so many different RIGHT ways to do it... why isn't there a universal standard?
knudeNoggin wrote:In the end a 9 (so I am told) is stronger than an 8 in all loadings so I use a 9
The strength difference is pretty marginal, too. How close to breaking a knot do you think you'll come? --or has anyone come? Were you thinking of using 5/16" rope, for instance? (But strength does have an appeal.)
Tubo Longo wrote: I have also been taught that the strength difference between a 8 and a 9 knot is pretty marginal.
Where a big difference chick in is in untying the knot: on a rebelay which sees a whole load of cavers going thru, a 9 get untied way more easily than a 8.
NZcaver wrote: According to testing done by Marbach and Rocourt in 1980 .... Of course, caving rope might have been constructed a little differently back in 1980 - although we are still talking kernmantel type.
Tim White wrote:Take a look at the recent study titled Knot Break Strength vs Rope Break Strength, by Dave Richards, Technical Director of the Cordage Institute. Some good data.
NZcaver wrote:Ralph E. Powers wrote:However; if there were to be a rescue load then certianly to prevent possible slippage a back up of a half-sheetbend/fisherman's knot would be a good idea at the base of the 8 knot...
Just a little FYI - current teaching within the NCRC is no back up knot with a figure 8.
Tim White wrote:Take a look at the recent study titled Knot Break Strength vs Rope Break Strength, by Dave Richards, Technical Director of the Cordage Institute. Some good data.
The article is published in the NSS Vertical Section’s Nylon Highway.
http://www.caves.org/section/vertical/nh/50/knotrope.html
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