For many years, ‘flat’ joining knots have been gaining popularity for joining pairs of ropes to be used for rappelling, but at the same time a number of rappel accidents, incidents, and deaths have generated controversy around them.
A flat knot is an ‘end knot’ tied in both ropes at once, so the ropes come out of the knot together; as a result, the two ropes are smoothly in line with each other on one side.
In other words, the knot is entirely to one side of the line of the ropes, so the ropes run smoothly over terrain without any tendency to snag on ridges, roots, or edges. This characteristic is much touted for reducing the incidence of ropes snagging during retrieval, but its significance is debatable, because such hangups likely happen far less often than crack jams, wrapping-around horns, blocks, or trees, and friction buildup along the ropes on a curving rappel line. All these ‘other’ causes of stuck ropes affect Flat Knots just as much as Inline Knots or ‘bends’.
A few accidents have involved rappel ropes coming apart, ie., the joining knots untieing, and led to a storm of debate about the best and worst rappel rope joining knots. The variously deemed Best and Worst flat rappel knots have both been implicated in some such accidents, while the circumstances in such cases are usually not completely known, and yet the same knots are successfully used in thousands of rappels everywhere with no problems at all: What CAN be happening?!
When tested, most such knots work very well if tied well and snug, to the extent that extreme carelessness in knot-tieing is suggested as the cause of most accidents.
Every climber develops a preference for some joining knot/s, so we hesitate to recommend a particular flat knot, but rather advise climbers to tie every knot neat (uniform & parallel: easily identifiable), pull all strands tight, one-by-one, and leave at least a foot or 30cm of tails protruding from it. Many climbers like to also tie a backup knot in the tails, though a backup knot obviously adds an element of bulk and extra risk of snagging.
Put a Ring on It: I have devised a simple alternative to backup knots, that eliminates the tendency of some flat knots to roll or capsize, potentially off the tails and resulting in a disaster. This is just an oval link of small transport chain (or equivalent), through which both rope ends are passed before the joining knot is tied. Such a basal ring prevents the ropes from pulling the exit loop of the knot apart, as well as adding an extra level of friction in the connection. It maintains the full ‘flatness’ of a flat knot and actually reduces terrain friction where it contacts rock or other features itself.
I have tested both the single-overhand flat knot (a.k.a. Euro Death Knot or EDK) and the figure-8 flat knot, each with a ring, to over 2000 pounds of tension, and they showed no tendency to fail.
More tests, including other knots, will be done.
More discussion and info, with photos, can be seen in the Safety Page, found under Resources on the Home Page.
Orvel, Safety Committee Chairman