I have watched students tasked with attaching a line to a fixed anchor point struggle and retie knots several times to achieve a slack fee connection. Try this method and you will achieve results every time.
How much do I
allow for the knot. Trial and error?
create a bight
in the line (11mm) and pull the line and anchorage together tightly, adjusting
the bight so that the two just meet. Note: the tighter these two are
pulled together, the tighter will be the attachment.
bight an additional 8" or 200mm, as a guide, measure and use the span of
your fingers as a guide. Then tie a figure of eight knot, dress and tension the
knot in the normal manner.
Finally make the
connection, you will find the knot to be in the perfect position. The system
works with all lines, the length of the addition will need to be adjusted to
accommodate different line diameters.
The major consideration in establishing any anchorage
system is the prevention or at least the management of shock loads. These
unwelcome forces can be caused by a number of reasons, whatever their cause they
can seriously overload a system, causing the failure of knots and anchorages
Prevention has always been better than cure. When a rope is under tension
and then shock loaded we have relied in the past on the elasticity built into
the line and the fact that knots will tighten slightly.
The energy dissipater has been around for
a while, but like most items was designed for a different use. Petzl use a
similar method of reducing shock loads in their Via ferrata lanyards, yet it has
never been actively applied to rope terminations.
The rope in use, either an 11mm or even 9mm is passed
through the holes in the device, it is very important to ensure that the correct
sequence of holes is followed as they differ in size for the varying diameters
of line. A diagram engraved on the body of the dissipater helps with this.
Personally, for our lines that are packed and ready for use, we leave them in
place. Most important is to leave a tail of about a metre and finish with a stop
use, this termination is as secure as any knot. However should the rope be shock
loaded the dissipater will allow the rope to pass through, absorbing energy in
the process. The stop knot is a preventative measure to stop the rope from
unravelling completely. Should you wish to prevent any movement in the rope
pass the knotted tail beneath the last turn on the dissipater.