Helical knots are used in rope climbing competetitions but as a caver I
feel it is too hard to tie. The prusik can be tied in both a left and
right handed configuration so that it can be "broken" (made to slide
up) by the correct hand easily. Dont use really new rope to tie
prusiks as it has a waxy material that makes it slip.
The best prusiks are made from hard 3 strand rope. They should be made
WITHOUT a slip knot for the foot loop. With both loops made, they
should extend to mid-thigh with one slightly longer than the other (the
upper one). I se why you would use a slip knot but this leads to the
slip knot getting too tight on your foot. The purpose is to keep the
loop from sliding off your foot. Instead, cavers use "Chicken Loops"
which are loops around their ankles. The foot loop runs under the
"Chicken Loop" so it cannot slide off the foot.
How on earth do you use the second halyard to descend without getting
OFF the prusiks, a dangerous thing to do unless you've really thought
it through. Its safer to simply down prusik although slower.
For sailing, Ive used a prusik tied around my anchor line leading back
to a winch to help pull up an anchor. When I pull in some line, I can
slide the prusik along the anchor line to pull in more.
I still prefer prusiks over mechanical ascenders