Take the tour ×  As, I have been using a Double Fisherman's knot
to join the two ropes. With some physics that I know, in Double
Fisherman's knot the same amount of pressure (stress) is applied
over the two turns of each rope, so making sure there is no
significant damage done to any of the rope. However I believe
that if the two ropes are not of equal thickness, or may be say
if the difference between the thicknesses is a considerably
huge, Double Fisherman's would(?) do some damage to the thinner
rope.  In that case how trustworthy are Sheet Bend and Zappelin
Bend?  Edit: I am Not going to use this for rappelling at all. I
intend to use that as a holding line when me and friends a re
swimming in a lake nearby. Having said this, We are not entirely
relying on this as well.  share|improve this question What
thickness of ropes are you trying to join? Is this for
rappelling? A "sheet bend" will join 2 ropes, but I've never
seen it recommended for rappelling. If you're trying to join a
pair of climbing ropes (i.