Pull direction in knots
Pull directions in knots affect the knot strength with a specific use. pulling the rope ends in different directions might distort the knot and create new nips, that are external to the knot, therefore having no friction between the ropes around it. When this happens, the knot stregth may be diminished by 20% or more.
Another example: there are three variants for an overhand knot on two ropes: water bend, overhand loop and overhand bend. In the first two variants the pull direction keeps the rope straight as it exits the knot. In the third, however, the rope bends sharply as it exits the knot, creating two new nips. In this form, the knot is significantly weake. It is also prone to capsizing in this form, which makes it less secure.
The use of a knot in a form that does not keep the "correct" direction of pull is considered wrong. Common examples are using a figure of eight loop around a large tree or bolder (correct - bowline), or as a loop in the middle of the rope )correct - alpine buterfly). the one case where a rope is deliberately used in its "wrong" form is when conecting two ropes for rappeling with an overhand bend. Although this bend is weaker than other bends, it has the one trait that makes it prefferable: it's ability to pass corners without getting stuck.
contributions to this page by: : Mica yaniv and others...