Somewhere (maybe here) I read about using a "figure 9 on a bight" (wrap twice around the standing side of the rope before pulling the loop through, instead of once) in situations (eg toprope anchor), because the 9 was easier to untie than the 8 after it's been loaded. Anyone aware of any problems or drawbacks with the figure 9?
I use figure 9's all the time when I know it will be weighted. I use it with rope, cord, and dyneema slings.
The figure 9 is very popular among cavers who fix and rappel and ascend the same rope. All that weight really cinches a normal 8 tight and the 9 really helps make life easier to untie when tearing down your setup.
it wonders for anchors as its easier to untie ... the downside is that it uses slightly more material than a fig8 which uses more material than an overhand ... for skinny slings (which MPers will tell you the many ways to die) it works well
its also very easy to tie ...
overhand ... twist and put it in the hole
fig 8 ... add another twist and put it in the hole
fig 9 ... again add another twist and put it in the hole
keep wrapping (figure nine, ten, eleven, so on) it to make it even easier to untie, or to use up more cordage to create a higher master point.
Additionally, you can throw a carabiner in the knot itself to make it even easier to untie. The only purpose of the carabiner in the knot is to give you a handle to work the knot loose later (don't clip into it and kill yourself). A good application is when tying knots in dyneema slings.
I use it with webbing because fig 8 tends to make the bight come out at a 90-degree angle to the strand and fig 9 corrects that. Not sure about actual knot strength, but the figure 9 just looks cleaner and loads more evenly