TimB wrote:1) What cord diameter and material of construction do you folks prefer? I have seen everything from 5mm on up to 7mm; nylon or?
The two standards are typically 7mm nylon or 5-6mm spectra/dyneema/technora cord. I used to use spectra for its low bulk but switched to nylon for several reasons. First being that although static, it has more stretch than spectra; drop testing has shown that a factor 1 fall on spectra-type cord produces forces > 20kn, which will kill you and also overload other anchor components such as biners and bolt hangers. Second being strength reduction due to repeated flexing; see
this summary and the
original report. PMI 6mm nylon is rated at 6.8kn; this means that a cordalette strand with a knot in it will only be approx. 6.8+(6.8*2/3)=11.3kn, which for me personally, is not strong enough to justify using it in an anchor.
2) What length cord? 15 feet, 20, ??
Typical length is 20 feet.
3) Knots: just use a double fisherman's or??
If using spectra-type cord, the recommendation is a triple fisherman's.
4) Should cords be made from static line or can you use a dynamic line?
I don't know of any reason not to use dynamic line, and I've wondered about using dynamic line to reduce anchor loads if you fall while at the belay, but then your cord is bulkier and weighs more - and I've never seen dynamic line sold by the foot.
If you're new to this, I would
highly recommend reading up on the testing John Long et al did before the release of his latest climbing anchors book, which called into question how well a cordalette actually equalizes and how bad extension really is - and let to the adoption of alternative schemes like the equalette. I'm not saying that cordalettes are bad or that I never use them, but a lot of people are still blindly placing cordalettes for all their anchors based on assumptions that have since been proven inaccurate.