ian mckenzie wrote:Because the deviation acts only as a change of direction for the force, I contend that the main anchor always remains at 100% but the deviation anchor force varies with the angle as per Tim's diagram.
Ian - sorry, the wording in my previous post about the main and deviation anchors "sharing" the load was probably a little ambiguous.
It's not stated in Tim's diagram, but it's reasonable to assume the tension on each side of the pulley sheave always stays equalized. This means your main anchor should always see about the same force regardless of the angle of deviation - assuming no friction at the deviation point (and no knot of course, that would make it a Y-hang). Just like you said in your post, if the deviation point is directly behind the anchor point (away from the load), the anchor will still see about the same force - just in the opposite direction.
Say your load is a big caver with gear, weighing about 220lbs total. You rig a 45 degree redirect over the hole. Once the caver is on-rope and below the redirect, your main rope anchor point sees about 1kN of force (the same as if there was no redirect). But your redirect anchor point (ignoring friction) should see an additional ~770N of force, or about 170lbs.
I could be wrong, but that's my understanding (edited to correct even more ambiguity).