Hi Tim,

"When should the running backstays be moved from the chain plate just aft of the stays to the attachment point at the rear of the sailboat?" "

- Generally, when you are flying the staysail in anything more than a light breeze, I'd use the running back that is to windward. The idea is to support (pull) on the mast from opposite where that sail is pulling.

"How much tension should be placed on the running backstays when they are attached to the chain plates?"

- I'd harden them up to the equivalent of a jib halyard or fully loaded jib sheet - fairly tight. If it is really blowing, you can sight up the mast and watch for any pump at the masthead or staysail attachment. You'd then want your running backs to be tight enough to eliminate any movement there. (within reason - you can hurt things by winding up on a big winch rather easily)

"Any idea on what the force in pounds would be placed on the attachment point at the rear of the sailboat by the running backs?"

- No idea

"Can I get by with a 1/2' single line from the backstay through a block to a winch?"

- Rather than a single line, I would at the very least stick a block on the end of the running back, and a block with a becket and shackle on the lower end, to make a simple tackle to make things easy on you & your winches. We made some setups like these for some valiants at one point a few years ago, but I don't remember the particulars.

Best of luck,

Jason