It can be done
Hi Bob,
Actually, it's really easy to mess things up either way. Even if you measure the old rig perfectly, with the mast out, you really should know whether or not it was tuned properly when it was in the boat. If it was slack, then it will be considerably longer once you tune the new pieces ó an inch or more on some of the longest pieces in your gang. Or if you measured the lengths with the rig in place, but neglected to deduct for stretch when making the new pieces, you'll have the same problem. Or if the rig was tuned, and you took it out and then measured it on the ground, when it would have shrunk, and then deducted for tune, the whole thing would be too short. I trust that you avoided all these pitfalls, but you see the point.
When we make a new gang, we love it when we can measure it in place, but this requires that the rake is right, all the diameters and tangs and chainplates make sense, and that the turnbuckles are keepers, too. And this happens fairly rarely, so we frequently step with one end done. We set up handy-billies, 6:1 advantage for the shrouds, twice that for the backstay, as catenary can throw things off, mark the wire a given distance up, just above the icicle hitch that attaches the handy-billy to the wire. This means we aren't trying to mark a length on the part of the wire which is distorted by the hitch. Then we remove the hitch, and measure down to cut. So if we make a mark, say, 6' up, we'll then measure down that length, minus the turnbuckle length, terminal length, and the anticipated amount of stretch.
If a client walks in the door with a gang of rigging, even if the turnbuckles were marked at their old locations, it's unlikely we'll be able to cut both ends in the shop, unless we calculate lengths using trig, or a CAD program, both of which can be more bother than just doing it on deck.
Fair leads,
Brion
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