"Kicking" Loft Blocks?

No doubt the progressive loft blocks are better than single line sheaves and idlers, but it becomes a value decision. Since most of my sets are 63' battens and 7 lines, the multiline blocks add a lost of cost.
Not sure how you can be so specific about the fleet angle between head block and shout line - would seem to very a lot depending on width of stage. With a normal 95-100' wide stage, it's near 20'.
Fleeting upstage or downstage seems to have more to do with obstructions like hangers and such. I'm going to suggest that most of my systems have both - especially around odd spaced sets like electrics or main curtains that don't fall on the normal 6 or 7 or 8 inch arbor centers.

The progressive block concept is THERN's standard, they don't do idlers. The precept is less friction in the system, closer fleet angles etc. justify the cost. And yes, it does add cost.

The "specific" fleet angles are only examples based on a 15' distance to the first block and 10'-0" cc spacing, using dimensions from blocks grooved for 1/4" cable and 3/4" purchase line. greater distances to the first block would, of course, decrease the fleet angle, shorter distances, increase the fleet angle.

As for when blocks must be off set and muled or angled, yes, it is usually obstructions such as HVAC, Plumbing or like a recent install where the lock rail wall was only half the stage depth. The upstage half of the stage is 40' wider than the down stage, and leads to a hallway and storage. The result was that all the arbors had to be grouped in the down stage area but the line sets went to the back wall. The result was the upstage line sets all had to be muled and some blocks had to be mounted at angles to the grid, up to 45d. Custom drilling and clips and in one case ( the 45d block) custom steel welded across the grid steel and the block mounted to that. Certified welder and Structural engineers stamp on the custom design of course. Actually for this particular job, we had an engineer do an analysis on the entire system, as I did not think the existing bar joist system was adequate for the rigging the client asked for. The result was we added panel point supports throughout and horizontal compression members between joists where we had lines muled up/down stage.

We install Clancy, H&H and Thern systems. Idlers on the first two and progressive on the latter. Both methods work just fine. Just depends on what the architect/consultant spec (if there is a consultant, note: ALWAYS have a consultant, don't let the architect talk you out of it!!!) and what the client asks for and is willing to pay for.
 
Consultants Brannigan and Lorelli use to always design systems with progressive blocks but I think it came from Bob Lorelli's pre-consultant career with a rigging manufacturer in either DC or Pittsburg region.

The multi line short line block also guards against unexpected elevation differences between head and loft block beams - though a problem that is diminished by all underhung blocks. I miss the ease of installation and respotting sets with upright headblocks but arbor travel and economy of construction work against that arrangement.
 

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