Stiffening Ladders

[rochem]

(I could have sworn we've already had a thread on this, but I couldn't find anything from the search, so my apologies if I missed it.)

What does everyone else do when you need to stiffen a sidelight ladder or similar position? I'm mainly speaking about ladders that you deadhang from the grid that can't be supported from the ground, due to space or other reasons. Obviously, if your ladder is hanging on one point 40' or more below the grid, any pressure to the ladder is gonna cause a lot of rotation and movement - and even with two points, you're still going to move a considerable amount, making focus very difficult and inaccurate. Also, say that you have a moving light on a ladder, or you have some strong air flow in your venue - how do you keep the ladder perfectly motionless?

I'm mainly referring to longer-term installations here, as for short gigs, most of us probably just leave it alone and it doesn't cause problems. But for more complex or longer-term installations, I'd feel very nervous about leaving this totally unstiffened. Also, on more and more plots, I'm starting to see a designer note that "all booms and ladders must be stiffened prior to focus."

The only real way I've ever seen this done is to attach one end of a pipe to the ladder with a cheeseborough, and the other end to an overhead electric or truss. But this isn't a great solution, and it obviously requires an overhead point that will never move - and unless the ladder is trimmed within a few feet of the ladder, this doesn't really work anyway.

So - anyone have any ideas?

 

[TheDonkey]

(I could have sworn we've already had a thread on this, but I couldn't find anything from the search, so my apologies if I missed it.)

What does everyone else do when you need to stiffen a sidelight ladder or similar position? I'm mainly speaking about ladders that you deadhang from the grid that can't be supported from the ground, due to space or other reasons. Obviously, if your ladder is hanging on one point 40' or more below the grid, any pressure to the ladder is gonna cause a lot of rotation and movement - and even with two points, you're still going to move a considerable amount, making focus very difficult and inaccurate. Also, say that you have a moving light on a ladder, or you have some strong air flow in your venue - how do you keep the ladder perfectly motionless?

I'm mainly referring to longer-term installations here, as for short gigs, most of us probably just leave it alone and it doesn't cause problems. But for more complex or longer-term installations, I'd feel very nervous about leaving this totally unstiffened. Also, on more and more plots, I'm starting to see a designer note that "all booms and ladders must be stiffened prior to focus."

The only real way I've ever seen this done is to attach one end of a pipe to the ladder with a cheeseborough, and the other end to an overhead electric or truss. But this isn't a great solution, and it obviously requires an overhead point that will never move - and unless the ladder is trimmed within a few feet of the ladder, this doesn't really work anyway.

So - anyone have any ideas?

I don't have any direct experience, but I'd say aircraft wire from a couple points, tied down to some other fixed structure. 2 wires per point in opposing directions.

 

[Footer]

Most ladders are not dead hung. Instead, the best thing to do is to hang service truss on hoists running upstage/downstage on each side of stage. That entire truss can be hung with 2 points. Then, off that truss you can either cheeseborough your ladders or rig them with spansets/chain/wire rope. This way, you can still bring the ladders into the deck... making them faster to hang/troubleshoot/whatever. The labor savings on the in makes it worth while. Along with that, the stability question goes away. The other option that I have done with good results if you must dead hang is to hang them off a mid rail. If you don't have a mid rail... once again best practice is to hand pipe or truss then hang cheeseborough the ladder to that. You could also always hang all the ladders off one point then cheeseborough pipe to each on making them all rigid.

Last time I did this in a dead hang situation (off the mid rail). The chains were at most 10' long and we did not have any of the twist issues. Also, the ladders were 3' wide:

 

[derekleffew]

...Also, say that you have a moving light on a ladder, ...

RSC Lightlock , distributed by Total Structures.

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Or, bridle the lighting ladder.

 

[rochem]

Rigging a service truss was my first thought, but that only really works if all your ladders are the same distance offstage. For example, the situation I'm working with right now as the upstage-most ladders much further onstage than the downstage-most ladders, roughly following the lines of the set - but due to scenic elements, they aren't located in enough of a straight line that one truss could work for all of them. And the midrail is also not an option, as it's much further offstage than any of the ladders. Would I really be better off rigging an individual pipe/truss for each ladder, then cheeseboroughing down off of that, instead of just dead-hanging from the grid? I'm sure there's a way to calculate this using physics, but would this actually have a significant effect on the rigidity of the ladder, considering that each ladder would still act as a pendulum of (roughly) the same length from the grid? If I'm thinking correctly, using a service truss only affects rigidity because of the huge increase in total weight on one structure (as opposed to multiple smaller weights spread across individual structures), increasing it's inertia and thus it's resistance to movement by outside forces. Therefore, rigging individual pipes or trusses above each ladder, then cheeseboroughing off of that would only provide a very slight improvement proportional to the added weight as a result of the truss/pipe and hardware. Is this correct?

The Lightlock is a pretty cool piece of equipment, but it doesn't correct for external forces like air currents or things contacting it, which is my chief concern. (Have you been seeing these come through fairly often? I have yet to see a single one on any tours that come through here, although we only get relatively small tours, so that's not that surprising. Also, any idea what the pricing is like for these things?) Bridling or breasting, possibly to the midrail, was probably going to be my next option so I could drop the junction height as much as possible to reduce the pendulum swing of the ladder, but I'd hate to have to run my long leg diagonally through the counterweight rigging, and rigging lots of individual three-point bridles is just way more trouble than it's worth.

 

[xander]

Without being in your exact situation, my first response would be to rig a more permanent upstage/downstage truss offstage of your linesets, perhaps stiffening to the midrail if possible (as has already been suggested). Then, for your specific show where you need the ladders farther onstage, rig separate trusses for those from the grid and stiffen them to your permanent truss offstage.

Or just tell your designers that it's a boom or nothing.

-Tim

 

[SteveB]

If not using them with Movers, I'm not sure I'd do anything other then try not to get them knocked about during focus. Generally the unit weight keeps them from moving much and short of a movie wind machine, I doubt airflow is going to be an issue during a performance, that wouldn't cause other issues that would require you to deal with otherwise.

Movers are a different story and you end up with vertically mounted box truss as well as a need to be careful about move timings.

If it becomes an issue and you and the space and clearance, I'd add horizontal pipe, maybe rigid 1-1/2" conduit, cheesborough'd top and bottom between all wing positions to get it to function as one unit. And maybe one or two pieces anchored to off stage building structure.