A couple years ago this same topic came up on the TD group section. What follows is, in part, one of my posts on the subject.
Kicking sheaves has been practiced as long as there has been
stage rigging with a "
grid", although it is slowly but surely dying out. As Derek said, there are two different rigging methods being discussed here. First the practice of "kicking" sheaves and second the use of mule blocks to redirect
lift line directions to allow angled and "
spot line" style rigging with a
counterweight line set. This discussion seems to be centered around the questions of "What", "Why" and "Is it a good Idea". To properly discuss these topics we must first define and describe the practices, the "What" and "Why".
Both methods are a direct evolution of
stage rigging from rope and pulley, to "Hemp Rigging" to
line set
Counterweight rigging. From the time of the Greeks and their "
Deus Ex Machina", when ever there was a need for an object to be raised or lowered, a pulley was mounted where needed, a rope was strung and "Voila!" the thing raised or lowered. What today we refer to as Hemp Rigging was not a lot different at first. A number of ropes were rigged through at first a group of pulleys mounted close together and later what was called a tandem
head block. At first there were no set locations for the loft blocks, they were placed on a show by show basis "as needed". As all the sheaves were individual units, and could be adjusted for angle and as
fleet angle with rope rigging is not as critical or restrictive as with
wire rope, the loft blocks could be placed almost anywhere. With the advent of the "
Wing and
Drop" style sets in the 16th century, loft blocks began to be arranged in parallel rows for each group. However at this time there were no battens as we know them today. Battens were wood boards permanently attached to a
drop. Individual lift lines had a small sand bag attached when not in use and if a
line was not needed for any reason, that
line was simply tied off and not used. With the development of the box set in the 29th century, the parallel rows of blocks were not as useful, as many side walls were hung at angles. During the 19th century Ballet and Opera tended to stay with the
wing and
drop style of set with "straight" dramas or comedy's tending toward box sets, especially toward the end of the century. Box sets relied more on the
spot line style with blocks positioned as needed and the only parallel rows of blocks were for the gas pipes which would eventually evolve into our
current pipe battens.
When
counterweight rigging was introduced in the last quarter of the 19th century, it was the first time a group of lift lines was "permanently" attached to a single
batten and a single weight device.
Stage technicians, designers et. al. were used to the flexibility of the hemp
system and simply moved the loft blocks if it became necessary. Especially at first,
line sets might be spaced at larger distances than is common today in large facilities. Unlike today's common
spacing of 6" or 8", it was not unusual to have several
line sets on 6" to 10" centers at the positions that often had scenic units and drops and to have two or three
foot gaps to the next group. The gas and gas/
electric lighting units were large and bulky and it was not unusual to move them a
foot or so up or
down stage to allow scenic units to
clear. This was easy, especially at first, as many grids were wood and the loft blocks were only clamped or lightly bolted down. It is reported, though I can find no empirical evidence to back it up, that some blocks were held in place with large el brackets or hooks and relied on resultant force to keep them in place. Thus moving them required no tools, simply kick them as needed, and the term was coined.
As
counterweight sets replaced hemp style rigging, the practice actually grew.
Stage technicians were simply used to designing pick points where the scenery needed them and then adjusting as needed. As steel grids became more common and
loft block attachment became more secure, the practice became a
bit more labor intensive but still common, and in fact, it is still practiced in many houses today.
All the major rigging manufacturers today discourage the practice because they have no control over who does it and what their rigging knowledge and skill are. Kicking the sheaves voids the installation/labor portion of any warranty. As a result manufacturers and installers often require the blocks to be welded in place, especially in under hung situations. Under hung head blocks are almost always required to be welded after the
bolt clips and final alinement adjustment is complete.
The second method of locating
lift line drop points involves mule blocks to redirect the lines to the desired location. This is not only common, but the standard method for rigging circular cycloramas,
orchestra shell rigging and other "non-standard" rigging uses. It is usually employed in permanent installation situations but occasionally for
one-off shows that have special rigging needs. Many big budget shows with special or unusual rigging needs simply tour with their own rigging
grid ( Jane Eyre or Phantom) which contains winches and chain motors where needed and then is flown from the building structure below the
house rigging. When using the
mule block method for temporary rigging, the lift lines change distance from the
head block to the
drop point, usually increasing the effective distance from the
head block. This is usually adjusted for by adding additional
trim chain in various lengths, as needed to equal out the lengths of the various lift lines. As a result this method is only used when there is sufficient
grid height to allow the units to
clear sight lines with the extra chain or where the
unit is never flown above playing height. If there are unused lift lines, they are simply sand bagged to provide tension or coiled and the coil provides sufficient weight and tension to keep the
line taut. I do not guarantee that is what is done in the OP's situation, but I would be interested in hearing their actual technique.
Now! Is Kicking Sheaves a good thing, a bad thing or somewhere in between? In and of itself, there is absolutely nothing wrong with "kicking Sheaves". HOWEVER ..... there are a large number of reasons why it can be a bad thing. It should never be allowed by anyone except the
house staff as they are ultimately responsible for the
safety, maintenance and general condition of the space. In addition, guests who kick blocks rarely replace them and they often don't tell the
house staff that it has been done. Today the practice is most common in large venues with permanent rigging staff who know what they are doing and how to do it.
The things that must be observed are simple and should be obvious to any rigger, but are often overlooked by touring crews or inexperienced staff.
1. If the changed position is to be parallel to the
plaster line, the short
line determines the maximum distance the
line set can be moved. The
fleet angle is greater the closer it is to the
head block.
2. Loft blocks should be angled if possible to reduce
fleet angle to the minimum.
3. All bolts and clips must be fastened down to the manufacturer's recommended torque settings.
4. If the
line set is never moved for the run of the show after being flown to it's
trim height, fleet angles can be exceeded, but only by VERY experienced riggers with total knowledge of the loading, the angles, the properties of the specific sheaves, the off axis loading capabilities of the mounting clips, the out of axis loads imposed by the
fleet angle on the
sheave housing and mounting brackets and any
dynamic loads that might be imposed.
5. All changes MUST be restored to the
system original specs and positions with proper alignment and fastening settings when the run is over.
6. After restoring to original condition, each and EVERY component of the entire
line set MUST be inspected for any changes in condition, damage or problems, and corrections made where necessary.
7. All changes, adjustments and restoration must be listed in the rigging maintenance log, dated and signed by the rigger in charge.
Note to all readers: Does your facility keep an up-to-date rigging maintenance log? Why not???
I stated earlier that the practice was slowly but surely dying out. That is because of the growth of automated rigging and the requirement of manufacturers to weld the blocks in place. Automated rigging such as package hoists do not lend themselves well to
block kicking and several types, such as
line shaft and
Prodigy make the practice impossible.
I'm sure I've skipped parts of the equation that others will
point out, if anyone has any questions, ask!
