"Hemp Flying"

[erroneousblack]

I can remember on a fit up many years ago in a London theatre 12, yes 12 were needed to get a hemp bar out! (3 men to 4 lines!). Of course that wouldn't be considered these days. (I hope)

 

My new venue has some hemp lines,(whichI'm hoping will be gone soon), and we've set a 50kg to a 2 man lift. Some regular visitors don't seem to like this, but quite frankly that's their tough titty!

[Chris Higgs]

The SWL may relate to the capacity of the structure supporting any pulleys or even flyrails.

I mentioned a forthcoming BS code of practice (BS7906:1) some time ago.

This will be published early in 2005 - so obtain copies from wherever you can.

 

I would like to copy part of it here, but I can't.

You really, really need to see it in context. (And, no, they don't pay me!)

There is an excellent chart and a table which considers cantilevers, the see-saw effect at long and short, simple spans and lists about 3 grades of material in 3 conditions on 3 spans.

It will put a stop to the dangerous, amateur calculations we have seen in the BR.

Sorry to sound like that but it's true.

 

The centre line of a three line set does categorically NOT ever carry 62% of the load unless it is a uniform load and the long and short are at the bar ends. The load case is more appropriate to trusses than barrels.

A perfect example.............

 

For what it's worth, I have seen many hemp sets carrying huge loads.

Of course LX hadn't flown the bar out, they'd rigged the kit with the bar already out.....

Makes a mockery of using the load the average man can be expected to pull as a guide, doesn't it?

With my ABTT hat on: the accepted safety factor used to derive a safe working load for overhead rigging components in the entertainment industry (not the grid or the barrel) should be 8:1. This is in the yellow book, incidentally, so it is as good as law, really. Not necessarily something I agree with personally, but it isn't difficult or costly to achieve.

HTH, it's meant to.

[robloxley]

I've just looked on the flints website and their artificial hemp has a breaking strain of 300Kg.

Surely if you're using a sensible diameter rope then the breaking strain is much higher than 300kg: e.g. about 1.4 tonnes for 12mm synthetic hemp. Flints website is a bit misleading as it seems to suggest in places that all their artificial hemp has a 300kg breaking strain.

Chris points out that the SWL also depends on lots of other components: tieing off rail, pulleys, total load on supporting structure, barrel length and position of hanging points etc. etc.; in addition many people rate the SWL of their hempsets as what they consider a sensible load to be handled, regardless of what the system might actually take dead-hung.

[la grande homme]

one of my venues has three five strand hemp bars, they are rated at 25kgs each. this is due to that being (I am told by the man who came to check them) the maximum reccommended load one person can lift according to LOLER. our ratchet winches on the other hand are rated at 250kgs.

 

All hemp is a frigging nightmare and (quite rightly) you are no longer allowed to put hemp lines into new theatres or refits - they should only temporary installs or already in existence in an older theatre. We have moved on from sailors in the rigging and so should our flying systems...

 

I'm not saying that every theatre should have NOMAD (tho it is an absolute joy ;) ) but (and I bet you'll all jump down my throat with stories about how you've done it safely for ever...) hemp is, in the end, with the best knots in the universe, only as strong as the bolt holding the cleat to the flyrail / wall / floor and that ain't good in fact its downright dangerous...

 

 

I bet it would make a lovely bonfire and then you could use the bars as booms on the side of stage...

 

...rant ends :)

[Ike]

hemp is...only as strong as the bolt holding the cleat to the flyrail / wall / floor and that ain't good in fact its downright dangerous...

What about if you tie it off to the rail? Hemp flying, IMHO, is not dangerous if the operators and maintenance staff are competent. By competent I mean they have the knowledge and experience to do there job.

[DSA]

We have moved on from sailors in the rigging and so should our flying systems...

Whilst I completely agree, for many small outfits cost will be the overriding factor. For example I guess the fly kit in existence at my University will stay for the time being (rather handy therefore that there are 3 whinched lx bars for the lights!)

 

With a bit of luck when they rebuild the Union we can have a nice new theatre with a modern fly system.

 

However for the time being it will stay...

 

I spoke to another person yesterday, and their response was that the HEMP was rated to 125Kg...however there was no mention of the bar! I find it amazing how people can just go on without really knowing what the SWL is (they all seem to practically ignore a notice at the moment).

 

David

[robloxley]

hemp is, in the end, with the best knots in the universe, only as strong as the bolt holding the cleat to the flyrail / wall / floor and that ain't good in fact its downright dangerous...

Remind me what the shear strength of an M10 8.8 bolt is then care to reconsider your statement. I'd also suggest that you notice the bolts holding the grid pulleys to the grid, or the counterweight frame to the wall, etc. - do you suggest these might fail too?

[Chris Higgs]

Any component will fail eventually. Load, age, flyman, whatever.

There is always a weak link that determines the capacity of the system or assembly.

The weak link is very often the building.

Buying the 'right' bits is easy.

Physically fitting them is within most people's capacity.

Where there are positioned, particularly in relation to other equipment and what else the structure has to do is the bit that requires proper understanding.

 

To ignore an SWL is a breach of LOLER, technically a criminal offence, should it ever be proven.

Every lifting machine or assembly must by law have a SWL made known to users by marks or notices on or near the equipment.

 

In response to a couple of posts:

1. There's no reference in LOLER (L113) to specific weights than can be lifted manually.

Even in the manual handling guidance, it's all down to risk assessment.

2. There is no legislation in the UK (yet) that prevents installing hemp sets.

 

HTH

[Loki]

Hi All

Just as a matter of interest how many theatres are there that still operate with a predominately hemp system?

[Dazzler]

Well, I can think of three...

 

Theatre Royal Brighton

Theatre Royal Lincoln

Theatre Royal Bury St. Edmunds

Buxton Opera House

 

I know the following used to have a fair few hemp lines but that may have changed now.

 

The Anvil in Basingstoke

The Hexagon in Reading

The Regent in Ipswich

 

I'm sure there are plenty more

 

Dazzler

[TheProff]

For a 'quick question' this thread has been going on a long time :)

 

At my society we only have two support points for flying - the main roof beams that run up and down stage a few feet in from each catwalk. Our bars are 2x2 timber on two 12mm hemp lines, and the stage area is about 24ft wide by 20 ft deep.

 

Because of restricted height we have to trip our cloths - sometimes folding them into thirds or quarters if we want a high back wall, which means more timber battens.

 

I did calculate the static SWL for the ropes, battens and cloths, and found we were well within their capacities. However, I have no data for the building structure! I am just very careful about the total load up there at any time.

[Ellis]

For the next show they have rigged an extra lighting bar off a hemp set (3 lines).  I have never used these before, so excuse me if my explaination is rather incorrect!

 

According to the yellow book, you should not hang lanters from a hemp bar unless there is secondary suspension for the bar!

[DSA]

I see. Perhaps a stupid question, but where does one get this 'yellow book' from?

 

I can't see it in the useful books thread.

 

David

[Andrew C]

http://images-eu.amazon.com/images/P/1904031056.02.MZZZZZZZ.jpg Here (& the BR gets dosh), here at the ABTT, or here ,ET Now's book page.

 

 

??? Do I have a moderator to thank for the correction? I just went off to check the old thread on Amazon links and when I came back it was all fixed!! What service! TVM :(

 

As Amazon claim difficulty in finding it, I've added a couple more options.

[DSA]

According to the yellow book, you should not hang lanters from a hemp bar unless there is secondary suspension for the bar!

Could someone please clarify exactly the term 'secondary suspension'. Must both suspensions be of differing materials? e.g. take a short scaff bar hanging off a hemp bar with two boom arms used as drops. Is it safe to say that one boom acts as the primary suspension, and that the second acts as the secondary suspension? (once first checking that the load/moments are acceptable i.e. high enough safety factor with just one boom.)

 

I have been having a recent discussion with someone about this very thing.

 

In the case of Hemp bars, would it not be OK to say that because there are 3 lines - and the hemps are checked anually etc., that if one failed then the other 2 would take the load until the bar could be safely lowered for replacement...??

 

'Fixed' secondary suspensions on a hemp bar would mean that they would be 'unflyable' anyway would it not?

 

David