View source for Breastlines & Brail Lines

 A short page about Breastlines & Brail Lines

Breastlines are ropes (normally hemp at RCS) which are tied tautly between the flyfloors in order to deviate a counterweight bar up or downstage. 

We use them to when there is a clearance issue between flown pieces. It is normal to breastline a static bar, such as LX, in order to let a flown set piece pass cleanly on its way In and out during the performance. 

It is possible to deviate a flown piece but this would be done using “running brails” rather than a breastline.

Points to consider

It is desirable to breastline a counterweight bar as low as possible; Ideally, just above the bar terminations. 

This is because the greater the distance between the pulley blocks in the grid and the bar the less force will be needed to deviate the bar.

This can be proved with maths

Horizontal Force = Load X (Horizontal Deviation / Vertical Distance from the pulley to the breastline)

Lets assume we want to move a fully loaded 400kg LX bar 200mm upstage using a breastline at flyfloor level

Our Load is 400kg

Our Horizontal Deviation is 200mm

Our Vertical Distance is 8000mm (grid pulley to flyfloor)

Horizontal Force = 400X(200/8000)

So the Horizontal Force required to move the fully loaded bar 200mm is  '''10kg'''

Lets run the numbers again but this time let’s try to breastline the bar on the grid

The Load is still 400kg

The Horizontal Deviation is still 200kg 

But the Vertical Distance is now 1000mm 

Horizontal Force = 400(200/1000)

This time we need '''80kg''' of force to move the bar 200mm


*Have a think about that next time you are on the grid trying to gain those extra few cm clearance pulling on the counterweight lines.