Tracking Lines, Skate Blocks etc.
It’s not always obvious how to calculate the vector forces at play in Tracking Lines and Skate Blocks. They involve a running element and extra ropes which complicate matters but it can be done with RigRite and it’s not too difficult.
Here we see a tracking line with RigRite overlaid. The force in the rope to the left is simple – 110% – but to the right there are two ropes and only one figure for force, how is it split between them?
As a rule, the force on one side of a pulley is equal to the force on the other; if it wasn’t the rope would run through the pulley until the forces even out. In this case the force in the tracking line is 110% to the left of the pulley so to the right it must also be 110%. The remainder of the force in that direction has to be taken by the mainline – 20%
For a Skate Block the logic is the same but you’ll find that the force in all three sections of rope is equal. They are the same rope after all, it just runs through some pulleys. The load will always move to a position that preserves this equilibrium, or as close as friction will allow.