Working with cranes and helicopters to remove trees is nothing new for Kiwi tree climbers and always makes for spectacular photos and footage. But rarely do we see the use of a simple tool like the Good Rigging Control System (GRCS) although it can lift a load of 900kg. The GRCS is a self-tailing sailboat winch with a 46 to 1 mechanical advantage that has been redesigned for tree work by Mister Good from the USA.
The great advantage of using the Good Rigging Control System (GRCS) for a rigging job is that the rigger can not only lower but also lift loads.
By eliminating the shock loading factor in your rigging system, larger sections can be removed in one. This is due to the lower forces generated while lifting a load in comparison to dropping a load into a rope. The capability of the GRCS to lower and to lift on the same drum allows for a very flexible movement of loads around obstacles like power lines, houses, or fences.
When mounting the GRCS to the tree it is good practice to place the GRCS so that the operator is not standing underneath the load when lifting or lowering.
Lifting a load
The best position for the rigging block when lifting a load is straight above the attachment point of the load once it has been erected. The load should be attached as farthest out as possible, using the leverage force to your advantage.
When lifting branches it is good practice to use a simple balancing system to prevent the branch from turning while it is being lifted. The least shock load occurs when the load can be lifted off the hinge without any slack in the rigging rope. To achieve this it is important to have the rigging block set higher than the tie-in point of the load once erected. Using a scarf angle that will close and allow the hinge wood to break once the load is fully erected will prevent the need for the climber/ EPV operator to enter the area under the load, making the operation quicker and safer.
Loads that cannot be completely lifted because of other branches or obstacles in the lifting path can be balanced horizontally with a balancing system or positioned against uncontrolled movement with tag lines. Always watch the rigging point closely when lifting a load to observe whether the load is lifting or the rigging point is bending. A too heavy load or a too strong hinge can prevent the load from moving, resulting in reversing a doubled force on the rigging point leading to catastrophic failure.
Removal of whole tree with the GRCS
In some locations it can be beneficial to fell a whole tree in one piece in a very controlled manner. When using the GRCS for this it is recommended to set up a floating rigging point on a rigging traverse which allows for maximum control. Tag lines connected to the floating rigging point can help direct the tree into the exact landing area. When lowering the tree the force on the tree stump increases and the tree can slip off the stump and slide uncontrolled. To avoid this, use a wide open face scarf with a high back cut creating control all the way to the ground. In some cases it can be necessary to use ropes or chains to prevent the tree from slipping off the stump.
Mechanical advantage system and the GRCS
In some cases I have found that the simple lifting capacity of 900kg was not sufficient for the task at hand. By creating a three to one mechanical advantage system out of the rigging rope and two pulleys the output capacity of the GRCS can be nearly tripled. When using this technique it is very important to choose a strong enough anchor point for the pulley.
Reference:
GRCS Tutorial Videos
Article: Buseman, Kai: Die Winsch als Hebevorrichtung. TASPO BAUMZEITUNG, 02, 2011.
