3.3 Final Position, Landing Supports and Derigging Access
Key Takeaways
Check support reactions and underlying structure for the actual CG location.
Plan sling-removal clearance before landing.
Verify the load is stable and restrained before releasing rigging.
Plan the destination before the pick
Final positioning specifies where and how the load will rest after the rigging is released. It includes orientation, support locations, foundation capacity, access and stability. A route that reaches the destination is incomplete if the load cannot be safely supported there or the slings cannot be removed without entering a crush zone.
Identify the receiving structure and approved support points. A machine base may be designed to rest on designated pads rather than any convenient part of its underside. A tank may need saddles; a long member may need supports that control bending. The support arrangement must withstand the load and preserve its required orientation after hoisting tension is removed.
Measure the landing envelope and available space for personnel to work from protected positions. Anchor bolts, projecting pipes, uneven grout, floor openings and nearby equipment can affect approach and placement. Establish which parts must be aligned while suspended and which adjustments can wait until the object is secured. A hand placed between a baseplate and foundation cannot safely guide the final inch of descent.
Select supports for the actual condition
Dunnage separates and supports the load, often providing space to remove slings. Its material, dimensions, arrangement and bearing surfaces must suit the weight and geometry. A universal stack-height ratio or timber capacity is not a substitute for an approved support design. Splits, damaged ends, uneven bearing and unsupported spans can reduce its effectiveness.
For a training example, assume an approved plan uses two support lines 12 ft apart under a 24,000-lb load. If its CG lies 4 ft from the left support and 8 ft from the right, the simple vertical reactions are 16,000 lb left and 8,000 lb right. Equal-sized supports are not proof of equal demand. Each support and the underlying floor must be suitable for its actual reaction and contact area.
| Landing question | Reason to resolve it early |
|---|---|
| Where may the load bear? | Prevents loading weak panels or unsupported shell sections |
| Can the support carry the reaction? | Avoids assuming equal distribution |
| Is the object stable after release? | Prevents a suspended balance from becoming a resting tip hazard |
| Can the sling be removed? | Avoids trapping it under the load |
| Where will personnel stand? | Keeps alignment work out of pinch and fall zones |
Check stability after the force transfer
A suspended object may be stable under a hook but unstable on narrow landing supports. As the load lowers, contact changes the force system. One end may touch first and carry a temporary concentrated reaction. A sloped surface can create sliding, and a high CG can create overturning. The plan should identify the sequence of contact and the measures that establish a safe resting condition.
If a load requires bolts, braces or chocks before release, specify that hold point. Keep hoisting support as planned until those restraints are installed and verified, without using the crane as an improvised long-term brace. The responsible person must confirm that the receiving structure and restraint method can carry the resulting forces.
Derigging problem
A basket sling lies beneath a machine whose base will sit directly on the floor. If the load is landed without suitable clearance or an approved alternative rigging arrangement, the sling becomes trapped. Pulling it out with the crane can damage the sling, destabilize the machine or introduce side loading. The correct solution belongs in planning: approved dunnage, accessible removable connections or another compatible handling method.
Threaded hoist rings also need removal access. A ring fitted beneath overhead equipment may become unreachable after final positioning. Shackles may be trapped against a wall even though the load fits. Include the volume needed to turn a pin or wrench and to handle the gear from a safe position. Installation clearance and removal clearance are different checks.
Coordinate the final approach
Define the person responsible for placement signals and how that person sees the supports. If the operator cannot see the point of placement, suitable signals are required. Establish a safe alignment method such as planned taglines or suitable tools, without placing hands under the object. Do not use a tagline to drag a fully weighted base sideways across its landing surface.
Lower in controlled increments and stop if contact occurs somewhere unintended. An unexpected gap beneath one support may indicate a distorted base, obstruction or uneven foundation. Increasing hoist slack to force the remaining end down can change the load path and damage the object. Investigate the discrepancy while the load is in a controlled condition.
Once the load is on approved supports, verify that it carries its own weight and that required restraints are effective before removing tension. Release connections only after the supported condition is established. Account for the weight and possible falling movement of the rigging itself during removal. A heavy shackle dropped after a successful landing is still a handling hazard.
The examination lesson is that removal is not an afterthought. Equipment requirements, lifting characteristics and the ability to remove rigging are named planning obligations. A complete answer considers the destination and the final supported state as carefully as the initial pick.
A basket sling would be trapped beneath the planned final position. When should the handling method be changed?
Before the lift, by planning suitable support clearance or an approved alternative connection
After landing, by dragging the sling free
During suspension, by cutting the sling
Only after the crane operator complains
Sections you finish are checked off in the contents.