Rooftop Set With a Jib, a 45-Degree Bridle, and Gusts to 24 mph
You are setting a 2,200 lb packaged rooftop unit on a one-story roof, 14 ft above grade. The RTU is 8 ft long, 4 ft wide and 4 ft tall, and the compressor is mounted on one end, so the center of gravity is roughly 8 in off the geometric center. The telehandler has a manufacturer's truss boom with a hook; its capacity chart shows 2,600 lb at 14 ft radius. The rigging will be a two-leg nylon bridle at 45° to horizontal, with about 70 lb of shackles and slings, and the slings are rated 2,000 lb vertical working load. Wind is 15 mph gusting to 24. The ground is level compacted base and the machine has been level-checked. A laborer is available for a tag line. The roof curb is on the far side, and once the boom is raised the operator's view of the curb will be blocked by the carriage.
1. Check the rigging and the capacity numbers. What governs and what must you verify before the load leaves the ground?
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Suspended weight is 2,200 lb plus about 70 lb of rigging, so 2,270 lb. At 45°, each leg tension is W / (2 sin 45°) = 2,270 / 1.414 = about 1,605 lb. That is under each sling's 2,000 lb vertical working load, so the slings are adequate with roughly 25% margin - but only if they are in good condition and correctly hitched. Check: sling tags legible, no cuts, burns, broken stitching or chemical damage; shackles and hooks rated, with a functioning safety latch; edge protection where the slings contact the RTU; equal leg length so the unit hangs level. Capacity: 2,270 of 2,600 lb is about 87% of chart, leaving only 330 lb of margin for wind and dynamics - that is tight, so treat the wind question seriously. Finally, confirm the lifting points are rated and the CG falls between them; with the compressor offset, pick so the unit does not hang nose-down.
2. Wind is 15 mph gusting to 24. Do you proceed?
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Not without checking the manual and the specifics. Many telehandler manuals limit operation to around 20 mph, and some set a lower limit for loads with large sail area; the RTU presents about 32 ft² to the wind when broadside. Gusting to 24 exceeds a typical 20 mph limit, so if the manual says 20, you stop and wait - you do not pick when the gusts are above the machine's stated limit, regardless of the steady-state number. Even below the limit, wind acts on the load: it swings, it rotates a sail-area load, and the tag line must be worked by someone standing outside the swing path who can let go. Combined with only 330 lb of margin on the chart, a gust that starts the load swinging can push you past capacity or put the load into the roof edge. Practical answer: hold until the gust cycle drops, or reschedule for the calmer morning window, and record the wind reading you used.
3. The operator will lose sight of the curb once the boom is up. How do you plan the set-down?
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Plan communication before the pick. Use a signal person positioned where he can see both the load and the curb and where the operator can see him - never under the load and never holding the load itself; he may handle the tag line from outside the swing path or a second person does. Agree on hand signals or radio protocol, including a distinct stop signal, and agree that any lost communication means the operator stops and holds. Walk the set-down: confirm curb orientation and that the unit will land on the curb, not on the rigging; approach the landing point slowly with the load stabilized; keep hands and feet clear as it lands; do not set the load down on slings you still need. Confirm with the GC that the roof structure is rated for the unit before it is landed. If at any point the operator cannot see the signal person, he stops.