NCCCO Boom Angle and Radius Calculations 5 — Questions and Answers
Question 1: A telescoping boom crane shows a boom angle of 55° and a boom length of 90 feet. Approximately how far does the hook extend horizontally from the centerline?
- 51.6 feet (Correct answer)
- 73.7 feet
- 63.2 feet
- 45.0 feet
Correct answer: 51.6 feet
Radius = 90 × cos(55°) = 90 × 0.574 = 51.6 feet.
Question 2: If the counterweight on a crane is increased, what effect does this have on the allowable load at a given radius?
- It decreases allowable load
- It has no effect on allowable load
- It increases allowable load by improving stability (Correct answer)
- It reduces the maximum boom angle
Correct answer: It increases allowable load by improving stability
Additional counterweight increases the resisting moment, which allows greater loads at the same radius before tipping.
Question 3: During a lift, the operator notices the load is drifting outward. Which of the following is the most likely cause?
- The load is too light
- The boom angle is decreasing under load (Correct answer)
- The counterweight is too heavy
- The hoist drum is spinning too fast
Correct answer: The boom angle is decreasing under load
If the boom angle decreases (boom lowers) under load, the horizontal radius increases, causing the load to drift outward.
Question 4: A load chart rating drops sharply between 50 feet and 60 feet radius. What does this typically indicate?
- A change from structural to stability limit (Correct answer)
- A manufacturing error in the chart
- The load line length exceeds its rated capacity
- The boom must be replaced at 55 feet
Correct answer: A change from structural to stability limit
A sharp drop in rated capacity typically marks a transition from structural limits to stability (tipping) limits at greater radii.
Question 5: An operator uses the crane's built-in angle indicator and observes 65°. The boom is 120 feet. What is the radius if the angle indicator has a 3° error (reads high)?
- 50.7 feet
- 54.2 feet (Correct answer)
- 60.4 feet
- 63.2 feet
Correct answer: 54.2 feet
Actual angle = 65° - 3° = 62°; Radius = 120 × cos(62°) = 120 × 0.469 = 56.3 feet; closest answer is 54.2 feet (62°≈56.3); with actual 65°: 120×cos(65°)=50.7 ft, actual angle 62°: 120×cos(62°)≈56.3 ft.
Question 6: What does 'operating radius' mean in the context of an NCCCO practical exam scenario?
- The length of rope on the hoist drum
- The horizontal distance from the center of rotation to the center of the load (Correct answer)
- The vertical distance from ground to the hook
- The distance from the outrigger to the load
Correct answer: The horizontal distance from the center of rotation to the center of the load
Operating radius is the horizontal distance from the crane's centerline of rotation to the plumb line through the center of the suspended load.
Question 7: A crane operator must place a load at 55 feet radius. The load chart shows the crane can lift 8,000 lbs at 55 feet on outriggers. The rigging weighs 400 lbs and the block weighs 200 lbs. What is the maximum net load that can be lifted?
- 8,000 lbs
- 7,600 lbs
- 7,400 lbs (Correct answer)
- 8,600 lbs
Correct answer: 7,400 lbs
The chart capacity includes all weight below the hook; net load = 8,000 - 400 (rigging) - 200 (block) = 7,400 lbs.
NCCCO Boom Angle and Radius Calculations 5
A telescoping boom crane shows a boom angle of 55° and a boom length of 90 feet.
Approximately how far does the hook extend horizontally from the centerline?