NCCCO Boom Angle and Radius Calculations 4

Question 1

A load must be set 35 feet from the crane centerline. The boom is 70 feet long. What boom angle is required?

Accepted Answer

60°

Answer

cos(angle) = radius/boom length = 35/70 = 0.5, so the boom angle = cos⁻¹(0.5) = 60°.

Question 2

On a lattice boom crane, the boom angle indicator shows 72°. The operator lowers the load 10 feet. What happens to the radius?

Accepted Answer

Radius remains unchanged

Answer

Lowering the load vertically on a plumb line does not change the horizontal radius—only boom movement changes radius.

Question 3

When using a jib on a lattice boom crane, how is the total working radius determined?

Accepted Answer

Boom horizontal component plus jib horizontal component

Answer

Total working radius equals the horizontal reach of the main boom plus the horizontal reach of the jib from the boom tip.

Question 4

An operator uses a radius calculator and finds the load will be at 42 feet radius. The load chart shows a maximum of 9,000 lbs at 40 feet and 7,500 lbs at 45 feet. What is the safe load limit?

Accepted Answer

7,500 lbs

Answer

When the actual radius falls between chart values, always use the capacity at the next larger (more conservative) radius listed.

Question 5

A crane is set up on a 2% side slope. How does this affect the working radius on the downhill side?

Accepted Answer

Radius increases

Answer

On the downhill side, the boom will effectively swing out further than indicated, increasing the actual working radius.

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO Boom Angle and Radius Calculations 4