With a fixed boom length, what happens to the crane's capacity as the radius increases?

• A. Capacity increases
• B. Capacity decreases
• C. Capacity stays the same
• D. Capacity doubles

Answer: (B)

Capacity is governed by stability moments. With the boom length fixed, the load’s radius—the horizontal distance from the crane’s base to the load—acts as a lever arm. The load moment equals weight times radius, so as the radius grows, that moment increases. Since the crane can only resist up to a certain maximum moment safely, the allowable weight must drop to stay within that limit. Therefore, the lifting capacity decreases as radius increases. The other options don’t fit because a larger radius makes tipping more likely, a constant capacity would ignore the changing moment, and “doubling” isn’t possible within the fixed stability limits.