A travelling derrick combines a derrick boom and hoisting system with a base that can move along a supporting track or structure. Real rated capacity depends on the complete derrick configuration and its load chart.
Considering a separate actuator-driven linkage
The illustrative moment balance below cannot select a derrick actuator or establish a lifting rating. For a separate actuator-driven linkage, force and stroke must be checked through the complete motion using the actual mounting geometry.
With leverage, force is traded against travel. A bracket change that improves force can also increase required stroke, slow the output motion, or move the actuator into a poor mounting angle.
The actuator stroke should also be checked against the useful motion, not just against the visible travel. End clearance, hard stops, bracket rotation, and wire routing can all reduce the usable stroke in the final build.
- Calculate actuator force at the worst bracket angle, not just at mid-stroke.
- Check stroke, retracted length, and extended length against the mechanism envelope.
- Confirm the structure can accept the higher loads created by a stronger actuator.
For a FIRGELLI actuator application, run the FIRGELLI actuator force calculator, then compare available stroke, force, and mounting envelope in the FIRGELLI linear actuator range. If the goal is to replace an existing unit, use the linear actuator replacement finder before assuming the new actuator is a direct fit.
Travelling Derrick Interactive Calculator
Enter an assumed available resisting moment, boom weight and horizontal centre-of-gravity radius, hook radius and an entered moment divisor. The result is an arithmetic hook-weight quotient, not rated or safe capacity.
Equation Used
- All moments use one stated reference axis and horizontal lever arms.
- Boom weight is represented as one resultant force at the entered horizontal CG radius.
- The entered resisting moment is an external assumption, not calculated by the tool.
- The entered divisor is not asserted to be a code safety factor.
- No configuration, load chart, wire rope, reeving, stability, structural strength, rail reaction, dynamics, wind or operational limit is checked.
Derrick Boom, Mast and Travelling Base
A derrick uses a boom, mast or supporting members, hoist machinery and wire-rope reeving to lift and move a freely suspended load. A travelling arrangement adds motion of the supporting base or structure.
ASME B30.6 covers specified derrick types and their construction, installation, operation, inspection, testing and maintenance. OSHA requires rated capacities at corresponding boom angles or operating radii to appear on the applicable load chart.
What This Calculator Does
The tool subtracts an entered boom-weight moment from an entered resisting-moment assumption. It divides the nonnegative remainder by hook radius and an entered divisor to produce an illustrative hook-weight quotient.
It does not derive resisting moment or rated capacity from a derrick configuration. Real lifting decisions must use the applicable manufacturer or qualified-person load chart and required procedures.
Illustrative Moment Balance
remaining entered moment = max(0, Mentered - Wb rcg)
illustrative hook-weight quotient = remaining/(rhook K)
Wb is treated as tons-force, radii are feet, moments are ton-force-feet and K is an entered divisor. The max operation prevents the displayed remainder from becoming negative; it does not establish stability.
Worked Arithmetic Example
For an entered resisting moment of 500 ton-force-feet, boom weight of 5 tons-force at a 20 ft horizontal radius, hook radius of 40 ft and divisor 1.25, the boom moment is 100 ton-force-feet. The remaining entered moment is 400 ton-force-feet and the illustrative quotient is 8.0 tons-force.
Model Boundary
- Calculated: one static scalar moment subtraction and quotient.
- Entered assumptions: resisting moment, boom resultant, horizontal radii and divisor.
- Not calculated: rated capacity, load-chart interpolation, mast or boom forces, guys or stifflegs, ballast, rail reactions, structural strength, rope and reeving capacity, wind, dynamics, out-of-level effects, travel, inspection, signaling or safe operation.
Frequently Asked Questions
Is the hook-weight quotient a safe load?
No. It is arithmetic from user-entered assumptions and is not rated capacity.
Why is the remaining moment clamped at zero?
To avoid displaying a negative quotient when the entered boom moment exceeds the entered resisting moment.
Does the divisor establish a regulatory safety factor?
No.
Where should rated capacity come from?
From the applicable load chart and the derrick manufacturer or qualified-person documentation required for the configuration.
Does the calculator include wind or dynamic loading?
No.
Can it approve a lift?
No.
References
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