| Scenario | Capacity (m³) | Fill (%) | Depth (m) | Swing (deg) | Cycle (s) | Loose Prod. (m³/h) | In-situ Prod. (m³/h) |
|---|---|---|---|---|---|---|---|
| Baseline grab | 1.50 | 85 | 12 | 110 | ~102 | ~33.7 | ~27.0 |
| Short swing | 1.50 | 85 | 12 | 70 | Lower cycle time via reduced swing angles. | Higher | Higher |
| Lower efficiency | 1.50 | 85 | 12 | 110 | Same mechanics, reduced effective working fraction. | Lower | Lower |
tlower = (Depth ÷ LowerSpeed) × 60 seconds
thoist = (Depth ÷ HoistSpeed) × 60 seconds
tswing = SwingAngle ÷ SwingRate seconds
Tcycle = tlower + tfill + thoist + tswing,loaded + tdump + tswing,return + tdelay
Vloose = Capacity × FillFactor
Vin-situ = Vloose ÷ (1 + SwellFactor)
Cycles/h = 3600 ÷ (Tcycle × Multiplier)
Q = V × Cycles/h × Efficiency where Q is production in m³/h
This model is suitable for grab, clamshell, and similar cyclic operations.
- Enter bucket capacity and a realistic fill factor from records.
- Set swell factor to convert loose volume to in-situ volume.
- Input depth and hoist/lower speeds based on equipment capability.
- Measure swing angles and estimate swing rates for loaded and return moves.
- Add fill, dump, and reposition times to represent actual delays.
- Choose an efficiency factor to reflect breaks and interference.
- Click Calculate to view results above the form, then export CSV or PDF.
1) Why cycle modeling matters in dredging
Dredging production is driven by repeatable cycles: lower, fill, hoist, swing, dump, and return. Even small timing errors compound quickly. For example, a 10‑second increase in cycle time can cut hourly cycles by 8–12% depending on baseline speed, reducing daily output and increasing cost exposure on fixed plant.
2) Breaking the cycle into measurable components
Time‑and‑motion observations should be captured in seconds for each segment. Lower and hoist are depth dependent, while swing depends on angle and operator technique. This calculator separates these items so you can update only what changed—such as barge position, depth, or swing distance—without rebuilding the entire estimate.
3) Typical ranges you can benchmark
Grab or clamshell cycles commonly fall between 40 and 120 seconds in open water operations, with deeper cuts and longer swing angles pushing higher. Fill time is often 8–20 seconds in sands and silts, but can rise beyond 30 seconds in stiff clay or debris. Reposition delays can dominate when working close to structures.
4) Capacity, fill factor, and swell conversion
Nominal bucket capacity rarely equals delivered volume. A practical fill factor of 70–95% is typical depending on material, cut control, and spillage. Swell factor converts loose to in‑situ; many soils range roughly 10–35%, so the same loose bucket load may represent significantly less in‑situ excavation.
5) Efficiency factor reflects real work time
Efficiency accounts for breaks, traffic, survey checks, and interference. Field values of 60–85% are common for uninterrupted production; complex sites may fall lower. Apply efficiency after calculating mechanical cycles per hour, so the model clearly distinguishes equipment capability from operational constraints.
6) Swing angle is a major productivity lever
Swing time is angle divided by swing rate, so reducing angle directly reduces cycle time. If loaded swing drops from 110° to 70° at 30°/s, the loaded swing segment falls from 3.7 s to 2.3 s. Combined with return swing reductions, this can deliver meaningful gains over a shift.
7) Using unit cost for bid and control
When an hourly operating rate is known, unit cost is computed as cost per hour divided by production. This supports quick scenario testing: compare deeper cuts, alternative dump points, or different efficiency assumptions. Track unit cost weekly to identify drift from plan and trigger corrective actions early.
8) Practical workflow for continuous improvement
Start with baseline inputs from logs, calculate expected production, then validate against measured daily volumes. Update one variable at a time—swing distance, fill time, or delays—to isolate root causes. Over time, your cycle library becomes a reliable planning tool for sequencing, crew allocation, and equipment selection.
1) What does “cycle multiplier” represent?
It scales the base cycle when one production “unit” needs multiple repeats, such as re-grabs, trimming passes, or multi-step positioning. Use 1 for a normal single-pass cycle.
2) How should I choose an efficiency value?
Use observed productive time divided by scheduled time. If a 10‑hour window yields 7.5 hours of true digging and swinging, efficiency is 75%. Adjust for site congestion and downtime.
3) Why do I need swell factor?
Swell converts loose volume in the bucket to in‑situ volume at the cut. Without it, you may overstate progress against design quantities that are typically measured in‑situ.
4) Are the hoist and lower speeds constant?
They are averages. Real speeds vary with load, operator behavior, and depth changes. If conditions vary widely, use time studies from multiple cycles and input a representative average speed.
5) How can I reduce cycle time quickly?
Shorten swing angles, improve barge positioning, and reduce reposition delays. Small changes across many cycles often outperform major equipment adjustments that are difficult to implement.
6) What if my operation uses pumps or continuous dredges?
This tool is designed for cyclic systems (grab, clamshell, backhoe). For continuous dredges, use a pipeline/flow-based production model rather than cycle segments.
7) Why does my measured output differ from the estimate?
Common reasons include underestimated delays, variable fill factor, inconsistent swing angles, and survey measurement timing. Update inputs from daily logs and re-run scenarios to align the model.