⚓ Ship Average Speed Calculator
Calculate true average speed across multiple voyage legs in knots (Nautical Miles per hour), km/h, or mph. Built for deck officers, fleet managers, and offshore workers. Free, instant, no login required.
Units
Voyage Legs
Ready to Calculate
Enter speed and duration for at least 2 legs, then click Calculate.
Results are for reference only.
Always verify with official logbook records.
How to Use This Calculator
🔧 Step-by-Step
- 1.Choose your input mode: Speed + Duration (time-weighted) or Speed + Distance.
- 2.Select your preferred units (knots, km/h, or mph for speed; NM, km, or mi for distance).
- 3.Enter the speed and duration (or distance) for each voyage leg. Add more legs as needed.
- 4.Click Calculate to see the true weighted average speed, total distance, and total time.
- 5.Expand the Leg Breakdown to review per-leg contributions. Click Clear to start over.
💡 Worked Example
Container vessel with 3 legs
- → Leg 1: Open sea — 14 kn for 8 hours (112 NM)
- → Leg 2: TSS transit — 10 kn for 4 hours (40 NM)
- → Leg 3: Port approach — 6 kn for 2 hours (12 NM)
- → Total Distance: 164 NM
- → Total Time: 14 hours
- → Average Speed: 164 ÷ 14 = 11.71 kn
Note: A simple arithmetic average would give (14+10+6)÷3 = 10 kn — which is incorrect!
⚠️ Why You Can't Just Average Speeds
A simple arithmetic mean of speeds is only valid when each leg covers the same duration. In real voyages, legs differ in both distance and time. A vessel steaming at 18 kn for 20 hours covers far more ground than one at 6 kn for 2 hours — so the fast leg dominates the true average. This calculator uses the weighted average formula: Total Distance ÷ Total Time, giving you the correct Speed Made Good.
📌 Real Use Cases
- Voyage Reports & Logbooks: Calculate actual average speed from noon-to-noon reports for Master's voyage summary.
- Passage Plan Appraisal: Verify overall Speed Made Good across multi-leg passage plans per SOLAS Ch V.
- Charter Party Verification: Compare actual average speed vs. speed warranty in time charter agreements.
- STCW Exam Preparation: Practice weighted average speed problems commonly tested in OOW and Master examinations.
- OSV Multi-Leg Runs: Offshore supply vessels frequently change speed across platform stops — calculate true average.
📐 Average Speed Formula
Average Speed = Total Distance (NM) ÷ Total Time (h)Time per Leg = Distance ÷ SpeedDistance per Leg = Speed × Duration| Leg | Speed | Duration | Distance |
|---|---|---|---|
| Open Sea | 14 kn | 8h | 112 NM |
| TSS | 10 kn | 4h | 40 NM |
| Approach | 6 kn | 2h | 12 NM |
| Total | 11.71 kn | 14h | 164 NM |
🔗 Related Maritime Tools
Navigation Standards
This tool assists in passage planning appraisal (SOLAS Ch V, Regulation 34) and voyage performance analysis. Always cross-reference with official logbook records and master's voyage reports.