Ship Speed Calculator Form
Example Data Table
| Scenario | Distance | Time | Speed | Fuel Burn | Notes |
|---|---|---|---|---|---|
| Coastal cargo run | 240 nm | 10 h | 24.00 knots | 28 t | Balanced cruise for schedule keeping. |
| Weather-adjusted passage | 180 nm | 9.5 h | 18.95 knots | 22 t | Useful during moderate head seas. |
| Efficient harbor approach | 36 nm | 3 h | 12.00 knots | 5 t | Lower speed improves maneuvering margins. |
Formula Used
Distance and time method: Speed in knots = distance in nautical miles ÷ total hours.
Propeller method: Speed in m/s = RPM × pitch × (1 − slip%) ÷ 60. Convert m/s to knots by multiplying by 1.94384449.
Hull speed estimate: Hull speed in knots = 1.34 × √(waterline length in feet).
Sea margin adjustment: Adjusted speed = base speed × (1 − sea margin ÷ 100).
Froude number: Froude = ship speed in m/s ÷ √(g × waterline length in meters), where g = 9.81 m/s².
How to Use This Calculator
- Enter the vessel name and select the calculation mode.
- Choose the preferred output speed unit.
- Fill the fields related to your chosen method.
- Add fuel burn and sea margin values for planning insight.
- Press Calculate ship speed to show results above the form.
- Download the output as CSV or PDF if needed.
Frequently Asked Questions
1. Why is ship speed usually shown in knots?
Knots match nautical miles per hour, so they fit marine charts, voyage planning, and standard bridge reporting better than land-based speed units.
2. Which method is best for real voyage analysis?
The distance and time method is usually best because it uses actual passage data. It reflects weather, loading, routing, and operational delays.
3. What does propeller slip mean?
Slip is the difference between theoretical propeller advance and actual movement through water. Higher slip often means lower efficiency or heavier resistance.
4. What is sea margin used for?
Sea margin reduces ideal speed to reflect real conditions such as wind, waves, fouling, and operational uncertainty during voyage planning.
5. Can this tool estimate fuel efficiency too?
Yes. When fuel burn is entered, the calculator shows fuel per hour and distance per fuel unit for quick comparison.
6. What is hull speed?
Hull speed is a practical estimate for displacement vessels. It links maximum efficient speed to waterline length and wave-making resistance.
7. Does this replace onboard performance software?
No. It is a planning and estimation tool. Bridge systems and sea trial data should guide final operational decisions.