ETA Current/Wind Compensation Calculator adjusts calm-water ETA by accounting for current component and a wind-related speed penalty. It is useful for updating arrival forecasts and operational timing when conditions degrade effective speed. The tool outputs compensated ETA and delay relative to calm-water baseline, helping crews communicate schedule impact quickly. Use it as an operations estimate and refine with observed speed-through-water and updated forecasts.
Use this calculator as one part of a broader passage-planning workflow. The
Marine Navigation Calculators toolkit
explains how CPA/TCPA, UKC, tide windows, route distance, set and drift, fuel range, and manoeuvring checks fit together.
You can also browse the full
Marine & Navigation category.
Enter the vessel, route, tide, current, or clearance assumptions exactly as labelled, then verify the result against official data and onboard judgment.
How to use this tool
Enter route distance and calm-water speed.
Input current component (head current positive) and wind speed penalty percentage.
Run the calculator and compare compensated ETA against calm-water ETA.
ETA Inputs
Result
Effective speed: 11.700 kn
ETA with current/wind: 10.26 h
ETA calm-water baseline: 8.00 h
Delay vs calm: 2.26 h
Formula or method
Combines the entered navigation assumptions with the tool's planning formula or rule set; it does not replace official navigation sources.
Worked example
Updating ETA in adverse conditions
Distance: 80 nm
Calm-water speed: 10 kn
Head current: 1 kn
Wind penalty: 10%
Result: The compensated ETA increases because effective speed is reduced by both current and wind penalty.
Compare the result with observed speed over ground and update it as conditions change along the route.
How to interpret the result
Effective speed is a simplified planning value, not a full performance model.
Head current and wind penalty reduce speed made good; favorable current can improve ETA if entered accordingly.
Weather, sea state, RPM limits, course changes, and current variation can change the real arrival time.
Use observed speed over ground and updated forecasts to refine the result during planning.
Common mistakes
Treating one current value as constant over a long route.
Applying a wind penalty without checking whether course changes alter the apparent effect.
Forgetting schedule margin for traffic, pilot windows, tide gates, or speed restrictions.
Using calm-water speed when fouling, load, or sea state has changed vessel performance.
Uses single scalar current component and aggregate wind penalty.
No speed changes from RPM limits, sea state, or route geometry.
Review note and limitations
Method - scalar effective-speed and ETA relation.
Does not replace official charts, notices, tide/current data, instruments, pilotage guidance, COLREGs obligations, or navigational judgment.
Planning support only. Confirm ETA decisions with navigation instruments, forecasts, vessel performance data, traffic conditions, and bridge procedures.
FAQ
What does current component mean?
It is the current effect along the route direction. A head current reduces effective speed; a following current can increase it.
Is wind penalty a weather-routing model?
No. It is a simplified speed reduction percentage for planning discussions. Use marine forecasts and vessel performance data for serious routing.
When should I rerun the ETA?
Rerun it when distance remaining, observed speed, current, wind, sea state, or operational constraints change materially.
Related tools and workflows
Related marine tools help connect the calculation with route planning, clearance, drift, tide, encounter, or fuel checks. Start with CPA/TCPA Risk Calculator, Under Keel Clearance Calculator, and Tide Window Planner when you need a quick follow-up check.