Speed Over Ground With Current Calculator

Work out speed over ground with current instantly with clear inputs, formula shown and shareable results.

About Speed Over Ground With Current Calculator

The current triangle adds the current vector to the ship's velocity through the water. Resolving the current into along-track and cross-track components gives speed over ground from the vector sum, and the cross-track part is what pushes the ship off the intended course.

Formula

Current triangle

along = drift x cos(set - heading); cross = drift x sin(same); SOG = sqrt((STW + along)^2 + cross^2)

Worked example

With the default values below, Speed Over Ground With Current Calculator returns Speed over ground of 12.75. Change any input above and every figure here is recalculated in your browser.

Inputs used

Speed through the water: 12 kt
Ship heading: 45 °
Current set (direction toward): 120 °
Current drift: 2.2 kt

Results

Speed over ground: 12.75 kt
Course over ground: 54.6 °
Along-track current component: 0.57 kt
Cross-track current component: 2.13 kt

Step by step

1Values used
2Current triangle
3Speed over ground= 12.75 kt
4Course over ground= 54.6 °
5Along-track current component= 0.57 kt
6Cross-track current component= 2.13 kt

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

Frequently Asked Questions

What is set and drift?

Set is the direction the current flows toward; drift is its speed. Together they form the vector added to the ship's water track.

How do I steer to counter a cross current?

Alter heading into the current by asin(cross-track component / speed through the water), the marine equivalent of a wind correction angle.