Course to Steer Calculator
When a current is running, the heading you steer through the water must differ from your desired track over the ground. The course to steer calculator solves the current triangle using vector components: your desired track (true course to destination), boat speed through water, and the current's set and drift. The calculator returns the course to steer and your resulting speed over ground along the desired track. All courses are in degrees true; add magnetic variation and compass deviation to convert to a compass course to steer.
Course to steer formula (vector components)
Water track vector: Vwx = Vboat * sin(CTS), Vwy = Vboat * cos(CTS)
Current vector: Vcx = Drift * sin(Set), Vcy = Drift * cos(Set)
Ground track vector: Vgx = Vwx + Vcx, Vgy = Vwy + Vcy
Solve: CTS such that atan2(Vgx, Vgy) = Desired track
sin(CTS - Desired) = -(Drift/Vboat) * sin(Set - Desired)
SOG = Vboat * cos(CTS - Desired) + Drift * cos(Set - Desired)
Uses law of sines applied to the current triangle. Valid when drift is less than boat speed.
Applying course to steer in practice
- Convert true course to steer to magnetic by subtracting westerly variation (or adding easterly variation).
- Convert magnetic to compass by applying compass deviation from your deviation card.
- If the current changes mid-passage, recalculate with updated set and drift.
- Verify your actual track with periodic GPS fixes and compare to the intended ground track.
Course to steer: frequently asked questions
What is course to steer?
Course to steer is the compass heading a vessel must maintain through the water so that, when combined with the current (set and drift), the actual track over the ground leads directly to the destination. It differs from the desired course by the current correction angle (WCA).
How is the current triangle solved?
The current triangle has three vectors: the boat's water track (boat speed at course to steer), the current vector (drift in direction of set), and the ground track (desired course, speed over ground). Using law of sines or vector components, the required course correction is calculated.
What happens if the current is too strong to make the destination?
If the current drift exceeds the boat's speed through water, it may be impossible to reach certain destinations on a single tack. The calculator will return an invalid result. In such cases, wait for a favorable tide or take a different approach.
Does leeway affect the course to steer?
Yes. Leeway is sideways drift caused by wind pressure on the hull and rig. Add the leeway angle (typically 3-8 degrees for a sailing vessel) to the current correction before applying the total correction to your desired course.
What is the difference between course to steer and track?
Course to steer (CTS) is the direction you point the bow through the water. Track (or course over ground) is the actual direction you move across the seabed. In the presence of current, CTS and track differ by the current correction angle.
Official sources
- National Geospatial-Intelligence Agency: Bowditch American Practical Navigator (Pub. 9).
- NOAA Tides and Currents: NOAA Current Predictions.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.