Work out speed over ground with current instantly with clear inputs, formula shown and shareable results.
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.
Current triangle
along = drift x cos(set - heading); cross = drift x sin(same); SOG = sqrt((STW + along)^2 + cross^2)
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.
Set is the direction the current flows toward; drift is its speed. Together they form the vector added to the ship's water track.
Alter heading into the current by asin(cross-track component / speed through the water), the marine equivalent of a wind correction angle.