What Is a Tidal Set and Drift Correction Calculator?
Set is the direction a current flows toward; drift is how fast it flows. Together they push a boat off its intended track. This calculator solves the classic navigation "current triangle" — given your boat speed and intended course, plus the current's set and drift, it finds the heading you must actually steer, and the resulting speed you'll make good over the ground.
This is the same vector method taught in coastal and inland piloting courses, traditionally solved by hand on a maneuvering board or chart plotter — this calculator does the trigonometry for you.
How to Read Your Results
Steer This Heading
The compass heading (true) to point your bow. It differs from your intended course because you're angling slightly into the current to counteract the sideways push.
Correction Angle
How far off your intended course line you need to point the bow, and to which side, to compensate for the current.
Speed Over Ground
Your actual speed made good along the intended course line, combining your boat speed and the current's effect.
Angle Between Current and Course
The raw angular difference between the current's set direction and your intended course — this determines how much the current pushes you off track.
Real-World Example
You want to make good a course of 090° true at 6 knots boat speed. The current is setting 150° true at 1.5 knots drift.
| Value | Amount |
|---|---|
| Angle between current and course | 60° |
| Correction angle | ≈12.5° |
| Heading to steer | ≈077.5° |
| Speed over ground | ≈6.6 kn |
Because the current is setting from behind and to the side, it both nudges the bow correction to about 12.5° and adds slightly to your speed over ground, pushing it above your 6-knot boat speed.
Tips for Using This Calculator
- Get set and drift from a current table or plotter for the specific time and location — both change throughout a tidal cycle.
- Re-check periodically on longer legs, since set and drift can shift meaningfully as the tide turns.
- "Cannot hold course" means the current is stronger than your boat relative to the angle involved — you'll need to adjust your intended course or wait for slack water.
- Combine with dead reckoning and periodic GPS fixes rather than relying on the correction alone for long passages.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team