Marine & Navigation

Drift Estimator

Estimate set-and-drift impact on course over ground and offset.

Last validated: 2026-02-14

Drift Estimator combines vessel heading/speed with current and wind-drift vectors to estimate course over ground, speed over ground, and accumulated offset. It is useful for coastal navigation checks, dead-reckoning updates, and understanding why track diverges from steered heading. The tool treats all vectors as steady over the selected duration, which is appropriate for quick planning intervals. Use it for situational awareness and confirm with live sensor data and chartplotter track history.

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Input Pattern

Enter values in the left panel, keep units explicit, run the calculation, then copy or share the result. Invalid fields are highlighted immediately.

Drift Inputs

Result

Course over ground: 96.06°

Speed over ground: 11.140 kn

Drift east-west: 4.311 nm

Drift north-south: -4.705 nm

Total drift offset: 6.382 nm

How to use this tool

Enter vessel course and speed, then current set/drift values.
Add optional wind drift direction/magnitude and set forecast duration.
Run estimation and review COG/SOG plus east/north and total drift offset.

Worked Example

Auto-generated from the tool's current default or entered inputs.

Example Inputs

Vessel course deg: 90.0
Vessel speed kn: 10.0
Current set deg: 140.0
Current drift kn: 1.2
Wind set deg: 130.0
Wind drift kn: 0.4
Duration h: 4.0
Course over ground deg: 96.06162908781738

Expected Outputs

Vessel course deg: 90
Vessel speed kn: 10
Current set deg: 140
Current drift kn: 1.2

Interpretation

Vessel course deg is 90.0. Use this as a decision input, not as a standalone conclusion.
Vessel speed kn is 10.0. Use this as a decision input, not as a standalone conclusion.
Current set deg is 140.0. Use this as a decision input, not as a standalone conclusion.
Cross-check the result against one alternate input set to validate sensitivity.

Scenario Compare (A vs B)

Use this to compare two input sets and quantify change in key outputs.

Scenario A

Vessel course deg

Vessel speed kn

Current set deg

Current drift kn

Wind set deg

Wind drift kn

Duration h

Course over ground deg

Scenario B

Vessel course deg

Vessel speed kn

Current set deg

Current drift kn

Wind set deg

Wind drift kn

Duration h

Course over ground deg

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Drift Estimator

Input Pattern

Drift Inputs

Result

How to use this tool

Worked Example

Example Inputs

Expected Outputs

Interpretation

Scenario Compare (A vs B)

Scenario A

Scenario B

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