Zero and negative VMG
A course 90° across the target has zero VMG; a course more than 90° away has negative VMG.
Sailing VMG & Tack/Gybe Comparison Calculator
Created by: Liam Turner
Last updated:
Compare two to four entered sailing options by current-adjusted VMG, leg time, distance sailed, manoeuvre penalty, and negative-VMG warnings.
Sailing VMG & Tack/Gybe Comparison Calculator
BoatingCompare entered sailing options by target-directed ground velocity and transparent manoeuvre penalties.
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What is a Sailing VMG & Tack/Gybe Comparison Calculator?
This calculator compares only the sailing options entered by the user and projects each ground vector toward a target.
It adds a transparent manoeuvre penalty and rejects zero or negative VMG from arrival-time ranking.
How the Sailing VMG & Tack/Gybe Comparison Calculator Works
Boat and optional current vectors create ground speed and course.
Their dot product with the target unit vector gives VMG. Positive VMG produces an arithmetic time.
VMG = ground vector · target unit vector
Leg time = distance ÷ positive VMG
Adjusted time = leg time + manoeuvre penalties
Input Guide and Conventions
Target bearing must represent a verified planning direction, not an unchecked straight line through hazards or restricted water.
Each option needs a realistic course and speed pair from observations, polars, or a clearly stated scenario.
The same current vector is applied to every option, so use the relevant direction-toward and drift for the modeled period.
Manoeuvre count and time penalty should include the actual loss expected from tack, gybe, sail handling, acceleration, and crew execution.
Examples
How to Interpret the Results
Positive VMG means the ground vector has a component toward the target. Zero VMG makes no target progress and negative VMG moves away.
The highest boat speed is not necessarily the best VMG because angle controls how much velocity points toward the target.
Adjusted time adds only entered manoeuvre penalties. Wind shifts, waves, traffic, layline error, current changes, and sail changes remain outside the result.
Best entered option means only the shortest arithmetic time among the supplied cases; it is not weather routing or a course recommendation.
Recommended Planning Workflow
Create options from realistic polar or observed speeds, then run current and manoeuvre sensitivity cases.
Reject routes that are unsafe, illegal, obstructed, or operationally inappropriate before comparing VMG.
Monitor actual ground track, speed, progress, traffic, and conditions and revise the plan continuously.
Common Applications
- • Tack comparison exercises
- • Current sensitivity
- • Manoeuvre-cost scenarios
Planning Tips
Enter realistic polar observations.
Use a verified navigable target leg.
Keep lookout, hazards, rules, and shifts outside this model.
Frequently Asked Questions
What is VMG?
Velocity made good here is the component of ground velocity toward the entered target bearing. It can be positive, zero, or negative.
Why can the fastest option lose?
A faster boat speed at a poor angle can have lower target-directed VMG. Manoeuvre penalties can also change the adjusted time.
How is current included?
The same entered current vector is added to every option before VMG is projected toward the target.
Is the best option a recommended tack or layline?
No. It is only the shortest modeled time among entered options. Wind shifts, current variation, waves, traffic, hazards, rules, sail changes, and manoeuvre execution are excluded.
Sources and References
- World Sailing. Equipment Rules of Sailing 2025–2028, accessed July 16, 2026; https://www.sailing.org/document/equipment-rules-of-sailing-2025-2028/.
- Offshore Racing Congress. Measurements and International Measurement System resources, accessed July 16, 2026; https://orc.org/measurements.
- US Sailing. Speed Guide Explanation, apparent/true wind mathematical relations, accessed July 16, 2026; https://www.ussailing.org/wp-content/uploads/2018/01/Speed-Guide-Explanation.pdf.
- Royal Yachting Association. Speed Charts and sailing-wind resources, accessed July 16, 2026; https://www.rya.org.uk/racing/speed-charts/.
- Empirical yacht-ratio and vector conventions are documented in each calculator.
Model limitation: The best entered arithmetic option is not weather routing, a safe layline, collision-avoidance advice, or permission to sail that course.