Isochrone weather routing
for offshore sailing races
What it does
Real NOAA GFS wind and wave data refreshed every 6 hours. Up to 16 days ahead across the full Pacific corridor.
A true isochrone solver finds the fastest path through the weather window — not just the rhumb line or great circle.
Built-in polars for SC40, Cal 40, J/120, and TP52. Upload your ORR cert for your own boat's exact polar.
Pac Cup: San Francisco to Kaneohe Bay. Transpac: San Pedro to Diamond Head. Switch races with one tap.
Use live GPS tracking to route from wherever you are right now. Optimal heading updates as the forecast evolves.
Once you've loaded a forecast, routing and live GPS tracking run locally with zero signal. Grab the grid in a coverage window — route until the next one.
One download per 6-hour GFS cycle — under 2 MB. No streaming map tiles; the chart is self-contained. GPS position uses no data at all.
No account. No subscription. Runs in your browser using open weather data. A hobby project, built for sailors.
How to use it
Select Pac Cup or Transpac. The app loads the right corridor, origin, and destination automatically.
Pick from built-in polars or upload an ORR certificate PDF. Adjust polar efficiency with the slider.
Dial in your start window. The solver finds the fastest routing through the forecast that actually fits your start.
Scrub the forecast timeline. Check gybe points, wind angles, and wave heights along the optimal track.
Using it offshore beta
The forecast is a single download per 6-hour GFS cycle — under 2 MB, no map tiles, no polling. Coverage on Pacific routes is broad but not guaranteed continuous; open-ocean gaps still occur.
Pull the forecast in any coverage window. Between windows, routing, scrubbing the timeline, and live GPS heading all run locally on the cached grid — no connection required. The app shows how old the forecast is so you can judge when it's worth refreshing.
Underway use is in early beta — this is a hobby project, not a commercial product. Not for navigation. Always cross-check with official NOAA forecasts, paper charts, and your standard offshore nav tools before and during any passage.
Free forever · No login required · Works best on desktop
Open the Router →Not for navigation · For planning and entertainment only · Always verify with official NOAA forecasts