Offshore & Satellite
Built for the boat that left the marina
Every weather app works great at the dock. Offshore, you have 2.4 kilobits per second, a satellite bill, and a real need for the answer. OpenSail treats bandwidth as the design constraint it actually is: corridor GRIBs cut to your passage, routing by email subject line, and an offline map that tells you the truth about its age.
Three tools, one workflow
Corridor GRIBs
Instead of downloading an ocean basin, download your corridor: the GRIB is cut to your route with the variables you pick and a size budget you set. Standard GRIB2, readable by every offshore tool you already run.
Routing by email (beta)
Send a route request as an email subject from Iridium GO, Winlink, or Sailmail. The full Rust solver runs ashore and replies with a plain-text plan plus a 50-point GPX your plotter will actually accept.
Honest offline mode
The app installs as a PWA and caches the last real forecast. Lose signal and the map keeps working, labeled with exactly how old the data is, escalating to a red do-not-route warning when age crosses the safety gate.
The 2.4 kbps route request
This is the whole interaction. No app, no browser, no session to keep alive on a flaky link. One subject line out, one compact reply back, computed by the same solver the web planner uses, with the same depth gating and the same refusal honesty. If the solver cannot find a safe route, the email says why instead of pretending.
To: route@opensail.app Subject: route 25.7,-80.2 to 26.5,-78.9 depart 2026-07-08T12:00Z mode balanced ── reply ────────────────────────── Route: 25.700,-80.200 -> 26.500,-78.900 Mode: balanced | Departs: 07-08 12:00 UTC Distance: 98 nm | Duration: 16.4 h Max wind: 18 kt | Max seas: 1.4 m GPX route attached (<=50 points).
What it does not do
Honest limitations
- Email routing is in beta, capped per day per account, and requires a registered account with a vessel configured. Test the round trip from your actual satellite client before you need it in anger.
- OpenSail is not a satellite communications provider. You bring the Iridium, Starlink, SSB, or shore Wi-Fi; we make every byte of it count.
- The offline cache is the last forecast you fetched, not a magically updating one. The banner tells you its age precisely so you never mistake it for live data.
Frequently asked questions
How do I get weather over an Iridium GO or SSB?
Two ways. Download a corridor GRIB before or during the passage: OpenSail cuts the file to your route corridor and budget so it fits satellite airtime instead of shipping you an ocean basin. Or skip the download entirely and email a route request: a one-line subject from any satellite mail client returns a plain-text plan and a GPX attachment sized for 2.4 kbps.
What is the email routing format?
One subject line: 'route 25.7,-80.2 to 26.5,-78.9 depart 2026-07-08T12:00Z mode balanced'. Departure defaults to now and mode to balanced, so the minimal request is just two coordinate pairs. The body is deliberately ignored, because the most limited satellite clients only do subjects well. The reply is a compact text plan (distance, duration, ETA, max wind and seas, comfort score) plus a chartplotter-safe GPX capped at 50 points. The feature is in beta; requests are capped per day per account.
How big are the GRIB files?
As big as your plan needs and no bigger. Corridor cutting plus variable selection typically lands passage files in the tens to hundreds of kilobytes rather than the multi-megabyte basin downloads generic GRIB services produce. The file is standard GRIB2, so any offshore tool that reads GRIB reads it.
Does the web app work with no signal?
The last real forecast you loaded is cached on your device and served with an explicit banner saying exactly how old it is. When a cached run gets old enough that routing on it would be unsafe, the banner goes categorical and red. Never a blank map, and never stale data dressed as fresh; that honesty rule is enforced in code and covered by tests.
Which chartplotters accept the exported routes?
The GPX export is point-capped to fit the route limits of Raymarine, Garmin, and B&G units, which quietly truncate or refuse oversized routes. There is also a time-animated KML for Google Earth and GRIB2 for your weather tools.
Is email routing secure? Could someone spoof my address?
Requests are only accepted from Resend-verified webhooks and only processed for registered account addresses, sent only to explicit routing addresses. Replies always go to the account email on file, never to a reply-to header, so the worst a spoofed sender can achieve is burning one of your daily requests and sending you one accurate email.
Keep exploring
Set the workflow up while you still have bandwidth
Create an account, add your vessel, and send yourself a test route by email before the passage, not during it.
Get set up free