40kn Sail RouterPlanning a passage
Routing rarely hands you a route to sail as it is. Use it to understand the weather, what it means for your passage, and what your options are.
The router will rarely give you a route you can sail exactly as drawn. It shows the fastest line through one forecast, with one set of assumptions, and the real weather and your real boat will differ. Its value is in what it helps you understand: how the weather develops along your passage, what that means for the route, and which options you have. This workflow is built around those questions.
What the router knows: the forecast wind, the currents forecast if you choose one, your polar and a simplified coastline. That’s all. It doesn’t consider waves, gusts, thunderstorms, depths, marks, small islands, shipping lanes or how tired the crew is. It finds the fastest route, not the safest.
For navigation, use official forecasts and nautical charts. You must not rely only on forecasts shown in this app to plan your route.
1. Read the weather before you route
Drag the time axis through your passage window and look at the layers in the layer bar. Gust, Waves, Isobars, Rain and CAPE (thunderstorm potential) are there for you to judge, because the router doesn’t use them. Where a layer has no data, the map shows a gap and the readout shows a dash. The app never fills that in with a guess.
Decide what you’re willing to sail in before you see what the router suggests. That’s much harder to do honestly afterwards.
2. Make the boat realistic
Set the polar, and lower Efficiency until it matches how you actually sail. Add tack and jibe penalties, and limits if you use them. Your boat covers this. An optimistic boat doesn’t only arrive later than planned: a faster boat can also get through a gap in the weather that your real boat would miss.
3. Choose forecasts that suit the passage
- Global models reach furthest and suit crossings and early planning.
- Regional models have a finer grid and show more coastal detail, but they cover less area and end sooner.
Look at the end of the forecast, too. The router won’t sail past it, so a long passage on a short forecast stops partway. Each model has its own page in Forecast models.
4. Add your limits
These settings in Routing setup restrict where the route may go. Each one can also turn a possible passage into “no route”, so add them on purpose and watch the status line.
| Setting | What it does |
|---|---|
| Avoid wind above / below | The route never passes through true wind outside the limit. Useful if you want to avoid a high wind area. Could lead to no route to the destination. |
| Land clearance | The least distance the route keeps from the coast, up to 1 nm. The start and destination must also be that far out. |
| Keep out | Lines the route may not cross. Draw them on the map or import them from a GPX track, and switch each one on or off. A keep-out line is a boundary the router never crosses, so it also never routes into a closed keep-out zone. Use them for shallows, traffic separation schemes, restricted areas or simply to force the router to choose one route over another. |
| Scale wind to | The router sails in this share of the forecast wind speed, with the direction unchanged. The map keeps showing the forecast as published. |
| Currents | Adds a currents forecast: the boat sails through the water and drifts with the current. |
Currents can stop short of your route. Where the currents forecast has no data, the router uses zero current. The route’s report has a
Currents:line showing how much of the route had current data, so check it, especially close to the coast.
5. Compare, and treat disagreement as information
The Compare row in Routing setup routes the same leg several times with one thing changed each time. This is the most useful part of the workflow.
| Compare | Question it answers |
|---|---|
| Forecasts | Do the models agree? |
| Departures | What if I leave later? Is there a better window? |
| Speeds | What if the boat is slower than I think? |
| Angles | What if I won’t sail that close to the wind, or that deep? |
Then look at the routes side by side, on the map and in the graphs:
- Similar routes and times suggest the plan isn’t sensitive to that assumption.
- Routes on opposite sides of a system suggest the forecast is uncertain or the decision is finely balanced. Don’t pick the fastest one without a reason you can explain.
- A big difference after a small change is a warning. If 5 % less speed means meeting a front you had just escaped, your margin is too thin.
- The strongest wind often matters more than the arrival time. The Routes list has a column for it on every route.
6. Walk the route through time
Pick the route you favour and drag the time axis from departure to arrival. Switch between Wind, Gust, Waves and CAPE as you go. Check the Route details graphs for the strongest wind and the long stretches of beating. Ask what you’d do if the weather arrived six hours early, and where you could go instead.
7. Check it on a chart
Export the route as GPX and load it into your chartplotter or navigation app. Check every leg against an up-to-date chart. The app’s map is a coastline, not a chart: a route can cross shallows, rocks or a small island that isn’t in it. Where it does, add a keep-out line and route again.
8. Route again as new forecasts arrive
Forecasts change, and a route is only current until the next model run. Before you leave, and at each opportunity on passage, check for a new run and route again from where you actually are. The forecast list shows each model’s run time, and the model pages show when each last updated. Offshore, this relies on what you downloaded before leaving.
The solver settings
The defaults suit most passages, and you rarely need to touch them.
- Adaptive time step (on by default) starts with short steps so the boat can leave a harbour or a narrow channel, stays at 20 minutes for the first day, where the forecast is most accurate, and then grows up to Max time step. The final approach is refined either way.
- Adaptive routing area (on by default) saves time by no longer exploring water far outside the corridor once the boat has a clear line to the destination. If the routing area looks too restricted, switch it off and compare.
A plan, not a promise. The weather will differ from the forecast. Keep checking, keep a weather eye open, and let seamanship have the last word.