Telltale

sailing · sailing knowledge

Weather routing for sailboats: polars, forecasts and currents

A router sails your boat through the forecast before you do: your polar for her speed, each model for the wind, the currents and the chart for the water. Telltale does it for every departure in your window.

By Telltale Team · Reviewed

Before you go

  1. Add your boat’s polar and draft.
  2. Pick a destination and a departure window. Plan a passage
  3. Choose a time, then save the route before you lose signal.

What a router needs

Your polar, your draft, the forecast and the currents. Without a forecast there is no route.

The polar gives her speed at each wind speed and angle; the confirmed draft keeps her in water deep enough. For the weather, Telltale takes the latest run of HRDPS, HRDPS West, HRRR and ECMWF IFS. For the water: CIOPS currents, CHS predictions at five passes, tide heights from IWLS, and daylight. Where no forecast covers the time, there is no route.

Off Piste’s polar in Telltale, a Salona 41 on her ORC 2026 certificate, at 12 kn of true wind: the target speed curve on port and starboard with diamonds at the best upwind and downwind VMG angles, and dots where she sailed in one race, coloured by percent of polar.
Off Piste’s polar (Salona 41, ORC 2026 certificate) at 12 kn true wind. The white curve is her target speed at each angle and the diamonds her best VMG angles; the dots are where she actually sailed in one race, which is how you check a polar before trusting a route to it.

References 1 2 3 4 5

Every departure, sailed

Each start time in your window is routed; the ones that break a rule are greyed with the reason. That is when she can leave.

Telltale sails each departure in the window, up to 200 of them. One that would break a rule below is greyed, with the first rule it breaks. The rest are under When she can leave; pick one to see its arrival time and the tightest margin on the way.

A Telltale passage plan from Eagle Harbour to Plumper Cove: departures that keep every rule and greyed ones, leave 12:55 and arrive 15:16, the arrival spread across four runs, and the legs.
In TelltaleWhen she can leave. Plan a passage from Conditions and Telltale sails every departure in your window: the ones that keep every rule, the greyed ones and why, and the arrival time across the models. Plan a passage

One route per model

HRDPS, HRDPS West, HRRR and ECMWF each give an arrival time. A wide spread means an uncertain day.

Each model is sailed as its own forecast, so the plan shows the spread of arrival times across them. A spread of a few minutes is a settled day. An hour or more means the wind is uncertain: plan for the slow arrival, and read the models again before you go.

To check against another router, export the route as GPX, or open a PredictWind GPX beside it.

References 1 2 3

Safety margins

Depth with a margin, distance off hazards, traffic lanes crossed square, Whiskey Golf, and limits tested against the worst model.

These are the floor: no setting turns them off.

  • Water deeper than her draft plus a margin, at the lowest predicted water.
  • 100 to 150 m off charted hazards.
  • Traffic lanes crossed at right angles.
  • Whiskey Golf avoided unless you confirm it is inactive.
  • Your wind and gust limits tested against the worst model, not the average.

Race routing

Leg by leg, with the side to leave each mark, gates, laps and lines.

For a race, Telltale routes the course one leg at a time from the start line: each mark with the side to leave it on, gates, laps and the finish. A race’s page lays the course from the sailing instructions over the chart, leg by leg, for an assumed draft.

The Fraser River Lightship Race 2026 in Telltale: the course from the sailing instructions drawn over the chart from the start off Jericho round Q62 at Point Grey and south toward T10, with Off Piste and the fleet at the start.
The Fraser River Lightship Race, 3 Oct 2026, with its planned course shown. Not for navigation.

Racing with Telltale

Save it and follow it offline

Routes stay on the phone. Offline it sails from your polar and the live wind.

A route saves as you plan it and syncs to the boat. Without a connection the phone keeps following it: arrival from your polar and the live wind, the next waypoint as you reach each one, and a buzz when you are off course. A new forecast or a reroute needs a connection.

What it leaves out

No waves yet, and no guessing past your polar’s strongest wind. Not for navigation.

Waves are not part of the routing yet. Above the strongest wind in your polar, Telltale does not extrapolate. Tacks and gybes are taken at the best VMG angle. A route is a suggestion for planning: keep official charts aboard, keep a lookout and check every leg yourself. If she doesn’t make the polar’s speeds, every arrival time is early, so check the polar against a few recorded sails.

Sources and review

Official references checked on 2026-10-11. Product details and schedules change; the provider’s page is the current word.

Take it to the water

Check the stations before you leave, then record the sail for the debrief.

Open ConditionsRecord a sail