Sailing Calc: Sailboat Racing

Sailing Calculator is a navigation companion for sailboat racing and cruising. When the next mark or your destination lies upwind, this tacking calculator works out how to reach it and shows the route on a map.

SETUP
Enter the start and target points: type them in, pick them on the map or take them from GPS. Then set the sailing parameters:
• wind direction
• dead angle (how close to the wind the boat can sail)
• drift margin
• average boat speed
The wind direction and speed for the start point can be downloaded from Open-Meteo. Below 10 kn the app warns that the direction of such a light wind may be misleading.

CALIBRATION
Two on-board tools help find your boat's real numbers.
• Dead angle: sail close-hauled on one tack and read the compass, then tack and do the same on the other tack. The app calculates the wind direction and the dead angle, in whichever order you sailed the tacks.
• Drift: hold a fixed course for a few minutes while GPS records the track. A line fitted through the GPS fixes gives the drift angle and speed over ground, shown on a plot of the track.

AUTOMATIC ROUTE
The app calculates a tacking route from start to target and draws it on the map. Legs are colour-coded by tack and labelled with length and course, and every turning point has a wind rose. You can mirror the route, add tacks, step the wind direction up or down and fine-tune the turning points. A summary panel shows the total distance and time.

MANUAL ROUTE
Plan the route yourself by tapping the map. Each tap snaps to an allowed course: one of the two close-hauled tack lines or a 15° grid outside the no-go zone. A tap inside the no-go zone snaps to the nearer tack line. Legs are red on port tack, blue on starboard tack and orange when motoring. Arrival times are shown at every point.

FORECAST MODE
Choose a departure time. Every point then takes the forecast wind for its own position and arrival time, so the route follows a changing wind. This helps in sailboat racing and on longer passages.
• The length of the wind line shows wind strength and is labelled in knots.
• A point with wind under 10 kn has no wind rose, and the next leg counts as motoring.
• Each leg is limited to 4 hours of sailing.

MAPS AND GPS
Maps use OpenStreetMap, with an optional OpenSeaMap overlay of buoys, lights and fairways. You can download a chosen area for offline use. With GPS switched on, the app shows your position and how far you are off the planned route, and to which side.

LANGUAGES
Available in Polish, English and German. Portrait orientation.

Sailing Calculator is a planning aid only. It does not replace official nautical charts, a compass or good seamanship.