Poor GPS data

GPS quality affects how accurate and useful the debrief replay is. Here's what causes common GPS problems and how to improve them.

Symptoms

• Track jumps around erratically (GPS noise)
• Straight-line sections where the boat clearly changed direction (satellite dropout)
• Speed readings are unrealistically high or low
• The track appears to start at one location and teleport to another
• The track doesn't move even though the sailor was racing

Cause: GPS not acquired before recording started

The most common issue. GPS needs to acquire satellite lock before it can record accurate positions. This typically takes 15–60 seconds outdoors with a clear sky view.

Fix: Start recording before leaving the dock or dinghy park, while the phone is outdoors. Wait until the speed display shows a plausible value (e.g. 0.0–0.3 knots while stationary) before launching.

Cause: Phone was indoors or below decks

If the phone is in a cabin, under a deck hatch, or inside a bag that blocks the sky, GPS signal is reduced or lost entirely.

Fix: Mount the phone where it has a clear view of the sky. Deck mounts, suction cups, or a lanyard around the neck all work. The phone face doesn't need to point up — the GPS antenna is inside the phone body.

Cause: Low battery mode

Android's battery saver modes often throttle or disable GPS updates to save power.

Fix: Disable battery saver while sailing. Go to Android Settings → Battery → Battery Saver and turn it off. Also see Battery optimisation for configuring the phone for all-day use.

Cause: GPS update rate (older devices)

Dinghy Coach records at 1 GPS update per second (1 Hz). Most phones support this. On some older or very budget devices, Android throttles GPS to a lower rate when battery saver or power management is active, resulting in choppy tracks.

Fix: Ensure battery optimisation is disabled for Dinghy Coach (see Battery optimisation) and that the phone isn't in any power-saving mode.

Cause: Multipath interference

GPS signals reflect off sails, rigging, and buildings. This is unavoidable at very close quarters near large structures but is generally minor on open water.

Fix: Mount the phone as high as possible on the boat and away from metal rigging where practical.

Assessing your GPS quality in the debrief

In the debrief view, zoom in to a known straight section of the track (e.g. a long upwind leg in steady breeze). If the track line is smooth and consistent, GPS quality is good. If it's jagged or shows small oscillations, there's noise — but this is usually cosmetic and doesn't significantly affect the statistics.

The manoeuvre detection algorithm filters out GPS noise using smoothing, so tack and gybe detection is robust to minor noise. Only severe noise (several metres of random jumps) will affect detection accuracy.