An anchor alarm watches whether your boat leaves the safe radius around the anchor point — and warns you before it gets critical. NauticCalc uses the GPS on the device for this, without a cloud. This guide shows how to set the anchor point, choose a sensible radius and sleep soundly.
Prerequisites
- GPS active and with a stable fix
- Anchor set, enough scope paid out
- iPhone charged or on a charging port for the night
Step 1: Set the anchor point
Open Anchor alarm and save the current position as the anchor point — ideally at the moment the anchor drops and holds. A point set early makes the radius more precise.
Step 2: Choose the radius
Choose the radius from scope plus a margin for swinging and the tidal range. Too tight leads to false alarms on every wind shift, too wide reports the dragging too late. Think of the arc the boat describes on the swinging circle.
Step 3: Activate the alarm
If the boat leaves the geofence, the app warns you. The alarm complements a watch and local knowledge — it does not replace a full anchor watch, especially in shifting wind or on poor holding ground.
Step 4: Night check
Before the night, check fix quality and battery level. Anchoring is often recorded automatically in the Logbook, so you can trace the sequence later.
Common mistakes
- Radius too tight → constant false alarms; too wide → warning too late
- Setting the anchor point late instead of when it drops
- Not considering the swinging circle and tidal range for the radius
- iPhone battery dead overnight
Read next: GPS & logbook · Anchor alarm feature