Module 19 - Electronic Navigation
Alarms and Waypoint Management
What you will learn
Set route, depth, traffic and arrival alerts as owned barriers with thresholds and actions rather than as background noise or proof of safety.
An alarm is useful only when its input is valid, its threshold protects a remaining margin, someone owns the response and the crew knows what happens next.
Electronic alarms are useful only if they are configured sensibly and understood by the crew. Cross-track error, depth, anchor, AIS CPA/TCPA, arrival, and guard-zone alarms can all reduce risk. Poorly set alarms create noise and may be ignored.
Waypoint arrival alarms deserve care. If the arrival circle is too large, the plotter may advance to the next leg before the vessel has safely reached the turning area. In pilotage waters, manually confirming a waypoint change may be safer than automatic advancement.
Brief an alarm before departure
A cross-track alarm is set wider than the safe corridor and an arrival circle could advance the route before the yacht reaches the turning area.
1. Derive the threshold
Set the alert from the route, vessel, position uncertainty and available sea room rather than a factory default.
2. Check the input
Identify the sensor and configuration on which the alarm depends.
3. Assign the response
Name who acknowledges it and the immediate action that preserves safety.
4. Test the behaviour
Confirm arrival, route advance, silence and reset behaviour before confined-water use.
Sense check: If the alarm sounds only after the protected margin is gone, it is not an early barrier.
Common mistake or limitation
- A configured alarm does not prove that its sensor input or threshold is valid.
- Repeated nuisance alarms train the crew to silence rather than interpret them.
- Automatic waypoint advance can create an unbriefed turn or new route leg.
- The arrival circle should not be treated as a precise physical turning point.
Recap
- Derive thresholds from the passage and remaining margin.
- Give each alarm an owner and a pre-briefed action.
- Test waypoint-arrival and route-advance behaviour before pilotage.
- Recheck alarms after route, profile, software or sensor changes.
Optional quick check
Section 5 of 18
A depth alarm is set to sound after the planned under-keel margin has already been consumed. What is wrong?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying Electronic Navigation
This public lesson is part of Revision Module 19. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.