What are the main sources of error in a standalone GNSS position fix that an OOW should be aware of?

A. GNSS is now essentially error-free and no longer needs to be considered

B. Satellite/receiver clock errors, ephemeris (orbital data) errors, ionospheric and tropospheric propagation delay, multipath (signal reflecting off structures before reaching the antenna), and satellite geometry (dilution of precision) all contribute to positional error, even though modern civilian GNSS accuracy is typically within a few metres under good conditions

C. The only source of error is deliberate government jamming, which is now permanently switched off worldwide

D. Error only occurs in polar regions

A. The tidal height at the time of transit to confirm sufficient under-keel clearance

B. The yacht's fuel consumption for that leg

C. The colour of the seabed shown on the chart

D. Only the distance to the next waypoint

A. Switch the ECDIS to standby mode and navigate by GPS position alone

B. Ignore it — ECDIS alarms are frequently false and can be left running

C. Assess the situation against the planned route and charted depths, take action to maintain safe water, and inform the Master if there is any doubt

D. Acknowledge and silence the alarm immediately so it does not distract the helmsman