Two celestial position lines obtained at different times can be combined into a running fix, similar to a visual/radar running fix. What extra factor is unique to a celestial running fix compared to one using terrestrial bearings?

A. Nothing extra — the technique is identical in every respect

B. Because the celestial body itself moves across the sky between observations (in addition to the observer's own DR run), the first position line must also be advanced to account for the body's changing geographic position, not just the vessel's movement — getting this transfer wrong introduces an additional error source not present in a purely terrestrial running fix

C. Celestial running fixes can only combine observations of the same single star, never different bodies

D. A celestial running fix requires exactly three observations, never two

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