What is the purpose of periodically 'swinging the ship' to produce or update a deviation card for the magnetic compass?

A. It is a legacy requirement with no current practical purpose now that gyro compasses exist

B. Deviation changes over the vessel's life as magnetic materials, cargo, structural work, or nearby electronic equipment change the local magnetic field at the compass position, and it also varies by heading — swinging the ship (turning through a series of known headings and comparing compass readings against true) produces an up-to-date deviation card so the magnetic compass remains a reliable independent backup

C. It is required only once, at the time the vessel is first built

D. It corrects variation, not deviation

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