Advanced Scenario Check: Compass

A yacht is approaching a fictional headland at night in cross-tide. After an alteration, the steering compass reads 112°C while the fluxgate shows 120° magnetic and GNSS COG varies around 126°T. The yacht is heeled. A portable loudspeaker and charging cable were placed beside the binnacle during the watch change. The plotter heading overlay and autopilot repeat the same fluxgate sensor.

The numbers do not form a majority. COG is ground movement, the two electronic displays share one magnetic sensor, and the steering compass may be affected by the new portable equipment or heel. The current card and variation predict 112°30′T from 112°C, but that is a hypothesis from recorded corrections, not the true answer to select.

State the first command before investigating detail: preserve the briefed safe water and reduce commitment as the vessel and traffic situation allow. Move portable magnetic and electrical items clear, maintain an outside lookout and assign one navigator to record each source, reference, time, heading, heel and configuration. Do not let troubleshooting displace vessel control.

Seek evidence that does not reuse the same failure path: a correctly identified charted transit or known bearing, depth trend, radar range, visual clearing limit and independently supported position as appropriate. If a reliable picture cannot be rebuilt before the last safe decision point, hold, divert or abandon the approach. Written revision can rehearse this judgement, but practical instruction and assessment aboard are required to demonstrate Yachtmaster command and instrument use.