No Good Weather Clause Triggered? There Are Still Three Ways to Prove Underperformance

When the Weather Doesn't Cooperate, the Claim Doesn't Just Disappear

A vessel performance claim traditionally depends on a “good weather” period — conditions clean enough to isolate hull fouling or engine issues from weather effects. But good weather periods aren't always available. Skuld's guidance sets out three alternative methodologies used to establish underperformance — hull fouling, an engine problem, or both — without waiting for one.

The Three Methods

The RPM Method works from engine log recordings, calculating the theoretical distance a vessel should travel per propeller revolution based on propeller pitch, and comparing that to the actual distance covered. The Reasonable Grounds Method (RGM) runs through seven stages: testing reported weather against hindcast data, examining speed, RPM, engine setting and slip, building speed/power curves from warranted data, then comparing promised versus achieved performance to calculate time lost, overconsumption, and resulting damage. The Digital Twin Model goes further still — a virtual replica of the vessel built from its technical parameters, using live AIS and weather data to calculate what consumption and speed should be at any given moment, and comparing that against warranted performance regardless of whether good weather occurred at all.