Managing stability
At management level the officer works with the yacht's approved stability information: understanding the metacentric height GM and the righting-lever (GZ) curve, the free-surface effect of slack tanks, the rise of the centre of gravity G as weight is added high, and the stability criteria the yacht must meet. Loading, ballasting, fuel and water management, and any change to the yacht — a heavy tender launched, a crane load, water on deck — must keep her within the approved conditions for the intended voyage. The GZ curve's shape, its range of positive stability and its angle of vanishing stability, is what really describes her safety at large angles.
- Interpret the stability book and the approved loading conditions for the yacht.
- Understand initial stability (GM), the GZ curve, and the free-surface effect of slack tanks.
- Manage tanks, weights and any modification to stay within the approved criteria.
- Know the stability implications and the actions for damage and flooding.
WARNING — Free surface and weight high are the enemies Slack tanks (free surface) and weight added high both reduce effective stability. Manage tankage — press up or empty — and keep heavy weights low, especially when taking green water or handling a crane load.
NOTE — Work from the approved information At this level stability is managed from the yacht's approved stability book and any loading computer, not from feel. Command means keeping the ship within the conditions a naval architect has approved.