Ship Stability, Ship Construction and Damage Control
Statical stability
GM = KM − KG, and free surface effect reduces effective GM by FSC = free surface moment ÷ displacement. Know the GZ curve and the IMO intact criteria: area to 30° at least 0.055 m·rad, to 40° at least 0.09 m·rad, between 30° and 40° at least 0.03 m·rad, maximum GZ at least 0.2 m occurring at or above 30°, and initial GM at least 0.15 m. Distinguish list (external healing moment) from loll (unstable equilibrium, corrected by lowering G or filling the low side).
Longitudinal strength
Shear force and bending moment, hogging and sagging, and the loading instrument. Sequence ballasting and discharging to keep still-water values inside limits.
Construction and damage control
Collision bulkhead position, double bottoms, watertight subdivision, cross-flooding, permeability, floodable length, down-flooding points and closing appliances. Damage control means isolate, set boundaries, monitor, recalculate the condition - and remember permeability affects flooding mass, not just volume.
Trap: omitting free surface in slack tanks, and treating angle of loll as list.
Worked example: a slack tank 12 m × 8 m has i = lb³/12 = 12 × 512 ÷ 12 = 512 m⁴; at 8,000 t displacement the FSC is 512 ÷ 8,000 = 0.064 m.