🔍 Key Concepts

• Transverse free surface moment and how it affects initial stability (GM). • Difference between lightweight condition and loaded condition on an offshore drilling unit like DEEP DRILLER. • Sign convention for moments (positive vs negative) as used in stability booklets and hydrostatic data.

💭 Think About

• Think about whether the vessel’s own permanent tanks (in lightweight condition) are normally pressed full, slack, or empty, and how that would influence transverse free surface moment. • Consider if a lightweight condition is expected to have a large, small, or zero free surface effect, and whether the sign would logically be positive or negative. • Ask yourself: would a realistic transverse free surface moment for a large MODU be expressed as a very large positive number, a small negative correction, or simply zero in the stability booklet for lightweight condition?

✅ Before You Answer

• Check how the lightship (lightweight) condition is formally defined in stability data: which tanks are assumed full, empty, or at a standard level. • Verify whether free surface moments are normally tabulated as positive quantities that reduce GM, and how any correction is applied in the trim and stability calculations. • Confirm from typical MODU stability booklets whether the lightweight transverse FSM is usually non‑zero or assumed to be 0 ft-long tons because all designated tanks are either pressed up or empty in the lightship condition.