You are master of a 400 GT coaster. After loading bulk cargo with a high GM, the vessel is very stiff. Your examiner asks what this means, what hazards it creates, and how you would assess it.

A. STIFF vs TENDER vessels: STIFF VESSEL (high GM): large metacentric height = short natural period of roll = rapid, jerky rolling motion. Signs: rolls quickly and violently when disturbed; does not stay inclined for long; feels very abrupt. Hazards: (1) Cargo shifting: rapid rolling generates high accelerations that can exceed the coefficient of friction of bulk cargo — bulk cargo can liquefy (if wet) or shift; lashings on deck cargo may be overstressed; containers may rack; (2) Crew welfare: rapid rolling causes fatigue, seasickness, injury risk; (3) Structural: repeated rapid rolling generates dynamic stress in the hull; (4) Equipment: high-speed roll causes items to fly off shelves, damage to compass pedestals, radar scanners, etc. TENDER VESSEL (low GM): long period rolling, slow and pendulum-like; the danger is that a large roll is completed SLOWLY — the vessel reaches a significant heel angle slowly and may not recover before the next wave reinforces the heel. Excessive tenderness (very low GM approaching the loll threshold) is dangerous. ASSESSMENT of stiffness: time the natural period of roll (T) using a stopwatch; GM ≈ (0.797 × B)² / T² where B is beam — this gives an approximate GM from the roll period. A high-beam vessel with a short roll period is stiff. Cross-reference with the stability booklet's calculated GM.

B. A stiff vessel is always safer than a tender one. Maximum GM is desirable in all loading conditions — a stiff ship cannot capsize.

C. Stiffness only affects passenger comfort. On a cargo vessel, a high GM is always preferred because it ensures maximum resistance to capsizing from beam-on wave action.

D. A stiff vessel rolls less than a tender one in the same sea conditions. The short roll period means fewer complete rolls per hour, reducing crew fatigue and cargo stress.

A. ANGLE OF LOLL: this is the classic presentation of negative GM (unstable equilibrium). Cause: the vessel's metacentric height (GM) has become negative — the metacentre (M) is now BELOW the centre of gravity (G). At 0° upright, the vessel has no restoring moment — but as she heels, the waterplane area shifts, moving B outward until a point of neutral equilibrium is found: this is the angle of loll (typically 5°-20°). The vessel "rests" here rather than returning upright. Common causes on a small coastal vessel: (1) Free surface effect from flooded compartments, slack tanks, or water in bilges; (2) Topside icing (raised G); (3) Cargo shift or absorption of water by deck cargo (timber); (4) Consumption of fuel and water from the bottom of tanks without compensating. IDENTIFICATION test: if you push the vessel toward the loll (to starboard) she returns to the loll angle; if you force her past the loll, the GZ curve at higher angles may generate restoring force — she "snaps" back to the loll. EMERGENCY ACTIONS: (1) DO NOT immediately ballast the high side (port) — if she rolls through the loll onto the other side, she may capsize; (2) Check and pump out bilges; (3) Fill double bottom ballast tanks SLOWLY starting with those on the LOW side (starboard) to raise M; (4) Reduce topweight; (5) Call master (if OOW); (6) Alert crew and consider reducing speed.

B. An 8° list to starboard means a weight has shifted to starboard — immediately correct by ballasting the port side to bring her upright, then investigate the cause.

C. A list that stays fixed at 8° is a permanent heel caused by off-centre loading. Correct it by shifting cargo from the starboard side to port before continuing.

D. A vessel that doesn't return from a list has insufficient GM. Calculate a righting lever at 8° using the GZ curve and if positive, the vessel is stable enough to continue.

A. IS CODE 2008 (International Code on Intact Stability) — criteria for cargo ships: the IS Code provides mandatory stability criteria for vessels under the 2008 International Code on Intact Stability (made mandatory under SOLAS II-1 and Load Lines). Minimum criteria: (1) AREA under GZ curve from 0° to 30° must be not less than 0.055 metre-radians; (2) Area from 0° to 40° (or flooding angle, whichever is less) not less than 0.09 metre-radians; (3) Area between 30° and 40° (or flooding angle) not less than 0.03 metre-radians; (4) GZ at 30° or greater must be not less than 0.20m; (5) Maximum GZ must occur at an angle of heel not less than 25°; (6) Initial GM (GM_0) must not be less than 0.15m. In this scenario: GM of 0.22m exceeds the minimum 0.15m — it satisfies this criterion. HOWEVER: GM alone does not determine acceptability — you must check ALL the criteria listed above (particularly the GZ curve at 30° and the area criteria). A vessel can have a positive GM but still fail the area criteria if the GZ curve drops too early. The stability booklet must be consulted to verify the full GZ curve for the proposed loading condition.

B. A GM of 0.22m is inadequate — the minimum for any vessel is 0.30m. Loading in this condition is not permitted under MCA regulations.

C. GM is the only stability criterion — a positive GM of any magnitude above zero is sufficient for a vessel to be considered stable and safe to sail.

D. The 0.22m GM is acceptable for a near-coastal voyage but would not meet the standards for an ocean passage. Near-coastal vessels have lower stability requirements.