Describe the five dangerous situations in heavy weather that IMO guidance warns masters and OOWs to avoid.

A. Dangerous situations in heavy weather are defined by Beaufort Scale force only. Forces 9 and above are automatically dangerous; below Force 9 no special precautions are required.

B. IMO guidance on heavy weather identifies three dangerous situations: fog, following seas, and strong tidal currents. Broaching and synchronous rolling are not separately categorised.

C. IMO MSC.1/Circ.1228 — FIVE DANGEROUS SITUATIONS IN HEAVY WEATHER: (1) SURF-RIDING / BROACHING: occurs in following or quartering seas when vessel accelerates down a wave face and loses steering — vessel broaches (turns beam-on). Prevention: reduce speed to avoid surf-riding; avoid wave overtaking speed; (2) REDUCTION OF INTACT STABILITY IN WAVES: righting lever (GZ) reduces significantly when a wave crest is amidships — vessel in wave trough has higher GM than on crest. In extreme cases this can cause capsizing when GZ disappears momentarily. Prevention: ensure adequate GM for conditions; avoid high deck cargo reducing freeboard; (3) RESONANT ROLLING (synchronous rolling): rolling period matches wave encounter period causing roll amplitude build-up. Prevention: alter course or speed to change encounter period; (4) PARAMETRIC ROLLING: righting lever changes periodically with wave passage, driving roll resonance at twice natural roll frequency. Prevention: alter course or speed; monitor for early signs (small increasing rolls); (5) SHIPPING GREEN WATER: bow submerged in steep seas — structural and flooding risk. Prevention: reduce speed; alter heading; ensure weathertight condition of hatch covers and fittings. PRACTICAL OOW APPLICATION: continuously assess: encounter period vs natural roll period; vessel behaviour in current conditions; sea state and wave steepness; speed vs wave speed. Alter course/speed proactively rather than reactively.

D. MSC.1/Circ.1228 applies only to passenger vessels and cruise ships. Cargo vessels have different heavy weather guidance under the Load Line Convention.

A. In heavy weather, reduce vessel speed to 3 knots and all cargo securing issues will self-correct due to reduced motion.

B. Cargo lashings are the bosun's responsibility. The OOW only needs to check hatch covers and report to the master when Force 9 is forecast.

C. PRE-HEAVY WEATHER CARGO SECURING CHECKS: (1) CARGO SECURING MANUAL: consult the vessel's approved Cargo Securing Manual (required under SOLAS VI/5.6 and CSS Code) — check lashing specifications for cargo type and sea conditions; (2) ROUND OF HOLDS: physically inspect all cargo lashings — check turnbuckles are tight and locked; check twist locks on containers; check blocking and bracing in tween decks; check that timber deck cargo lashings are tight; (3) HATCH COVERS: verify all hatch covers are properly closed, battened, and cleat dogs tightened. Check compression bars for integrity. Any hatch that leaked previously — doubly inspect; (4) DECK FITTINGS: secure all moveable deck equipment — liferaft cradles checked, anchors properly housed and lashed, spare parts containers secured, paint lockers locked; (5) WEATHER DECK: walk the main deck — nothing left unsecured. A 25-litre oil drum loose in heavy weather becomes a lethal projectile; (6) NOTIFY MASTER: report inspection result and any concerns; (7) LOG: record the inspection, lashings checked, any adjustments made; (8) ADDITIONAL LASHINGS: if existing lashings are borderline, add preventive lashings now — much easier before the weather than in it; (9) VESSEL SPEED/HEADING: the master should consider reducing speed and/or altering heading to mitigate rolling — synchronous rolling with natural roll period can cause cargo shift even with good lashings.

D. Notify the charterer that cargo delivery may be delayed due to heavy weather. No lashing checks are required as cargo was secured at loading port.

A. Heavy rolling in following seas is normal for container vessels and requires no action unless roll exceeds 15 degrees.

B. Increasing roll in moderate seas indicates cargo has shifted to one side. Stop engines immediately and await the vessel to self-right before investigating the hold.

C. Apply full rudder to the high side to counteract the roll. Reducing speed is not recommended as it reduces rudder effectiveness.

D. PARAMETRIC/SYNCHRONOUS ROLLING — recognition and action: WHAT IS HAPPENING: this is likely parametric rolling (also called parametric resonance). It occurs when: (a) The vessel is in head seas, following seas, or quartering seas; (b) The encounter frequency of waves is approximately twice the vessel's natural roll period; (c) The vessel's righting lever (GZ) changes significantly through the wave cycle — typically because the wave crest alternately ships forward and aft, altering the waterplane area and hence stability. Parametric rolling can produce extremely large roll angles rapidly (30°+ in a few cycles) in conditions that appear moderate. It is particularly dangerous on large container vessels (high GM, low freeboard amidships). SIGNS: (a) Increasing roll amplitude with each cycle; (b) Roll developing in otherwise calm-seeming conditions; (c) Rolls occurring in pairs (resonance pattern). IMMEDIATE ACTION: (1) ALTER COURSE: changing heading relative to the waves typically breaks the resonance immediately — this is the most effective action; (2) CHANGE SPEED: altering speed changes the encounter frequency and may break resonance; (3) CALL MASTER immediately; (4) REDUCE SPEED in any case to reduce dynamic forces on lashings; (5) Log the event. DO NOT ignore increasing roll — parametric rolling can capsize a vessel.