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Parametric Rolling vs Synchronous Rolling & Emergency Towing

Master
Chief Mate

times asked: 6; times asked
questions: 3; questions
last asked: 2026; last asked

The slides, written out

AI-drawn illustration. Simplified to explain the idea, not to scale.

Slide 1 · PARAMETRIC ROLLING, SYNCHRONOUS ROLLING & EMERGENCY TOWING

PARAMETRIC ROLLING, SYNCHRONOUS ROLLING & EMERGENCY TOWING Maritime Stability & SOLAS Emergency Preparedness

Slide 2 · PARAMETRIC vs

PARAMETRIC vs SYNCHRONOUS ROLLING Understanding the Two Major Roll Resonance Phenomena PARAMETRIC ROLLING SYNCHRONOUS ROLLING Occurs in head or following seas Periodic changes in transverse stability (GM) caused by wave crests and troughs can excite the ship's roll motion. Occurs in beam or quartering seas Wave encounter period is approximately equal to the ship's natural roll period, causing roll motions to build up. Resonance Condition Significant resonance may occur when the wave encounter period is approximately equal to either the ship's natural roll period or about one-half of it, depending on vessel and stability characteristics. Progressive Amplification Each successive wave reinforces the roll motion as excitation occurs at the ship's natural rolling frequency. Commonly Observed In Large container ships, PCC/PCTCs and ships with wide midship sections and fine ends. Operational Hazards • Large roll angles • Deck immersions & green water • Cargo shift and structural stress • Risk of progressive flooding • Possible reduction of GM and loss of stability Early Warning Signs • Gradual increase in roll angle in seas that do not appear severe • Occurs in head or following seas • Builds up incrementally over time Most Critical When Ship has limited steerage way or is unable to alter speed or course. PARAMETRIC ROLLING (HEAD / FOLLOWING SEAS) SYNCHRONOUS ROLLING (BEAM SEAS) Crest GM decreases Trough GM increases Crest GM decreases Waves arrive in phase with the ship's roll, causing roll amplitude to build up cycle by cycle. Most dangerous because it can develop in seas that do not look severe. Key Takeaway Both phenomena are forms of roll resonance. The master's ability to recognize the signs early and take action is critical to safety. Primary Actions Alter heading Follow stability booklet Alter speed Maintain steering control Monitor roll & encounter period

Slide 3 · PREVENTION & BEST PRACTICES

PREVENTION & BEST PRACTICES Practical measures to avoid dangerous roll resonance AVOIDING PARAMETRIC ROLLING (HEAD / FOLLOWING SEAS) 1. ALTER HEADING Change course 45°–90° to put the sea on the beam (or near-beam) to break the timing between wave crests and the ship's roll. 2. ALTER SPEED Increase or reduce speed to change the wave encounter period so it no longer matches the roll period or half of it. 3. FOLLOW STABILITY BOOKLET Adjusting ballast changes the ship's natural roll period. Any alteration of GM should be made only within approved stability limits and in accordance with the stability booklet. 4. USE STABILIZERS (IF FITTED) Activate fin or tank stabilizers, if available, to reduce roll amplitude and prevent build-up. 5. MAINTAIN EFFECTIVE STEERING CONTROL Maintain effective steering control. If necessary, adjust steering strategy in accordance with the vessel's operating guidance and prevailing sea conditions. AVOIDING SYNCHRONOUS ROLLING (BEAM / QUARTERING SEAS) 1. REDUCE SPEED Usually the most effective action. Reducing speed shortens the encounter period and pulls the ship out of synchronism with the waves. 2. ALTER COURSE Turn 20°–30° into the swell to reduce roll amplitude. Avoid turning into head/following seas which may trigger parametric rolling. 3. MONITOR WEATHER ROUTING Use up-to-date forecasts and routing advice to avoid sea states that may cause roll resonance. 4. MAINTAIN STEERAGE WAY Maintain engine and steering readiness. Loss of power removes your ability to change speed or course to break synchronism. 5. CONTINUOUS BRIDGE MONITORING Continuously monitor roll angle, encounter period, and ship response. Take early action before large roll angles develop. MASTER'S KEY ACTIONS MONITOR ROLL ANGLE • Use roll indicator • Set alarm limits • Watch for increasing trends MONITOR ENCOUNTER PERIOD • Understand TE vs TR • Adjust speed/course early USE WEATHER ROUTING • Avoid high-risk conditions • Plan alternative routes • Reassess regularly MAINTAIN STABILITY AWARENESS • Keep within approved limits • Check GM and loading • Follow stability booklet Early recognition and timely action are the most effective ways to prevent dangerous roll resonance and its consequences. Safety at sea starts with awareness.

Slide 4 · EMERGENCY TOWING

EMERGENCY TOWING ARRANGEMENTS & PROCEDURES SOLAS COMPLIANCE & MASTER'S ACTION PLAN SOLAS REGULATORY FRAMEWORK SOLAS II-1/3-4 Emergency towing arrangements and procedures Applies to: Tankers of 20,000 DWT and above Requirements: Arrangements fitted at both ends Capable of rapid deployment Operable without main power At least one arrangement pre-rigged and ready Emergency Towing Procedures (ETP) All passenger ships (by 1 Jan 2010) All cargo ships built on or after 1 Jan 2010 All cargo ships built before 1 Jan 2010 (by 1 Jan 2012) Also consider: SOLAS II-1/3-8 (Towing and mooring equipment) for ships built on/after 1 Jan 2007 (Excludes emergency towing gear under Reg. 3-4) EMERGENCY RESPONSE FLOW 1 ASSESS THE SITUATION Assess sea state, drift, hazards Check damage and stability Determine towing necessity 2 COMMUNICATE Establish VHF/SSB communication If main power is lost, use emergency battery VHF Broadcast PAN-PAN / MAYDAY with position & intentions 3 MUSTER THE CREW Muster at assigned stations Assign towing preparation team Ensure safety brief and PPE 4 RETRIEVE THE ETB Use the copy on the bridge Review rigging diagrams, strong points and SWLs Plan the towing configuration 5 RIG TOWING ARRANGEMENT Deploy pre-rigged arrangement or rig as per ETP Lead through Panama lead Use chafing protection Prepare pickup line and buoy 6 COORDINATE WITH TUG Establish tow communication Agree on hand signals / channel Pre-tow briefing and plan 7 MONITOR THE TOW Monitor line tension & catenary Check chafing points Maintain communications Be ready for emergency release as per ETP The Master remains responsible for the safety of the ship. EMERGENCY TOWING PROCEDURES BOOKLET (ETB) MUST INCLUDE SHIP PARTICULARS Name, call sign, IMO number, dimensions, tonnage, draft & displacement range EQUIPMENT DETAILS Anchors (type, weight), cables, chains, shackles, connection types, lengths & proof loads STRONG POINTS & LOCATIONS Location of towing equipment and strong points (fore & aft) SWL Equipment capacities and Safe Working Loads (SWLs) RIGGING DIAGRAMS Assembly and rigging diagrams for towing arrangements OPERATING PROCEDURES Communication procedures, tow release arrangements, checklists, responsibilities and safety considerations COPY LOCATIONS (MIN. 3) Bridge Forecastle space Ship's office or Cargo Control Room KEY POINTS FOR BEING TOWED PREPARE EARLY Early preparation saves time and reduces risk. USE APPROVED GEAR Use only approved equipment and strong points. CREW SAFETY FIRST Ensure clear areas, wear PPE and follow safe procedures. COMMUNICATION IS KEY Maintain continuous communication with the tug. BE READY TO ACT Monitor constantly and be ready to adjust or release. Emergency towing arrangements and procedures are critical for saving lives, the ship, cargo and the marine environment. STAY PREPARED. SAIL SAFE.

In exams

Asked 6 times across 3 different questions, most recently in 2026. Asked most in Master (5), Chief Mate (1).

Drafted by SailR from our daily lessons. AI-drawn illustration. Simplified to explain the idea, not to scale. Last updated 19 Oct 2026.

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