Dynamic stability

1
Dynamic stability

• Risk model, based on IMO guidance to the master
  for avoiding dangerous situations in following
  and quartering seas .
• Output frequency of occurrence per year of
• No, Minor, Major, Severe, Catastrophic effects on
  ship
• No, Minor, Significant, Severe, Catastrophic
  effects on human
• Rules implemented in a long term analysis risk
  model, in Excel worksheet form, by Sirehna.
• Time domain simulations performed by SSRC for
  comparison with the rules.

2
Dynamic stability principle (1/3)

• IMO rules account for 4 dangerous events
• Surf-riding/broaching
• Successive waves attack
• Synchronous roll
• Parametric roll
• For given ship characteristics (length, natural
  period) and operation condition (speed, wave
  period and incidence) the rules say if the ship
  is in safe or dangerous situation for each event.

3
Dynamic stability principle (2/3)

• Long term probability of being in safe or
  dangerous conditions calculated by combining
• Wave scatter diagram
• Wave incidence distribution
• Probabilities converted into frequency of each
  effect occurrence per year using conversion
  matrices and correction factors, accounting for
• Risk of each effect when individual events occur
• Type of steering device water jet or others
  (broaching, successive waves)
• Presence of active stabilisation (sync/param.
  roll)
• Crew Quality (HFQ)

4
Dynamic stability principle (3/3)

• Conversion matrices and correction factors

All values determined by judgement and from known
incidents in SEA
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Dynamic stability input
6
Dynamic stability output
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Dynamic stability - validation

• Prediction of being in safe / dangerous situation
  using IMO rule compared to direct time domain
  simulations by SSRC IMO rules are conservative.
• Final risk values delivered by the model seem
  reasonable compared to practical observations of
  incidents related to dynamic stability.

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Dynamic stability
Any Questions ?