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					Information from SSRC - Universities of
Glasgow and Strathclyde, regarding the
passenger ship heeling moment formulas in
draft regulation II-1/7-2
Survival Against Heeling Moment
      (in draft Harmonised Regulations)
Heeling Moments Applicable
  ( the values are calculated for a sample ship)
Heeling Moment Applied




        1945 ton-m          3179 ton-m




 M heel = max (M passengers, M wind, M survival craft) … !
    Heeling Moment Due to Side Wind

 Maximum wind speeds (gusts) are determined during each individual
averaging period. Gust information is important for risk assessment studies of
damage to constructions and buildings, and in our case creating a substantial
heeling moment on a vessel with relatively large superstructure.

 The duration of the gust is an important consideration and is often related to
the intended application. Some applications require information about
extreme values of the shortest gusts (~1 second duration), while in other
cases, the damaging gusts are those that blows the entire structure (5-10
seconds duration).
Heeling Moment Due to Side Wind
Heeling Moment Due to Side Wind
     Heeling Moment Due to Side Wind

  Wind Speed,                           Wind Gust

               V(t)



   Mean Speed,
         Vmean




                                   Wind Speed,
                                                    Time, t
Wind Speed                                V(t)
 Spectrum,                                                Max. speed
  Swind (ω )
                                   Mean Speed,
                                         Vmean
                                                              PDF

                                                     Min. speed
                      frequency,   ω                 for a conservative
                                                     consideration
           Maximum Heeling Moment
Wind gusts blow in a direction that follows the wave progression; therefore
this should be applied consistently to the most conservative damage scenario
without overlooking the physical reality.

 Since the most critical damage flooding scenario occurs when the damage
opening faces to incoming waves at 90 Degrees, therefore the wind can be
taken as a corrective factor for the heeling that might be present due to
damage in the first place. The survival factor-s with all its components ought
to consider survival in waves.

  The existing proposal: ignores this fact and penalises the vessels with a large
lateral profile.

   M heel = Max [ M passengers , M wind , M survival craft ]
            Maximum Heeling Moment
  It is therefore suggested that a suitable wind speed value must be calculated
considering maximum and minimum wind speed variations, perhaps mean
wind speed can be used, then this would result in the net heeling moment
applicable being obtained through passenger heeling moment being reduced
by about 1/3 for a typical passenger vessel.

  The foregoing argument then replaces the maximum moment consideration
as follows:

M heel = Max [ (M passengers - M wind) , M survival craft ]

 Ignoring wind altogether can be considered if a conservative approach were
to be followed but at least it will not be as unrealistic as the currently adopted
approach.

				
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posted:4/8/2011
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