solas 2009 / chapter II-1/07

[nettersheim]

Hello all,

The attained index A in probabilistic rules of Solas 2009 is calculated as per:

A = 0,4.As + 0,4.Ap + 0,2.Al

(As, Ap and Al being the sub attained index obtained in load case "full", "partial" and "light").

How is justified such rule ?

I am scratching head with this question for many years ; in previous Solas 1992 for cargo ships it was the same philosophy with worst approach i.e only two loading cases. In old resolution A265 (for passenger ships as an equivalent to Solas 1960/74) it was also the same thing, with 3 drafts.

I understands it means that vessels are operated 40% of time at full load, 40% of time at partial load and 20% of tim in lightship condition.

I have no acceptable answers nor explanations from people I have questioned about it (some of them having been involved in delegation to IMO / sub commitee SLF !).

The formula above quoted for A looks a very simple (too much simple) approach to damage stability. For a container vessel for exemple operated nearly all time at full load or more than 75% of deadweight, the situation is such that in case of damage to the hull, attained index A at time of damage will not be sufficient and the vessel will be at serious risk.

Any idea or comment on this ?

Francois-Xavier Nettersheim

[Perm Stress]

A year ago I was scratching my head at similar questions.

The only answer I found was:
"The rules are written this way, so your design has to comply".