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The variation of A with the length of the machinery space is seen to be modest in the considered range
of 25.2111 to 421x1. The Attained Index A has a maximum for L equal to about 38m, since the suvivabil-
ity factor s for simultaneous damage to the main deck and machinery space becomes less than one
when L is larger than this value. Smaller values of L will give lesser s-values for simultaneous damage
to the main deck and the compartments aft or fore of the machinery space. This is due to submergence
of down-flooding points as a result of a large trim. The optimal length of L corresponds to about 30 per
cent of the length of the vessel, but 40 per cent of the volume below the main deck.

The height H of the main deck above the tank top strongly influences the Attained Index A. The prin-
cipal reason is that the probability of damage to the main deck decreases with its distance above the
still water line. The draughts in full and partial load conditions are 5.8m and 5.52111, respectively and
the height of the double bottom is 2m. The variation in Figures 4 and 5 thus corresponds to a main
deck 1.2m to 3.7m above the draught in full load. For the as-built vessel H=6.5m. For H below this
value large variations in A with H are seen, especially when the SOLAS Part B-1 Regulations are ap-
plied. This is due to the linear decrease of the probability of damage to the main deck with the distance
from the water line. For SLF 43/3/2 this decrease first starts when the main deck is more than 3m abo-
ve the water line and hence the main deck will be damaged with a probability of one for nearly all
cases shown in Figure 5. The Attained Index A is, however, generally lower for SOLAS Part B-1 than
for SLF 431312 for the reason discussed in the previous chapter.

4 CONCLUSIONS
Based on the present parameter study the following recommendations can be given for use of the prob-
abilistic damage stability regulations in the initial design phase:
Define the hull form and insert the transverse and horizontal bulkheads required by the rules
and those considered as necessary for separation of cargo, hel, ballast and machinety
Specifi down-flooding points and centre of gravity G
Calculate the Attained Index A. If it is lower than the required index R, then make a sensitivity
analysis for A with respect to the positions of transverse and horizontal bulkheads to find the
subdivision with maximum A. If still not sufficient, insert additional transverse bulkheads if
possible, otherwise try to lower G, raise the down-flooding points or insert longitudinal bulk-
heads. The required changes are estimated by sensitivity analyses

References
Jensen J.J., Baatmp J. and Andersen P. (1995). Probabilistic Damage Stability Calculations in Prelimi-
nary Ship Design, Proc. PRADSPS, Vol.l, 1.565-1.577, Eds. H. Kim and J.W. Lee, The Society of
Naval Architects of Korea, Korea

Koelman H.J. (1995). Damage Stability Rules in Relation to Ship Design. Proc. WEMT’95, 45-56,
Eds. J.J. Jensen and V. Jessen, The Danish Society of Naval Architecture and Marine Engineering,
Copenhagen, Denmark

Sen P. and Gerigk M.K. (1992). Some Aspects of a Knowledge Based Expert System for Preliminary
Ship Subdivision Design for Safety, Proc. PRADS’92, Vol. 2, 1187-1197, Eds. J. Caldwell and G.
Ward, Elsevier Publ. Ltd., UK