Page 327 - Introduction to Naval Architecture

312 SHIP DESIGN

Vulnerability

A ship might be quite safe while it remains intact but be very likely to
suffer extensive damage, or loss, as a result of a relatively minor
incident. For instance, a ship with no internal subdivision could
operate safely until water entered by some means. It would then sink.
Such a design would be unduly vulnerable. This is why in the safety case
the designer must consider all the ways in which the ship may suffer
damage.
Because they expect to suffer damage in action, vulnerability is an
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important consideration for warships. ' Each new design is the
subject of a vulnerability assessment to highlight any weak elements.
This considers the probability of each of the various methods of attack
an enemy may deploy, their chances of success and the likely effect
upon the ship. The likelihood of retaining various degrees of fighting
capability, and finally surviving, is calculated. A fighting capability would
be a function such as being able to destroy an incoming enemy missile,
The contribution of each element of the ship and its systems to each
fighting capability is noted. For instance, to destroy a missile would
require some detection and classification radar, a launcher and
weapon, as well as electrics and chilled water services and a command
system. Some elements will contribute to more than one capability. For
each form of attack the probability of the individual elements being
rendered non-operative is assessed using a blend of calculation,
modelling and full scale data. If one element is particularly liable to be
damaged, or especially important, it can be duplicated to reduce die
overall vulnerability. This modelling is similar to that used for reliability
assessments. The assessments for each form of attack can be combined,
allowing for the probability of each form, to give an overall vulnerability
for the design and the computations can become quite lengthy. Some
judgements are very difficult to make and the results must be
interpreted with care. For instance, reduced general services such as
electricity may be adequate to support some but not all fighting
capabilities. What then happens, in a particular battle, will depend
upon which capabilities the command needs to deploy at that moment.
For this reason the vulnerability results are set in the context of various
engagement scenarios. In many cases, the full consequences of an
attack will depend upon the actions taken by the crew in damage
limitation. For instance how effectively they deal with fire, how rapidly
they close doors and valves to limit flooding. Recourse must be made to
exercise data and statistical allowances made for human
performance.
Whilst such analyses may be difficult they can highlight design
weaknesses early in the design process when they can be corrected at