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68 NAVY ENGINEERING BULLETIN MARCH 2003
ALAN LEGGE
The Importance of
Reliability, Availability and
Maintainability in
Engineering for the RAN
The Navy lives with the consequences of poor engineering and, in
extremis, dies with it. Equipment in a warship has to be reliable in use,
available when required, and maintainable at sea.
There is nothing new about
engineers and operators wanting
their machinery to be reliable and
maintainable. As the
Seamanship Manual advised in
1861:
“Engines and machinery,
liable to many accidents may
fail at any moment, and there
is no greater fallacy than to
suppose that ships can be
navigated on long voyages
without masts and sails, or
safely commanded by officers
who have not a sound
knowledge of seamanship…”
It might reasonably be asked,
therefore, what has changed?
Why the particular emphasis on
reliability and maintainability?
What is wrong with good
engineering judgement?
Fifty years ago the machinery fit
of a warship was large and
inefficient. It consisted, almost
entirely, of the main propulsion
system and occupied a
significant proportion of the
ship’s total volume. Although
physically large and heavy, the
number of components in the
machinery fit was not large and
the materials used were not
particularly sophisticated. This
machinery could – and did –
break down, but a large
engineering department borne for
labour-intensive watch keeping
and preventative maintenance
duties effected repairs. Even if
the breakdown was serious
enough to prevent a ship from
sailing, there were plenty of ships
to cover the loss.
As weapon systems and the
requirements of modern warfare
developed, this situation could
not continue. Lessons learnt in
World War II caused demands of
higher efficiency and endurance
to be made on the main
propulsion system, necessitating
the use of sophisticated materials
and higher stressed components.
Equipment became less tolerant
of operator error and this,
combined with the need for
remote machinery operation in
nuclear, biological or chemical
warfare environments, led to the
introduction of complex control
systems.
Meanwhile, weapon systems and
their sensors became larger,
heavier and demanded more
auxiliary support services. The
Marine Engineering Department
grew in scope to satisfy this
demand, adding sophisticated
electrical, chilled water,
refrigeration and extensive
hydraulic systems to its
responsibilities. However, the
greater space required for
weapons reduced substantially
the space and weights that could
be made available for marine
engineering. The equipment
became more compact, more
efficient and more complex.
Operators had to become more
highly trained, but were,
themselves, less numerous
because of lack of space,
recruiting problems, and the cost
of training. A ship unable to
proceed to sea in 2000 is a
serious loss to the RAN with only
nine frigates and destroyers on
the active list.
Poor reliability or maintainability
in modern warships can no longer
be tolerated. Support is very
expensive – both in terms of
administrative organisation and
cost of spares; ships are few, as
are the crews that man them.
The traditional “ good engineering
judgement” approach to design
assessment is just not adequate
for the complex, interdependent
systems in naval engineering
today. Perhaps, in days gone by,
the procurement authority would
examine a drawing submitted by
a contractor and use judgement
to identify weaknesses in
material, component choice or
arrangement. With such a method
one can never be sure that
absolutely every component has
been considered for its effects in
the event of failure. Nor can one
be absolutely sure that all the
failure modes have been
considered. A hydraulic valve, for
example, can fail open, fail set,
and fail shut or leak. The effect
on the parent system will vary
greatly depending on which