Page 320 - Practical Design Ships and Floating Structures

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(Future Possibilities)

Predictability Margins on
--222b Ancillaries
Scenarios ~

L

Fig 1: Reasons for Upgrading and the Six Frameworks . _. I

To guide the designer through the problem, an approach using a hierarchy of design scenarios is
suggested. The main factors which might give rise to a need for such changes, and some of the features
which can be built into an initial design to minimise their impact are illustrated in Fig 1.

In response to these drivers for upgrading, it is proposed that the potential upgrade solutions can be
classified into six broad frameworks, represented on the right hand side of Fig. 1. These range from a
‘bare minimum’ design for the current market, with no in-built upgrade potential, through four
intermediate options, to a ‘future-proof’ version with substantial over-design. The six frameworks are:
Framework 1 : A ship or plant designed only for today‘s requirement with minimal margins.
Framework 2: The basic requirements for some upgrades are built-in, such as additional hull strength,
space for increased services or larger weight margins.
Framework 3: Additional services (power distribution, piping systems, ventilation etc.) to support an
upgrade are provided, i.e. the design is “fitted for but not with”.
Framework 4: Additional auxiliary equipment (e.g. bigger cranes, and bigger electrical generators) is
provided.
Framework 5: Some items of major equipment (e.g. the main propulsion system in a ship) are
oversized in anticipation of an upgrade.
Framework 6: The ship is designed and built as the most generous that capital can provide, i.e.
overdesigned by today’s requirements.

These frameworks are used in conjunction with the possible reasons for upgrading identified by the
designer to evolve a set of alternative upgrade strategies at the concept design stage, with associated
preliminary designs. The methodology described below can then be used to assist in choosing between
them. It is obvious that to be attractive the through life benefits must be significantly greater than the
initial ‘extra’ investment and this must show in the NPV for the ship, Fig. 2.