As ship design advances, particularly with regard to
structural optimisation and high speeds to meet market
demands, there is a tendency for noise and vibration
problems to become more pronounced. In some instances
this manifests itself in the difficulty of achieving a
satisfactory solution within the operational and design
constraints of the ship, while in other cases progress has
brought other excitation sources to the fore.
Design practice should include elements of model testing,
calculation and heuristic deduction from previous
experience. While in many instances all three elements are
included in the design process in some cases the model
testing phase is omitted, frequently on the grounds of cost.
Where significant power in the context of a particular hull
form or a restriction on draught has to be accommodated,
then cavitation testing of the propeller in a properly scaled
wake field and measurement of the associated propeller
induced hull surface pressures is particularly valuable in
terms of stabilising cavitation and minimising excitation.
Notwithstanding the desirability of undertaking the three
basic elements of design, it must be appreciated that error
bounds are associated with each of these elements and, at
best, they are a guide for achieving a good design together
with sound engineering judgement. In the case of
cavitation testing it is the scale effects between model and
full scale which may be complex; for computation it is the
accuracy of the mathematical model and for heuristic
deduction it is the closeness of previous designs and
operating conditions to the subject ship under
consideration.
The attainment of an optimised shipboard environment is
not simply about the setting of criteria. Rather it is the
placing of the criteria in the context of the whole design
process such that they are realistic and achievable within
the bounds of current knowledge and engineering practice.
Furthermore, these criteria should not restrict innovation
and development, but should embrace flexibility for those
who wish to market an enhanced product, albeit at
additional cost, or to include emerging technologies.
Nevertheless, in all cases the assessment criteria should
seek to embrace the total effects of noise and vibration
rather than address partial aspects.