2.1 Current practice
suggests that a reasonable probability of achieving an acceptable
vibratory behaviour for a ship due to hydrodynamic excitation can
be obtained if the blade rate hull surface pressures given in
Table 10.2.1 Typical hull surface
pressures
are not exceeded. The
pressures are single amplitude peak values (half peak-to-peak).
Table 10.2.1 Typical hull surface
pressures
|
Ship type
|
Typical blade rate hull surface pressure range
|
|
|
± kPa (peak)
|
| Cruise ship
|
1 -
2
|
| Ro/Ro Ferry
|
2 -
4
|
| Container and fast
cargo ships
|
3 -
6
|
| Slow bulk
carriers
|
4
-7
|
2.2 The higher blade
rate harmonic hull pressures should always descend in a monotonic
fashion with increasing harmonic number. As a guide, the magnitude
of the twice blade rate component should be around half of the first,
with the third being of very small proportions. Discrete harmonics
beyond the third should be negligible.
2.3 Significant broadband
excitation at up to 10 times blade rate frequencies should be avoided
as these characteristics have the potential to excite a range of structural
frequencies.