Page 468 - Practical Design Ships and Floating Structures

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6 FULL SCALE TRIALS

After completion of the sea trials, during which extensive speed and vibration measurements have been
carried out, it could be concluded that the vessel satisfied all targets. The attained trial speed in loaded
condition was even significantly higher than the speed predicted based on previous experience. The
speed-power :diction together with the attained speed during speed runs is indicated in Figure 6.

SPEED / POWFR PRFDICTION AND TRIAL VALUE

200% I---
I

I
-PREDICT10
rn
TRIALVAL

20%
0%
9.0 10.0 11.0 12.0 13.0
SHIP SPEZll (KNOTS)

Figure 6: Power prediction together with the attained speed during speed runs

We like to point out that with model tests a better estimate of the trial speed would have been possible.
PARNASSOS did not provide a speed-power prediction because the flow simulation was incomplete
(no waves, flow around fore body not calculated to reduce costs). So, it is concluded that even for low-
budget vessels it is recommendable - if time permits - to conduct at least a propulsion test to verify the
attained speed. In the present case, a lighter engine and gearbox and smaller propeller would have
sufficed. The extra expenses of overpowering amply exceeded the costs of model tests.
The measured vertical vibration levels at a blade frequency of 17 Hz. in empty condition (worst case)
in the aft body are indicated in the table below:
Position

Main deck
Mess room
Wheel house
4.3

Adverse comments are according to interim guidelines of Bureau Veritas “not probable” with these
values.