Page 104 - Practical Design Ships and Floating Structures

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wind, waves and current.
0 Dynamic positioning simulations, to verify the ability of the ship to hold station in wind and
current.
Based on the standard manoeuvres and the track change ability manoeuvres with the SurSim
simulation program, it was concluded that all steering arrangements provided a controllable ship, with
a slight preference to podded propulsion. The application of a sufficiently large centre line skeg
however, proved to be necessary to ensure the directional stability of the ship.
Using dynamic tracking and positioning simulations, conducted with the h4ARIN program DPSIM, the
deviations from the track and steering actions were compared for all steering arrangements. By
applying the appropriate controller coefficients, the ship met the requirements, irrespective of the
steering arrangement. The difference between the final results of the configurations was small and
therefore no conclusions were drawn regarding the best arrangement.
Besides the above mentioned simulations, also calculations were conducted to determine the required
bow thruster power in order to be able to berth or unberth without tug assistance up to BF7.

4 MODELTESTS
Based on the desk study results, in combination with operational and economic requirements, the
single-screw, single-rudder option was selected for the model test phase of the project. The complete
model tests program was based on the results of the desk study, concentrating on risk areas and
therefore minimising the number of tests.
4.1 Calm Water

A paint smear test was conducted in order to position the appendages such that least resistance and
disturbance of the flow was achieved. The speed-power relation and propeller hull interaction was
determined by means of resistance and propulsion tests. Finally, a wake survey was conducted to
determine the essential wake distribution.

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1207
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Figure 2: Result of the wake survey
The results presented in Figure 2 were found to be very favourable for a single screw vessel, showing
that the solution of exposed shafts even for a single screw vessel is worthwhile, when cavitation
inception is an item that needs to be considered.