Dimensiones de la gestión de la calidad

For all case studies the data sheet block coefficient is higher than the block coefficient model output. The current block coefficient formula is calculated with the modern formula of Ayre and is a general formula for all types of ships. Different formulas for the block coefficient are analyzed in order to see if the obtained block coefficient can be closer to the data sheet. These formulas are from a paper of Schneekluth and Bertram [39].

Case Study 1 Case Study 2 Case Study 3

Data sheet Block Coefficient 0.556 0.653 0.630

Ayre 0.502 0.635 0.617

Modern Ayre 0.472 0.605 0.587

Schneekluth and Bertram 0.475 0.552 0.547

Jensen (1994) 0.540 0.584 0.562

Table 4.4: Block coefficients according to different formulas from [39]

The older variant of the currently used Ayre formula is the most close the the data sheet block coefficients if compared for all the case studies. For this reason the older variant of Ayre is used to approximate the block coefficient. However further research is suggested for the block coefficient particular for cruise ships.

The discrepancy for the draught can be explained by the different ship types. These type of RoRo passen- ger ferry ships are designed for draughts mainly depending the operational route whereas cruise ships are designed for draught depending on the used ports. Furthermore the draught for ferry ships is sometimes limited because of the use of bow door.

In all three case studies the bow thruster has a large difference if compared to the data sheets. This can be explained due to the heavy wind criteria that is used for the power calculation of the bow thruster in the model [26]. This wind criteria represents heavy wind gusts in areas where these RoRo passenger ships do not operate. In addition this wind criteria is a client wish and not prescribed by regulation.

The case studies show acceptable deviations in ship particulars, installed power and transit load balance. Only the second case study has some discrepancies that are on the edge of the standard error of regression. Subsequently with the adjusted block coefficient and the explanation for the deviating draught it is overall concluded that the output from the model is similar to the existing ships with an acceptable deviation.

4.2. Safe Return to Port Output Validation

SRtP regulation is relatively new (2010). Little information is available for the validation of the SRtP power calculation because of the novelty of SRtP in combination with the fact that Royal IHC has not built passen- ger ships in the last decade. The SRtP model is validated with a case study ship.

The case study ship’s particulars are described in table 4.5.

Case Study Ship

Gross Tonnage GT 30500 tons

Length Overall Loa 203 m

Waterline Length Lwl 182 m

Length between perpendiculars Lpp 175.4 m

Breadth B 26.2 m

Draught T 5.95 m

Block coefficient Cb 0.671 -

Table 4.5: Case study ship’s particulars

The SRtP resistance consists out of three parts: the added wave resistance, the wind resistance and the calm water resistance as described in section 3.4.

40 4. Model Validation

Figure 4.4: Added wave resistance model output analyzed with respect to the available data of the case study ship

4.2.1. Added Wave Resistance

The added wave resistance part is calculated for different ship speeds to be compared to the available SRtP added wave resistance data.

v [knots] Data[kN] Model [kN] Delta [kN] Delta [%]

4 190.5 75 115.5 60.63

6 218.1 130 88.1 40.39

8 249.5 189 60.5 24.26

9 265.7 219 46.7 17.58

10 283.8 251 32.8 11.56

Table 4.6: Added wave resistance from available data, model outcome, the delta and the percentage delta relative to the available data

There is a significant deviation between the outcome of the model and the available data. This significant difference was clarified in cooperation with MARIN. The currently used STAWAVE-2 method of MARIN was extended during a JIP (Joint Industry Project) which has resulted in the SPAWAVE method. Unfortunately the background and details are not publicly available (E).

Because the STAWAVE-2 calculation is now the most accurate available calculation for wave added resistance this will be used for the model regardless of the deviation in results. Because of the limited available data the outcome is analyzed for the case study ship and the outcome of the model will be corrected accordingly. This rough estimate will be addressed in the recommendations of this thesis for further research.

In the left figure of figure 4.4 the delta in resistance is stated between the available data of the case study ship and the outcome of the model. A linear relationship is obtained between the delta resistance and the ship speed. In the right figure of figure 4.4 the delta in resistance relative to the available case study ship’s is plot- ted against the ship speed. This is as expected still a linear relationship.

The SRtP requirement from DNV-GL as described in section 3.4 describes a required SRtP ship speed of six knots. The correction factor for the added wave resistance according to the formula displayed in the right figure of figure 4.4 will then be:

Correction Factor= −8.1869∗6+91.466=42% (4.1)

It is assumed that the model outcome corrected with this 42 % correction factor is representative for the added wave resistance.