Page 181 - Practical Design Ships and Floating Structures

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4.3 Effects of Side-hull Location in Transverse Direction
Numerical calculations were carried out to investigate the effect of the side-hull's transverse location
on the wave resistance characteristics of the trimaran. The trimaran with symmetry type side-hull was
used for the calculation. Figure 11 shows the calculation results for the transverse locations
Ys/Lpp=0.125-0.225 while the longitudinal location is fixed at Xs/Lpp=O.15 at 30 knots. Figure 12
shows the calculated wave height for the main hull only in transverse direction at main hull center
Xs=O.O, which corresponds to the O.lLside-hullaft of side-hull. From these two figures it seems that the
wave resistance is related with the wave height a little, which the side-hull stem encounters.
The maximum difference of the wave resistance coefficient CW due to the transverse locations does not
exceed 10% of that due to the longitudinal locations.

Figure 1 1 : Calculated CW curve according to Figure 12: Wave height generated by main hull
the transverse locations of side-hull in transverse direction (30 knots)

4.4 Discussion on the Optimum Location of Side-hull
The present topic is to find out the easy way to predict the optimum location of side-hull at initial
design stage. The resistance characteristics of trimaran are highly affected by the wave interference
between the main hull and the side-hull. Therefore, the optimum location of side-hull is supposed to be
the place where the waves generated by the main hull and the side-hull cancel out each other. Figure
13 shows the wave profile generated by main hull at 30 knots (Fn=0.45) and five locations of side-hull
at the transverse location Ys/Lpp=O.125. This relative location seems to show a close relation with the
wave resistance as shown in figure 8. Therefore, it can be said carefully that the trimaran has favorable
resistance performance when the side-hull stem is located near the primary wave hollow generated by
the main hull.

Figure 13: Relation between wave profile and side-hull location (30 knots)