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whole tested Fn range, and the wave resistance coefficients C, relative to the model scale h = 10 are
about 10% larger than the coefficients C, relative to model scale A= 20.
Anyway as the wave resistance coefficient of the two models in scale h = 10 and h = 20, should be the
Same at equal Fn, the form coefficient 1 + k (Fn), function of Froude number, has been also determined
by the relation

So obtained values of I+k (Fn) are very close to the value one in the Fn range 0.70 - 1.00; this could
be considered as confirmation of the equality of the wave resistance with the residuary resistance
coefficient for the tested trimaran configuration.

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

Figure 9: Trimaran form factor by Hughes Figure 10: Comparison between geosims
method results - ITTC’78 correlation

5 CONCLUSIONS
Systematic resistance model tests have been carried out for a trimaran ship equivalent to operating
high speed craft.
Different locations of side hulls were tested; the optimal position was identified as well as the
correspondent running trim
At the designed high Froude numbers of the considered trimaran, the Wigley side hull form seems not
realistic. However, because of a lower total resistance this side hull form could be adopted at lower
Froude numbers.
The investigation on the model ship correlation by the geosim model tests highlights that the ITTC’57
is preferable to ITTC ’78 methodology in the range of Fn = 0.70 - 1.00; the opposite is true for Fn <
0.60.
The results of this research are valid only for the examined hull forms. Further research will show if
the obtained results are applicable to other trimaran hull forms.
Acknowledgments
This work was supported by the Italian Ministry of University and Scientific Research in the frame of
the 1999-2001 research plan.

References
Ackers B.B., Micheal T.J., Tredennick O.W., Landen H.C., Miller E.R., Sodowsky J.P., Hadler J.B.
(1 997). An investigation of the Resistance Characteristics. of Powered Trimaran Side-Hull. SNAME
Trans. 105,349-380