Although the form factor k obtained by means of the classical low speed towing tank technique is presently utilized in many institutions for the application of ITTC'78 model-ship correlation, there is not an universal enthusiasm for its use in predicting full-scale resistance from model tests data.
The reasons for the reluctance to introduce the form factor are mainly due to the considerations regarding the effects of Reynolds and Froude numbers on the value of k.
Various geosim model tests carried out by different institutions highlight the influence both of Reynolds and of Froude numbers on the form factor, but the associated physics is far from being completely understood.
In order to obtain further information on the scale effect on the form factor, we have carried out experimental tests in two different towing tanks with geosim models of three parent hulls of Series 60, having block coefficient CB = 0.60, 0.70 and 0.80.
In the paper the experimental results obtained with the nine models of the multiple above mentioned geosim model tests are presented and analyzed. The main aim of the paper is to furnish a contribution both on the valuation of the scale effect on the form factor and on the preparation of a practical guideline for its determination.
