Geometrically similar models

Subtitle: An investigation of some problems resulting from their resistance values

Article type: Research Article

Authors: Ridgely-Nevitt, Cedric

Affiliations: Webb Institute of Naval Architecture, New York

Abstract: This is an empirical paper trying to correlate the resistances of varying size models of the same hull form. A large amount of existing model data was discarded because it suffered from either lack of adequate stimulation or from restricted channel effects. Extensive tests, on a series of small models, were undertaken to eliminate the former effect and corresponding large models selected where reasonable assurances of freedom from either of these difficulties could be established. The resulting comparisons confirm the necessity of abandoning either a plate friction or any other single line as a means of extrapolating from one model to another. Instead, a family of lines of varying slope are necessary. These slopes vary with the hull shape. Furthermore, it was found that, for a large majority of the forms investigated, there is a further requirement of varying the slope of the expansion lines with speed. The latter effect is contrary to the Froude assumption. In addition to the eleven displacement hull forms considered, two planing forms were also analyzed. The method of testing – towing along an inclined shaft line – results in marked scale effects on trim and wetted surface. The investigation was carefully limited to model sizes, since adequate experimental evidence was available only within this area. Similarly, the results are applicable only to smooth surfaces. It was felt that the expansion problem must first be solved for models with smooth surfaces, before extrapolation to full size ships with rough surfaces can be undertaken with any degree of validity.

DOI: 10.3233/ISP-1959-65903

Journal: International Shipbuilding Progress, vol. 6, no. 59, pp. 311-339, 1959