A Comparison of the Model and Full Scale Transom Wave of the R/V Athena

Over the past few years the U.S. Office of Naval Research has sponsored a series of measurements of the transom wave of the R/V Athena and of a 1/8.25-scale model (NSWCCD Model 5365) of the ship. The objectives of the testing were to characterize the free surface wave behind the ship’s transom at both model and full scale for use in identifying hydrodynamic features and for developing and validating numerical simulation tools. The focus of this paper is the comparison of these full scale and model scale measurements, specifically a comparison of the time-averaged free-surface stern wave profiles and the dominant hydrodynamic features, the rooster tail for example. Both the field measurements and the model scale tow tank measurements were made in as calm as possible ambient conditions. Full scale data was collected in the relatively protected waters of St. Andrews Bay, Florida. The winds, which typically build as the day progresses, were minimal, and it was a new moon during the test period, so tidal excursions were also minimized. While measurements were obtained for ship speeds ranging from 3.1 to 6.2 m/s (6 to 12 knots), equivalent to Froude number range based on length (47 m) of 0.14 to 0.29, respectively, the focus of the comparison is for the 0.24 Froude number (10.5 knots full scale) case. Measurements of the full scale stern wave were made by a scanning laser altimeter, while measurements at model scale were made using a traversing set of conductivity finger probes.