Drag Losses of New Ships Caused by Hull Finish

The performance of finishes representing hull surfaces in trials condition is investigated. The coefficient AC is determined at full scale for many examples. The accuracy of the measurements used to get the actual data on the velocity loss functions Au+ of the surfaces is also investigated. It is sufficient to provide reliable values of AC. The sample of hull finishes is large enough to permit generalization. Provided serious faults of preparation and coating are not permitted, the drag of the finishes is between 2 and 10 percent larger than the perfectly smooth. Thus performance is diverse. The cause is the random topography of low-drag new finishes. The surface features, which are varied, restrict the turbulent fluctuations in the very part of the boundary layer which governs Au+. Variety in surface topography means significant diversity in Au+. Thus, to get AC for trials comparison, the actual loss function of the surface in question must be measured. To get AC for a design at the project stage, the most probable value should be calculated from the data bank of loss functions of new finishes.