Velocity measurements in close proximity to a ship’s hull 1

Abstract

In this paper, experiments to determine the relation between velocity in the boundary layer, the distance from the surface of the body, and the shearing stress at this surface are described. Various lengths of pontoon were used at two speeds, and the deduced law $\frac{\mathit{u}}{{\mathit{u}}_{\ast }}=4.98log\frac{{\mathit{u}}_{\ast }\mathit{y}}{\mathit{v}}+6.54$ agrees very closely with that found by Ludwieg and Tillmann, but differs considerably from the more commonly used Nikuradse value.

Velocities in the boundary layer of two ships were also measured. The first was a trawler, two traverses being made at approximately the same distance from the bow, about 0.6 of the length of the ship. The traverse in the position on the flat bottom gave a typical velocity distribution curve, but that carried out in the side position showed marked fluctuations in the value of $\frac{\mathit{u}}{\mathit{U}}$ with increasing y. The second ship was an ore carrier, traverses being made in six positions around a girth about 0.3 of the ship’s length from the bow. Considerable variations were observed, both of the boundary-layer width and the free-stream velocity at the edge of the boundary layer.

An attempt was made by using the pontoon results, and also by using Ludwieg and Tillmann’s formula, to find ${\mathit{C}}_{\mathit{f}}^{\prime }$ at each of the positions, but the disagreement between the two methods throws some doubt on the validity of their use in 3-dimensional flow.