A method is presented for determining inner and outer boundary layer length scales from a succession of drag measurements of a cylindrical body in order to estimate flow noise and for computational modeling of the dynamics of towed arrays in a fluid medium. A succession of measurements of the total drag on a cylinder under tow at uniform known conditions (flow speed, fluid density, fluid viscosity, cylindrical body geometry) is taken. After each measurement, the cylinder is truncated by a fixed amount, and the process is repeated for the length of the cylinder. The measurements provide a spatially and temporally averaged measure of the mean wall shear stress and momentum thickness, from which the inner and outer length scales can be determined. The inner and outer boundary layer length scales may then be used for estimation of flow noise on towed cylindrical bodies and arrays.