The stylus ball diameter is exactly that of the BMT original. The BMT Hull Roughness Analyser is accepted as the industry standard instrument for the measurement of hull roughness and offers proven benefits to ship operators, ship builders, ship repairers and coating manufacturers.
The correlation between hull roughness and ship efficiency can be made with a variety of equations derived from empirical studies, e.g. the equations for increase in the frictional resistance coefficient due to hull roughness proposed by Marintek or Bowden and Davidson, or the increase in power due to hull roughness proposed by Townsin et al. Hull roughness is typically measured using a hull roughness gauge, giving (Rt50) which is the average peak-to-trough height over a distance of 50 mm.
The short wavelength cut off is a function of the stylus ball diameter.
Currently standards for hull roughness measurement are in process of development by NACE; TG 461 – Standard for Hull Roughness Measurements on Ship Hulls in Dry Dock and ISO is looking into standardization of hull roughness measurements.