Harold T. Johnston

The decay of maximum velocity within the initial stages of a propeller wash

The velocity characteristics of the submerged jet produced by a rotating ship propeller are described in terms of the maximum velocity measured on the propeller plane. Detailed measurements of velocities have been taken in the zone of the wash close to the propeller. The maximum velocity has been found to decay with distance from the propeller source. The maximum velocity in the zone of formation of the propeller jet has been shown to depend upon the efflux velocity and the blade area ratio for the propeller.

The use of flow duration curves as a data quality tool

Abstract The end user of river flow data may have no knowledge of the quality control measures applied in their generation. Therefore, an independent quality indicator is needed to give confidence in their use. The use of long-term flow duration curves as an indicator of data quality is proposed. This method visually highlights irregularities in river flow data and enables the type and location of the error to be readily located. The method has been applied to data held by the Rivers Agency in Northern Ireland, leading to increased confidence in the database.