Measuring air bubble layer characteristics around the hull of a ship model

The effect of an air bubble layer around the hull of a ship, a so-called ‘Masker’ system, was evaluated with a new measurement system. The goal of the measurements was to gain insight in the influence of air flow rate and ship speed on air bubble layer thickness and void fraction distribution at several locations around the hull and on underwater radiation noise (URN) levels [1]. At MARIN, experience with measuring air bubble curtains was built up in offshore installation-related projects. However, measuring air bubble layer effects on a moving ship model was a new challenge. Six in-house developed sensors were mounted to a carriage around the hull. The sensor carriage can be moved to different stations to allow investigation of the axial variation in the bubble layer. Tests were performed for a matrix of conditions covering variations in model speed, air flow rate and sensor carriage location. The collected data was post-processed and visualised using custom built scripts. The average void fraction per needle, air layer thickness and normalized layer void fraction are presented. In conclusion, the measurement system provided good insight in air bubble layer thickness in addition to ‘standard’ observations using high speed video recordings.