Design of research vessels- propeller cavitation and bubble sweep down in operational conditions

A critical aspect in the operation of special purpose research vessels is the interference by the flow over the hull and propellers with acoustic sensors. Low noise propellers are designed for these vessels that have delayed cavitation inception characteristics allowing the propeller to operate free of cavitation for a specified operational speed range. These propellers are often designed and tested on model scale for ideal trial conditions. In reality, however, the low noise characteristics of the ship and propellers are substantially influenced by the operational conditions that the ship experiences. Serious downtime is for example to be experienced when the sonar equipment is disturbed by air bubbles.

In this paper first an overview and discussion is made on the approach in low noise propeller design and the effect of operational conditions on the design. It is further shown how model tests in waves carried out in a depressurized towing tank provide valuable insight in the performance of the propellers in operational conditions. Furthermore, other typical issues such as bubble sweep down as a source of malfunctioning of the echo sounders can be investigated.