The manoeuvring components of the vessel were coated in a protective solution, which slows the affect of pressure changes causing cavities.
The image above shows the cavities which are caused when the shafts, propelled, tri, tabs or rudders are activated through high levels of pressure changes. Find proper propeller protection !
Aaron Dia Pemberton. RYA qualified skipper. Trawler yacht captain of T&Eadapt