Current propeller monitoring methods are mostly based on dedicated processes e.g. dry-docking inspections or using additional onboard equipment. Potentially, seismic sensors can be deployed to analyze passing ships to draw conclusions about the propeller condition. The advantage of this novel approach lies in the flexibility of installing the sensor on the sea bed or on shore and, hence increasing the accessibility to full-scale operational data. An experimental study with different propeller geometries and advance ratios has been performed. All propellers could be distinguished based on the recorded seismic spectra, showing the feasibility of this novel monitoring method.
Emissions from shipping such as air pollution caused by CO2 but also underwater radiated noise (URN) have a major environmental impact disturbing marine life and especially cetaceans. The International Maritime Organization (IMO) introduced comprehensive regulations aiming at the reduction of CO2-emissions. Ships have to comply with the Energy Efficiency Existing Ship Index and must calculate their rating for the annual operational Carbon Intensity Index (CII). But also initiatives (Robinson and Trounce, 2016) and guidelines (IMO, 2014) to reduce URN underline the rising awareness of the consequences of global maritime transport on underwater life. To reduce the emissions of CO2 and other greenhouse gases, the energy demand of ships needs to be reduced. One important measure is the minimization of the total resistance. This can be achieved by keeping propeller and ship hull in a clean and intact condition or by lowering the ship speed. Both named measures help also to reduce a ship's URN noise level while maintaining good propeller and hull conditions depends on the available methods to monitor the condition. With newly developed methods and sensors, an increasing amount of ship operational data is collected, motivated by the possibility to enhance the operational performance (Jabary et al., 2023).
Collecting information about the propeller condition during the ship life is either done in shipyards at regular dry dock inspections or in service using different available onboard technologies, such as monitoring shaft or bearing vibrations. Another method is the visual inspection done by divers or remotely operated vehicles (ROV). However, monitoring the propeller under normal operating conditions from outside the ship is challenging and usually not performed.
