Influence of CPP control

The possible reduction of underwater radiated noise (URN) from a chemical tanker by running according to a combinatory curve instead of fixed RPM is assessed by model-scale tests in a cavitation tunnel. The model-scale measurements are validated against full scale measurements of URN and full scale cavitation observations. The measurements are performed on the chemical tanker M/T Olympus as part of the AQUO project. This ship is representative of a large portion of the coastal trade. The results show that lowering the RPM instead of reducing the pitch requires less power, produces less cavitation and generates lower URN when operating at reduced speed with a ship equipped with controllable pitch propellers (CPP). Solutions that make it possible to operate shaft generators at a variable RPM running according to a combinatory curve are becoming commercially available on the market. The fuel savings achieved by operating according to a combinatory curve at reduced speeds also justify the investment in such solutions from a strictly economic point of view. This is valid for new-builds as well as for retrofitting on existing ships.