Designing efficient hulls using CFD

Russell is right to be enthusiastic. The results so far appear to represent a considerable return on the added cost of performing the analysis.

When the scheme started, Russell envisaged they would only be looking at the propeller, enabling a better understanding of the inflow. However, the project’s scope has changed dramatically since then and CJR is already looking at the whole underwater package for several manufacturers, in the UK and beyond. The CFD team can now help customers improve their designs in areas such as props, rudders and hull form, as well as propeller tunnels, spray analysis, superstructure airflow and drag calculation.

But how did the project get started and what made CJR invest in an area none of its direct competitors were involved?

‘We have always strived to use technology to improve the performance and efficiency of our products and our robotic manufacturing tool offers us complete repeatability to the design – something which is difficult to achieve with hand finishing,’ explains Russell.

‘There was also a shift in the work we were doing and we saw more and more customers from the semi-production market. In this arena, it is a no-brainer to optimise the propellers and sterngear, because the cost is absorbed with every boat produced. CFD was simply the next step.

‘For the last four years we were using a bespoke in-house program which was developed by our head of design, Marek Skrzynski. It utilised a vortex lattice and lifting surface methods to design the propellers,’ says Russell. ‘Although was an advanced program, it still came with some limitations: the program has the ability to calculate the propeller performance in a non-uniform inflow, but it assumes that it is uniform over the entire propeller disk, because we generally just didn’t have the data to accurately prove otherwise. In reality, that is never the case and the flow encounters various obstacles before it reaches the propeller. Each obstacle has an effect and will cause flow differences across the propeller plane.

‘This meant our first objective was to simulate flow around the hull using CFD; this allowed us to have a far more accurate and detailed input for the propeller design program,’ he continues. ‘The success of this meant we quickly moved on to including the flow around the sterngear appendages to allow design optimisation, as well as fully automating the process so we can generate the data needed for propeller design within two days of receiving a hull geometry.’