CFD feeds fuel efficiency at Seawork
Streamlines are used to determine the flow into the propeller plane.
Seawork exhibitor CJR Propulsion’s in house design team has been investigating how computational fluid dynamics (CFD) can improve performance and efficiency for workboats.
CFD has been used to optimise hull form of large vessels within the commercial sector since the 1980s. However, CFD has evolved dramatically since then and today, advancements in computer technology allow for far more complex calculations to be answered in hours rather than days.
The project has already yielded some exciting results, and with the promise of further developments still to come through a better understanding of the water flow around the hull, the implications for the workboat sector and beyond are huge.
Mark Russell, managing director for CJR Propulsion, commented on recent projects. ‘We’ve been working with several workboat manufacturers over the past few months identifying how optimising the propellers can help improve top speed, efficiency and reduce vibration and noise. By using the experience and knowledge we gained from working in the superyacht industry we have been able to apply the same standards and design processes to our workboat customers. And, the results from two recent sea trials, both of which feature CFD optimised propellers, have been fantastic.’
Russell continued to explain a little about the CFD process and where the gains come from. ‘Each project has reported significant increases to top speed, compared to the customer’s expectations, and this is due to the flow around the hull being simulated and understood, meaning you get a far more uniform inflow to the propeller. Meanwhile, the propeller itself has also been re-designed with a wake-adapted profile which optimally exploits the inflow.’
CJR achieve this by using data provided by the manufacturer to create 3D CFD predictions of the hull with a free surface. This provides estimates of the hull drag and running trim at cruise speed. The flow field into the propeller is calculated using CFD, and is used to design a wake optimised propeller. The propeller race is also modelled, allowing rudder design and efficiency to be improved.
One of the recent CJR customers to benefit from CFD analysis is Mustang Marine. The project manager discussed the results. ‘This was not a new hull design so we were able to use historic data from previous builds for comparison. We had a figure in mind, based on the previous sea trials, but with the new propeller and sterngear we managed to exceed the contract speed by two knots. Add that to the reduction in noise and vibration and it’s clear it’s made a real difference to her performance and hopefully her overall efficiency as well.’
According to CJR, there are plenty more improvements still to come. Mark Russell concluded, ‘We’re just scratching the surface of this area and believe that with more data and increased buy in from the boat builders we can double the speed increase and optimise every element of the underwater appendages, in the process creating a workboat that’s not only is fast and quiet but also incredibly energy efficient.’
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