While concept design of the Future Submarine is reportedly progressing on schedule under Project Sea 1000, questions continue to be asked about the pumpjet propulsion system that is seen as a key feature of the Collins-class replacement.
These queries range from the general to the specific – how does a pumpjet system work, why is it a better option than a sophisticated propeller; and, by the way, what about the reports suggesting that pumpjets are too inefficient at low speeds to make sense on a conventionally-powered submarine?
Several seemingly-ambivalent statements raised early doubts about whether the pump jet system would definitely be used, or whether it remained an option. Some doubts still exist. Certainly the capability was an effective discriminator in the sales pitch by DCNS (now Naval Group) for its Shortfin Barracuda Block 1A, with the company’s then CEO for Australia Sean Costello stressing in early 2016 the significance of France’s readiness to transfer to Australia sovereign control and use of pumpjet propulsion technology resident only in France, the UK and the US.
If selected, the Shortfin Barracuda would utilise a pumpjet propulsor that combined a shrouded rotor and a stator within a duct to significantly reduce the level of radiated noise and avoid cavitation, he said. The stealth and hydrodynamic performances of the system were of course classified, Costello understandably but unhelpfully added.
Yet in October 2017, Naval Group executive director Jean-Michel Billig commented that the Future Submarine may end up with a conventional propeller – a remark swiftly followed by a DCNS statement that although the inclusion of a pumpjet propulsor had been a key element of the company’s winning bid, the Commonwealth would have the final say on the forms of propulsion that would used in the project.
Head of the Future Submarine project, Rear Admiral Greg Sammut, subsequently confirmed at Senate Estimates that a pumpjet system would be used, adding that some claims about the capability were misleading. “It’s not purely for use in nuclear submarines; it can be efficient across the entire speed range, taking account of the submarine’s size, the speed required and stealth,” he stated. “It needs to be tuned to the hull of the submarine; the hull needs to be tuned to the pumpjet.” This in essence rebutted comments on the subject made by former Collins-class commander Philip Stanford prior to selection of the Shortfin Barracuda. Stanford, then a senior member of the team representing the unsuccessful German bidder TKMS and its Type 216 design, noted that average speeds during the long transits required by Australian submarines were about 10 knots, albeit with moderately faster sprints interspersed with much slower speeds while snorkelling at periscope depth.
“When you’re on station and you’re there for six weeks, if you’re ever doing more than four knots there’s something wrong. If you can be doing two or three knots that’s much better. It’s only when you get above double digits or the high teens that the pumpjet starts to deliver greater efficiencies.”
Lees verder op Australiandefence.com.au/