Page 26 - Australian Defence Magazine August 2018

UNDERWATER TECHNOLOGY
PROPULSION
“The size of the Future Submarine means
a pumpjet is a real game changer for optimising the performance of the submarine in its intended role.”
Australia has learned a lot from their use
of the Collins class submarine but the Future Submarine will be different again.
“It’s not like a propeller where you can design your propeller open loop i.e. without considering the interaction with the hull, and then attach the propeller to the hull. The water flow over the hull to the pump jet is so integral you’ve got to design it as a pair, and the hull and the pump jet have to be tuned together, it’s a total system that you’re building.”
“One of the issues with pumpjets and the reason they’re not used on diesel-electric submarines is they’re much heavier than a conventional propeller, although they have a smaller diameter.
“As the size of the submarine increases (the Future Submarine’s 4,700 tonne sub- merged displacement is significantly heavier than the 3,407 tonnes of the Collins-class it will replace) you start to get to the point where a pump jet can become sensible.”
Although pump jet propulsion would be new to the RAN, the technology was well- known to DSTG.
“We’ve invested heavily in our hydrody- namics and hydroacoustics program over the past 20 years and this is includes the computational models as well as experimen- tal facilities that confirm modelling results,” Dr Kershaw said to ADM.
“We’ve been able to develop our analysis on a generic pumpjet design and thus con- firm our understanding of pumpjet perfor- mance; you basically build it up from first principles.
“Our analysis at the moment is all around analysing current options but we will be looking at what’s ahead in the fu- ture and enable Australia to develop the sovereign capability to take best advantage of pumpjet technology.”
Classified information
It was worth noting, however, that mod- ern pumpjets were primarily employed on military submarines and torpedoes and information was very limited and tightly held, making it difficult to review perfor- mance predictions.
“DST though, is in the position where we can access certain privileged information, so we can get validation of our analysis capa- bilities,” Dr Kershaw noted.
Pumpjet design had advanced over many years with a particular focus on the char- acteristics of all the components, although much of that was classified.
Some propellers were highly specialised and highly complex. Pump jets had com- plexities in other aspects but the moving ro- tor was not as complex as a normal propeller, benefitting sustainment.
So will pump jet technology definitely be used for the Future Submarine?
“That is what is currently in the design and that’s what a lot of our science and technology program is about; having the capability to do the independent analy- sis on the technologies and capabilities
planned for the Future Submarine, in- cluding the pump jet program,” Dr Ker- shaw said to ADM.
Discussions were currently underway with Naval Group and the French govern- ment regarding closer collaboration on a range of technologies and this would in- clude pump jets, Dr Kershaw disclosed.
The program was still being worked on, and on the Australian side would involve a government-only team to comply with French security regulations.
“One thing I would like to emphasis is that Australia’s geographic circumstanc- es require a larger conventional subma- rine than those currently produced for export to other parts of the world. The size of the Future Submarine means a pumpjet is a real game changer for op- timising the performance of the subma- rine in its intended role, and ensuring re- gional superiority in undersea warfare,” Dr Kershaw concluded.
Comment
Should pumpjet propulsion have already been selected for the Future Submarine while assessments are still underway, it’s to be hoped a robust albeit necessarily unclassified explanation will be forth- coming sooner rather than later to allay any lingering concerns regarding the sys- tem’s anticipated performance in Austra- lian service.
Much like the F-35 stealth debate, the lack of true performance characteristics thanks to inevitable classified nature of the techni- cal data make a true assessment for those outside the tent difficult.
26 | August 2018 | www.australiandefence.com.au
DEFENCE