Propulsion

Propulsion for the new age of navies

Expanding mission profiles and a growing demand for flexibility are driving creativity in propulsion solutions that combine speed, power, silence and manoeuvrability. 

  • Text:Global Marketing and Communication

    Photo:©Kongsberg Maritime

  • Craig Taylor
    Senior Manager PR & Communications
    (+44) 774 9584 285

The future waits for no navy. Rising geopolitical tensions and evolving threats have led to big operational demands on navies – speed combined with stealth, fast deployment and loitering capability and power delivered with low noise. Propulsion solutions need to adapt as well.  At Kongsberg Maritime, one answer lies in combining propulsion systems in a way that increases operational profiles without sacrificing key requirements.  

Rushing to be silent

One example is the combination of waterjet and propellers in a hybrid propulsion package that allows high-speed sprints but still enables patrolling operations, even in stealth mode. This system could be applied to surface combatant vessels, whereas waterjets are normally used in craft under 50 metres LOA (length overall) for fast attack purposes.  


“We are widening the operational profile of larger vessels such as corvettes and frigates by combining waterjets with props,” says Fredrik Appel, Kongsberg Maritime’s Director Products, Waterjet Systems.  
In one case for the Indonesian Navy, Kongsberg Maritime will combine a twin, controllable pitch propeller (CPP)-configured shaftline system with a single Kamewa Waterjet powered by a 23MW gas turbine engine.  

“The combination of propellers and waterjets is quite a challenge to design,” says Göran Grunditz (above), Kongsberg Maritime’s Director of Hydrodynamics. Though simple in theory, making all the parts work together efficiently requires considerable testing and refinement. Göran points to the difficulty of getting a pair of CPPs to adjust to the high speeds generated by the waterjet without causing undue noise or resistance. 


“To maintain the power of the propellers, we need to increase the pitch of the blades quite significantly and keep increasing the pitch as the speed increases. That is a unique operating condition,” he says.  

Göran and his team at the company’s Hydrodynamic Research Centre (HRC) in Kristinehamn, Sweden, are fine-tuning the details on the underwater profile of a new vessel equipped with a waterjet-CPP combined propulsion system. Working with CFD (computational fluid dynamics) software, the HRC is creating models that can be tested in dedicated tunnels then further refined beyond what even the latest software can achieve.  


“We are testing some alternative design features like super-cavitating profile shapes,” says Göran. “It’s about building new capabilities and pushing the limits. From our perspective, this is the type of product we want to see, because we learn a lot.”  

Diesel for speed, electric for loitering

While the waterjet solution for the Indonesian Navy points to the larger use cases for waterjets and propellers, the surge of interest in unmanned and remotely operated vessels points to smaller-use cases for waterjets combined with electric rim drives. “USVs [unmanned surface vehicles] will be taking over a lot of roles – from minesweeping, protection of mother ships, attack mode that includes fast in-fast out operations and launching missiles,” says Fredrik.  

 

Nils Waltré, Kongsberg Discovery Sales Manager, is a former submarine officer and sea captain. He reckons that geopolitical shifts and crewing pressures have supercharged the need for unmanned solutions. “The number of sailors in the world is declining rapidly but the demand for ocean-going vessels is going up, so everything is going in this direction,” he says. 


Nils and Kongsberg Maritime engineers are working on vessel concepts for USV deployment that will rely on a combination of waterjets and electric pods.  
Such vessels would use waterjets powered by diesel engines to get to an operational zone quickly then switch to electrically powered rim drives to reduce underwater noise and allow for the relay of survey information and commands with the mother ship.  


A key design challenge will be getting all the elements, including the different propulsion systems and positioning sensors, to talk to each other for easy control and responsiveness.  

Pods have the power 

One possible outcome of the increased focus on unmanned aerial vehicles (UAVs) and USVs in the naval sector is a proliferation of small carrier vessels designed to host and deploy unmanned craft or even a squadron of helicopters. Such carriers would rely on podded propulsion and dynamic positioning for stability in flight operations, rather than size and bulk.  


Patrik Kron (left), Kongsberg Maritime’s Chief of Naval Systems, points to the French Navy’s Mistral-class of carriers, which combined small-scale helicopter and amphibious operations, as a glimpse into the future.  


“They [the Mistral class] projected a development which could take a decade or more for some big navies to pick up, but other navies not linked to that tradition [of large-scale carrier operations] might do,” Patrik says.

He adds that South Korea is a good example of an innovative country that takes the best technology available now to start creating such solutions.  Though Patrik is reluctant to call smaller, multi-purpose carriers a trend, he admits that more questions are being asked about the possibilities of such carriers, rather than large carriers that require a small navy just to protect and support it.  

Power and silence on ice

The other big direction for many navies is north, to the Arctic. Naval spending on polar-class vessels is rising as climate change opens Arctic shipping lanes and access to resources. To operate in Arctic waters, vessels need the extra power that comes from a thicker propeller – but this comes at a sacrifice. A thicker propeller blade generates the power needed to break ice, but it also generates more noise.  
Göran and the HRC team have years of experience handling top-tier naval requirements. For ice-capability combined with quiet operation, he points to Kongsberg Maritime’s work with ice-class research vessels, such as RRS Sir David Attenborough, a 130m vessel capable of breaking through ice while operating in absolute silence.  


“A navy ship needs to be silent for many reasons but, from a design perspective, development is very similar [to the RRS Sir David Attenborough],” says Göran. “We use the same design philosophy, even though they are very different hull types.” 
The performance demands on propellers of this nature require a mix of strength, efficiency and underwater noise reduction. “You can see them as the corners of a triangle and you need to design within that triangle to find the sweet spot for your operations.”

Integrated systems that save existing vessels

A final, major trend noted by Kongsberg Maritime’s propulsion experts is the desire to make better use of existing equipment. Patrik says that new solutions on existing platforms may be a key element in future naval development, such as improved diesel-electric propulsion systems on vessels that enhance stealth or silent operations while maintaining traditional performance requirements. New spending doesn’t necessarily mean big risks on new designs, he adds. 
The condition monitoring solutions currently used by commercial vessels may wind up more widely deployed on naval vessels.  


“They [naval vessels] have a lot of sensors, obviously, but they might not control their propellers and rudders as well as advanced commercial ships,” says Göran. “Navy vessels must listen for submarines, for example, but they don’t make use of their own data for controlling their operations. They also don’t operate their own propellers in a way that maximises their silent capability.”