Cost versus capability in electric naval ships

Cost versus capability

All new warship programmes must achieve a careful balance of operational capability, acquisition cost and total ownership cost, but with so many seemingly conflicting requirements it is difficult to converge on a clearly optimal and winning design.  

Richard Partridge, Chief of Naval Systems, Rolls-Royce, shares his views on the benefits of hybrid propulsion and how it balances costs and capability.

More electric

An emerging global macro-trend in naval engineering over the last fifteen years has been a decisive migration to ‘more electric’ propulsion due to progressively increasing electrical load demand and a focus on affordability.

All-electric and hybrid electro-mechanical arrangements are routinely demonstrating merit since 1990 in the Royal Navy Type 23 ASW frigate and subsequent modern frigate programmes. These include the Royal Navy Type 26, German Navy F125, Spanish Navy F110, Italian and French Navies’ FREMM, Republic of Korea Navy FFX-II frigate and Finnish Navy SQ2020 frigate programmes.

Naval Hybrid Electric configuration

All of these programmes have served to de-risk the hybrid option, have been thoroughly evaluated by the respective country’s Navy, meet tough survivability requirements and yet are configured with a single gas turbine for main propulsion; very compelling indeed is the horizon for affordable, world-class Naval propulsion systems and their answer to the survivability and redundancy question.

Why are other Navies around the world choosing the hybrid propulsion plant solution for their future frigate programmes?  First, it’s the low-risk, immediate availability of a proven reliable (class standard) 36-40 MW gas turbine as the prime mover in a relatively simple, yet flexible COmbined Diesel eLectric Or Gas (CODLOG) arrangement optimised to a warship hull design and operational profile.  

First class results for hybrid Daegu frigate

Hybrid Daegu frigate 

“Although the power and propulsion system design influences ship performance, operational capability and costs throughout the service life of the program, it can transform a competing design into a decisive winner if architected intelligently."

Richard Partridge, Chief of Naval Systems, Rolls-Royce
Richard Partridge
Chief of Naval Systems, Rolls-Royce

Standout features

Other attributes that come with the hybrid propulsion plant design;  

Game-changing acoustic signature management

Game-changing acoustic signature management – the hybrid drive system is ultra-quiet because it uses an electric motor decoupled from the main reduction gearbox. This provides an exceptionally quiet machinery state and creates an environment to maximise performance of the undersea warfare systems and other mission systems associated with anti-submarine warfare.

Vital space and weight reduction

Vital space and weight reduction for more fuel capacity or mission systems equipment such as the Vertical Launch System through the installation of fewer total engines and auxiliary systems with simpler inlet and exhaust ducting. 

Extra space for crew accommodations

Extra space for crew accommodations via a single-gas turbine hybrid architecture, enabling overall shorter ship lengths and enhanced affordability for given military capability.

Enhanced range

Enhanced range using controllable or fixed pitch propellers in concert with diesel-electric propulsion at cruise speed (~16 knots) and below, providing higher system efficiency to meet and exceed threshold (and objective) range requirements with specified fuel capacity. Equally important with the single-36-40MW MT30 gas turbine in a CODLOG arrangement simulated modelling using a typical frigate operational profile achieves a 2%-3% fuel consumption savings over the conventional CODOG arrangement. 

Inherent operational flexibility in electrical power generation

Inherent operational flexibility in electrical power generation with the availability of up to 18MW of installed electrical capability while operating at 27 knots by using the electric propulsion motors in a power take-off mode.  

Game-changing propulsion

This represents game-changing propulsion and warfighting capability, certainly when considering the potential future installation of directed energy weapons.

Simple, proven engineering plant

Finally, it’s a simple, proven engineering plant – the 36-40MW gas turbine may be viewed as an enabler for the inherently simple CODLOG arrangement where electrical and mechanical systems are not required to power-share as in the case of the CODLAG arrangement. 

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