In 2012 US sales of electric and hybrid cars doubled, and we are told that before long more and more of us will be driving electric cars. The motor industry’s response to rising fuel costs and environmental legislation has been to develop new technology aimed at reducing emissions and fuel consumption. Sound familiar? What about electrically-powered ships?
Shock to the System
In electrical propulsion systems the power generated by the engines is converted to electricity before being transferred to the propeller(s) via electric motors. In conventional ships the engine is connected mechanically to a propeller either directly or via a reduction gearbox.
Vessels powered by electric systems are already well established in certain sectors. Our Graph of the Week shows that following a dip in 2008-09, contracting numbers for these ships have quickly recovered to levels seen during the height of the shipping boom. In 2011-12 464 new electric ships were contracted compared with 453 in 2006-07. Last year 1 in 8 new vessel contracts was for an electrically-powered ship.
Electric power is well suited to dynamically-positioned offshore development and support vessels, where manoeuvrability is a key factor and there is a large variation in the demand for power between transit and station-keeping. Increased demand for higher-spec units within these sectors, for example to explore and develop oil and gas fields in deeper waters, has helped to boost the share constituted by electric vessels.
Lower noise and vibration and the greater flexibility in terms of engine size and location makes electric-power well suited to cruise and seismic survey ships, while dual-fuel diesel electric systems are widely used on modern LNG carriers. Vessels that operate on short voyages and close to shore such as ferries and dredgers are also equipped with electrical propulsion, while higher torque at low speed can make these systems suitable for vessels operating in icy conditions, for example.
Against the backdrop of much lower contracting in the larger “volume cargo” sectors, the outlook for a number of specialised sectors has remained more robust, and this changing product mix is reflected in the growing share of electric ships seen in the graph.
What’s the Charge?
Cost and power limits mean that until now electric propulsion has not been a viable option for large vessels with heavy cargoes. However, with the market placing a greater emphasis on fuel efficiency, a number of innovative designs are being seen incorporating hybrid mechanical/electric propulsion, waste heat and exhaust gas recovery, alternative fuels and high voltage shore connection being adapted for larger cargo ships. Could this be the start of a long-term trend towards the increasing electrification of the whole fleet? Maybe the future is electric?