Archives for posts with tag: Propulsion

The introduction of new environmental regulations is leading the shipping industry to look for ways of reducing its emissions of harmful gases. This week we focus on two separate but related issues: the way in which vessels are powered, and the type of fuel that they use. New technologies are being adopted, with certain ship types leading the way…

Electric Therapy

The majority (96%) of active merchant vessels are powered by mechanical systems in which a form of fuel oil powers a main engine (usually a 2 or 4-stroke diesel) which is connected to the propeller. Most other vessels are “diesel-electric”, in which the power generated by the (4-stroke) main engine(s) is converted to electricity before being transferred to propeller(s) or thruster(s) via electric motors.

By optimising the loading of the engines, diesel-electric systems can lower fuel consumption and emissions. These systems are well established in sectors such as offshore, tugs and passenger, where manoeuvrability, variation in power demand and engine noise are important considerations. For larger cargo vessels, where demand for power is generally higher and more consistent, conventional mechanical systems remain more efficient and cost-effective. Our Graph of the Week shows that against a backdrop of reduced contracting in the larger cargo sectors, electrically-driven ships have assumed a greater share of the newbuilding market, accounting for 22% of reported newbuilding contracts so far this year.

Battery Charged

The next step for electric power may be more widespread adoption of batteries in main propulsion systems. There are 22 vessels in service and 14 on order that use batteries, mostly alongside either conventional diesel or dual-fuel generating sets. As well as reducing emissions when using battery power, these can enhance efficiency by optimising engine loads and transferring surplus power to or from the batteries as required. For smaller ferries intended for short routes, all-electric propulsion systems are feasible.

Gas Treatment

LNG has been identified as a cleaner fuel capable of reducing vessel emissions in line with new regulations. Clarksons Research’s World Fleet Register currently identifies 542 merchant ships in the fleet and on order capable of using LNG fuel. 351 of these are LNG carriers, which can use cargo boil-off to fuel a choice of turbine, dual-fuel diesel electric or dual-fuel 2-stroke main engines. In other sectors LNG fuel has taken longer to gain market share, but there are signs that where ship designs and the supply of bunkers allow, it is becoming more popular. Out of the 130 contracts recorded so far in 2017, 21 are for vessels capable of using LNG fuel. These include 4 Aframax tankers, the largest vessels other than LNG carriers to adopt dual-fuel 2-stroke engines.

More efficient power systems and cleaner fuels are two examples of how the shipping industry is responding to the challenges set by new environmental regulations. Alongside other developments in vessel design and operating practices, shipping is steering towards a more efficient and cleaner future. Have a nice day!

SIW1266:Graph of the Week

SIW1064imagelIn 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.

Current Trends

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?