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 Electrically driven Royal Navy Type 45 destroyer. Inset: Water cooled resistors enable electric braking on hybrid vessels

Analysts at IDTechEx have issued a new report – Electric Boats

and Ships 2017-2027 – looking at this fragmented but often highly profitable and growing sector. There are already over 100manufacturers of electric boats and

ships. The report finds that themarket for hybrid and pure electric boats and ships will rise rapidly tomore than $20 billion worldwide in 2027 for non-military versions. Recreational boats is the largest and fastest growing electricmarinemarket in sales number, followed by underwater leisure and autonomous underwater vehicles. The on-water commercialmarine category is currently the largestmarine EV valuemarket. Leisure craft on inland waterways, notably in theUSA and Europe, will become the largest sector asmore places fromGermany to India ban internal combustion engines or, as with SunMoon Lake in Taiwan, the operators unanimously agree to go clean and quiet. Huge environmental pressures aremaking owners of industrial

and commercial seagoing craft address the issue of propulsion. According to the report, one large ship can emit the global warming carbon dioxide of 70,000 cars, the acidic nitrogen oxides of twomillion cars and the carcinogenic particulates of 2.5million cars. All-electric systems consist of an electricmotor being powered

by a battery pack.Hybrid electric systems consist of a fuelled engine and energy storage used to propel the craft sometimes (parallel hybrid) or to charge the battery (series hybrid). Traditional “electric drive” where there is no substantial battery

and therefore no pure electricmode or even downsized engine is mainly suited to large craft: it is seen in diesel-electric and nuclear-electric ships and submarines. Although themarinemarket is not the largest addressable

market for Li-ion batteries, it is expected to be amajor secondary valuemarket due to the battery typically being unusually large, 1MWh not being unusual. Technical limitations facing such Li-ion batteries include energy and power density, life, charge rate, size and weight. Another factor hindering the fast adoption of electric and hybridmarine technology is the ability tomaintain and find replacement components for such propulsion systems.

HYBRID RETROFITS Beyond new electric craft, there is already a substantial and growing business in retrofit of hybrid electric ferries and other ships with pure electric or hybrid electric powertrains. There is also potential to sell hundreds of thousands of pure electric outboardmotors yearly as they becomemore affordable andmore energy harvesting is provided on the craft to charge the batteries, improving range. For five years theMSNadorias serviced the inland waterways of

distributed to variousmotors, including those driving the propeller shaft(s), and other consumer loads. The logic behind all-electric ship design is two-fold. First, ship

layout: a largemotor does not need to be in themiddle of the ship, which is prime passenger and cargo space. Second, energy efficiency: traditional ships could have up to four diesel engines running at low power under normal operating circumstances. This oftenmakes theminefficient. By using smaller diesel engines together with a couple of gas turbines, the right number of prime movers can be fired up to suit power demand, whether it is a fully- laden oil tanker afloat at sea or stationary at port.

theNetherlands, between Groningen, Amsterdamand Rotterdam. Originally, it was powered by a single diesel engine with a conventional direct drive to a single propeller.Now, on board the MSNadorius, the huge potential in converting to hybrid is no longer a vision but a reality. A hybrid retrofit has given this inland container carrier a huge 15 per cent saving not only in fuel, but also in CO2 emission. Since themain diesel engine now runsmuch less, there is 60 per cent lessmaintenance cost and higher uptime than for its identical sister ship. With the conventional direct drive configuration, there was a

mechanical connection between the diesel engine and the propeller. So, the propeller speed was directly proportional to the engine speed. Thismeans there aremany situations in which the engine does not operate at optimumefficiency. This inefficiency is greatly reduced by the diesel-electric

drive because there is an electric transmission between the generator and the propeller. Electrical transmission allows

 February 2017 /// Environmental Engineering /// 11

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