If you have read my blog recently then you will also realise that the question of the rising cost of diesel fuel has also been causing a lot of concern and controversy in the UK boating community. So I thought I would carry out an investigation into the practicality of running a boat on pure electric or on hybrid propulsion systems such as combined diesel and electric power.
Although there are drawbacks to hybrid systems – some of which I list below – it reminds me of the early days of the commercialisation of the microcomputers in the 80’s when every advance could be met with derision and scepticsm particularly by those that always think the glass is half empty. Having spent my working career in software development, I have an easy acceptance of rapid change; of innovations that cause step changes; of being periodically surprised by the ingenuity of physicists, chemists, and materials scientists that have created a tipping point so many times over the past 20 years.
This is what will happen in boat building now. I believe that all the drawbacks that people cite will be overcome. Many are already within reach 
and lie within the bounds of the current technical horizons of boat design, alternative energy generation, electrical storage, and hybrid propulsion systems.
So with this in mind I set off to research the “state of the art” in pure electric or hybrid propulsion for boats. A good place to start is the very comprehensive US Dept of Energy web site and the related “Energy Efficiency and Renewable Energy ” program of the US Dept of Energy. Here you will find out a lot about energy conservation and the US government’s attempts to encourage initiative in all areas of industry, travel, and domestic power and propulsion systems
A long time ago in a land far away…
Of course it is tempting to think that these are new ideas but in fact in 1912 Jack Delmar-Morgan created a motor yacht that was unique. His yacht Mansura was designed to run selectively under petrol, electric or sail power alone or under any combination of these sources. The petrol engine could be started electrically and the yacht was equipped with electric lighting, cooking and water heating systems. The hybrid power train delivered 9 knots under petrol power, between 5 and 8 knots under electric power and 11 knots under both but just as impressive was the silent running and ease of her operation and maneuverability.
It was in memory of him that the Mansura Perpetual Challenge Trophy was launched earlier this year. The idea was to inspire an international competition, recognising innovation in the design, development and operation of marine vessels with hybrid or all-electric propulsion systems. Hundreds of entries were received and of these 25 hybrid designs were followed up in Australia, Canada, France, the Netherlands, Switzerland, the United Kingdom and the USA as the competition gathered momentum and international recognition, leading to a final shortlist of five contestants from four nations.
Hybrid boats…
This year the Mansura Trophy was awarded to Lagrange Construction Navale de Bordeaux for their Lagoon 420 . All Lagoon 420s will have the new propulsion system as standard – the diesel only version is an option! The propulsion system comprises two electric motors connected to propellers by straight shaft transmissions, one generator and two sets of 6 batteries. When batteries are 100 % charged, the boat will be able to function with both motors for approximately two hours (depending on speed). When batteries are 80% charged, the generator will automatically start and charge the batteries in order to provide electricity for the motors. When sailing, propellers will recharge the batteries. Built using Leroy Somer’s Motor Technology , the new motors offer strong savings in carbon dioxide emissions and engine maintenance.
The Lagoon 420 is a full size cruising cat, there are a large number of smaller pleasure boats that combine solar, diesel, electric and of course sail to create a hybrid boat. There are even giant container vessels that use alternatives to just diesel power including the strange SkySail pictured here.
Here are links to just a few of the designs available…
Of course at the other end of the scale there is the Queen Mary 2 – Four 250 ton Rolls-Royce Mermaid™ electric propulsion pods totalling 80MW drive the QM2 along at almost 30 knots! Ok – its not that simple – The vessel is powered by four Wärtsilä diesel engines, supplemented by two gas turbines. With a total output of 118MW, the power plant develops 157,000hp. The actual propulsion is carried out by four 20MW Rolls Royce MerMaid podded propulsion units, two fixed and two azimuthing through 360°. They incorporate an electric AC motor that directly drives a fixed-pitch propeller with highly skewed blades for low noise and vibration.
So how efficient are these systems ?
It seems that the two most popular suppliers of hybrid systems are Steyr and Leroy-Somer .. plus the Emotion electric drive unit and the OSSA Powerlite genset and accessories
Steyr Motors is now shipping their MO 256/H45 diesel-electric hybrid marine engine that couples a 250hp Steyr diesel engine with a 48 volt 14hp electric motor.
Steyr provides an example that demonstrates the advantages of the engine. They replaced the engines of an older pleasure boat – a 34ft cabin cruiser with twin diesel 225hp engines that cruised at 21 knots and burned 20 gallons per hour. The same boat with two of their new diesel-electric hybrids cruised at 25 knots and burned 12 gallons per hour. So, it’s faster and consumes much less fuel. Well I assume that the diesels replaced were of an old type and not as efficient as a modern unit – but still it makes you think.
Common criticisms..
1. Batteries are too heavy /take up too much space?
Taking the Fastcat435 for example, it uses 11 normal sized 60Ah car batteries – but they can be distributed to advantageous positions in the boat, and depending on the whole system you may not have a conventional generator or other items of equipment.
2. The batteries would cost too much?
Again the Fastcat 435 quote approx. US$1,850 each or US$21,000 for the set of 11 batteries with an anticpated 10 years of life. I dont think any system has been shown to be cheaper in year1. They probably cost 10% more over the cost of a new boat.
3. Certain batteries are a fire risk
Well, lead acid or GEL are no more risk in a hybrid than they are in a normal boat and thats not very much, but some hybrids are using the Lithium Ion batteries that were blamed for the fire on the cat Playstation some years ago. However the Lithium Ion Phosphate batteries will not catch fire and are used on the Airbus aircraft for that reason.
4. Bearings on electric motors wear out.
The development of brushless direct current motors using neodymium magnets has reduced this type of wear.
It seems that I have only talked about problems but here are some excellent resources from advocates of the technology:
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…and a good 7 pages of debate on the Cruising Forum
This is an extract from Tim Murphy’s article…”Bill Choice, who circumnavigated from 1989 to 2000 aboard a Wauquiez Centurion 47. “The advantages of a hybrid approach for sailboats are even greater than for automobiles, because sailboats have another source of power to tap: the wind,” Choice says. He reckons his hybrid system, which incorporates two gensets and two motors, will cost a third more than if he’d installed two traditional diesel engines and a genset. But for him, that initial investment is outweighed by the advantages, which include cost of ownership and fuel savings brought about by the efficiencies gained throughout the propulsion system; less noise, fumes, vibrations, and heat in the aft cabins; easier maintenance on the gensets; greater maneuverability with faster prop response and greater torque for motoring into wind and swells; regeneration capabilities, especially at sea; better weight distribution of equipment around the boat; and improved resale potential.”
Well time will tell!
more suited to solar panel charging systems…was the safety aspect – “No Venting”. When batteries are mounted for bow thrusters or an anchor windlass they are often sited under the bed or at least somewhere within the fore cabin. So any improvement in safety here would be of interest.
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