The quiet pull of green power

Most boaters are of the opinion that "Green is Good", although – as yet – only a small number have responded to the conscience-call with a down payment on hybrid. This may be because any idea about making a saving on diesel is quickly squashed when the upfront investment is calculated.

However, there are other useful ideas that can be found alongside going the greener route – one of them being an almost unlimited amount of onboard power for liveaboards.

Domestic power
Liveaboards have benefited from crossover technology. The JCB J444 is actually the 'digger' engine from JCB but it’s been very well marinised by Mermaid. It's a workhorse, a four cylinder engine giving 84hp. Mermaid has been working with Hybrid Marine in developing a 20kW parallel hybrid solution which is ideally suited to Dutch barge and wide beam vessels.

The system not only offers silent clean propulsion but is also a 10kW generator as standard, providing the vessel with a high degree of self sufficiency in terms of domestic power.

Graeme Hawksley of Hybrid Marine adds that a hybrid package provides much more than fuel savings. "Hybrids cost more than a standard prolusion engine and must justify themselves by the extra features provided, such as clean quiet operation, large amounts of electric energy - replacing the requirement for a separate generator - and high levels of redundancy."

Hybrid Marine systems use Victron charger/inverters as an integral part of the power package. These devices handle providing AC mains from the hybrid battery banks in complete silence and can boost any shore power capability with energy from the batteries during periods of high load.

Parallel argument
But, Mr Hawksley says, amp for amp, the parallel arrangement works out the most cost effective to install. His point is that for a serial installation all the propulsion power must pass through the electrical generator and the electric drive motor.

He says, this is because if you require a reasonable amount of propulsion power this involves very large and expensive generators and motors. Also, when running under high loads the engine is working as efficiently as it is able, at this time the best way to transmit power is through a low-loss gear box (you lose around 3 to 5%).

However, he explains typical losses through a serial hybrid generator linked in line with a motor are in the region of 10% to 15%. “Therefore at high loads the serial hybrid actually works out less efficient than the engine it has replaced,” he adds.

Against this, the parallel hybrids keep that important link between the engine, the gearbox and the propeller, so when it is more efficient to do so, power is transmitted mechanically. Under moderate-to-low loads, where hybrids have the most to offer in efficiency improvements, the electric motor can be employed.

As parallel hybrids add to a basic engine transmission some systems can be retrofitted very easily to existing installations. This gives a couple of benefits. One is that the footprint remains fairly small, and it gives you enhanced redundancy "because the engine can still work even if the hybrid is offline, and the hybrid will still give you power even if the engine goes down”.

One way for a catamaran to take advantage of hybrid technology is with a serial system, which involves one central generator and an electric motor in each hull.

On the other hand a parallel hybrid could be fitted to each hull giving multiple levels of redundancy (four independent ways to propel and two separate ways to generate). If you require only one engine then a parallel hybrid can be fitted in one hull and the battery bank and a separate electric motor in the other hull. “This, arguably, gives you the best of both worlds,” says Mr Hawksley.

One owner of a liveaboard catamaran has installed two Hybrid Marine parallel systems, one engine per hull. It seems the owner is a keen diving enthusiast, and the power he generates from cruising will easily cope with his domestic needs, plus running the compressor equipment for his favourite hobby. It seems he simply doesn't really need to come back onshore...

Mastervolt itself has been looking at the series versus parallel hybrid argument, and although it has developed an E-prop series hybrid for the market, it is still working with parallel systems – the Hybridmaster series. There are five models to the range, running between 3.5 and 20kW, all recharging from a belt offset from the motor – although each installation is a little different, depending on the original set up. The gear reduction ratio is achieved by varying the motor and shaft pulley diameters.

A series response
David Okey of Mitchell Powersystems, however, argues that Steyr Motors (which has a well-established series hybrid in its stable), has a more flexible system as series parallels can be inserted into various drive trains, such as waterjets without any trouble - whereas, he says the parallel systems “have more limited application”.

Steyr Motors won a DAME award in 2008 for its hybrid technology and the company has also been working with Mastervolt on a range of serial hybrid power packs. These power packs simply feed the electric motor driving the boat, and the diesel engine becomes part of an efficient generator set that charges the batteries for domestic and propulsion applications.

The Mastervolt gensets combine a two cylinder horizontal marine diesel engine (based on the robust M1 monoblock) with an efficient permanent magnet generator especially developed for these applications.

The simpler serial diesel-electric hybrid is easily translated into a modular set up. Taken in combination with the mass balancing system, this pretty much guarantees a quiet and smooth operation.

As the entire system is modular, each power module (eg, AC/DC/AC converter, DC/DC converter…) is able to be mounted either on the genset itself or used “standalone” and mounted elsewhere in the boat (you just have to connect it with cables and hoses for the cooling).

The system is designed for producing a maximum power output of 40kW with just a 25kW diesel engine, the peak power is taken from the batteries. Further, the control centre allows an easy visualisation of the operating condition of the entire system.